Download Appendix G – SMR Hydrology Model Guidance Manual
Transcript
San nta Marg M gariita R Regioon Hyd H drolo ogy Mod del Guida G ancee Doocum mentt Prrepared By: Santaa Margarita Reegion Copermitttees: Riversid de County Floood Control and Water Conservvation District, Cou unty of Riversiide, and the citties of Murrietaa, Temecula, an and Wildomar With assistance a from m: Cleear Creek Solutions, S In nc. www.cleearcreeksolu utions.com April 20144 Santa Margarita Region Hydrology Model Guidance – April 2014 This page has been intentionally left blank. Santa Margarita Region Hydrology Model Guidance – April 2014 To download the Santa Margarita Region Hydrology Model and the electronic version of this document, please go to http://www.floodcontrol.co.riverside.ca.us/NPDES/SantaMargaritaWS.aspx#SMdocs If you have questions about SMRHM or its use, please contact: Clear Creek Solutions, Inc. 360-943-0304 (8 AM – 5 PM Pacific time) ii Santa Margarita Region Hydrology Model Guidance – April 2014 End User License Agreement End User Software License Agreement (Agreement). By clicking on the "Accept" Button when installing the Santa Margarita Region Hydrology Model (SMRHM) Software or by using the Santa Margarita Region Hydrology Model Software following installation, you, your employer, client and associates (collectively, "End User") are consenting to be bound by the following terms and conditions. If you or User do not desire to be bound by the following conditions, click the "Decline" Button, and do not continue the installation process or use of the SMRHM Software. The SMRHM Software is being provided to End User pursuant to a sublicense of a governmental licensee of Clear Creek Solutions, Inc. Pursuant to the terms and conditions of this Agreement, End User is permitted to use the SMRHM Software solely for purposes authorized by participating municipal, county or special district member agencies of signatory programs which are organized on a county-wide basis for implementation of stormwater discharge permits issued by the California Regional Water Quality Control Board, under the National Pollutant Discharge Elimination System. The End User is not permitted to use the SMRHM Software for any other purpose than as described above. End User shall not copy, distribute, alter, or modify the SMRHM Software. The SMRHM incorporates data on soils, climate and geographical features to support its intended uses of identifying site-appropriate modeling parameters, incorporating user-defined inputs into longterm hydrologic simulation models of areas within the Santa Margarita Region , and assisting design of facilities for flow duration control as described in the accompanying documentation. These data may not be adequate for other purposes such as those requiring precise location, measurement or description of geographical features, or engineering analyses other than those described in the documentation. This program and accompanying documentation are provided 'as-is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by End User. Clear Creek Solutions Inc. and the governmental licensee or sublicensees disclaim all warranties, either expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions Inc., or authorized representatives be liable for any damages whatsoever (including without limitation to damages for loss of business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions Inc., has been advised of the possibility of such damages. Software Copyright © by Clear Creek Solutions, Inc. 2005-2013; All Rights Reserved. iii Santa Margarita Region Hydrology Model Guidance – April 2014 FOREWORD The Santa Margarita Region Hydrology Model (SMRHM) is a tool for analyzing the hydromodification effects of land development projects and sizing solutions to mitigate the increased stormwater runoff from these projects. This section of the guidance documentation provides background information on the definition and effects of hydromodification and relevant findings from technical analyses conducted in response to regulatory requirements. It also summarizes the current Hydromodification Management Standard and general design approach for hydromodification control BMPs, which led to the development of the SMRHM. Regulatory Context The California Regional Water Quality Control Board (Regional Board) requires stormwater programs to address the increases in stormwater runoff rate and volume from New Development and Redevelopment projects where those increases could cause increased erosion of receiving channels. Phase 1 municipal separate stormwater system (MS4) permits in Riverside County contain requirements to develop and implement hydromodification management plans (HMPs) and to implement associated management measures. iv Santa Margarita Region Hydrology Model Guidance – April 2014 TABLE OF CONTENTS End User License Agreement ............................................................................................iii FOREWORD ...................................................................................................................... iv Regulatory Context ............................................................................................................. iv Acknowledgements ............................................................................................................ iv INTRODUCTION TO SMRHM ........................................................................................ 1 QUICK START .................................................................................................................. 3 MAIN SCREENS ............................................................................................................. 35 MAP INFORMATION SCREEN ..................................................................................... 36 GENERAL PROJECT INFORMATION SCREEN ......................................................... 37 SCHEMATIC EDITOR .................................................................................................... 39 LAND USE BASIN ELEMENT ...................................................................................... 40 LATERAL BASIN ELEMENT (Pervious) ...................................................................... 43 LATERAL I BASIN ELEMENT (Impervious) ............................................................... 44 TRAPEZOIDAL POND ELEMENT ............................................................................... 45 VAULT ELEMENT ......................................................................................................... 49 TANK ELEMENT ............................................................................................................ 51 IRREGULAR POND ELEMENT .................................................................................... 53 PONDPAD INTERFACE ................................................................................................. 54 GRAVEL TRENCH BED ELEMENT ............................................................................. 56 SAND FILTER ELEMENT ............................................................................................. 58 OUTLET STRUCTURE CONFIGURATIONS ............................................................... 60 INFILTRATION ............................................................................................................... 66 AUTO POND .................................................................................................................... 67 CHANNEL ELEMENT ................................................................................................... 69 FLOW SPLITTER ELEMENT ........................................................................................ 71 TIME SERIES ELEMENT ............................................................................................... 73 STAGE-STORAGE-DISCHARGE TABLE ................................................................... 74 SSD TABLE ELEMENT .................................................................................................. 75 BIORETENTION ELEMENT .......................................................................................... 78 POINT OF COMPLIANCE .............................................................................................. 85 CONNECTING ELEMENTS ........................................................................................... 87 ANALYSIS SCREEN ...................................................................................................... 90 FLOW DURATION ......................................................................................................... 92 FLOW FREQUENCY ...................................................................................................... 94 DRAWDOWN .................................................................................................................. 95 HYDROGRAPHS ............................................................................................................. 96 LID BMP SIZING ............................................................................................................ 97 REPORTS SCREEN ....................................................................................................... 104 v Santa Margarita Region Hydrology Model Guidance – April 2014 TOOLS SCREEN ........................................................................................................... 106 LID ANALYSIS SCREEN ............................................................................................. 110 OPTIONS ........................................................................................................................ 114 DURATION CRITERIA ................................................................................................ 115 SCALING FACTORS .................................................................................................... 116 TIPS AND TRICKS FOR LID PRACTICES AND FACILITIES ................................ 118 INFILTRATION BASIN/POND .................................................................................... 119 INFILTRATION TRENCH ........................................................................................... 122 PERMEABLE PAVEMENT .......................................................................................... 125 BIORETENTION (STANDARD DESIGN) .................................................................. 128 BIORETENTION (VERTICAL SIDESLOPES) ........................................................... 130 BIORETENTION (PLANTER BOX) ............................................................................ 132 SAND FILTER BASIN .................................................................................................. 134 EXTENDED DETENTION BASIN ............................................................................... 136 APPENDIX A: DEFAULT SMRHM HSPF PERVIOUS PARAMETER VALUES ... 140 APPENDIX B:DEFAULT SMRHM HSPF IMPERVIOUS PARAMETER VALUES 157 APPENDIX C: ADDITIONAL GUIDANCE FOR USING SMRHM .......................... 161 Infiltration Reduction Factor ..................................................................................... 161 Flow Duration Outlet Structures – Practical Design Considerations ........................ 162 Drawdown time and treatment/vector considerations ............................................... 163 APPENDIX D: SMRHM REVIEWER CHECKLIST ................................................... 167 APPENDIX E: SMRHM BACKGROUND ................................................................... 169 Effects of Hydromodification ................................................................................... 169 Development of the Santa Margarita Region Hydrology Model .............................. 169 SMRHM OVERVIEW ................................................................................................... 170 BIORETENTION MODELING METHODOLOGY .................................................... 172 vi Santa Margarita Region Hydrology Model Guidance – April 2014 ACRONYMS and ABBREVIATIONS AGWETP AGWRC AGWS ASCE ASTM AT BASETP BMP C CCS CEPSC CF CFS d DEEPFR Dev. DMA D85 Ft GWVS h Headr HMP HSPF H/V I IFWS in. INFEXP INFILD INFILT INTFW IRC K KVARY LID LSUR LZETP LZS Active Groundwater Evapotranspiration Fraction Active Groundwater Recession Constant (per day) Initial Active Groundwater Storage (inches) American Society of Civil Engineers American Society of Testing and Materials Tributary Area Base Flow (from groundwater) Evapotranspiration Fraction Best Management Practice Runoff Coefficient Clear Creek Solutions Interception storage (inches) Correction Factor Cubic Feet per Second Surface ponding depth (feet) Fraction of groundwater to deep aquifer or inactive storage Development Drainage Management Area 85th percentile, 24-hour rainfall depth Foot Initial Groundwater Vertical Slope (feet/feet) Hydraulic head (feet) The water height over the notch/orifice bottom Hydromodification Management Plan Hydrologic Simulation Program in Fortran Ratio of horizontal to vertical distance Gradient of the water table surface (slope) Initial interflow (inches) inch Infiltration Exponent Infiltration ratio (maximum to mean) Infiltration (inches per hour) Interflow index Interflow Recession Constant (per day) Hydraulic conductivity (inches per hour) Variable groundwater recession Low Impact Development Length of surface flow path (feet) Lower Zone Evapotranspiration fraction Initial Lower Zone Storage (inches) vii Santa Margarita Region Hydrology Model Guidance – April 2014 LZSN m Mitigated MS4 N NRCS NSUR NTS Phi POC Predev Q q QBMP Qcp RETS RETSC SLSUR SMMWW SMR SMRHM SSD Stormwater runoff SURS SWMM Theta Tr TSS USDA UZS UZSN VBMP VU WDM WEF Wh WS WWHM Lower Zone Storage Nominal (inches) rank (largest event, m = 1) The developed land use with mitigation measures (as selected by the user). Municipal Separate Storm Sewer System Number of years Natural Resources Conservation Service Surface roughness (Manning's n) for impervious area Not to Scale Soil porosity Point of Compliance Predevelopment: the native land cover conditions prior to any land use development. Flow rate (cfs) Darcy flux (cm/hr) LID BMP flow rate (cfs) Critical Flow (cfs) Initial surface retention storage (inches) for impervious area Surface retention storage (inches) for impervious area Slope of surface flow path (feet/feet) for impervious area Stormwater Management Manual for Western Washington Santa Margarita Region Santa Margarita Region Hydrology Model Stage Storage Discharge Stormwater that does not soak into the ground and either flows directly into surface waterways or is channeled into storm drains Initial surface runoff (inches) for impervious area Stormwater Management Model Notch Angle Return period (years) Total suspended solids United States Department of Agriculture Initial Upper Zone Storage (inches) Upper Zone Storage Nominal (inches) LID BMP design volume 85% unit storage volume Watershed Data Management Water Environment Federation Notch Width Water Surface Western Washington Hydrology Model vii Santa Margarita Region Hydrology Model Guidance – April 2014 This page has been intentionally left blank. vii Santa Margarita Region Hydrology Model Guidance – April 2014 INTRODUCTION TO SMRHM SMRHM is the Santa Margarita Region Hydrology Model. SMRHM is based on the WWHM (Western Washington Hydrology Model) stormwater modeling software platform. WWHM was originally developed for the Washington State Department of Ecology. More information about WWHM can be found at www.clearcreeksolutions.com. More information can be found about the Washington State Department of Ecology's stormwater management program and manual at http://www.ecy.wa.gov/programs/wq/stormwater/manual.html. Clear Creek Solutions is responsible for SMRHM and the SMRHM guidance documentation. This guidance documentation is organized so as to provide the user an example of a standard application using SMRHM (described in Quick Start) followed by descriptions of the different components and options available in SMRHM. The Tips and Tricks section presents some ideas of how to incorporate LID (Low Impact Development) facilities and practices into the SMRHM analysis. Riverside County's Design Handbook for Low Impact Development Best Management Practices (September 2011) has the most up-to-date information regarding BMP standards and should be consulted prior to the start of any SMRHM LID BMP modeling. Appendices A and B provide a full list of the HSPF parameter values used in SMRHM. Appendix C contains additional guidance and recommendations by the stormwater programs that have sponsored the SMRHM development. Appendix D is a checklist for use by SMRHM project reviewers. Appendix E provides additional background information on SMRHM. Throughout the guidance documentation notes using this font (sans-serif italic) alert the user to actions or design decisions for which guidance must be consulted that is external to the SMRHM software, either provided in Appendix C of this guidance documentation or by the Copermittee with jurisdiction over the project site. Purpose The purpose of SMRHM is to size hydromodification management or flow control BMPs to mitigate the effects of increased stormwater runoff (peak discharge, duration, and volume) from proposed land use changes that impact natural streams, wetlands, and other water courses. SMRHM provides: A uniform methodology for the SMR A more accurate methodology than single-event design storms An easy-to-use software package 1 Santa Margarita Region Hydrology Model Guidance – April 2014 SMRHM is based on: Continuous simulation hydrology (HSPF) Actual long-term recorded precipitation data Measured pan evaporation data Existing vegetation (for predevelopment conditions) Regional HSPF parameters Computer Requirements Windows 2000/XP/Vista/7/8 with 300 MB uncompressed hard drive space Internet access (only required for downloading SMRHM, not required for executing SMRHM) Pentium 3 or faster processor (desirable) Color monitor (desirable) It is important to know the following information prior to using SMRHM for a project: Knowledge of the site location and/or street address Knowledge of the actual distribution of existing site soil by category (A, B, C, or D) Knowledge of the actual distribution of existing and proposed site land cover by category (forest, shrub, grass, or urban) Knowledge of the actual distribution of existing and proposed site topography by category (flat, moderate, steep, or very steep) Knowledge of the planned distribution of the proposed development (buildings, streets, sidewalks, parking, lawn areas) overlying the soil categories 2 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 QUICK STA ART Quick k Start very briefly b describes the steeps to quickkly size a stoormwater ruunoff detentiion pond using u SMRH HM. New users should d read the ddescriptions of the SMR RHM screenns, elemen nts, and anallysis tools beefore going through t the steps describbed below. 1. Opeen SMRHM M. SMRH HM will open with a map p of the SMR R. 3 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 The map m controlss can be useed to enlarg ge a specificc area on thhe street mapp layer. Thhis option n helps to loccate the speccific project site. s When the street map m layer is enlarged a sufficient am mount the inndividual strreet names aare shown n on the map p. 4 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 2. Select the projject site loca ation. Locatee the project site on the map. m Use th he map contrrols to magniify a portionn of the map,, if needed d. Select th he project sitte by left cliicking on thhe map locattion. A redd circle will be placed d on the map identifying the project site. s The model m will th hen automatiically select the approprriate rain gaauge record for the projeect site. The SMR has four long-term 15-minute prrecipitation records: Eaastern Slopes, Temeccula Valley, Western Plaateau, and Wildomar/No W rth Murrietaa. For thiis example we w will use th he Temeculaa Valley rainn gauge. The sitte name, add dress, and citty informatio on is optionaal. It is not uused by SMR RHM, but w will be inclluded in the project repo ort summary.. 5 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 3. Use the tool bar (immediately above the t map) to move to thee Scenario Editor. Click on th he General Project P Inforrmation buttton. The General G Projject Informa ation button will bring up the Schematic Editor. E The scchematic ediitor screen co ontains two scenarios: Predev velopment an nd Mitigated d. ent scenario First set s up the Predevelopm P o and then the Miitigated scen nario. Left cllick on the Land L use Baasin elementt under the Drainaage Elementts heading. The Land use Basin elemen nt representts a drainage managem ment area (DMA A). Select any grid ceell (preferably near the top of the grid) and a left clicck on that grid. g The DMA D will appearr in that grid cell. 6 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 To thee right of thee grid is thee land use in nformation aassociated w with the DM MA. Select tthe approp priate soil, land l cover, and land slo ope for the Predeveloppment scenarrio. Soils aare based on NRCS geeneral catego ories A, B, C, C and D. Land cover c is based on the naative vegetaation for the Predevelopment projecct area and tthe planneed vegetation for the planned deveelopment (M Mitigated scenario). Noon-urban lannd cover can c be forest, shrub, and d/or grass. In n contrast, thhe developedd landscape will consist of urban vegetation (lawns, floweers, planted shrubs and ttrees) and is regularly irrrigated. Land slope s is diviided into flaat (0-5%), moderate m (5-110%), steep (10-20%), aand very steeep (>20% %) land slopees. HSPF parameter values v in SM MRHM havee been adjussted for the different sooil, land coveer, and lan nd slope cateegories. For thiis example we w will assum me that the Predevelopm P ment land usee is: D soil grass vegeetation moderate slope (5-10% %) DMA equ uals 10 acress 7 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 Note th hat the Predevelopment land use nev ver includes man-made iimpervious aareas. Existiing imperv vious areas must m be mod deled as theey were prioor to any lannd use develoopment on tthe projectt site. The do ownstream discharge d fro om this DMA will be seelected as ouur point of ccompliance ffor the Preedevelopmen nt scenario. Right click k on the DM MA and highhlight Conneect to Point of Complliance (the point p of com mpliance is defined as the locationn at which the stormwaater runofff from both th he Predevelo opment scen nario and thee Mitigated sscenario are compared). The Point P of Co ompliance screen s will be shown n for Predev velopment DMA D 1. The T POC (Point ( of Compliance) Outlet O has beeen checkeed for bo oth surface runoff and a interflo ow (shallow w subsurfacee flow). Theese are thee two flow components c of stormwaater runofff. Do not ch heck the gro oundwater box b unless there is observed o and d documentted base fllow on the project site. Click the Connecct button in the low rig ght cornerr to connect this t point off compliancee to the Preedevelopmen nt basin. 8 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 After the t point of compliance has been ad dded to the D DMA, the laand use basinn element w will changee. A small box with a bar chart grraphic and a number w will be shownn in the low wer right corner c of th he element. This smalll POC boxx identifies this DMA as a point of compliiance. The number n is th he POC numb ber (e.g., PO OC 1). 9 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 4. Set up the Mitiigated scena ario. First, select s the Miitigated scen nario tab at the t top of thee grid. Place a land use basin elemeent on the grid to repreesent the sam me DMA, ass selected in the Predeveelopment sceenario. 10 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 For thee Mitigated scenario DM MA we will input i the folllowing inforrmation: Pervio ous area: D soil urban veg getation moderate slope (5-10% %) 4.5 acres Imperv vious area: Roads, moderate slop pe: 2.5 acres Roof Areaa: 1.5 acres Parking, flat f slope: 1.5 acres The im mpervious land category includes roaads, roofs, siidewalks, paarking, driveeways, and aany other impervious i surfaces. s Alll are modeled the samee; the surfacee runoff prodduced from an imperv vious land surface s only y varies by land l slope ((steeper sloppes producee more surfaace runofff than flatter slopes). The neext step is to o add a mitig gation facilitty downstreaam of the DM MA. For thhis example w we will usse a trapezo oidal stormw water pond (also ( knownn as a detenttion basin) tto provide tthe requireed hydromod dification miitigation. 11 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 Place the t trapezoid dal pond eleement below w the DMA inn any cell onn the grid. IIt doesn't haave to be directly d below w the DMA, but it must be somewheere on a low wer row in thhe grid. Right click c on the DMA and select Conneect To Elemeent. A greenn line will apppear with oone end co onnected to the t DMA. 12 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 Pull th he other end d of the line down to the trapezo oidal pond with the mouse m pointeer and cllick on the pond. Thiss action willl bring up the From m Basin to Conveyance n. screen As with the Predeevelopment scenario we t only conn nect the surfa face flow and d want to the intterflow (shalllow subsurfface seepagee) from th he basin to the t pond. Cllick OK. 13 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 A line will then bee shown conn necting the DMA D to the trapezoidal pond. 14 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 Right click on thee trapezoidaal pond elem ment to connnect the ponnd's outlet tto the point of hlight and cliick on Connect to Point Of Compliaance. compliiance. High 15 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 The Po oint of Com mpliance screeen will be shown s for thhe pond. Thhe pond has one outlet ((by defaultt). The outfflow from thee pond will be b comparedd with the Prredevelopmeent runoff. T The point of complian nce is desig gnated as POC P 1 (SM MRHM allow ws for multtiple points of compliiance). Clicck on the Con nnect button n. 16 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 The po oint of comp pliance is sh hown on the pond elemeent as a smaall box with the letter "A A" and nu umber 1 in th he bar chart symbol s in th he lower righht corner. NOTE E: The letteer "A" stan nds for An nalysis and designates that this iis an analyssis locatio on where fllow and sta age will be computed c aand the outtput flow an nd stage tim me series will be mad de available to the user. The numb ber 1 denotees that this is POC 1. You can c have an n analysis lo ocation with hout havingg a point off compliancee at the sam me locatio on, but you u cannot have a poin nt of complliance that is also nott an analyssis locatio on. 17 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 5. Siziing the trapezoidal pon nd. A trap pezoidal storrmwater pon nd can be siized either m manually orr automaticaally (using tthe Auto Pond P featuree). For this example e Autto Pond will be used. (G Go to page 48 to find moore inform mation about how to man nually size a stormwaterr pond, detenntion basin, or other HM MP BMP.)) Click on o the Auto Pond button n and the Au uto Pond scrreen will apppear. The uuser can set tthe pond depth d (defau ult: 4 feet), pond p length to width raatio (default: 1 to 1), poond sidesloppes (defau ult: 3 to 1), and the outtlet structuree configurattion (defaultt: 1 orifice aand riser wiith rectang gular notch weir). w 18 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 To opttimize the po ond design and a create thee smallest poond possiblee, move the A Automatic Pond Adjuster A poin nter from the left to the right. r The po ond does nott yet have an ny dimensions. Click thhe Create Poond button tto create inittial pond dimensions, d which will be the startiing point forr Auto Pondd's automatedd optimizatiion processs to calculatte the pond size s and outlet structure dimensions. NOTE E: Dependin ng on the complexity c ngth of the precipitatiion of the projject, the len record d and the computation c nal speed of the comp puter, Auto Pond mayy take 1 to 15 minuttes to run. Runnin ng Auto Pon nd automatess the followiing SMRHM M processes: 1. 1 2. 2 3. 3 4. 4 5. 5 the 15--minute Pred developmentt scenario ruunoff is com mputed for thhe 30-50 yeaars of record (it varies depending on o the rain ggauge used), the Preedevelopmen nt runoff flo ood frequenncy is calcullated based on the parttial duration peak flows, the ran nge of flows is selected for the flow w duration (110% of the 22-year peak to the 10-year peak), this flow range is divided d into 100 incremeents, and the num mber of 15--minute Predevelopmennt flow valuues that exceeed each floow increment level (Prredevelopmeent flow durration) are ccounted to ccreate the floow duration curves and d accompany ying tabular results. Next, SMRHM computes c thee post-development runnoff (in thee Mitigated scenario) aand t the pond. But before b the ruunoff can bee routed throough the poond routes the runoff through ond must be given dimeensions and an outlet coonfiguration.. Auto Pondd uses a set of the po rules based b on thee Predevelop pment and Mitigated M sccenario land uses to givve the pond an initial set of dimen nsions and an a initial outtlet orifice ddiameter andd riser (the rriser is givenn a defaultt rectangularr notch). Th his informattion allows SMRHM too compute a stage-storaggedischaarge table forr the pond. 19 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 With this initial po ond stage-sto orage-dischaarge table SM MRHM: 1. 1 2. 2 3. 3 routes the t 15-minu ute post-projeect runoff thhrough the pond for the 30-50 years of record to create thee Mitigated flow f time serries, counts the numberr of 15-minu ute Mitigateed flow valuues that exceed each floow increment level (this is the Mitiigated flow dduration), annd computtes the ratio of Mitigateed flow valuues to Predevvelopment fl flow values ffor each flow incremeent level (comparing thee Predeveloppment and M Mitigated floow duration results). If any of the 100 in ndividual raatio values iss greater thann allowed byy the flow duuration criteria then th he pond failss to provide an a appropriaate amount oof mitigationn and needs tto be resizedd. Flow duration d resu ults are show wn in the pllots above. The verticaal axis show ws the range of flows from f 10% of the 2-year flow (0.40 cfs) c to the 100-year flow ((8.66 cfs). T The horizonntal axis iss the percen nt of time that t flows exceed e a floow value. Plotting poositions on tthe horizontal axis typ pically rangee from 0.001% to 1%, as explained bbelow. For the entire 30- to 50-year simulation period p (depeending on thhe period off record of tthe precipitation statio on used) all of the 15-miinute time stteps are cheecked to see if the flow ffor that tim me step is greater g than the minimu um flow durration criterria value (0.40 cfs, in thhis examp ple). For a 50-year 5 simu ulation perio od there aree approximattely 1,600,000 15- minuute values to check. Many of th hem are zero o flows. Thhe 10% of thhe Predeveloopment 2-yeear flow value v is typiccally exceedeed less than 1% of the tootal simulatioon period. 20 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 This fllow duration n check is do one for both h the Predeveelopment floows (shown in blue on tthe screen n) and the Miitigated flow ws (shown in n red). If all of o the Mitig gated flow duration d valu ues (in red) are to the leeft of the Prredevelopmeent flow duration d valu ues (in bluee), then the number of occurrencess decreases and the poond successsfully mitigaates the addiitional erosiv ve flows prooduced by thhe developmeent. If the Mitigated M flow duration n values (in red) r are far tto the left off the Predevelopment floow duratio on values (iin blue), theen the pond d can be m made smallerr and still m meet the floow duratio on criteria. Auto Pond P goes th hrough an iteeration process by whicch it changess the pond ddimensions aand outlet configuratio on, then insstructs SMR RHM to ag ain compute the resultting Mitigatted ns, and decid de if it has m made the ressults better oor worse. Thhis runofff, compare fllow duration iteratio on process continues c until Auto Pon nd finally cooncludes thatt an optimum m solution hhas been found f and th he Mitigated d flow duratiion values (iin red) are aas close as ppossible to tthe Predev velopment fllow duration n values (in blue). b Whenn this occurss the Auto P Pond Finish hed messag ge appears on o the screen n. 21 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 The usser has the option o to continue to manually optiimize the poond by manuually changiing pond dimensions and/or thee outlet stru ucture confi figuration. (Manual opptimization is explain ned in more detail on paage 48.) Aft fter making tthese changees the user should click on the Op ptimize Pon nd button to o check the results andd see if Autoo Pond cann make furthher improv vements. (bottom len The final fi pond dimensions d ngth, bottom m width, efffective ponnd depth, aand sideslo opes) and ou utlet structu ure informatiion (riser heeight, riser diameter, riiser weir typpe, weir notch n height and width, and a orifice diameter d andd height) aree shown on tthe trapezoiddal pond screen s to the right of the Schematic grid. g NOTE E: If Auto Pond selec cts a bottom orifice d diameter sm maller than the smalle est diame eter allowed d by the lo ocal municip pal permittiting agencyy then the user has th the option n of specify ying a minim mum allowa able bottom m orifice dia iameter eve en if this siize diame eter is too large to meet m flow duration d criiteria for th his elementt. Addition nal mitiga ating BMPs may be e required d to meett local hyydromodifica ation contr trol requirrements. Please P see e Appendix x C or co onsult with the Cope ermittee w with jurisdiiction over the project site for mo ore details. For manua al sizing infformation see page 48. 22 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 6. Rev view analysiis. The Analysis tool bar button (third from the left) brinngs up the A Analysis scrreen where tthe user caan look at th he results. Eaach time series dataset iss listed in thhe Analyze D Datasets box in the low wer left corn ner. 23 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 To rev view the flow w duration analysis at th he point of coompliance select the PO OC 1 tab at tthe bottom m and make sure that both b the 501 1 POC 1 Prredevelopmeent flow and 801 POC C 1 Develo oped flow arre highlighteed. 24 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 The flow duration n plot for both Predevelo opment and Mitigated fflows will bee shown aloong with th he specific flow valuess and numbeer of times Predevelopm ment and M Mitigated flow ws exceed ded those flo ow values. The T Pass/Faiil on the righht indicates w whether or nnot at that floow level the t flow con ntrol standard d criteria weere met and the pond paasses at that flow level ((in this ex xample from 10% of the 2-year flow to the 10-yeear). If not, a Fail is shoown. NOTE E: A single Fail F fails the hydromodiffication pondd design criteria. 25 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 Pond drawdown/re d etention timee is computeed on the Annalysis screenn. NOTE E: This info ormation is not require ed for basicc sizing of tthe flow durration facilitty, but ca an assist th he user in determining d g the overalll suitabilityy of the mitig igated desig gn in me eeting addiitional, rela ated requirrements fo or treating stormwater runoff an nd minim mizing risk of vector (mosquito) ( breeding p problems. See page 98 for mo ore descriiptions of th his SMRHM M feature, and a Append dix C for disscussion an nd reference es for the ese requirements. Click on o the Stagee tab at the bottom to gett the Mitigat ed pond stagge time seriees. 26 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 Click on the tab labeled Dra awdown. This T is wherre the pond drawdown/rretention tim me resultss will be show wn. 27 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 Select the pond yo ou want to analyze a for drawdown/re d etention timee (in this exxample theree is only one pond: Traapezoidal Po ond 1) by cliicking on thee dataset andd highlightinng it. 28 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 Click on the Analy lyze Stage button and th he computedd pond stagees (pond watter depths) aare summaarized and reeported in teerms of drain n/retention tiime (in days). For th his example, the maximu um stage co omputed durring the enttire 30-50 yeear simulation period d is 3.40 feeet. This max ximum stage has a draawdown tim me of 1 day, 20 hours, 33 minutees, and 8 secconds. Ponds may have drain d times in i excess off the allowedd maximum of hours. T This can occcur when a pond has a small botttom orifice. If this is nnot acceptabble then the user needs to changee the pond outlet o config guration, maanually run tthe Mitigatedd scenario, and repeat tthe analyzze stage com mputations. A situation may m occur w where it is noot possible too have both an accepttable pond drrawdown/rettention time and meet thhe flow durattion criteria. NOTE E: See Appe endix C or the local municipal m pe ermitting ag gency for an n overview of other requiremen nts that ma ay apply reg garding dra awdown tim me, and sug ggestions ffor essing situa ations where re it is not possible p to meet all d drawdown/re retention tim me addre guidellines and also a meet the t flow durration criteria. The g guidance do ocumentatio on assum mes that the t flow duration d criiteria take precedencce unless the user is instruc cted otherw wise by the local munic cipal permittting agenccy. 29 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 7. Produce reportt. Click on o the Repo orts tool bar button (fourrth from the left) to generate a projeect report wiith all of the t project in nformation and a results. The prroject report can be geneerated as eith her a Microsooft Word file or a PDF ffile. 30 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 Scroll down the Reeport screen n to see all off the results. 31 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 8. Sav ve project. To sav ve the projecct click on Fiile in the upp per left cornner and select Save As. 32 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 Selectt a file namee and save th he SMRHM project file. The user ccan exit SMR RHM and latter reload d the project file with all of its inform mation by gooing to File, Open. 33 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 9. Exitt SMRHM. To exiit SMRHM click c on Filee in the uppeer left cornerr and select Exit. Or cliick on the X in the red d box in the upper u right hand h corner of the screenn. 34 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 MAIN SCRE EENS SMRH HM has six main screen ns. These main m screenss can be accessed througgh the buttoons shown n on the tool bar above or o via the Vieew menu. The siix main screeens are: Map M Information General G Projeect Informatiion Analysis A Reports R Tools T LID L (Low Im mpact Develo opment) Anaalysis Each is i discussed in more detaail in the folllowing secti ons. 35 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 MAP P INFORM MATION SCREEN S The Map M screen contains c cou unty informaation. The precipitationn gauge andd precipitatiion factor are shown to o the right of the map. They T are bassed on the prroject site loccation. The usser can prov vide site info ormation (op ptional). Thhe site namee and addresss will help to identiffy the projecct on the Report screen n and in thee printed repport provideed to the loccal municipal permittiing agency. The usser locates th he project siite on the map m screen byy using the mouse and lleft clickingg at the project site lo ocation. Rig ght clicking on the mapp re-centers the view. The + andd – button ns zoom in and a out, resp pectively. The T cross haiir button zoooms out to tthe full counnty view. The arrow keys k scroll th he map view w. 36 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 GEN NERAL PR ROJECT INFORMA I ATION SC CREEN The Prroject screen n contains all of the inforrmation aboout the projecct site for thhe two land uuse scenarrios: Predev velopment land l use co onditions annd Mitigateed (developped) land uuse conditions. To change c from m one scenaario to anotther click oon the tab ccontaining tthe priate scenarrio name at th he top of thee grid. approp Predev velopment is defined as a the nativ ve land coveer conditionns prior to any land uuse develo opment. Ru unoff from the Predeveelopment sccenario is uused as the target for tthe Mitigaated scenario o compliancee. The modeel will acceppt any land uuse for this sccenario. Mitigaated is defineed as the dev veloped land d use with m mitigation meeasures (as sselected by tthe user). Mitigated is used for sizing hyd drologic conttrol and waater quality facilities. T The runofff from the Mitigated M scen nario is com mpared with tthe Predevellopment scennario runofff to determ mine compliaance with flo ow duration criteria. c The Run R Scenario o button exeecutes the ru unoff calcullations for thhe scenario shown on tthe screen n. Note: Any chang ges made by y the user to t the elemeent dimensiions and other input aare not an nalyzed by SMRHM S un ntil the Run Scenario bu utton is cliccked. 37 Santa Margarita Region Hydrology Model Guidance – April 2014 Below the Run Scenario button are the Elements. Each element represents a specific stormwater-related feature (drainage elements, flow connections, BMPs, etc.) and is described in more detail in the following section. 38 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 SCHE EMATIC EDITOR E The Prroject screen n also contaiins the Schem matic Editorr. The Scheematic Editoor is the gridd to the rig ght of the elements. Th his grid is where w each eelement is pllaced and linked togethher. The grrid, using thee scroll bars on the left and a bottom, expands as large as neeeded to contaain all of the t elementss for the project. A maxiimum of 5000 elements iss allowed. NOTE E: All movem ment of watter on the grrid must bee from the toop of the grrid down. The sp pace to the riight of the grrid will conttain the approopriate elem ment informaation. To sellect and placce an elemeent on the grrid, first left ft click on thhe specific eelement in tthe Elements menu an nd then drag the elementt to the seleccted grid squuare. The selected elemeent will ap ppear in the grid g square. The en ntire grid caan be moveed up, down n, left, or riight using thhe Move Ellements arroow button ns. The grrid coordinaates from onee project can n be saved ((Save x, y) and used for new projeccts (Load x, y). 39 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 LAND D USE BA ASIN ELE EMENT The Laand use Basiin element reepresents a DMA D that caan have any combinationn of soils, lannd cover, and land slopes. A DMA producces three typpes of runofff: (1) surfaace runoff, ((2) interflo ow, and (3) groundwaterr. Surfacce runoff is defined as the overlan nd flow thaat quickly reeaches a M MS4 facility or receiviing water. Su urface runofff mainly com mes from im mpervious suurfaces. Interflow is shallo ow, subsurfface flow prroduced by pervious laand categoriies and variies based on soil charracteristics and a how thesse characteriistics are alttered by landd developmeent practicces. Groun ndwater is th he subsurfaace flow thaat typically does not eenter a MS44 facility, bbut provid des base flow w directly to a channel. The usser can speccify where each e of thesee three sourrces of flow w should be directed. T The defaultt setting is for fo the surfacce runoff and d interflow tto go to the M MS4 facilityy; groundwatter should d not be con nnected unlesss there is observed o basse flow occuurring in MS S4 facilities in the DM MA. 40 Santa Margarita Region Hydrology Model Guidance – April 2014 Table 1 shows the different pervious land types represented in the Land use Basin element. Table 1. SMRHM Pervious Land Types PERLND No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 Soil Type A A A A A A A A A A A A A A A A B B B B B B B B B B B B B B B B C/D C/D C/D C/D C/D C/D C/D C/D C/D C/D C/D Land Cover Forest Forest Forest Forest Shrub Shrub Shrub Shrub Grass Grass Grass Grass Urban Urban Urban Urban Forest Forest Forest Forest Shrub Shrub Shrub Shrub Grass Grass Grass Grass Urban Urban Urban Urban Forest Forest Forest Forest Shrub Shrub Shrub Shrub Grass Grass Grass Land Slope Flat (0-5%) Moderate (5-10%) Steep (10-20%) Very Steep (>20%) Flat (0-5%) Moderate (5-10%) Steep (10-20%) Very Steep (>20%) Flat (0-5%) Moderate (5-10%) Steep (10-20%) Very Steep (>20%) Flat (0-5%) Moderate (5-10%) Steep (10-20%) Very Steep (>20%) Flat (0-5%) Moderate (5-10%) Steep (10-20%) Very Steep (>20%) Flat (0-5%) Moderate (5-10%) Steep (10-20%) Very Steep (>20%) Flat (0-5%) Moderate (5-10%) Steep (10-20%) Very Steep (>20%) Flat (0-5%) Moderate (5-10%) Steep (10-20%) Very Steep (>20%) Flat (0-5%) Moderate (5-10%) Steep (10-20%) Very Steep (>20%) Flat (0-5%) Moderate (5-10%) Steep (10-20%) Very Steep (>20%) Flat (0-5%) Moderate (5-10%) Steep (10-20%) 41 Santa Margarita Region Hydrology Model Guidance – April 2014 44 45 46 47 48 C/D C/D C/D C/D C/D Grass Urban Urban Urban Urban Very Steep (>20%) Flat (0-5%) Moderate (5-10%) Steep (10-20%) Very Steep (>20%) The user does not need to know or keep track of the HSPF PERLND number. That number is used only for internal tracking purposes. The user inputs the number of acres of appropriate basin land use information. Pervious land use information is in the form of soil, land cover, and land slope. For example, "A, Grass, Flat" means NRCS soil type A, natural grass vegetative cover, and flat (0-5%) land slope. There are four basic soil types: A (well infiltrating soils), B (moderate infiltrating soils), C (poor infiltrating soils), and D (really poor infiltrating soils). There are four basic land cover categories: forest, shrub, grass and urban landscaped vegetation. Native land cover is assumed to be grass and refers to the natural (non-planted) vegetation. In contrast, the developed landscape will consist of urban vegetation (lawns, flowers, planted shrubs and trees). Urban vegetation is irrigated in SMRHM. Land slope is divided into flat (0-5%), moderate (5-10%), steep (10-20%), and very steep (>20%) land slopes. HSPF parameter values in SMRHM have been adjusted for the different soil, land cover, and land slope categories. SMRHM HSPF soil parameter values take into account the hydrologic effects of land development activities that result from soil compaction when "Urban" is specified. The impervious land use category includes roads, roofs, sidewalks, parking, driveways, and any other impervious surfaces. All are modeled in the same manner: the surface runoff produced from an impervious land surface only varies by land slope (steeper slopes produce more surface runoff than flatter slopes). 42 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 LATE ERAL BA ASIN ELEM MENT (Pe ervious) Surfacce runoff dispersion fro om impervio ous surfacess onto adjaccent pervious land can be modelled using pervious and impervious i lateral l basinns. For exam mple, surfacce runoff froom an imp pervious parrking lot caan sheet flow w onto an aadjacent lawnn prior to ddraining intoo a MS4 facility. f Thiis action slow ws the surfaace runoff annd allows foor some limitted infiltration into th he pervious lawn l soil prior to discharrging into a M MS4 facilityy. The peervious laterral basin is similar s to th he standard lland use bassin except thhat the surfaace runofff from the latteral basin goes g to anoth her adjacent lateral basinn (imperviouus or perviouus) rather than directly y to a MS4 facility f or reeceiving watter. By definnition, the pervious laterral basin contains c onlly a single peervious land d type. Impeervious area is handled sseparately wiith the im mpervious lateral basin (L Lateral I Bassin). The usser selects th he pervious lateral l basin n land type b y checking tthe appropriiate box on tthe Availa able Soil Typ pes (PERLN NDs) screen n. This inforrmation is auutomaticallyy placed in tthe Soil Types T (PER RLNDs) box x above. Once O enteredd, the land type can be changed bby clickin ng on the Ch hange button n on the righ ht. The usser enters thee number off acres repressented by thee lateral basiin land type.. If the lateral basin n contains tw wo or more pervious p landd use types tthen the userr should creaate b for eacch. a sepaarate lateral basin 43 Santa Margaarita Region Hyydrology Model G Guidance – Apriil 2014 LATE ERAL I BA ASIN ELE EMENT (IImperviou us) The im mpervious laateral basin is i similar to o the standarrd land use bbasin exceptt that the suurface runofff from the lateral imperv vious basin goes g to anothher adjacentt lateral basiin (impervioous or pervious) rather than t directly y to a MS4 4 facility oor receiving water. Byy definitionn, the imperv vious laterall basin con ntains only impervious land typess. Pervious area is hanndled separaately with thee pervious laateral basin (Lateral ( Basiin). The usser selects th he imperviou us lateral bassin land typee by checkinng the approppriate box oon the Availa able Impervvious Covera age’s (IMPL PLNDs) screeen. This iinformation is automatiically placed d in the Impeervious Typee (IMPLND) D) box abovee. Once enteered, the landd use type caan be changeed by clickin ng on the Ch hange button n on the rightt. The usser enters the number off acres repreesented by thhe lateral im mpervious basin land typee. To model parking lott surface run noff dispersiion onto adjjacent lawn connect thee Lateral I B Basin t the down nstream Lateeral Basin ((the lawn). In the moddel's calculaations (the parking lot) to m the parkin ng lot is addeed to the surfface of the laawn (urban vegetation). The surfacee runoff from total surface runofff will then be directed to MS4 faccility or receeiving waterr selected byy the user. 44 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 TRAP PEZOIDA AL POND ELEMEN NT In SM MRHM theree is an ind dividual pond (detention basin) b element for each type t of pon nd and hyd drologic control facility. The pond element e shown n above is for a trap pezoidal pond. This is the most commo on type of hyd drologic conttrol facility. A trap pezoidal pon nd has dimeensions (bottom m length and d width, dep pth, and sideslo opes) and an a outlet sttructure consistting of a riseer and one or o more orificees to contro ol the releease of runofff from the po ond. A trap pezoidal i the option to in nfiltrate pond includes surfacee runoff, if the soiils are approp priate and there t is su ufficient depth to the underrlying groun ndwater table. 45 Santa Margarita Region Hydrology Model Guidance – April 2014 The user has the option to specify that different outlets be directed to different downstream destinations, although usually all of the outlets go to a single downstream location. Auto Pond will automatically size a trapezoidal pond to meet the required flow duration criteria. NOTE: Auto Pond is available only in the Mitigated scenario. Quick Pond can be used to instantly add pond dimensions and an outlet configuration without checking the pond for compliancy with flow duration criteria. Quick Pond is sometimes used to quickly create a scenario and check the model linkages prior to sizing the pond. Multiple clicks on the Quick Pond button incrementally increase the pond size. The user can change the default name "Trapezoidal Pond 1" to another more appropriate name, if desired. Precipitation and evaporation must be applied to the pond unless the pond is covered. The pond bottom elevation can be set to an elevation other than zero if the user wants to use actual elevations. All pond stage values are relative to the bottom elevation. Negative bottom elevations are not allowed. The pond effective depth is the pond height (including freeboard) above the pond bottom. It is not the actual elevation of the top of the pond. Pond sideslopes are in terms of horizontal distance over vertical. A standard 3:1 (H: V) sideslope would be given a value of 3. A vertical sideslope has a value of 0. The pond bottom is assumed to be flat. The pond outlet structure consists of a riser and zero to three orifices. The riser has a height (typically one foot less than the effective depth) and a diameter. The riser can have either a flat top or a weir notch cut into the side of the top of the riser. The notch can be either rectangular, V-shaped, or a Sutro weir. More information on the riser weir shapes and orifices is provided later in this guidance document. After the pond is given dimensions and outlet information the user can view the resulting stage-storage-discharge table by clicking on the Open Table arrow in the lower right corner of the pond information screen. This table hydraulically defines the pond's characteristics. The user can use either Auto Pond to size a pond or can manually size a pond. Follow the steps below for manual sizing a pond using an outlet configuration with one orifice and a riser with rectangular notch (this is usually the most efficient design): 1. 2. Input a bottom orifice diameter that allows a discharge equal to the lower threshold (e.g., 10% of 2-year) Predevelopment flow for a stage equal to 2/3 the height of the riser. This discharge can be checked by reviewing the pond's stage-storage-discharge table. Input a riser rectangular notch height equal to 1/3 of the height of the riser. 46 Santa Margarita Region Hydrology Model Guidance – April 2014 3. 4. 5. 6. 7. Initially set the riser notch width to 0.1 foot. Run Predevelopment and Mitigated scenarios. Go to Analysis screen and check flow duration results. If pond passes flow duration criteria then decrease pond dimensions. If pond fails flow duration criteria then change (in order of priority) bottom orifice diameter, riser notch width, pond dimensions. Iterate until there is a good match between Predevelopment and Mitigated flow duration curves or fatigue sets in. Pond input information: Bottom Length (ft): Pond bottom length. Bottom Width (ft): Pond bottom width Effective Depth (ft): Pond height from pond bottom to top of riser plus at least 0.5 foot extra Left Sideslope (H/V): ratio of horizontal distance to vertical; 0 (zero) for vertical pond sides Bottom Sideslope (H/V): ratio of horizontal distance to vertical; 0 (zero) for vertical pond sides Right Sideslope (H/V): ratio of horizontal distance to vertical; 0 (zero) for vertical pond sides Top Sideslope (H/V): ratio of horizontal distance to vertical; 0 (zero) for vertical pond sides Riser Height (ft): Height of overflow pipe above pond bottom Riser Diameter (in): Pond overflow pipe diameter Riser Type (options): Flat or Notched Notch Type: Rectangular, V-Notch, or Sutro. For a rectangular notch: Notch Height (feet): distance from the top of the weir to the bottom of the notch Notch Width (feet): width of notch; cannot be larger than the riser circumference. For more information on riser notch options and orifices see discussion in OUTLET STRUCTURE CONFIGURATIONS section. Infiltration: Yes (infiltration into the underlying native soil) Measured Infiltration Rate (in/hr): Native soil infiltration rate Infiltration Reduction Factor: 1/Native soil infiltration rate safety factor (see page 69) Use Wetted Surface Area (sidewalls): Yes, if infiltration through the pond sideslopes is allowed If infiltration is used then the user should consult the Infiltration discussion on page 69. NOTE: See Appendix C or consult with the local municipal permitting agency for additional considerations regarding infiltration and determination of the appropriate infiltration reduction factor. A pond receives precipitation on and evaporation from the pond surface. The Precipitation Applied to Facility and Evaporation Applied to Facility boxes should be checked. 47 Santa Margaarita Region Hyddrology Model G Guidance – Aprill 2014 NOTE E: The detention pond section dia agram show ws the gene eral configu uration use ed in design ning a pond d and its ou utlet structure. This diiagram is frrom the Wa ashington S State Deparrtment of Ecology's 2005 Sto ormwater M Manageme ent Manual for Wesstern Washington. Consult C with h the Cope ermittee wi with jurisdicttion over p project site e on equirementts. speciffic design re 48 Santa Margaarita Region Hyddrology Model G Guidance – Aprill 2014 VAUL LT ELEM MENT The sttorage vault has all of th he same chaaracteristics of the trapezzoidal pond, except thatt the user do oes not speccify the sideslopes (by definition d theey are zero) and the vauult is assumeed to have a lid (no preccipitation or evaporation). Auto Vault V and Qu uick Vault work w the sam me way as A Auto Pond annd Quick Poond. Go to ppage 48 to find f information on how to manually y size a vaultt or other HM MP facility. NOTE E: Auto Vau ult is availab ble only in the t Mitigateed scenario.. Vault input i inform mation: Bottom m Length (ft)): Vault botttom length Bottom m Width (ft): Vault botto om width Effectiive Depth (fft): Vault heiight from vaault bottom m to top of riser r plus att least 0.5 fo oot extra Riser Height (ft): Height of overflow piipe above vault bottom m Riser Diameter (in): Vault overflow piipe diametter Riser Type T (option ns): Flat or Notched N Notch Type: Rectaangular, V-N Notch, or Suttro 49 Santa Margarita Region Hydrology Model Guidance – April 2014 For a rectangular notch: Notch Height (ft): distance from the top of the weir to the bottom of the notch Notch Width (ft): width of notch; cannot be larger than the riser circumference For more information on riser notch options and orifices see discussion in OUTLET STRUCTURE CONFIGURATIONS section. Infiltration: Yes (infiltration into the underlying native soil) Measured Infiltration Rate (in/hr): Native soil infiltration rate Infiltration Reduction Factor: 1/Native soil infiltration rate safety factor (see page 69) Use Wetted Surface Area (sidewalls): Yes, if infiltration through the vault sides is allowed If infiltration is used then the user should consult the Infiltration discussion on page 69. NOTE: See Appendix C or consult with the Copermittee with jurisdiction over the project site for additional considerations regarding infiltration and determination of the appropriate infiltration reduction factor. A vault is usually covered and does not receive precipitation on and evaporation from the vault surface. The Precipitation Applied to Facility and Evaporation Applied to Facility boxes should not be checked unless the vault top is open to the atmosphere. 50 Santa Margarrita Region Hyddrology Model G Guidance – Aprill 2014 TANK K ELEME ENT A storrage tank is a cylinder placed p on itts side. Thee user speciffies the tankk's diameter and length. Auto Tank T and Qu uick Tank work w the sam me way as A Auto Pond annd Quick Poond. Go to ppage 48 to find f information on how to manually y size a vaultt or other hyydrologic conntrol facilityy. NOTE E: Auto Tan nk is availab ble only in the Mitigateed scenario. There is a Quick Tank T option n that createss a tank, but do oes not check for complliance with the t flow duratio on criteria. Tank input i inform mation: Tank Type: T Circullar or Arched d For Ciircular: Diameeter (ft): Tan nk diameter Length h (ft): Tank length l For Arrched: Heightt (ft): Tank height h 51 Santa Margaritta Region Hydroology Model Guuidance – April 22014 Width h (ft): Tank width w (at wid dest point) Length h (ft): Tank length Riser Height (ft):: Height of overflow pipe p above tank bottom m; must be less than taank diameter or heightt D (in n): Tank oveerflow pipe diameter d Riser Diameter Riser Type T (option ns): Flat or Notched N Notch Type: Rectaangular, V-N Notch, or Suttro For a rectangular r notch: n Notch Height (feeet): distancee from the top t of the weir to o the bottom m of the notch h Notch Width (feet): width of notch; cannot c be larger than the riseer circumfereence For more m informaation on riseer notch options and orificees see discussion n in OUTLET O STRU UCTURE CO ONFIGURA ATIONS seection. Infiltraation: Yes (infiltration into the underlying u native soil) Measu ured Infiltrattion Rate (in//hr): Native soil infiltrattion rate Infiltraation Reducttion Factor: 1/Native soiil infiltrationn rate safety factor (see ppage 69) Use Wetted W Surfacce Area (sideewalls): Yess, if infiltratiion through tthe tank sidees is allowedd If infilltration is used then the user u should consult c the IInfiltration ddiscussion onn page 69. NOTE E: See App pendix C orr consult with w the Cop permittee w with jurisdicction over tthe projec ct site for additional a consideratio c ons regardiing infiltratio on and dettermination of the ap ppropriate infiltration i re eduction fa actor. A tank k is covered d and does not receivee precipitatioon on and eevaporation from the taank surface. The Preccipitation Ap pplied to Fa acility and E Evaporation Applied to Facility boxxes should d not be checcked. 52 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 IRRE EGULAR POND P EL LEMENT An irrregular pond d is any pon nd with a shape s that ddiffers from the rectanggular top off a trapezo oidal pond. An irregullar pond hass all of the same charaacteristics off a trapezoiddal pond, but b its shapee must be defined by the user. The Auto A Pond op ption is not available a forr an irregularr-shaped ponnd. Go to ppage 48 to finnd inform mation on how w to manuallly size an irrregular pondd or other HM MP facility. To creeate the shap pe of an irreg gular pond th he user clickks on the Oppen PondPaad button. Thhis allowss the user to access the PondPad interface (see beelow). 53 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 Pond dPad Interrface The Po ondPad interrface is a grrid on which h the user caan specify thhe outline off the top of tthe pond and a the pond d's sideslopess. The user selects the t Line bu utton (secon nd from the top on the upper left corner of tthe Pad screen). Once the Line L button is turned onn the user m moves the m mouse over tthe PondP grid to o locate thee pond's corrner points. The user ddoes this in a clockwisse direction to outlinee the pond's top perimetter. The useer can selectt individual points by cclicking on tthe point button b immeediately belo ow the line button. b Oncee selected, anny individuaal point can be moved d or repositio oned. 54 Santa Margarita Region Hydrology Model Guidance – April 2014 The default sideslope value is 3 (3:1). The sideslopes can be individually changed by right clicking on the specific side (which changes the line color from black to red) and then entering the individual sideslope value in the slope text box. The grid scale can be changed by entering a new value in the grid scale box. The default value is 200 feet. PondPad Controls and Numbers Clear: Line: Point: The Clear button clears all of the lines on the grid The Line button allows the user to draw new lines with the mouse The Point button allows the user to move individual points to alter the pond shape and size Sq Ft: Grid Scale: Grid X: Grid Y: Converts the computed pond area from square feet to acres and back. Changes the length of a grid line. Default grid scale is 200 feet Horizontal location of the mouse pointer on the grid (0 is the upper left corner) Vertical location of the mouse pointer on the grid (0 is the upper left corner) Area: Slope: Top area of the pond (either in square feet or acres) Sideslope of the selected line (side of the pond) 55 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 GRAVEL TRE ENCH BED D ELEME ENT The grravel trench bed is used to spread an nd infiltrate runoff, but aalso can havve one or moore surfacee outlets represented by an outlet strructure with a riser and m multiple orifi fices. The user u specifi fies the treench length h, bottom m width, tottal depth, bottom slopee, and lefft and right sideslopes. s The material layers rep present the gravel//rock layers and th heir design n characcteristics (thiickness and porosity). p Quick Trench willl instantly crreate a graveel trench bed with default vallues withou ut checkiing it for compliancy y with flow w duratio on criteria. The grravel trench h bed input information n: Trench h Length (ft)): Trench bed d length. 56 Santa Margarita Region Hydrology Model Guidance – April 2014 Trench Bottom Width (ft): Trench bed bottom width Effective Total Depth (ft): Height from bottom of trench bed to top of riser plus at least 0.5 feet extra Bottom Slope of Trench (ft/ft): Must be non-zero Left Sideslope (ft/ft): H/V ratio of horizontal distance to vertical; 0 (zero) for vertical trench bed sides Right Sideslope (ft/ft): H/V ratio of horizontal distance to vertical; 0 (zero) for vertical trench bed sides Infiltration Rate (in/hr): Trench bed gravel or other media infiltration rate Layer 1 Thickness (ft): Trench top media layer depth Layer 1 Porosity: Trench top media porosity. Layer 2 Thickness (ft): Trench middle media layer depth (Layer 2 is optional) Layer 2 Porosity: Trench middle media porosity Layer 3 Thickness (ft): Trench bottom media layer depth (Layer 3 is optional) Layer 3 Porosity: Trench bottom media porosity Riser Height (ft): Height of trench overflow pipe above trench surface Riser Diameter (in): Trench overflow pipe diameter Riser Type (options): Flat or Notched Notch Type: Rectangular, V-Notch, or Sutro For a rectangular notch: Notch Height (feet): distance from the top of the weir to the bottom of the notch Notch Width (feet): width of notch; cannot be larger than the riser circumference For more information on riser notch options and orifices see discussion in OUTLET STRUCTURE CONFIGURATIONS section. Native Infiltration: Yes (infiltration into the underlying native soil) Measured Infiltration Rate (in/hr): Native soil infiltration rate Infiltration Reduction Factor: 1/Native soil infiltration rate safety factor (see page 69) Use Wetted Surface Area (sidewalls): Yes, if infiltration through the trench sideslopes is allowed. If infiltration is used then the user should consult the Infiltration discussion on page 69. NOTE: See Appendix C or consult with the Copermittee with jurisdiction over the project site for additional considerations regarding infiltration and determination of the appropriate infiltration reduction factor. Gravel trench bed receives precipitation on and evaporation from the trench surface. The Precipitation Applied to Facility and Evaporation Applied to Facility boxes should be checked. 57 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 SAND D FILTER R ELEMEN NT The saand filter is a water quality facility. It does not infiltrate surrface runoff,, but is usedd to filter runoff r throu ugh a mediu um and send d it downstrream. It caan also havee one or moore surfacee outlets represented by an outlet strructure with a riser and m multiple oriffices. The user u must specify th he facility dimensions (botto om length and a width, a sideslopes. The effective depth, and hydrau ulic conducttivity of the sand filter and th he filter maaterial depth h are also needed d to size th he sand filtter (default values are 1.0 inch h per hour an nd 1.5 feet, respectively). NOTE E: When using u the sand s filter eleme ent check with Appen ndix C or the Co opermittee with jurisdiiction over the project p site e to deterrmine the requirred treatme ent standard d (percent of the e total runo off volume treated t by the sa and filter). 58 Santa Margarita Region Hydrology Model Guidance – April 2014 The filter discharge is calculated using the equation Q = K*I*A, where Q is the discharge in cubic feet per second (cfs). K equals the hydraulic conductivity (inches per hour). For sand filters K = 1.0 in/hr. Sand is the default medium. If another filtration material is used then the design engineer should enter the appropriate K value supported by documentation and approval by the reviewing authority. Design of a sand filter requires input of facility dimensions and outlet structure characteristics, running the sand filter scenario, and then checking the volume calculations to see if the Percent Filtered equals or exceeds the treatment standard percentage. If the value is less than the treatment standard percentage then the user should increase the size of the sand filter dimensions and/or change the outlet structure. The sand filter input information: Bottom Length (ft): Sand filter bottom length Bottom Width (ft): Sand filter bottom width Effective Depth (ft): Height from bottom of sand filter to top of riser plus at least 0.5 feet extra Left Sideslope (ft/ft): H/V ratio of horizontal distance to vertical; 0 (zero) for vertical sand filter sides Bottom Sideslope (ft/ft): H/V ratio of horizontal distance to vertical; 0 (zero) for vertical sand filter sides Right Sideslope (ft/ft): H/V ratio of horizontal distance to vertical; 0 (zero) for vertical sand filter sides Top Sideslope (ft/ft): H/V ratio of horizontal distance to vertical; 0 (zero) for vertical sand filter sides Riser Height (ft): Height of sand filter overflow pipe above sand filter surface Riser Diameter (in): Sand filter overflow pipe diameter Riser Type (options): Flat or Notched Notch Type: Rectangular, V-Notch, or Sutro For a rectangular notch: Notch Height (feet): distance from the top of the weir to the bottom of the notch Notch Width (feet): width of notch; cannot be larger than the riser circumference. For more information on riser notch options and orifices see discussion in OUTLET STRUCTURE CONFIGURATIONS section. Infiltration: Yes (infiltration through the filter material) Hydraulic Conductivity (in/hr): Filtration rate through the sand filter Filter material depth (ft): Depth of sand filter material (for runoff filtration) Sand filter receives precipitation on and evaporation from the sand filter surface. The Precipitation Applied to Facility and Evaporation Applied to Facility boxes should be checked. 59 Santa M Margarita Regionn Hydrology Moodel Guidance – April 2014 OUT TLET STR RUCTURE E CONFIG GURATION NS The trrapezoidal po ond, vault, taank, irregulaar pond, gravvel trench beed, and sandd filter all usse a riser for thee outlet struccture to contrrol dischargee from the faacility. The riiser is a verrtical pipe with w a heightt above ponnd bottom (ttypically onne foot less tthan the effectiive depth). The T user speecifies the risser height annd diameter. The riser can havee up to threee round orificces. The bo ttom orifice is usually loocated at thee bottom of the pond and/o or above any y dead storaage in the faacility. Thee user can sset the diameter and heightt of each oriffice. The user u specifiees the riser type as eitther flat or notched. The weir nnotch can bbe either rectangular, V-nottch, or a Sutrro weir. Thee shape of eaach type of w weir is show wn below. Rectan ngular Notch h V-Notch 60 Sutro Santa Margarita Region Hydrology Model Guidance – April 2014 By selecting the appropriate notch type the user is then given the option to enter the appropriate notch type dimensions. Riser and orifice equations used in SMRHM are provided below. Headr = the water height over the notch/orifice bottom. q = discharge Riser Head Discharge: Head = water level above riser q = 9.739 * Riser Diameter * Head ^ 1.5 Orifice Equation: q = 3.782 * (Orifice Diameter) ^ 2 * SQRT(Headr) Rectangular Notch: b = NotchWidth *- (1- 0.2 * Headr) where b >= 0.8 q = 3.33 * b * Headr ^ 1.5 Sutro: Wh = Top Width + {(Bottom Width- Top Width)/Notch Height }* Headr Wd = Bottom Width - Wh (the difference between the bottom and top widths) Q1 = (rectangular notch q where Notch Width = Wh) Q2 = (rectangular notch q where Notch Width = Wd) q = Q1 + Q2 / 2 V-Notch: Notch Bottom = height from bottom of riser to bottom of notch Theta = Notch Angle a = 2.664261 - 0.0018641 * Theta + 0.00005761 * Theta ^2 b = -0.48875 + 0.003843 * Theta - 0.000092124 * Theta ^2 c = 0.3392 - 0.0024318 * Theta + 0.00004715 * Theta ^2 Y over H = Headr / (NotchBottom + Headr) Coef = a + b * Headr + c * Headr ^2 q = (Coef * Tan(Theta / 2)) * (Headr ^ (5 / 2)) These equations are provided from the Washington State Department of Ecology’s 2005 Stormwater Management Manual for Western Washington. The outlet designs are shown 61 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 below.. They have been reprod duced from Volume V III oof the Stormw water Manaagement Manua al for Westerrn Washingto on which haas more inforrmation on th the subject. 62 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 63 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 The ph hysical confiiguration of the outlet structure shouuld include pprotection foor the riser aand orifices to preven nt clogging of the outtlet from ddebris or seediment. V Various outllet configu urations are shown below. They have been reproduced from Volum me III of tthe Stormw water Manag gement Man nual for Wesstern Washinngton which has more in nformation on the sub bject. 64 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 Riserr protection structures. Diagrams D coourtesy of W Washington S State 65 Depaartment of Ecology. Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 INFIL LTRATION Infiltraation of sto ormwater ru unoff is a recomm mended solution s iff certain conditions are met. These conditions include: a soils report,, testing, ground dwater proteection, pre-seettling, and approp priate constru uction techn niques. NOTE E: See App pendix C or o consult with th he Coperm mittee with ju urisdiction over the projec ct site for additional consid derations regarding r infiltration and determinatio d on of the ap ppropriate infiltra ation reducttion factor. The usser clicks on n the Infiltraation option arrow to change in nfiltration frrom NO to YES. This actiivates the infiltration input options: o meaasured infilttration rate, infiltraation reductiion factor, an nd whether or nott to allow in nfiltration th hrough the wetted d sideslopes/walls. The in nfiltration red duction facto or is a multiiplier for thee measured iinfiltration raate and shouuld have a value of 1.0 00 or less. It I is the samee as the inveerse of a safeety factor. F For example, a safety factor of 2 is equal to a reduction faactor of 0.50 . Infiltraation occurs only through the bottom m of the facillity if the weetted surfacee area optionn is turned d off. Otherw wise the entirre wetted su urface area iss used for inffiltration. After the t model iss run and flo ow is routed d through thhe infiltrationn facility thee total volum me infiltraated, total volume throu ugh the riserr, total voluume throughh the facilityy, and perceent infiltraated are repo orted on thee screen. Iff the percentt infiltrated is 100% then there is nno surfacee discharge from f the faccility. The percent infiltrrated can be less than 1000% as long as the surrface discharrge does not exceed the flow f duratioon criteria. 66 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 AUTO O POND Auto Pond P automatically creaates a pond size and deesigns the ouutlet structurre to meet tthe flow duration d critteria. The user can eitther create a pond from m scratch oor optimize an existin ng pond design. Auto Pond P requirees that the Prredevelopmeent and Mitiigated basinss be definedd prior to usiing Auto Pond. P Click king on the Auto A Pond button bringgs up the Auuto Pond wiindow and tthe associaated Auto Po ond controlss. Auto Pond P contro ols: Autom matic Pond Adjuster: A Th he slider at th he top of the Auto Pond window alloows the userr to decidee how thorou ughly the pon nd will be deesigned for eefficiency. T The lowest ssetting (01 min)) at the left constructs c an n initial pond d without chhecking the fflow duratioon criteria. T The second d setting to the right creates and sizes a ponnd to pass thhe flow durration criterria; howev ver, the pond d is not neceessarily optim mized. The higher settinngs increase the amount of optimiization. The highest seetting (farth hest right) w will size thee most efficiient (smalleest) pond, but b will resu ult in longer computation nal time. 67 Santa Margarita Region Hydrology Model Guidance – April 2014 Pond Depth: Pond depth is the total depth of the pond and should include at least one foot of freeboard (above the riser). The pond's original depth will be used when optimizing an existing pond; changing the value in the Pond Depth text box will override any previous set depth value. The default depth is 4 feet. Pond Length to Width Ratio: This bottom length to width ratio will be maintained regardless of the pond size or orientation. The default ratio value is 1.0. Pond Sideslopes: Auto Pond assumes that all of the pond's sides have the same sideslope. The sideslope is defined as the horizontal distance divided by the vertical. A typical sideslope is 3 (3 feet horizontal to every 1 foot vertical). The default sideslope value is 3. Choose Outlet Structure: The user has the choice of either one orifice or rectangular notch or three orifices. If the user wants to select another outlet structure option then the pond must be manually sized. Create Pond: This button creates a pond when the user does not input any pond dimensions or outlet structure information. Any previously input pond information will be deleted. Optimize Pond: This button optimizes an existing pond. It cannot be used if the user has not already created a pond. Accept Pond: This button will stop the Auto Pond routine at the last pond size and discharge characteristics that produce a pond that passes the flow duration criteria. Auto Pond will not stop immediately if the flow duration criteria have not yet been met. The bottom length and width and volume at riser head will be computed by Auto Pond; they cannot be input by the user. Auto Vault and Auto Tank operates the same way as Auto Pond. There are some situations where Auto Pond will not work. These situations occur when complex routing conditions upstream of the pond make it difficult or impossible for Auto Pond to determine which land use will be contributing runoff to the pond. For these situations the pond will have to be manually sized. Go to page 48 to find information on how to manually size a pond or other HMP facility. NOTE: If Auto Pond selects a bottom orifice diameter smaller than the smallest diameter allowed by the Copermittee with jurisdiction over the project site then additional mitigating BMPs may be required to meet local hydromodification control requirements. Please see Appendix C or consult with the Copermittee with jurisdiction over the project site for more details. For manual sizing information see page 48. 68 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 CHA ANNEL EL LEMENT The Channel C elem ment allows the user to o route surfa face runoff ffrom a landd use basin or facility y through an n open chann nel to a down nstream desttination. The channel c crosss section is representeed by a traapezoid and is used with Manningg's equation to calcu ulate discharrge from th he channel. If a trapeezoid does nnot accurateely hould repressent the channnel with an independenttly represent the crosss section then the user sh U X-Sectioons option. calculaated SSD Taable elementt or use the Use The user u inputs channel bo ottom width h, channel length h, channel bo ottom slope, channel leftt and right sideslo opes, maxim mum chann nel depth, and the channeel's roughn ness coefficient (Man nning's n value)). The userr can selecct channel type and associated Manning's n from m a table lisst directly above the Chan nnel Dimen nsion inform mation or directlly input the channel's c Maanning's n vaalue. The channel c is used to rep present a natural n or artificiial open ch hannel thro ough which water is routed d. It can be used to conn nect a basin to a pond or a po ond to a pon nd or multiplle channels can c linked togeth her. 69 Santa Margarita Region Hydrology Model Guidance – April 2014 Channel input information: Channel Bottom Width (ft): Open channel bottom width Channel Length (ft): Open channel length Manning's n coefficient: Open channel roughness coefficient (user menu selected or input) Slope of Channel (ft/ft): Open channel bottom slope Left Sideslope of Channel (ft/ft): H/V ratio of horizontal distance to vertical; 0 (zero) for vertical channel sides Right Sideslope of Channel (ft/ft): H/V ratio of horizontal distance to vertical; 0 (zero) for vertical channel sides Maximum Channel Depth (ft): Height from bottom of channel to top of channel bank. Infiltration: Yes (infiltration into the underlying native soil) Measured Infiltration Rate (in/hr): Native soil infiltration rate Infiltration Reduction Factor: 1/Native soil infiltration rate safety factor (see page 69) Use Wetted Surface Area (sidewalls): Yes, if infiltration through the channel sideslopes is allowed. If infiltration is used then the user should consult the Infiltration discussion on page 69. NOTE: See Appendix C or consult with the Copermittee with jurisdiction over the project site for additional considerations regarding infiltration and determination of the appropriate infiltration reduction factor. 70 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 FLOW W SPLITT TER ELEM MENT The flo ow splitter divides d the runoff r and sends it to tw wo different destinationss. The splittter has a primary p exitt (exit 1) and d a secondarry exit (exit 2). The useer defines hoow the flow w is split beetween thesee two exits. The usser can defin ne a flow co ontrol structu ure with a riiser and from m one to thrree orifices ffor each exit. The flow control sttructure work ks the same way as the ppond outlet structure, wiith ht and diameter, the riserr weir type ((flat, rectanggular notch, V Vthe useer setting thee riser heigh notch, or Sutro), an nd the orificce diameter and a height. For more m informaation on risser notch op ptions and oorifices see discussion in OUTLE ET STRU UCTURE CO ONFIGURA ATIONS secction. 71 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 The seecond option n is that the flow f split caan be based oon a flow thhreshold. Thhe user sets tthe flow th hreshold value in cubic feet f per seco ond (cfs) forr exit 1 at whhich flows inn excess of tthe thresho old go to ex xit 2. For ex xample, if th he flow thresshold is set tto 5 cfs thenn all flows leess than orr equal to 5 cffs go to exit 1. Exit 2 gets g only the excess flow w above the 5 cfs threshoold (total floow minus exit 1 flow)). 72 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 TIME E SERIES S ELEMEN NT SMRH HM uses tim me series of precipitation, evaporatiion, and runnoff stored iin its databaase (HSPF F WDM file)). The user has the optio on to create or use a tim me series file external froom SMRH HM in SMRH HM. This may m be a tim me series of flow values created by another HSP PF model. An examp ple is offsitee runoff enteering a projeect site. If tthis offsite rrunoff is in an existin ng WDM filee and is the same period d as SMRHM M data and the same siimulation tim me step (1 15-minute) th hen it can bee linked to SMRHM moddel using thee Time Seriees element. To link k the externaal time series to SMRHM M the user cllicks on the Choose WD DM button annd identiffies the exteernal WDM file. The external WD DM's indiviidual time sseries files aare shown n in the Timee Series Outt box. The selected inpuut dataset is tthe time seriies that will be used by b SMRHM. 73 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 STAG GE-STOR RAGE-DIS SCHARGE E TABLE E The stage-storage s e-discharge table hydrraulically reepresents anny facility that requirres stormw water runofff routing. Th he table is au utomaticallyy generated bby SMRHM when the usser inputs storage faciility dimensiions and outtlet structuree informatioon. SMRHM M generates 91 o stage, surrface area, sttorage, surfaace dischargge, and infilttration valuees starting att a lines of stage value of zeero (facility bottom heiight) and inncreasing inn equal incrrements to tthe mum stage vaalue (facility y effective deepth). maxim When the user or SMRHM S ch hanges a faciility dimensiion (for exam mple, bottom m length) or an orificee diameter orr height, thee model imm mediately reccalculates thhe stage-storaage- discharrge table. The usser can inputt to SMRHM M a stage-sto orage-dischaarge table creeated outsidde of SMRHM M. To usee a stage-sto orage-dischaarge table crreated out off SMRHM tthe SSD Taable elementt is requireed. See thee SSD Tablee element deescription beelow for moore informatiion on how to load su uch a table to o SMRHM program. p 74 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 SSD TABLE ELEMENT E T The SSD Table iss a stage-sto orage-dischaarge table exxternally prooduced by thhe user and is identiccal in formaat to the stag ge-storage-d discharge tabbles generateed internallyy by SMRH HM for pon nds, vaults, tanks, t chann nels, etc. The eaasiest way to o create a SSD Table ou utside of SM MRHM is too use a spreaadsheet withh a separaate column for f stage, su urface area, storage, andd discharge (in that ordder). Save tthe spread dsheet file as a a commaa-delimited file. A texxt file can also be creeated, if moore conven nient. The SS SD Table mu ust use the following fo uniits: Stage: feeet Surfacce Area: acrees Storag ge: acre-feet Dischaarge: cfs A fifth h column can be used to o create a seecond dischaarge (cfs). T This second discharge ccan be infiiltration or a second surfface discharg ge. 75 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 Certain n rules applly to the SSD D Table wh hether it is ccreated insidde or outsidee of SMRHM M. These rules are: 1. 1 Stage (feet) ( must start at zero o and increaase with eacch row. Thhe incrementtal increase does not have h to be co onsistent. 2. 2 Storagee (acre-feet) must start at a zero and inncrease withh each row. S Storage valuues should be physicallly based on n the corressponding deppth and surrface area, bbut HM does not check extern nally generat ated storage vvalues. SMRH 3. 3 Discharrge (cfs) mu ust start at zero. z Dischharge does nnot have to increase wiith each ro ow. It can sttay constant or even deccrease. Disccharge cannoot be negativve. Discharrge should be based on n the outlett structure's physical diimensions annd charactteristics, butt SMRHM does not ccheck externnally generaated discharrge values. 4. 4 Surfacee area (acres) is only used u if preciipitation to aand evaporaation from tthe facility y are applied.. To inp put an extern nally generated SSD Tab ble, first creaate and save tthe table outtside of SMRH HM. Use thee Browse buttton to locate and load thhe file into S SMRHM. 76 Santa Margarita Region Hydrology Model Guidance – April 2014 The first three columns (Stage, Area, and Storage) will automatically show in the table. To use the additional columns (Column 4, 5, etc.) click on the Not Used at the head of the table and select the appropriate option. For externally calculated discharge (cfs) select Manual in Column 4. To have SMRHM calculate discharge based on outlet structure dimensions select Outlet Structure. If infiltration is included then click on Not Used in Column 5 and select the appropriate option. 77 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 BIOR RETENTIO ON ELEM MENT The Bioretention B element reepresents a bioretentionn area or rain garden. In modeliing shorthand terms SMRHM S hass abbreviated d "bioretenttion" to the default nam me "bio swale". This name can be changed by the user. The biioretention element has two t availablee outlet struccture configuurations: (1) verticall orifice pluss overflow (2) riser ou utlet The usser is requireed to enter th he following informationn about the bbioretention: Swale Length (ft): length dimeension of sw wale surface bbottom Swale Bottom Wid dth (ft): widtth dimension n of swale suurface bottom m Effectiive Total Deepth (ft): com mputed by SM MRHM Bottom m Slope of Swale S (ft/ft): the slope off the swale leength; must bbe greater thhan zero Left Sideslope (ft//ft): H/V ratiio of horizon ntal distancee to vertical; 0 (zero) forr vertical swaale sides Right Sideslope (ft/ft): H/V ratio r of horizontal distaance to verttical; 0 (zero) for verticcal swale sides 78 Santa Margarita Region Hydrology Model Guidance – April 2014 For the three amended soil material layers the user inputs: Layer Thickness (feet): depth of amended soil Type of amended soil: 24 different soil types are included; the user can also create their own soil type using the Edit Soil Type button NOTE: Amended soil layers 2 and 3 are optional. Infiltration to the native soil can be turned on by setting Native Infiltration to YES. The parameters for native soil infiltration are: Measured Infiltration Rate (inches per hour): infiltration rate of the native soil Infiltration Reduction Factor: between 0 and 1 (1/Native soil infiltration rate safety factor (see page 69) Use Wetted Surface Area (sidewalls): YES or NO; YES allows infiltration to the native soil through the sidewalls of the swale; otherwise all infiltration is through the bottom only If infiltration is used then the user should consult the Infiltration discussion on page 69. NOTE: See Appendix C or consult with the Copermittee with jurisdiction over the project site for additional considerations regarding infiltration and determination of the appropriate infiltration reduction factor. The user has two bioretention surface outlet configuration choices: (1) Vertical Orifice + Overflow or (2) Riser Outlet Structure. 79 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 The in nput informattion required d for the verttical orifice plus overfloow is: Vertical Orifice Diameter (inches): diametter of verticaal opening beelow the weeir E (in nches): vertiical distancee from the top of the amended sooil Vertical Orifice Elevation om of the veertical orificee surfacee to the botto Width of Over-roaad Flow (feett): weir/streeet length v orifiice plus overrflow: Diagraam of bioreteention with vertical 80 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 Wid dth of Over-ro oad Flow Ov ver-road Floodin ng Freeboard Vertical Orifice D Diameter Nativ ve Soil Effective Vertical Orifice e Elevation Layer 1 Amende ed Soil Layer 2 Underdrain Layer 3 Native Soil S Riser outlet o structu ure option: 81 Total Natiive Soil Santa Margaritta Region Hydroology Model Guuidance – April 22014 The in nput informaation requireed for the riiser outlet structure is: Riser Height abo ove Swale Surface (feeet): depth of surface ponding p beffore the riserr is overto opped Riser Diameter (inches): ( diameter of the stand pipe p Riser Type: T Flat or Notched Notch Type: Rectaangular, V-N Notch, or Sutro For a rectangular r notch: n Notch Height (feet): distance from f the top p of the weeir to the botttom of the notch n Notch Width (feeet): width off notch; cann not be larg ger than the riser circum mference For more m information on risser notch op ptions and orifices seee discussionn in OUTLET STRU UCTURE CO ONFIGURA ATIONS seection. To usse the underdrain click k the Underrdrain Usedd box and input an unnderdrain pipe diameter (feet), un nderdrain ou utlet orifice diameter (innches), and ooffset (inchees). The offfset definees the heightt of the botttom of the underdrain pipe above the bottom m of the low west amend ded soil layer. 82 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 The am mended soil layer fills with w stormwater runoff ffrom the topp on down too where it ccan drain to t the nativee soil (if Naative Infiltrattion is set too YES) and//or the underdrain pipe (if Underrdrain Used box is check ked). Water enters the underdrain u when w the am mended soil bbecomes satturated downn to the top of the underdrain. The underdraain pipe fills and conveyys stormwateer runoff prooportionally to the dep pth of ameended soil saaturation. When W the ameended soil iss fully saturaated the underdrain pipee is at full capacity. Discharge D fro om the underdrain pipe iis controlledd by the undderdrain orifiice diametter. If nativ ve infiltratio on is turned on o then nativ ve infiltrationn will start w when/if storm mwater runoff: 1. 1 2. 2 3. 3 starts to fill the undeerdrain (if an n underdrainn is used). enters th he amended soil (if Use Wetted W Surfface Area (siidewalls) is sset to YES). saturatess the amend ded soil layeer(s) to 2/3rdds of the tottal amendedd soil depth (if there iss no underdraain and Wetted Surface Area is set tto NO). 83 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 There is a simple swale option. It is computationnally much faster thann the standaard bioreteention. Beffore using th he simple sw wale option read the noote on the sscreen and tthe inform mation below w to understand the limitaations of the simple swalle. The sttandard bio oretention ro outine uses HSPF Spe cial Actions to check the availabble amend ded soil storaage and com mpares it witth the storm mwater runofff inflow rate. Because of the check done by y HSPF Speccial Actionss simulationss using bioreetention take much longger n using bio oretention. Simulations that normallly take onlyy seconds m may than siimulations not take multiple m minu utes when on ne or more bioretention b facilities aree added, deppending on tthe compu utational speed of the com mputer used d. One so olution to thiis problem is to use the simple swalle option (chheck the Use Simple Swaale box). The simple swale does not n include HSPF H Speciial Actions. It is less acccurate than tthe standaard swale. Tests T have sh hown that th he simple sw wale option sshould only be used whhen the sw wale area (an nd volume) is relatively small compaared to the ccontributing basin area. If in dou ubt, model th he bioretentio on both way ys and see hoow close thee simple swaale answer is to the staandard swalee method. The T standard d swale methhod will alw ways be moree accurate thhan the sim mple swale. 84 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 POIN NT OF CO OMPLIANCE SMRH HM allows for f multiple points p of co ompliance (m maximum off 59) in a sinngle project. A point of o compliancce is defined d as the locaation at whiich the Predeevelopment and Mitigatted flows will w be analy yzed for com mpliance with h the flow coontrol standaard. The point p of com mpliance is selected by b right cliccking on thhe element at which tthe compliiance analyssis will be made. m In the example abbove, the poiint of complliance analyysis will bee conducted at the outlett of the trapeezoidal pond . Additiional points of complian nce can be added by c licking on tthe ADD buutton and thhen highlig ghting the POC number to be used for the elem ment. Once a POC num mber is addedd it cannott be removed d, but if it is not used theen it has no eeffect. 85 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 Once the point of compliaance has beeen selecteed the elem ment is mo odified on the Schem matic screen n to includee a small box b with the t letter "A" (for An nalysis) in the lower right cornerr. This identtifies the outtlet from this t element as a point off compliancee. The number n 1 neext to the letter "A" is the numbeer of the POC C (POC 1). 86 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 CON NNECTING G ELEME ENTS Elements are conn nected by rig ght clicking on o the upstreeam elementt (in this exaample DMA 1) d then left clicking c on the Connecct To Elemeent option. By doing so and seelecting and SMRH HM extends a line from the upstream m element tto wherever the user waants to conneect that eleement. 87 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 The usser extends the t connectiion line to th he downstreeam elementt (in this exaample, a ponnd) and leeft clicks on n the destin nation elem ment. This aaction bringgs up the F From Basin to Conveeyance box that t allows the t user to specify whicch runoff coomponents tto route to tthe downsstream elemeent. Stormw water runo off is deffined in the t SMRH HM as surfface flow plus p interflo ow. Both boxes should be b checked. Groun ndwater shou uld not be checked for the t standaard land developmen nt mitigatiion analysis. Groun ndwater sho ould only be checkeed when there is observed o and a docum mented base flow occurrring from the t upstreaam basin. After the approp priate boxees have beeen checkeed click the OK O button. 88 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 The fin nal screen will w look likee the above screen. s Thee basin inform mation screeen on the rigght will sh how that DM MA 1 stormw water runofff flows to Trrapezoidal Poond 1 (grounndwater is nnot conneccted). 89 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 ANA ALYSIS SCREEN S N The Analysis tool bar button (third from the left) brinngs up the A Analysis scrreen where tthe user caan look at th he results off the Predevelopment annd Mitigatedd scenarios. The Analyssis screen n allows the user to anallyze and com mpare flow ddurations, fllow frequenncy, drawdow wn times, hydrograph hs, and LID BMP B sizing by calculatiing VBMP annd QBMP usinng the Rationnal od. Metho 90 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 The usser can analy yze all time series datassets or just fl flow, stage, pprecipitationn, evaporatioon, or poin nt of compliiance flows by b selecting the approprriate tab beloow the list oof the differeent datasetts available for analysis.. 91 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 FLOW DURATION Flow duration d at the t point of compliance c (POC 1) is tthe most com mmon analyysis. A plot of the flo ow duration values v is sho own on the left, the flow w values on thhe right. The flow duration n flow range is from the lower l threshhold flow freequency valuue (10% of tthe 2-yearr value) to th he upper threeshold flow frequency f vaalue (10-yeaar value). As shown in tthe flow duration d tablle to the righ ht of the flow w duration ccurves, this flow range iis divided innto approx ximately 100 0 levels (flow w values). The diivision of th he flow rangee into a larg ge number off levels is im mportant to m make sure thhat the ero osive flows do d not increaase between n the lower thhreshold (100% of the 2-yyear flow) and the 2-y year flow frrequency vallue and betw ween increassing flow freequency levels (3-year, 4year, 5-year, 5 etc.).. The majorrity of the errosive flows occur between the 10% % of the 2-yeear flow value v and thee 2-year flow w frequency value. It is important too divide the flow levels in that raange into multiple levell steps to no ot miss any occasions w when the M Mitigated flow ws exceed d the Predev velopment flo ows. For eaach flow leveel/value SMR RHM counts the numbeer of times thhat the flow at the Point of Compliance for the Predev velopment scenario s (P Predev) excceeds that specific floow level/v value. It doees the same count c for thee Mitigated sscenario flow w (Mit). The total numbber of cou unts is the number of simulated 15-minute 1 tim me steps thhat the flow w exceeds thhat specifi fic flow levell/value. 92 Santa Margarita Region Hydrology Model Guidance – April 2014 The Percentage column is the ratio of the Dev count to the Predev count. This ratio must be less than or equal to 100% for flow levels/values between the lower threshold (10% of the 2-year flow) and the 5-year flow and 110% for flow levels/values between the 5-year flow and the upper threshold value. If the percentage value does not exceed this maximum ratio (100% for the lower threshold to the 5-year flow value and 110% for the 5-year flow value to the 10-year value) then the Pass/Fail column shows a Pass for that flow level. If they are exceeded then a Fail is shown. A single Fail and the facility fails the flow duration criteria. The facility overall Pass/Fail is listed at the top of the flow duration table. 93 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 FLOW W FREQU UENCY Flow frequency f pllots are show wn on the lefft and the 2-,, 5-, 10-, andd 25-year freequency valuues are on n the right. Flow frequeency calculations are baased on seleccting partial duration floow values and ranking g them by their Cunnanee Plotting Poosition. The Cu unnane Plottting Position n formula is: Tr = (N N+a)/(m-b) where Tr = return period p (yearrs) m = raank (largest event, e m = 1) N = nu umber of yeaars a = 0.2 2 b = 0.4 4 Probab bility = 1/Tr The reeturn period value, Tr, is i used in SM MRHM to ddetermine thhe 2-year, 5--year, 10-yeear, and 25 5-year peak flow f values. If necessarry, the 2-yeaar, 5-year, 100-year, and 225-year valuues are interpolated fro om the Tr vaalues generatted by Cunnnane. 94 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 DRAWDOWN N The drrawdown sccreen is used d to computte pond stagges (water ddepths). Thhese stages aare summaarized and reeported in teerms of drain n/retention tiime (in days). For th his example, the maximu um stage co omputed durring the enttire 30-50 year simulatiion period d is 3.40 feeet. This max ximum stag ge has a draawdown tim me of 1 day,, 20 hours, 33 minutees, 8 secondss (approximaately 45 hou urs). Ponds may have drain d times in excess off the allowe d maximum m. This can occur whenn a pond has h a small bottom b orificce. If this iss not acceptaable then thee user needss to change tthe pond outlet o config guration, man nually run th he Mitigatedd scenario, annd repeat thee analyze staage compu utations. A situation maay occur wh here it is noot possible too have both an acceptabble pond drawdown/ d retention r tim me and meet the t flow durration criteriaa. NOTE E: The flow w duration criteria tak ke precedence unlesss the user is instructted otherw wise by App pendix C orr the Coperrmittee with h jurisdiction n over the p project site . 95 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 HYDR ROGRAP PHS The usser can grap ph/plot any or o all time series s data bby selecting the Hydrogrraph tab. T The Createe Graph screeen is show wn and the user u can sellect the tim me series to plot, the tim me intervaal (yearly, monthly, m daaily, or 15--minute), annd type of data (peakss, average, or volum me). The fo ollowing num mbering systtem is used for f the flow ttime series: 500-59 99: Predevellopment flow w (Predevelo opment scenaario) 700-79 99: Inflow to o the POC (M Mitigated run noff enteringg the BMP ffacility) 800-89 99: POC flow w (Mitigated d flow exitin ng the BMP ffacility) The seelected time series are sh hown. To grraph the seleected time seeries the useer clicks on tthe Graph button. 96 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 The hy ydrograph sh hows the yeearly maxim mum/peak floow values foor each timee series for tthe entire simulation period p (in thiis example, from f 1974 thhrough 20100). The grraph can be either e saved or printed. 97 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 LID BMP B SIZIN NG Riversside County y and local municipalitties use thee Rational M Method (Q = C*I*A) to calculaate the LID BMP design n volume, VBMP, and floow rate, QBM are MP. These calculations a completely separaate from the other runofff calculationns produced by SMRHM M using HSP PF. unty's Desig gn Handbookk for Low Im mpact Devellopment Best Managemeent See Riiverside Cou Practices (Septem mber 2011) fo or the most up-to-date innformation rregarding BMP standardds. ould be consu ulted prior to o the start off any SMRH HM LID BMP P modeling. The haandbook sho The caalculation off the BMP deesign volume VBMP, andd flow rate QBMP is done on this screeen. The usser first enterrs the 85th peercentile, 24 4-hour rainfaall depth (D855). 98 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 und for any location l in th he The D85 can be fou Santa Margarita M Region R from the t Isohyeta al Map buttoon on the SM MRHM map screen. 99 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 The D85 for the project p site can be foun nd on the iisohyetal maap based onn the projecct's locatio on. 100 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 The efffective impeervious fracttion is calcullated in the m model basedd on the tribuutary area (A AT) for thee post-devellopment land d cover. Th he user inpuuts the num mber of acress of each laand cover and a the mod del calculatess the runoff coefficient, c C. 101 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 Click on the Calcculate button at the botttom of the screen to ccalculate thee BMP desiign me, VBMP, and d flow rate, QBMP. volum 102 Santa Margarita Region Hydrology Model Guidance – April 2014 This page has been intentionally left blank. 103 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 REP PORTS SCREEN S N The Reports R tool bar button (fourth ( from m the left) brrings up thee Report screen where tthe user can look at all a of the prroject input and output. The project report caan be saved or d. printed The project reporrt contains the project input inforrmation provvided by thhe user andd a summaary of the project outpu ut informatio on producedd by SMRHM M. The projject report ccan be gen nerated as eitther a Microsoft Word fiile or a PDF file. 104 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 This iss an examplee of the projeect report in the format oof a Microsooft Word filee (RTF formatt). 105 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 TOO OLS SCR REEN The Tools T screen is accessed d with the Tools T tool baar (second ffrom the rigght). The tw wo purposses of the To ools screen are: a (1) To allow users u to view w SMRHM HSPF H PERL LND parameeter values. See Appenddix A for a listt of the SMR RHM HSPF PERLND P paarameter valuues. (2) To allow users u to expo ort time seriees datasets. 106 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 To exp port a time series datasett click on thee Export Daataset box. T The list of avvailable time seeries datasetts will be sh hown. The user u can seleect the start and end datees for the daata they want w to exporrt. The tim me step (15--minute, daiily, monthly, yearly) cann also be specified. If tthe user wannts daily, monthly, or yearly data the user is given g the choice of eitheer selecting tthe maximum m, minim mum, or the sum of the 15 5-minute vallues. Click the t Export button. b 107 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 The usser providess a file namee and the forrmat or typee of file. Thhe file type can be ASC CII text, comma c delim mited, Accesss database,, recharge, S SWMM, or WWHM. Click Save to save th he exported time t series file. f 108 Santa Margarita Region Hydrology Model Guidance – April 2014 This page has been intentionally left blank. 109 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 LID ANALYS A SIS SCR REEN The LIID tool bar button b (farth hest on the right) brings uup the Low IImpact Deveelopment Scenarrio Generato or screen. The LID scenario generator can c be used to comparee the amounnt of runoff from differeent land ty ypes and com mbinations. The user caan quickly ssee how chaanging the laand use affeccts surfacee runoff, inteerflow, grou undwater, and d evapotransspiration. NOTE E: The LID scenario geenerator worrks only in the Mitigatted scenarioo. 110 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 The eaasiest way to o compare different land d use scenariios is to placce all of them m on the sam me Schem matic Editor screen grid. Each DMA A can then reepresent a ddifferent landd use scenarrio. Because the LID scenario gen nerator only y compares rrunoff volum me there is no need to do any routing throug gh a MS4 faccility or receeiving water.. For thiis example th he four DMA As are assign ned the folloowing land uuses: DMA 1: 1 acre A, Grass, Mod derate (5-10% %) derate (5-10% %) DMA 2: 1 acre C, Shrub, Mod derate (5-10% %) DMA 3: 1 acre C, Grass, Mod DMA 4: 1 acre D, Urban, Mod derate (5-10% %) Each basin b is assig gned a differrent POC (po oint of comppliance) for tthe LID anallysis. 111 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 Click on the Com mpute LID Base Data a button to generate thhe LID anallysis data aand summaarize the surrface runoff, f, interflow, groundwater g r, precipitatiion, evaporaation, and tootal runofff for all of the basins. Th he results wiill be shown for each bassin in terms of its POC. For DM MA 1 (1 accre of A, Grrass, Moderaate slope) thhe distributiion of the prrecipitation is: Surfacce runoff = 0.242 0 inches per year Interflow = 2.133 inches per year y ndwater = 2.0 089 inches per p year Groun Evaporation = 11.4 419 inches per p year The su um of the surface s runo off + interflo ow + grounndwater + eevaporation equals 15.8883 inches per year. The T precipitaation at this site s equals 1 5.910 inches per year. T The differennce is becaause 2% of the t groundw water goes to deep or inaactive grounddwater and iis not includded in the LID table. To loo ok at the other DMAs click on thee Select PO OC To arrow w and selectt the DMA of interesst. The LIID analysis results r can be b presented d in terms off either inchees per year oor acre-feet pper year by y checking the t appropriaate box in th he lower righht portion off the LID anaalysis screenn. 112 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 To com mpare the different POC Cs side-by-sid de as bar chaarts click onn the Water B Balance Chart.. The water w balancee chart graph hically displaays the runooff distributioon for all foour POCs siddeby-side. In the barr chart the bottom red is the surface runoff. Aboove in yellow w is interflow w; undwater an nd blue for ev vapotranspirration. then grreen for grou DMA 1 (POC 1) is i an A soil with grass land l cover oon a moderaate slope andd produces tthe least amount a of su urface runofff and interfllow (the sum m of surfacee and interfloow is the tottal stormw water runoff) f). DMA 2 is a C soil with shru ub land coveer on a mod erate slope; it producess more surfaace runofff and interflo ow than DMA A 1. DMA 3 is a C so oil with grasss land cover on a modeerate slope; it producess more surfaace ow than eitheer DMA 1 orr DMA 2. runofff and interflo DMA 4 is a D so oil with urbaan land cov ver on a mo derate slopee. Urban laand covers aare irrigateed. Urban produces p thee largest amo ount of surfaace runoff annd interflow w in addition to a largee amount of evapotransp piration due to t the additioon of irrigatiion water. A max ximum of sev ven scenario os can be graaphed at one time. 113 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 OPT TIONS Option ns can be acccessed by go oing to View w, Options. This will brring up the O Options screeen and th he ability to modify the built-in deffault duration criteria foor flow duraation matchinng and scaling factorss for climate variables. 114 Santa Margarita Region Hydrology Model Guidance – April 2014 DURATION CRITERIA The flow duration criteria are: 1. If the post-development flow duration values exceed any of the predevelopment flow levels between the lower threshold (10% of the two-year) and five-year predevelopment peak flow values then the flow duration standard has not been met. 2. If the post-development flow duration values exceed any of the predevelopment flow levels between the 5-year and the upper threshold (100% of the 10-year) predevelopment peak flow values more than 10 percent of the time (110 Percent Threshold) then the flow duration standard has not been met. 3. If more than 10 percent of the flow duration levels exceed the 100 percent threshold then the flow duration standard has not been met. The duration criteria in SMRHM can be modified by the user if appropriate and the local municipal permitting agency allows (see NOTE below). The user can conduct the duration analysis using either (1) durations based on Predevelopment flow frequency, or (2) durations based on user defined flow values. If using durations based on Predevelopment flow frequency, the percent of the lower limit can be changed from the default of the 10% of the 2-year flow event to a higher or lower percent value. The lower and upper flow frequency limits (2-year and 10-year) also can be changed. If using durations based on user defined flow values, click on that option and input the lower and upper flow values. The default pass/fail threshold is 100% for the flows between 10% of the 2-year and 5year flow. This value cannot be changed by the user. The default pass/fail threshold is 110% for the flows between the 5-year and 10-year flow. This value can be changed by the user. The duration criteria can be changed for a single POC. Click on the Update button once all of the changes have been made. To return to the default values click on the Restore Defaults button. NOTE: Any change(s) to the default duration criteria must be approved by the Copermittee with jurisdiction over the project site or specified in Appendix C. 115 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 SCAL LING FAC CTORS The usser can change the scalin ng factors fo or precipitatioon (minimum m and maxim mum) and ppan evaporration. NOTE E: Any change in defa ault scaling factors req quires appro oval by the Copermitte ee with ju urisdiction over o the pro oject site orr Appendix C. Click on the Upd date button once o all of the changess have beenn made. Too return to tthe defaultt values click k on the Resstore Defaullts button. 116 Santa Margarita Region Hydrology Model Guidance – April 2014 This page has been intentionally left blank. 117 Santa Margarita Region Hydrology Model Guidance – April 2014 TIPS AND TRICKS FOR LID PRACTICES AND FACILITIES There are many different tips and tricks that can be used to tailor SMRHM to solve different stormwater runoff management problems. This section presents only a fraction of the tricks that we and others have found and used, but it should give you a good idea of the options and flexibility built into SMRHM. The tips and tricks show how different LID/BMPs elements. can be represented by SMRHM LID/BMP practices and facilities reduce the need for and the size of hydrologic control facilities. LID/BMP practices and facilities typically try to mimic the natural environment and provide source control and storage of runoff. Riverside County's Design Handbook for Low Impact Development Best Management Practices (September 2011) include eight (8) practices that can be modeled using the comparable SMRHM elements. This handbook has the most up-to-date information regarding BMP standards and should be consulted prior to the start of any SMRHM LID BMP modeling. The eight LID BMPs are: 1. 2. 3. 4. 5. 6. 7. 8. Infiltration Basin Infiltration Trench Permeable Pavement Bioretention (standard design) Bioretention (vertical sideslopes) Bioretention (planter box) Sand Filter Extended Detention Basin Each of these eight LID BMPs are described below. NOTE: Many of these LID/BMP practices and facilities rely on infiltration into native soils. See Appendix C or consult with the Copermittee with jurisdiction over the project site for additional considerations regarding infiltration and determination of an infiltration reduction factor, where appropriate. 118 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 INFIL LTRATION BASIN//POND Figuree courtesy off Riverside County C Flood d Control annd Water Connservation D District An inffiltration basin allows stormwater s runoff r to ennter the basiin above groound and thhen infiltraate through the t bottom of o the basin into i the nativve soil beneaath the basinn. Overflow w is controlled by an ov verflow outllet. For the purpose of flow contrrol the disch harge from tthe overflow w outlet shouuld not exceeed the preedevelopmen nt discharge from the prroject site foor the flow dduration rangge specified by the Co opermittee with w jurisdictiion over the project site . In SM MRHM the in nfiltration baasin is repressented by thee trapezoidaal or irregulaar-shaped poond elemen nt. 119 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 The po ond dimensio ons and paraameters to ad djust to repreesent an infiiltration basiin are: Bottom m Length (ft)): Infiltration n basin lengtth Bottom m Width (ft): Infiltration n basin width h Effectiive Depth (fft): Infiltratio on basin height from baasin bottom tto top of riseer plus at leaast 1.0 foo ot of freeboaard Left Siideslope (H//V): ratio of horizontal distance d to veertical for innfiltration basin sides Bottom m Sideslope (H/V): ratio o of horizontaal distance too vertical foor infiltrationn basin sides Right Sideslope (H H/V): ratio of o horizontal distance to vvertical for iinfiltration bbasin sides Top Siideslope (H//V): ratio of horizontal distance d to veertical for innfiltration bassin sides Riser Height H (ft): Height H of inffiltration bassin/pond oveerflow pipe aabove basin soil surface Riser Diameter D (in n): Infiltratio on basin overrflow pipe diiameter Riser Type: T Flat Infiltraation: Yes (in nfiltration in nto the underrlying nativee soil) Measu ured Infiltratiion Rate (in//hr): Native soil infiltratiion rate Infiltraation Reducttion Factor: 1/Native soiil infiltrationn rate safety ffactor (see ppage 69) Use Wetted W Surfaace Area (sidewalls): Yes, Y if infiltrration througgh the basinn sideslopes is alloweed. If infilltration is useed then the user u should consult c the IInfiltration ddiscussion onn page 69. 120 Santa Margarita Region Hydrology Model Guidance – April 2014 Any changes made by the user to the element dimensions and other input are not analyzed by SMRHM until the Run Scenario button is reclicked. The Riverside County Design Handbook for Low Impact Development Best Management Practices specifies the following criteria for infiltration basins: Maximum drawdown time: 72 hrs Maximum tributary area: 50 ac Maximum depth: 5 ft Maximum sideslopes: 4 to 1 NOTE: See Appendix C or consult with the Copermittee with jurisdiction over the project site for additional considerations regarding infiltration and determination of the appropriate infiltration reduction factor. An infiltration basin/pond receives precipitation on and evaporation from the basin surface area. The Precipitation Applied to Facility and Evaporation Applied to Facility boxes should be checked. 121 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 INFIL LTRATION TRENC CH Figuree courtesy off Riverside County C Flood d Control annd Water Connservation D District An inffiltration treench is simiilar to the infiltration i bbasin. How wever, there is no bottoom dischaarge pipe or underdrain. Water must m infiltratee into the nnative soil uunderlying tthe gravel layer of the planter. Ov verflow is co ontrolled by an overflow w outlet. For the purpose of flow contrrol the disch harge from thhe overflow w outlet shouuld not exceeed the preedevelopmen nt discharge from the prroject site for the flow du duration rangge specified bby the loccal jurisdictio on. In SMRHM the infiltration trench is repressented by thhe gravel trennch bed elem ment. 122 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 The gravel trench h bed dimen nsions and parameters to adjust too represent an infiltratiion trench are: Trench h Length (ft)): Infiltration n trench leng gth Trench h Bottom Wiidth (ft): Infi filtration tren nch width Effectiive Total Deepth (ft): Infiltration treench height from bottom m of trench to top of risser plus att least 0.5 feeet extra Bottom m Slope of Trench T (ft/ft): Must be no on-zero Left Siideslope (ft/ft): 0 (zero) for vertical infiltration i tr trench sides Right Sideslope (ft ft/ft): 0 (zero) for vertical infiltrationn trench sidess n/hr): Infiltrration trench soil infiltrattion rate Infiltraation Rate (in Layer 1 Thicknesss (ft): Infiltraation trench soil s layer deepth Layer 1 Porosity: Infiltration I trrench soil po orosity Layer 2 Thicknesss (ft): Infiltraation trench gravel g layer depth Layer 2 Porosity: Infiltration I trrench gravell porosity Layer 3 Thicknesss (ft): Infiltraation trench gravel g layer depth Layer 3 Porosity: Infiltration I trrench gravell porosity. NOTE E: Layers 2 and 3 are optional. o Riser Height H (ft): Height H of infiltration treench overflow w pipe abovve trench botttom. If a w weir is prefferred insteaad of a riser,, then set th he riser heighht to the weeir height annd set the risser diametter to the weeir length. 123 Santa Margarita Region Hydrology Model Guidance – April 2014 Riser Diameter (in): Infiltration trench overflow pipe diameter Riser Type: Flat Native Infiltration: Yes (infiltration into the underlying native soil) Measured Infiltration Rate (in/hr): Native soil infiltration rate Infiltration Reduction Factor: 1/Native soil infiltration rate safety factor (see page 69) If infiltration is used then the user should consult the Infiltration discussion on page 69. Any changes made by the user to the element dimensions and other input are not analyzed by SMRHM until the Run Scenario button is reclicked. The Riverside County Design Handbook for Low Impact Development Best Management Practices specifies the following criteria for infiltration trenches: Max drawdown: 72 hrs Max tributary area: 10 ac Max depth: 8 ft Sideslope: 0 to 1 (vertical) Trench width must be greater than depth NOTE: See Appendix C or consult with the Copermittee with jurisdiction over the project site for additional considerations regarding infiltration and determination of the appropriate infiltration reduction factor. The infiltration trench receives precipitation on and evaporation from the trench surface. The Precipitation Applied to Facility and Evaporation Applied to Facility boxes should be checked. 124 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 PERMEABLE E PAVEME ENT Figuree courtesy off Riverside County C Flood d Control annd Water Coonservation D District Permeeable pavem ment LID op ptions inclu ude porous asphalt or concrete annd grid/lattiice system ms (non-conccrete) and paving block ks. The use of any of thhese LID opptions requirres that ceertain minim mum standarrds and requ uirements arre met relateed to subgraade, geotextile materiial, separatiion or botttom filter layer, base material, wearing laayer, drainaage convey yance, accep ptance testin ng, and surfacce maintenan ance. NOTE E: Permea able pavement can be e used in pllace of con nventional p pavement ffor roadw ways, sidew walks, drive eways, and parking lotts. Check with Appen ndix C or th he Coperrmittee with h jurisdictio on over the project site e to find ou ut under wh hat condition ns perme eable pavem ment is allo owed. Permeeable pavemeent can be reepresented by b the permeeable pavemeent element in SMRHM M if the folllowing threee conditions are met: 1. 1 2. 2 3. 3 The inffiltration ratte of the perm meable paveement is greeater than thee peak rainffall rate. The infiltration ratte of the perrmeable pavvement is grreater than tthe underlying native soil. There is i subgrade layer l of crusshed rock/graavel betweenn the permeaable pavemeent and thee native soil. 125 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 The peermeable pav vement dimeensions and parameters p aare: Pavem ment Length (ft): Roadwaay length Pavem ment Bottom Width (ft): Roadway R wiidth Effectiive Total Deepth (ft): Heeight from bottom of peermeable pavvement subggrade to top of pavem ment plus at least 0.5 feett extra Bottom m Slope (ft/fft): Pavemen nt slope or grrade. Effectiive Volume Factor: zero o unless the bottom b slopee is greater thhan 2%. The efffective volu ume factor is i a value beetween zeroo and 1.00. It is only uused when tthe bottom m slope is grreater than 2%. 2 The efffective voluume factor iis the fractioon ratio of tthe averag ge maximum m water dep pth behind a check daam in the ggravel layer (Sublayer 1) compaared to the maximum m grravel layer depth d (Sublaayer 1). Foor example, if the averaage maxim mum water height is 6" an nd the graveel depth is 9"" then the Efffective Voluume Factor = 0.67 7 (6/9). The effective vo olume factor is multipliedd by the Subblayer 1 storrage volume to determ mine the actu ual maximum m volume av vailable for stormwater runoff storaage before tthe check dam is overrtopped and the water in n the gravel llayer depth ((Sublayer 1)) proceeds too a downsstream conveeyance faciliity. Pavem ment Thickneess (ft): Perm meable pavem ment layer ddepth Pavem ment Porosity y: Permeablee pavement porosity p Sublay yer 1 Thickn ness (ft): Sub bgrade graveel layer depthh 126 Santa Margarita Region Hydrology Model Guidance – April 2014 Sublayer 1 Porosity: Subgrade gravel porosity. Sublayer 2 Thickness (ft): Sand layer depth (if appropriate) Sublayer 2 Porosity: Sand porosity Ponding Depth above Pavement (ft): Height at which surface runoff occurs NOTE: Check with Appendix C or the Copermittee with jurisdiction over the project site to find out if ponding on the surface of the pavement is allowed. Underdrain Diameter (inches) and Height (feet) above bottom layer-native soil interface. The underdrain is optional. Native Infiltration: Yes (infiltration into the underlying native soil) Measured Infiltration Rate (in/hr): Native soil infiltration rate Infiltration Reduction Factor: 1/Native soil infiltration rate safety factor (see page 69) If infiltration is used then the user should consult the Infiltration discussion on page 69. Any changes made by the user to the element dimensions and other input are not analyzed by SMRHM until the Run Scenario button is re-clicked. The Riverside County Design Handbook for Low Impact Development Best Management Practices specifies the following criteria for permeable pavement: Max drawdown: 24 hrs Max tributary area: 10 ac Max reservoir (gravel subgrade) depth: 1 ft Max pavement slope: 0.03 Permeable pavement bottom slope: zero Aggregate porosity: 0.40 NOTE: See Appendix C or consult with the Copermittee with jurisdiction over the project site for additional considerations regarding infiltration and determination of the appropriate infiltration reduction factor. 127 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 BIOR RETENTIO ON (STAN NDARD DESIGN) D Figuree courtesy off Riverside County C Flood d Control annd Water Connservation D District Bioretention (stan ndard design n) allows sto ormwater runnoff to enteer the biorettention faciliity above ground and then infiltraate through th he mulch layyer, engineeered soil meddia, and gravvel storagee layers befo ore exiting th hrough a discharge pipe.. For th he purpose of flow co ontrol the discharge froom the pipee should noot exceed tthe predev velopment diischarge from m the projecct site for thee flow durattion range sppecified by tthe local ju urisdiction. In SMRHM the bioretention (sstandard dessign) is repreesented by thhe bioretention element. 128 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 The biioretention dimensions d and a parameteers to adjustt to represennt the bioreteention standaard design n are discusseed on page 81. 8 The Riiverside Cou unty Design Handbook for f Low Impaact Development Best M Management Practices specifiess the followiing criteria for fo bioretentiion (standardd design): Minimum m width: 6 ft Sideslopee: 4 to 1 Maximum m ponding deepth: 0.5 ft Mulch top p layer: 2 to 3 inches deeep (above am mended soil layer) Minimum m amended so oil layer dep pth: 1.5 ft Maximum m amended soil s layer dep pth: 3 ft Maximum m amended soil s porosity:: 0.30 Maximum m gravel layeer: 1 ft (below amended soil layer) Gravel lay yer porosity: 0.40 Minimum m underdrain n diameter: 0.5 ft No infiltraation to nativ ve soil 129 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 BIOR RETENTIO ON (VERT TICAL SID DESLOPE ES) Figuree courtesy off Riverside County C Flood d Control annd Water Coonservation D District Biorettention with vertical sid deslopes allo ows stormw water runofff to enter thhe bioretention facility y above gro ound and theen infiltrate through thee mulch layeer, engineereed soil meddia, and grravel storagee layers before exiting th hrough a disccharge pipe. For th he purpose of flow co ontrol the discharge d froom the pipee should noot exceed tthe predev velopment discharge from the projecct site for thee flow durattion range sppecified by tthe Coperrmittee with jurisdiction j over the pro oject site. In SM MRHM the bioretention n (vertical sideslopes) is represennted by thee bioretention elemen nt. 130 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 The biioretention dimensions d and a parameteers to adjustt to represennt the bioreteention standaard design n are discusseed on page 81. 8 The Riiverside Cou unty Design Handbook for f Low Impaact Development Best M Management Practices specifiess the followiing criteria for fo bioretentiion (vertical sideslopes):: Minimum m width: 2 ft Sideslopee: 0 to 1 Maximum m ponding deepth: 0.5 ft Mulch top p layer: 2 to 3 inches deeep (above am mended soil layer) Minimum m amended so oil layer dep pth: 1.5 ft Maximum m amended soil s layer dep pth: 3 ft Maximum m amended soil s porosity:: 0.30 Maximum m gravel layeer: 1 ft (below amended soil layer) Gravel lay yer porosity: 0.40 Minimum m underdrain n diameter: 0.5 ft No infiltraation to nativ ve soil 131 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 BIOR RETENTIO ON (PLAN NTER BO OX) Bioretention in th he form off a planter box allowss stormwatter runoff to enter the bioreteention faciliity above ground g and then infiltraate through the mulch laayer, engineeered soil media, m and gravel g storag ge layers beefore exiting g through a discharge d pip pe. For thee purpose off flow control, the disch harge from the pipe should no ot exceed the Predev velopment discharge d frrom the project site fo or the flow duration ran nge specified by the loccal jurisdictio on. In SMRHM the planter box bioretention iss representedd by the biorretention eleement. The bioretention b dimensionss and param meters to aadjust to reepresent thee planter bbox bioreteention are diiscussed on page p 81. 132 Santa Margarita Region Hydrology Model Guidance – April 2014 The Riverside County Design Handbook for Low Impact Development Best Management Practices specifies the following criteria for planter box bioretention: Minimum width: 2 ft Sideslope: 0 to 1 Maximum ponding depth: 0.5 ft Mulch top layer: 2 to 3 inches deep (above amended soil layer) Minimum amended soil layer depth: 1.5 ft Maximum amended soil layer depth: 3 ft Maximum amended soil porosity: 0.30 Maximum gravel layer: 1 ft (below amended soil layer) Gravel layer porosity: 0.40 Minimum underdrain diameter: 0.5 ft No infiltration to native soil 133 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 SAND D FILTER R BASIN Figuree courtesy off Riverside County C Flood d Control annd Water Connservation D District A sand d filter basin n allows storrmwater runoff to enter the sand filtter above ground and thhen filtratee through thee filter mediaa before exitting through a discharge pipe. In SMRHM the saand filter bassin is represeented by the sand filter eelement. 134 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 The saand filter dim mensions an nd parameters to adjust to represennt the sand ffilter basin aare discussed on page 61. The Riiverside Cou unty Design Handbook for f Low Impaact Development Best M Management Practices specifiess the followiing criteria for fo the sand ffilter basin: Maximum m tributary arrea: 25 ac Maximum m basin depth h: 5 ft Maximum m Sideslope: 4 to 1 Sand filteer top below bottom orifiice: min 4 inn Sand filteer top layer: min m 18 in off sand Sand filteer bottom lay yer: min 10 in of gravel Sand filteer underdrain n diameter: 6 in Sand filteer underdrain n bottom: 1 in i above botttom gravel llayer No infiltraation to nativ ve soil 135 Santa Margaritaa Region Hydrollogy Model Guidance – April 20014 EXTE ENDED DETENTIO D ON BASIN N Figuree courtesy off Riverside County C Flood d Control annd Water Coonservation D District The ex xtended deteention basin n is a combiination storm mwater pondd (forebay), gravel trennch (conneector trench)), and sand filter f (filter drain). In S SMRHM theere is not a ssingle elemeent that reepresents thiss combinatio on. 136 Santa Margaritaa Region Hydroology Model Guiidance – April 20014 In SM MRHM the extended e dettention basin n is represeented by treaatment trainn connectingg a trapezo oidal pond (or irregularr pond) elem ment to a ggravel trenchh element too a sand filter elemen nt, in that order. There is also the option o of creeating the ex xtended deteention basin''s stage-storaage- discharrge table outside o of SM MRHM and inputting it as a a SSD Taable element. The trrapezoidal pond p dimenssions and paarameters too adjust to represent thhe forebay aare discussed on page 46. The irrregular pon nd dimensio ons and parrameters to adjust to rrepresent thhe forebay aare discussed on page 56. The grravel trench dimensions and parametters to adjusst to represennt the connector trench aare discussed on page 59. The sand filter dimensions d and parameeters to adjuust to repreesent the fiilter drain aare discussed on page 61. The SS SD element is discussed on page 78.. The Riiverside Cou unty Design Handbook for f Low Impaact Development Best M Management Practices specifiess the followiing criteria for fo the extendded detentioon basin: 137 Santa Margarita Region Hydrology Model Guidance – April 2014 Minimum tributary area: 5 ac Maximum drawdown: 72 hrs Maximum Sideslope: 4 to 1 Trench bottom slope: 1% Minimum filter drain depth: 2.33 ft 138 Santa Margarita Region Hydrology Model Guidance – April 2014 This page has been intentionally left blank. 139 Appendix A APPENDIX A: DEFAULT PARAMETER VALUES Santa Margarita Region Hydrology Model Guidance – June 2013 SMRHM HSPF PERVIOUS The default SMRHM HSPF pervious parameter values are found in SMRHM file defaultpersp.uci. HSPF parameter documentation is found in the document: Bicknell, B.R., J.C. Imhoff, J.L. Kittle Jr, T.H. Jobes, and A.S. Donigian Jr. 2001. Hydrological Simulation Program – Fortran, User's Manual for Version 12. AQUA TERRA Consultants. Mountain View, CA. 140 Appendix A Santa Margarita Region Hydrology Model Guidance – June 2013 Table 1. SMRHM Pervious Land Types PERLND No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 Soil Type A A A A A A A A A A A A A A A A B B B B B B B B B B B B B B B B C/D C/D C/D C/D C/D C/D C/D C/D C/D C/D C/D C/D Land Cover Forest Forest Forest Forest Shrub Shrub Shrub Shrub Grass Grass Grass Grass Urban Urban Urban Urban Forest Forest Forest Forest Shrub Shrub Shrub Shrub Grass Grass Grass Grass Urban Urban Urban Urban Forest Forest Forest Forest Shrub Shrub Shrub Shrub Grass Grass Grass Grass Land Slope Flat (0-5%) Moderate (5-10%) Steep (10-20%) Very Steep (>20%) Flat (0-5%) Moderate (5-10%) Steep (10-20%) Very Steep (>20%) Flat (0-5%) Moderate (5-10%) Steep (10-20%) Very Steep (>20%) Flat (0-5%) Moderate (5-10%) Steep (10-20%) Very Steep (>20%) Flat (0-5%) Moderate (5-10%) Steep (10-20%) Very Steep (>20%) Flat (0-5%) Moderate (5-10%) Steep (10-20%) Very Steep (>20%) Flat (0-5%) Moderate (5-10%) Steep (10-20%) Very Steep (>20%) Flat (0-5%) Moderate (5-10%) Steep (10-20%) Very Steep (>20%) Flat (0-5%) Moderate (5-10%) Steep (10-20%) Very Steep (>20%) Flat (0-5%) Moderate (5-10%) Steep (10-20%) Very Steep (>20%) Flat (0-5%) Moderate (5-10%) Steep (10-20%) Very Steep (>20%) 141 Appendix A 45 46 47 48 Santa Margarita Region Hydrology Model Guidance – June 2013 C/D C/D C/D C/D Urban Urban Urban Urban Flat (0-5%) Moderate (5-10%) Steep (10-20%) Very Steep (>20%) 142 Appendix A Santa Margarita Region Hydrology Model Guidance – June 2013 Table 2. SMRHM HSPF Pervious Parameter Values – Part I PERLND No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 LZSN 5.20 4.80 4.50 4.20 5.20 4.80 4.50 4.20 5.20 4.80 4.50 4.20 5.00 4.60 4.20 3.80 5.00 4.70 4.40 4.10 5.00 4.70 4.40 4.10 5.00 4.70 4.40 4.10 4.80 4.40 4.00 3.60 4.80 4.50 4.20 4.00 4.80 4.50 4.20 4.00 4.80 4.50 4.20 4.00 4.60 INFILT 0.100 0.075 0.055 0.045 0.090 0.070 0.045 0.040 0.090 0.070 0.045 0.040 0.060 0.050 0.040 0.030 0.080 0.060 0.045 0.035 0.070 0.055 0.040 0.030 0.070 0.055 0.040 0.030 0.050 0.040 0.030 0.025 0.050 0.045 0.035 0.030 0.045 0.040 0.030 0.025 0.045 0.040 0.030 0.025 0.040 LSUR 400 350 300 200 400 350 300 200 400 350 300 200 400 350 300 200 400 350 300 200 400 350 300 200 400 350 300 200 400 350 300 200 400 350 300 200 400 350 300 200 400 350 300 200 400 143 SLSUR 0.05 0.10 0.15 0.25 0.05 0.10 0.15 0.25 0.05 0.10 0.15 0.25 0.05 0.10 0.15 0.25 0.05 0.10 0.15 0.25 0.05 0.10 0.15 0.25 0.05 0.10 0.15 0.25 0.05 0.10 0.15 0.25 0.05 0.10 0.15 0.25 0.05 0.10 0.15 0.25 0.05 0.10 0.15 0.25 0.05 KVARY 0.80 0.80 0.80 0.80 0.80 0.80 0.80 0.80 0.80 0.80 0.80 0.80 1.20 1.20 1.20 1.20 1.20 1.20 1.20 1.20 1.20 1.20 1.20 1.20 1.20 1.20 1.20 1.20 1.80 1.80 1.80 1.80 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 3.00 AGWRC 0.985 0.985 0.985 0.985 0.955 0.955 0.955 0.955 0.955 0.955 0.955 0.955 0.997 0.997 0.997 0.997 0.980 0.980 0.980 0.980 0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.995 0.995 0.995 0.995 0.980 0.980 0.980 0.980 0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.995 Appendix A 46 47 48 Santa Margarita Region Hydrology Model Guidance – June 2013 4.20 3.80 3.50 0.030 0.022 0.020 350 300 200 0.10 0.15 0.25 3.00 3.00 3.00 LZSN: Lower Zone Storage Nominal (inches) INFILT: Infiltration (inches per hour) LSUR: Length of surface flow path (feet) SLSUR: Slope of surface flow path (feet/feet) KVARY: Variable groundwater recession AGWRC: Active Groundwater Recession Constant (per day) 144 0.995 0.995 0.995 Appendix A Santa Margarita Region Hydrology Model Guidance – June 2013 Table 3. SMRHM HSPF Pervious Parameter Values – Part II PERLND No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 INFEXP 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 INFILD 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 DEEPFR 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.06 0.06 0.06 0.06 0.12 0.12 0.12 0.12 0.12 0.12 0.12 0.12 0.12 0.12 0.12 0.12 0.36 0.36 0.36 0.36 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.45 145 BASETP 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.08 0.08 0.08 0.08 0.08 0.08 0.08 0.08 0.08 0.08 0.08 0.08 0.08 0.08 0.08 0.08 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 AGWETP 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Appendix A 46 47 48 Santa Margarita Region Hydrology Model Guidance – June 2013 3.00 3.00 3.00 2.00 2.00 2.00 0.45 0.45 0.45 0.15 0.15 0.15 0.00 0.00 0.00 INFEXP: Infiltration Exponent INFILD: Infiltration ratio (maximum to mean) DEEPFR: Fraction of groundwater to deep aquifer or inactive storage BASETP: Base flow (from groundwater) Evapotranspiration fraction AGWETP: Active Groundwater Evapotranspiration fraction 146 Appendix A Santa Margarita Region Hydrology Model Guidance – June 2013 Table 4. SMRHM HSPF Pervious Parameter Values – Part III PERLND No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 CEPSC see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 see Table 6 UZSN 1.00 0.80 0.60 0.50 0.90 0.70 0.50 0.40 0.80 0.70 0.55 0.30 0.70 0.50 0.35 0.30 1.00 0.80 0.60 0.50 0.90 0.70 0.50 0.40 0.80 0.70 0.55 0.30 0.70 0.50 0.35 0.30 1.00 0.80 0.60 0.50 0.90 0.70 0.50 0.40 0.80 0.70 0.55 0.30 0.70 NSUR 0.35 0.35 0.35 0.35 0.30 0.30 0.30 0.30 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.35 0.35 0.35 0.35 0.30 0.30 0.30 0.30 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.35 0.35 0.35 0.35 0.30 0.30 0.30 0.30 0.25 0.25 0.25 0.25 0.25 147 INTFW 4.50 4.00 3.00 2.00 4.00 3.20 2.60 1.80 4.00 3.20 2.60 1.80 3.00 2.40 1.60 1.00 4.00 3.00 2.00 0.80 3.00 2.40 1.60 0.60 3.00 2.40 1.60 0.60 2.00 1.20 0.80 0.60 2.00 1.50 1.00 0.40 2.00 1.20 0.80 0.40 2.00 1.20 0.80 0.40 1.00 IRC 0.80 0.50 0.45 0.40 0.70 0.45 0.40 0.35 0.70 0.45 0.40 0.35 0.40 0.35 0.30 0.30 0.80 0.50 0.45 0.40 0.70 0.45 0.40 0.35 0.70 0.45 0.40 0.35 0.40 0.35 0.30 0.30 0.80 0.50 0.45 0.40 0.70 0.45 0.40 0.35 0.70 0.45 0.40 0.35 0.40 LZETP see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 see Table 7 Appendix A 46 47 48 Santa Margarita Region Hydrology Model Guidance – June 2013 see Table 6 see Table 6 see Table 6 0.50 0.35 0.30 0.25 0.25 0.25 CEPSC: Interception storage (inches) UZSN: Upper Zone Storage Nominal (inches) NSUR: Surface roughness (Manning's n) INTFW: Interflow index IRC: Interflow Recession Constant (per day) LZETP: Lower Zone Evapotranspiration fraction 148 0.70 0.50 0.35 0.35 0.30 0.30 see Table 7 see Table 7 see Table 7 Appendix A Santa Margarita Region Hydrology Model Guidance – June 2013 Table 5. SMRHM HSPF Pervious Parameter Values – Part VI PERLND No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 CEPS 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 SURS 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 UZS 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 IFWS 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 149 LZS 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 3.50 3.50 3.50 3.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 3.50 3.50 3.50 3.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 3.50 AGWS 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 1.50 1.50 1.50 1.50 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 1.50 1.50 1.50 1.50 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 1.70 GWVS 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.10 0.10 0.10 0.10 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.10 0.10 0.10 0.10 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.10 Appendix A 46 47 48 Santa Margarita Region Hydrology Model Guidance – June 2013 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.01 0.01 0.00 0.00 0.00 CEPS: Initial interception storage (inches) SURS: Initial surface runoff (inches) UZS: Initial Upper Zone Storage (inches) IFWS: Initial interflow (inches) LZS: Initial Lower Zone Storage (inches) AGWS: Initial Active Groundwater storage (inches) GWVS: Initial Groundwater Vertical Slope (feet/feet) 150 3.50 3.50 3.50 1.70 1.70 1.70 0.10 0.10 0.10 Appendix A Santa Margarita Region Hydrology Model Guidance – June 2013 Table 6. SMRHM HSPF Pervious Parameter Values: Monthly Interception Storage (inches) PERLND No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 JAN 0.15 0.15 0.15 0.15 0.13 0.13 0.13 0.13 0.12 0.12 0.12 0.12 0.11 0.11 0.11 0.11 0.15 0.15 0.15 0.15 0.13 0.13 0.13 0.13 0.12 0.12 0.12 0.12 0.11 0.11 FEB 0.15 0.15 0.15 0.15 0.13 0.13 0.13 0.13 0.12 0.12 0.12 0.12 0.11 0.11 0.11 0.11 0.15 0.15 0.15 0.15 0.13 0.13 0.13 0.13 0.12 0.12 0.12 0.12 0.11 0.11 MAR 0.15 0.15 0.15 0.15 0.13 0.13 0.13 0.13 0.12 0.12 0.12 0.12 0.11 0.11 0.11 0.11 0.15 0.15 0.15 0.15 0.13 0.13 0.13 0.13 0.12 0.12 0.12 0.12 0.11 0.11 APR 0.20 0.20 0.20 0.20 0.14 0.14 0.14 0.14 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.20 0.20 0.20 0.20 0.14 0.14 0.14 0.14 0.11 0.11 0.11 0.11 0.11 0.11 MAY 0.20 0.20 0.20 0.20 0.15 0.15 0.15 0.15 0.10 0.10 0.10 0.10 0.11 0.11 0.11 0.11 0.20 0.20 0.20 0.20 0.15 0.15 0.15 0.15 0.10 0.10 0.10 0.10 0.11 0.11 JUN 0.20 0.20 0.20 0.20 0.15 0.15 0.15 0.15 0.10 0.10 0.10 0.10 0.11 0.11 0.11 0.11 0.20 0.20 0.20 0.20 0.15 0.15 0.15 0.15 0.10 0.10 0.10 0.10 0.11 0.11 152 JUL 0.20 0.20 0.20 0.20 0.15 0.15 0.15 0.15 0.10 0.10 0.10 0.10 0.11 0.11 0.11 0.11 0.20 0.20 0.20 0.20 0.15 0.15 0.15 0.15 0.10 0.10 0.10 0.10 0.11 0.11 AUG 0.20 0.20 0.20 0.20 0.15 0.15 0.15 0.15 0.10 0.10 0.10 0.10 0.11 0.11 0.11 0.11 0.20 0.20 0.20 0.20 0.15 0.15 0.15 0.15 0.10 0.10 0.10 0.10 0.11 0.11 SEP 0.20 0.20 0.20 0.20 0.15 0.15 0.15 0.15 0.10 0.10 0.10 0.10 0.11 0.11 0.11 0.11 0.20 0.20 0.20 0.20 0.15 0.15 0.15 0.15 0.10 0.10 0.10 0.10 0.11 0.11 OCT 0.20 0.20 0.20 0.20 0.15 0.15 0.15 0.15 0.10 0.10 0.10 0.10 0.11 0.11 0.11 0.11 0.20 0.20 0.20 0.20 0.15 0.15 0.15 0.15 0.10 0.10 0.10 0.10 0.11 0.11 NOV 0.20 0.20 0.20 0.20 0.14 0.14 0.14 0.14 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.20 0.20 0.20 0.20 0.14 0.14 0.14 0.14 0.11 0.11 0.11 0.11 0.11 0.11 DEC 0.18 0.18 0.18 0.18 0.13 0.13 0.13 0.13 0.12 0.12 0.12 0.12 0.11 0.11 0.11 0.11 0.18 0.18 0.18 0.18 0.13 0.13 0.13 0.13 0.12 0.12 0.12 0.12 0.11 0.11 Appendix A 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 Santa Margarita Region Hydrology Model Guidance – June 2013 0.11 0.11 0.15 0.15 0.15 0.15 0.13 0.13 0.13 0.13 0.12 0.12 0.12 0.12 0.11 0.11 0.11 0.11 0.11 0.11 0.15 0.15 0.15 0.15 0.13 0.13 0.13 0.13 0.12 0.12 0.12 0.12 0.11 0.11 0.11 0.11 0.11 0.11 0.15 0.15 0.15 0.15 0.13 0.13 0.13 0.13 0.12 0.12 0.12 0.12 0.11 0.11 0.11 0.11 0.11 0.11 0.20 0.20 0.20 0.20 0.14 0.14 0.14 0.14 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.20 0.20 0.20 0.20 0.15 0.15 0.15 0.15 0.10 0.10 0.10 0.10 0.11 0.11 0.11 0.11 0.11 0.11 0.20 0.20 0.20 0.20 0.15 0.15 0.15 0.15 0.10 0.10 0.10 0.10 0.11 0.11 0.11 0.11 153 0.11 0.11 0.20 0.20 0.20 0.20 0.15 0.15 0.15 0.15 0.10 0.10 0.10 0.10 0.11 0.11 0.11 0.11 0.11 0.11 0.20 0.20 0.20 0.20 0.15 0.15 0.15 0.15 0.10 0.10 0.10 0.10 0.11 0.11 0.11 0.11 0.11 0.11 0.20 0.20 0.20 0.20 0.15 0.15 0.15 0.15 0.10 0.10 0.10 0.10 0.11 0.11 0.11 0.11 0.11 0.11 0.20 0.20 0.20 0.20 0.15 0.15 0.15 0.15 0.10 0.10 0.10 0.10 0.11 0.11 0.11 0.11 0.11 0.11 0.20 0.20 0.20 0.20 0.14 0.14 0.14 0.14 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.18 0.18 0.18 0.18 0.13 0.13 0.13 0.13 0.12 0.12 0.12 0.12 0.11 0.11 0.11 0.11 Appendix A Santa Margarita Region Hydrology Model Guidance – June 2013 Table 7. SMRHM HSPF Pervious Parameter Values: Monthly Lower Zone Evapotranspiration PERLND No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 JAN 0.60 0.60 0.60 0.60 0.50 0.50 0.50 0.50 0.40 0.40 0.40 0.40 0.50 0.50 0.50 0.50 0.60 0.60 0.60 0.60 0.50 0.50 0.50 0.50 0.40 0.40 0.40 0.40 0.50 0.50 FEB 0.60 0.60 0.60 0.60 0.50 0.50 0.50 0.50 0.40 0.40 0.40 0.40 0.50 0.50 0.50 0.50 0.60 0.60 0.60 0.60 0.50 0.50 0.50 0.50 0.40 0.40 0.40 0.40 0.50 0.50 MAR 0.60 0.60 0.60 0.60 0.50 0.50 0.50 0.50 0.40 0.40 0.40 0.40 0.50 0.50 0.50 0.50 0.60 0.60 0.60 0.60 0.50 0.50 0.50 0.50 0.40 0.40 0.40 0.40 0.50 0.50 APR 0.70 0.70 0.70 0.70 0.60 0.60 0.60 0.60 0.45 0.45 0.45 0.45 0.60 0.60 0.60 0.60 0.70 0.70 0.70 0.70 0.60 0.60 0.60 0.60 0.45 0.45 0.45 0.45 0.60 0.60 MAY 0.75 0.75 0.75 0.75 0.65 0.65 0.65 0.65 0.50 0.50 0.50 0.50 0.65 0.65 0.65 0.65 0.75 0.75 0.75 0.75 0.65 0.65 0.65 0.65 0.50 0.50 0.50 0.50 0.65 0.65 JUN 0.75 0.75 0.75 0.75 0.65 0.65 0.65 0.65 0.55 0.55 0.55 0.55 0.65 0.65 0.65 0.65 0.75 0.75 0.75 0.75 0.65 0.65 0.65 0.65 0.55 0.55 0.55 0.55 0.65 0.65 154 JUL 0.75 0.75 0.75 0.75 0.65 0.65 0.65 0.65 0.55 0.55 0.55 0.55 0.65 0.65 0.65 0.65 0.75 0.75 0.75 0.75 0.65 0.65 0.65 0.65 0.55 0.55 0.55 0.55 0.65 0.65 AUG 0.75 0.75 0.75 0.75 0.65 0.65 0.65 0.65 0.55 0.55 0.55 0.55 0.65 0.65 0.65 0.65 0.75 0.75 0.75 0.75 0.65 0.65 0.65 0.65 0.55 0.55 0.55 0.55 0.65 0.65 SEP 0.75 0.75 0.75 0.75 0.65 0.65 0.65 0.65 0.55 0.55 0.55 0.55 0.65 0.65 0.65 0.65 0.75 0.75 0.75 0.75 0.65 0.65 0.65 0.65 0.55 0.55 0.55 0.55 0.65 0.65 OCT 0.75 0.75 0.75 0.75 0.65 0.65 0.65 0.65 0.55 0.55 0.55 0.55 0.65 0.65 0.65 0.65 0.75 0.75 0.75 0.75 0.65 0.65 0.65 0.65 0.55 0.55 0.55 0.55 0.65 0.65 NOV 0.65 0.65 0.65 0.65 0.55 0.55 0.55 0.55 0.45 0.45 0.45 0.45 0.55 0.55 0.55 0.55 0.65 0.65 0.65 0.65 0.55 0.55 0.55 0.55 0.45 0.45 0.45 0.45 0.55 0.55 DEC 0.60 0.60 0.60 0.60 0.50 0.50 0.50 0.50 0.40 0.40 0.40 0.40 0.50 0.50 0.50 0.50 0.60 0.60 0.60 0.60 0.50 0.50 0.50 0.50 0.40 0.40 0.40 0.40 0.50 0.50 Appendix A 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 Santa Margarita Region Hydrology Model Guidance – June 2013 0.50 0.50 0.60 0.60 0.60 0.60 0.50 0.50 0.50 0.50 0.40 0.40 0.40 0.40 0.50 0.50 0.50 0.50 0.50 0.50 0.60 0.60 0.60 0.60 0.50 0.50 0.50 0.50 0.40 0.40 0.40 0.40 0.50 0.50 0.50 0.50 0.50 0.50 0.60 0.60 0.60 0.60 0.50 0.50 0.50 0.50 0.40 0.40 0.40 0.40 0.50 0.50 0.50 0.50 0.60 0.60 0.70 0.70 0.70 0.70 0.60 0.60 0.60 0.60 0.45 0.45 0.45 0.45 0.60 0.60 0.60 0.60 0.65 0.65 0.75 0.75 0.75 0.75 0.65 0.65 0.65 0.65 0.50 0.50 0.50 0.50 0.65 0.65 0.65 0.65 0.65 0.65 0.75 0.75 0.75 0.75 0.65 0.65 0.65 0.65 0.55 0.55 0.55 0.55 0.65 0.65 0.65 0.65 155 0.65 0.65 0.75 0.75 0.75 0.75 0.65 0.65 0.65 0.65 0.55 0.55 0.55 0.55 0.65 0.65 0.65 0.65 0.65 0.65 0.75 0.75 0.75 0.75 0.65 0.65 0.65 0.65 0.55 0.55 0.55 0.55 0.65 0.65 0.65 0.65 0.65 0.65 0.75 0.75 0.75 0.75 0.65 0.65 0.65 0.65 0.55 0.55 0.55 0.55 0.65 0.65 0.65 0.65 0.65 0.65 0.75 0.75 0.75 0.75 0.65 0.65 0.65 0.65 0.55 0.55 0.55 0.55 0.65 0.65 0.65 0.65 0.55 0.55 0.65 0.65 0.65 0.65 0.55 0.55 0.55 0.55 0.45 0.45 0.45 0.45 0.55 0.55 0.55 0.55 0.50 0.50 0.60 0.60 0.60 0.60 0.50 0.50 0.50 0.50 0.40 0.40 0.40 0.40 0.50 0.50 0.50 0.50 Appendix A Santa Margarita Region Hydrology Model Guidance – June 2013 This page has been intentionally left blank. 156 Appendix B Santa Margarita Region Hydrology Model Guidance – June 2013 APPENDIX B: DEFAULT SMRHM HSPF IMPERVIOUS PARAMETER VALUES The default SMRHM HSPF impervious parameter values are found in SMRHM file defaultpersp.uci. HSPF parameter documentation is found in the document: Bicknell, B.R., J.C. Imhoff, J.L. Kittle Jr, T.H. Jobes, and A.S. Donigian Jr. 2001. Hydrological Simulation Program – Fortran, User's Manual for Version 12. AQUA TERRA Consultants. Mountain View, CA. Table 1. SMRHM Impervious Land Types IMPLND No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 IMPLND Name Roads Roads Roads Roads Roof Area Driveways Driveways Driveways Driveways Sidewalks Sidewalks Sidewalks Sidewalks Parking Parking Parking Parking Land Slope Flat (0-5%) Moderate (5-10%) Steep (10-20%) Very Steep (>20%) All Flat (0-5%) Moderate (5-10%) Steep (10-20%) Very Steep (>20%) Flat (0-5%) Moderate (5-10%) Steep (10-20%) Very Steep (>20%) Flat (0-5%) Moderate (5-10%) Steep (10-20%) Very Steep (>20%) 157 Appendix B Santa Margarita Region Hydrology Model Guidance – June 2013 Table 2. SMRHM HSPF Impervious Parameter Values – Part I IMPLND No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 LSUR 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 SLSUR 0.05 0.10 0.15 0.25 0.05 0.05 0.10 0.15 0.25 0.05 0.10 0.15 0.25 0.05 0.10 0.15 0.25 NSUR 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 RETSC 0.10 0.09 0.08 0.06 0.10 0.10 0.09 0.08 0.06 0.10 0.09 0.08 0.06 0.10 0.09 0.08 0.06 LSUR: Length of surface flow path (feet) for impervious area SLSUR: Slope of surface flow path (feet/feet) for impervious area NSUR: Surface roughness (Manning's n) for impervious area RETSC: Surface retention storage (inches) for impervious area 158 Appendix B Santa Margarita Region Hydrology Model Guidance – June 2013 Table 3. SMRHM HSPF Impervious Parameter Values – Part II IMPLND No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 RETS 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 SURS 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 RETS: Initial surface retention storage (inches) for impervious area SURS: Initial surface runoff (inches) for impervious area 159 Appendix B Santa Margarita Region Hydrology Model Guidance – June 2013 This page has been intentionally left blank. 160 Appendix C Santa Margarita Region Hydrology Model Guidance – June 2013 APPENDIX C: ADDITIONAL GUIDANCE FOR USING SMRHM Scope and Purpose: This appendix includes guidance and background information that are not incorporated into the SMRHM software, but which the user needs to know in order to use SMRHM for designing projects in the participating jurisdictions. The three main topic areas in this appendix are flagged in the main guidance documentation text by specially formatted notes under the SMRHM elements or software features to which they are related: Appendix C Topic Infiltration Reduction Factor Flow Duration Outlet Structures (includes sizing of low-flow orifice and alternative configurations) Drawdown (drain) time for flow duration facilities Relevant Sections in Guidance documentation Infiltration, page 69; applicable when specifying characteristics of a facility (pond, vault, tank, some LID elements) if "yes" is selected as the Infiltration option. Outlet Structure Configurations, pages 63-68; applicable when specifying characteristics of a flow duration facility. Drawdown (Analysis screen), page 98. This guidance was originally created by the stormwater programs of Alameda, Santa Clara, and San Mateo Counties. Please consult with the local municipal permitting agency for additional considerations. Additional guidance and references are also discussed at the end of this appendix. Infiltration Reduction Factor The Western Washington Hydrology Model included this factor to reflect the requirement in the Stormwater Management Manual for Western Washington (SMMWW), to incorporate a Correction Factor (CF) to determine long-term infiltration rates; the inverse of the CF is the Infiltration Reduction Factor in SMRHM. The SMMWW gives three methods for determining CF: 1) a table providing empirical correlations between long-term infiltration rates and USDA Soil Textural Classification; 2) American Society of Testing and Materials (ASTM) gradation testing at full-scale infiltration facilities; or 3) In-situ infiltration tests, preferably using a Pilot Infiltration Test specified in an appendix of the SMMWW. Application of a CF or safety factor attempts to account for clogging and the reduction in infiltration over time, which might apply to the bottom of a flow duration pond or the top layer of a bioretention facility. However, a safety factor is also used to account for uncertainties in the available estimate of in-situ infiltration rates. The SMMWW notes that its suggested CF values, which range from 2 to 4, "represent an average degree of long-term facility maintenance, TSS reduction through pretreatment, and site variability in the subsurface conditions", and that increases or decreases to these factors should be considered 161 Appendix C Santa Margarita Region Hydrology Model Guidance – June 2013 for unusual situations. Suggested safety factors in other texts and guidance generally range from 1 to 4. Santa Margarita Region County MS4 permits may require some form of tracking and verification for treatment and hydromodification facilities. In addition, designers should not be overly conservative in selecting a very high safety factor, since this might lead to over-controlled (lower) post-project flows and an increase risk of causing impacts from deposition or sedimentation in the receiving channels. In the absence of other guidance, it is suggested that the SMRHM Infiltration Reduction Factor not be less than 0.25 or greater than 0.5. Note: Santa Margarita Region County stormwater programs may also restrict the use of infiltration for treatment purposes in certain conditions; since the flow duration facilities are also performing some treatment, designers should discuss treatment measure design with the applicable jurisdiction. Flow Duration Outlet Structures – Practical Design Considerations Low-flow Orifice Sizing The diameter of the low-flow (bottom) orifice is an important design parameter for flow duration facilities, since flows discharged through this outlet should be at or below the project threshold for controlled flows (Qcp). However maintenance and/or other practical considerations may dictate a practical limit to how small this orifice may be, which may be larger than the optimal theoretical diameter determined by Auto Pond. As an example, Riverside County specifies a minimum orifice diameter of 1.0 inch. While the user can manually set a minimum size for the low-flow orifice, doing so before running Auto Pond is not recommended as this may impair the program's ability to optimize the pond configuration. The following general approach is suggested for designing a pond when there is a small value for the low end of the flow matching range: 1. 2. 3. 4. First estimate the minimum pond volume allowing Auto Pond to freely determine the diameter and placement of all orifices. Then manually accept all of the pond settings except low-flow orifice diameter. Set the low-flow orifice to the desired minimum size, after consulting the local municipal permitting agency. Manually run the mitigated scenario as described on page 48 and review the Analysis screen to check if the revised mitigated flow still passes the flowduration criteria for curve matching. If so, proceed with the pond design using the revised outlet. If the revised design shows Fail scoring at one or more flow levels, excess flow durations may be reduced somewhat by reducing the depth of the pond which lowers the head above the orifice. As an alternative, further mitigation can be applied to the low-flow orifice flow by adding an additional infiltration measure 162 Appendix C Santa Margarita Region Hydrology Model Guidance – June 2013 downstream. This can be sized either approximately by estimating an average excess flow from the orifice or with the help of SMRHM by returning to the screen for the pond characteristics and specifying a different Downstream Connection for the bottom orifice, which is then connected to an additional element. With this revision to the post project scenario, the POC for the system would then be located at the downstream end of the additional low- flow mitigation. Alternative Outlet Configurations SMRHM has two default types of outlet configurations (multiple orifice or orifice plus weir notch) based on a standpipe riser structure detailed in the SMMWW. The entire standpipe is usually within a cylindrical enclosure or manhole to exclude trash and larger particles that could clog the outlet. The SMMWW notes that orifices can also be placed on a tee section or a vertical baffle within the same type of enclosure. An alternative configuration is a flat headwall with orifices and/or notches, protected by racks or gratings. This may be fabricated from a large steel plate, similar in construction to the extended detention outlets specified in the Denver (Colorado) manual referenced below. This alternative outlet can be simulated in the SMRHM as a very large diameter standpipe, where the width of the top notch is equal to the overflow width at the top of the plate between its supports. Drawdown time and treatment/vector considerations Flow duration control facilities are designed to detain stormwater runoff onsite for an extended period of time. The drawdown time is a concern to designers in relation to three areas of design besides hydromodification management: 1. Standing water for extended periods provides a potential habitat in which mosquitoes can breed. T h e C o p e r m i t t e e s work with their local mosquito abatement or vector control agencies to develop guidelines for hydrologic control facility design; the Riverside County Design Handbook for Low Impact Development Best Management Practices identifies that hydrologic control facilities must achieve 100% drawdown within 72 hours. Provisions for access and inspection by vector control personnel are also required. Contact the local permitting agency for details of local vector control provisions, which apply to both treatment measures and flow duration facilities. 2. Stormwater runoff that is detained also undergoes water quality treatment through settling and/or infiltration of pollutants. The focus of water quality management is reducing mean annual loads and typical concentrations of pollutants in receiving waters, so treatment design focuses on typical storms which contain the bulk of annual stormwater runoff volume. The MS4 permit and guidance documents describe the Copermittees design criteria for volume based treatment measures, which apply to a wider range of projects than the hydromodification management requirements. Recommended drawdown times 163 Appendix C Santa Margarita Region Hydrology Model Guidance – June 2013 for detention structures are typically at least 48 hours, but not to exceed 72 hours within Riverside County. 164 Appendix C 3. Santa Margarita Region Hydrology Model Guidance – June 2013 Flood control facility design criteria is intended to control peak flows for large sized storms (with expected recurrence intervals such as 25, 50 or 100 years). Hydrologic control facilities typically require capture and detention of a specified volume of stormwater runoff, which then is discharged out at flows that can be safely conveyed by downstream channels without undue risk of flooding. Hydrologic control facilities usually are required to drain within 24 hours after the end of the design storm in order to be empty for the next storm event. This concern that hydrologic control facility storage remains available for large events has led the Copermittees to require that any storage volume for water quality not be credited for flood control, a feature that is sometimes referred to as "dead storage". Although many factors affect the drawdown time, the suggestions below may help SMRHM users in evaluating these other requirements. If flow duration control is required for a project site, it is recommended that the design process start by using SMRHM to obtain a preliminary design for the flow duration pond, vault, or tank. Then check the performance of the facility for vector control concerns, and against treatment and/or flood control design criteria as appropriate. The latter are both based on the concept of a single empirical "design storm" which does not directly correspond to the flow duration approach using frequency analysis in a long-term simulation. Stormwater runoff treatment design requires the use of volume-based runoff coefficients, which although similar in concept to runoff coefficients used for flood control, are determined differently. Runoff coefficients used for flood control were derived for large storms with some conservatism built-in to estimates of peak flow rates and water surface elevations. Runoff coefficients for stormwater runoff treatment have been adjusted to reflect runoff from small storms where a greater percentage of the rainfall is held within the catchment. Vector Management If the maximum allowed drawdown (72 hours) is seldom or never exceeded over the simulation period, then likelihood of mosquito breeding in the facility is very low and the design for the pond, vault or tank does not need to be modified. If a maximum allowed drawdown time is exceeded then the system may need to be redesigned to reduce the drawdown time. The designer should consider additional reductions in impervious area and/or LID elements to help reduce the facility size. To evaluate the frequency and distribution of larger events in more detail, use the Hydrograph tool (page 99) to plot monthly peaks for several years at a time of the mitigated (post-project) scenario to get an idea of how often the discharge that corresponds to the maximum allowed drain time would be exceeded during warmer months, when mosquito development times are shortest. 165 Appendix C Santa Margarita Region Hydrology Model Guidance – June 2013 Treatment Credit Use the applicable design criteria to determine the minimum treatment volume for the postproject scenario. Look at the pond volume representing a 2-day drawdown in the SMRHM's flow duration drawdown table. If this is larger than the calculated treatment volume, no further treatment design is needed. If the pond volume is less than the treatment volume, or always drains in less than 2 days, most or all of the water quality criteria may still be met if the combination of infiltration loss and detainment captures 80% of the runoff from the site. Infiltration loss for each pond stage is shown in the StageStorage-Discharge table, accessed by selecting the "Open Table" option at the bottom of the main Pond screen. Flood Control Detention Design criteria must be obtained from the Copermittee with jurisdiction over the project site, as well as any other policies or restrictions that may apply to drainage design. A single design storm event can be imported as a time series (page 76) and applied to the postproject scenario instead of the simulated precipitation record. If additional live storage is needed, it may be added to upper levels of the same facility or provided elsewhere on the site. Guidance by Other Agencies Some agencies in other parts of the United States have developed extensive guidance for design of hydrologic control facilities. Two manuals are discussed below that provide detailed discussions or examples that may be helpful to users of SMRHM, although the suitability of these recommendations for Riverside County conditions has not been verified. These documents can help provide context and ideas for users for SMRHM, but adapting these ideas requires the exercise of professional engineering judgment. Mention of the procedures and details in these documents does not imply any endorsement or guarantee that they will be appropriate for addressing the Hydromodification Management Standards in Santa Margarita Region. Stormwater Management Manual for Western Washington (SWMMWW) was prepared by the Washington Department of Ecology for implementation in 19 counties of Western Washington. The latest (2012) edition in 5 volumes is on the Web at: http://www.ecy.wa.gov/programs/wq/stormwater/manual.html. Design recommendations from this manual were the basis for many features of the WWHM that have been carried over into SMRHM. Portions of Volume 3 (Hydrology) that may be of interest to project designers include: Pages 3-2 through 3-18 illustrate several types of roof downspout controls, simple pre-engineered designs for infiltrating and/or dispersing runoff from roof areas in order to reduce runoff volume and/or increase potential groundwater recharge. Pages 3-50 to 3-63 discuss outlet control structures, their maintenance and source equations modeled into WWHM and SMRHM 166 Appendix C Santa Margarita Region Hydrology Model Guidance – June 2013 Pages 3-75 to 3-93 regarding Infiltration Reduction Factor Urban Storm Drain Criteria Manual by the Denver Urban Drainage and Flood Control District is on the Web at: http://www.udfcd.org/downloads/down_critmanual.htm. Volume 3 covers design of stormwater runoff treatment measures, including extended detention basins on pages S-66 through S-77 and structural details shown on pages SD-1 to SD-16. Although these designs are not presented for hydromodification management control, the perforated plate design concept allows fine-tuning of drawdown times and is adaptable for use in flow duration facilities. 167 Appendix D Santa Margarita Region Hydrology Model Guidance – June 2013 APPENDIX D: SMRHM REVIEWER CHECKLIST SMRHM Reviewer Checklist: Yes No 1. Received SMRHM project (WHM and WH2) files? 2. Received SMRHM WDM (WDM) file? 3. Received SMRHM report (DOC) file? 4. Project (WHM) file loads okay? 5. Project location matches location on SMRHM screen? 6. Predevelopment scenario runs okay? 7. Mitigated scenario runs okay? 8. Compare SMRHM Report screen with report file: a. Project location descriptions match? b. Precipitation gauges match? c. Precipitation scales match? d. Flow frequency results match? e. All flow duration values PASS? f. Any pervious (PERLND) land use changes? g. Any impervious (IMPLND) land use changes? h. Any scaling factor changes? i. Any duration criteria changes? j. pond dimensions match? k. pond outlet structure info matches? 9. SMRHM pond dimensions match drawings? 10. Infiltration set to YES for infiltration pond? 11. Total SMRHM drainage area matches drainage maps/drawings? 12. Mitigated drainage area(s) match Predevelopment? 13. Predevelopment vegetation correct? 14. Mitigated land use areas correct? 15. Routing correct? 16. Check facility drawdown (if included): a. Used POC Mitigated stage? b. Drawdown times okay? 17. Options set to default values? 18. Other issues? SMRHM submittal APPROVED? 168 Appendix D Santa Margarita Region Hydrology Model Guidance – June 2013 This page has been intentionally left blank. 169 Appendix E Santa Margarita Region Hydrology Model Guidance – June 2013 APPENDIX E: SMRHM BACKGROUND Effects of Hydromodification Urbanization of a watershed modifies natural watershed and stream processes by altering the terrain, modifying the vegetation and soil characteristics, introducing pavement and buildings, installing drainage and flood control infrastructure, and altering the condition of channels through straightening, deepening, and armoring. These changes affect hydrologic characteristics in the watershed (rainfall interception, infiltration, runoff and channel flows), and affect the supply and transport of sediment in the MS4 and receiving waters. The change in runoff characteristics from a watershed caused by changes in land use conditions is called hydrograph modification, or simply hydromodification. As the total area of impervious surfaces increases in previously undeveloped areas, infiltration of rainfall decreases, causing more water to run off the surface as overland flow at a faster rate. Storms that previously didn't produce runoff under rural conditions can produce erosive flows. The increase in the volume of runoff and the length of time that erosive flows occur ultimately intensify sediment transport, causing changes in sediment transport characteristics and the hydraulic geometry (width, depth, and slope) of channels. The larger runoff durations and volumes and the intensified erosion of streams can impair the beneficial uses of the stream channels. Development of the SMRHM The concept of designing a flow duration control facility is relatively new and, as described above, requires the use of a continuous simulation hydrologic model. To facilitate this design approach, Clear Creek Solutions (CCS) has created a user-friendly, automated modeling and flow duration control facility sizing software tool adapted from its Western Washington Hydrology Model (WWHM). The WWHM was developed in 2001 for the Washington State Department of Ecology to support Ecology's Stormwater Management Manual for Western Washington 1 and assist project proponents in complying with the Western Washington hydromodification control requirements. The SMRHM is adapted from WWHM Version 4, but has been modified to represent Riverside County hydrology and enhanced to be able to size other types of control measures and LID techniques for flow reduction as well. SMRHM is a useful tool in the design process, but must be used in conjunction with local design guidance to ensure compliance for specific projects. The reader should refer to Appendix C and guidance from the Copermittee with jurisdiction over the project site for additional information and suggestions for using the SMRHM. 1 Washington State Department of Ecology. 2001. Stormwater Management Manual for Western Washington. Volume III: Hydrologic Analysis and Flow Control Design/BMPs. Publication No. 99-13. Olympia, WA. 170 Appendix E Santa Margarita Region Hydrology Model Guidance – June 2013 SMRHM Overview The SMRHM software architecture and methodology is the same as that developed for Bay Area Hydrology Model, San Diego Hydrology Model, South Orange County Hydrology Model, and WWHM and uses HSPF as its computational engine 2. Like these models, SMRHM is a tool that generates flow duration curves for the pre- and post-project condition and then sizes a flow duration control pond/basin or vault and outlet structure to match the predevelopment curve. The software package consists of a user-friendly graphical interface with screens for input of predevelopment and post-project conditions; an engine that automatically loads appropriate parameters and meteorological data and runs continuous simulations of site runoff to generate flow duration curves; a module for sizing or checking the control measure to achieve the hydromodification control standard; and a reporting module. The HSPF hydrology parameter values used in SMRHM are based on best professional judgment using our experience with calibrated watersheds in other parts of California. SMRHM uses the Riverside County long-term 15-minute precipitation data records selected to represent SMR rainfall patterns. HSPF is the U.S. Geological Survey and U.S. Environmental Protection Agency continuous simulation hydrology software package maintained by AQUA TERRA Consultants. The HSPF continuous simulation hydrology model is preferred over single- event hydrology models because of its ability to compute and keep track of all of the individual components of the hydrologic cycle including surface runoff, interflow, groundwater, soil moisture, and evapotranspiration. HSPF, since its introduction in 1980, has become the industry standard for hydrologic modeling. One of the major advantages of continuous simulation hydrologic modeling is the ability to accurately determine soil moisture conditions immediately prior to storm events. Singleevent hydrologic models have to make assumptions about the antecedent soil moisture conditions – assumptions which are often not accurate or appropriate. This is an important distinction because antecedent soil moisture conditions play a major role in determining the amount and timing of runoff. Not all continuous simulation hydrologic models handle the calculation of soil moisture conditions in the same level of detail. HSPF uses a potential evapotranspiration time series to compute actual evapotranspiration each time step. HSPF uses parameter values to determine the proportion of the actual evapotranspiration from interception storage, upper soil layer storage, lower soil zone layer storage, groundwater storage, and base flow. Other continuous simulation hydrologic models, SWMM included, use a much more simplified approach to determining soil moisture. Such simplified approaches do not accurately reflect the seasonal and daily variability of the actual evapotranspiration and its effects on soil moisture. 2 SMRHM is based on WWHM Version 4. 171 Appendix E Santa Margarita Region Hydrology Model Guidance – June 2013 Santa Margarita Region Hydrology Model Guidance – May 2013 SMRHM computes stormwater runoff for a site selected by the user. SMRHM runs HSPF in the background to generate a 15-minute runoff time series from the available rain gauge data over a number of years. Stormwater runoff is computed for both predevelopment and post-project land use conditions. Then, another part of the SMRHM routes the post-project stormwater runoff through a hydrologic control facility of the user's choice. SMRHM uses the Predevelopment peak flood values from a partial duration series of individual peak events to compute the predevelopment 2-year through 25-year flood frequency values 3 . The post-project runoff 2-year through 25-year flood frequency values are computed at the outlet of the proposed hydrologic control facility. The model routes the post-project runoff through the hydrologic control facility. As with the predevelopment peak flow values, partial duration post-project flow values are selected by SMRHM to compute the developed 2-year through 25-year flood frequency. The Predevelopment 2-year peak flow is multiplied by a percentage (10 percent) to set the lower limit of the erosive flows, in accordance with the current HMP performance criteria. The predevelopment 10-year peak flow is the upper limit. A comparison of the predevelopment and post-project flow duration curves is conducted for 100 flow levels between the lower limit and the upper limit. The model counts the number of 15-minute intervals that predevelopment flows exceed each of the flow levels during the entire simulation period. The model does the same analysis for the post-project mitigated flows. LID BMPs have been recognized as opportunities to reduce and/or eliminate stormwater runoff at the source before it becomes a problem. They include compost-amended soils, bioretention, permeable pavement, green roofs, rain gardens, and vegetated swales. All of these approaches reduce stormwater runoff. SMRHM can be used to determine the magnitude of the reduction from each of these practices and the amount of stormwater runoff detention storage still required to meet HMP requirements. 3 The actual flood frequency calculations are made using the Cunnane flood frequency equation. 172 Appendix E Santa Margarita Region Hydrology Model Guidance – June 2013 Bioretention Modeling Methodology The bioretention element is also known as a landscape swale or rain garden. The SMRHM bioretention element is a special conveyance feature with unique characteristics. The element uses the HSPF hydraulic algorithms to route runoff, but the HSPF routing is modified to represent the two different flow paths that runoff can take. The routing is dependent on the inflow to the swale and the swale soil capacity to absorb additional runoff. HSPF Special Actions is used to check the swale soil capacity to determine the appropriate routing option. A bioretention facility is a swale in which the native soils have been excavated and replaced with amended soil. At the downstream end of the swale, a weir or riser controls the surface discharge from the swale and detains runoff, encouraging it to infiltrate into the amended soil. Infiltration from the amended soil to the native soil is also possible, depending on the properties of the native soil. Swales can include an underdrain pipe. The amended soil placed in the swale is assumed to have storage capacity equal to its porosity and volume. Stormwater runoff infiltrates from the surface of the swale to the amended soil at an infiltration rate set by the user. The infiltration rate cannot exceed the available storage capacity of the amended soil. The available storage capacity is determined each time step by HSPF Special Actions. Once the amended soil is saturated then water has the opportunity to infiltrate into the underlying native soil at the native soil's infiltration rate. The native soil infiltration is input by the user and is assumed to be constant throughout the year. Inflow to the swale can exceed the amended soil infiltration rate. When this occurs, the extra water ponds on the surface of the swale. The extra water can then infiltrate into the soil during the next time step or can flow out of the swale through its surface outlet if the ponding exceeds the surface outlet's storage. Runoff in both the surface storage and amended soil storage is available for evapotranspiration. Surface storage evapotranspiration is set to the potential evapotranspiration; the amended soil evapotranspiration pan evaporation factor is set to 0.50 to reflect reduced evapotranspiration from the amended soil. In the amended soil water movement through the soil column is dependent on soil layer characteristics and saturation rates for different discharge conditions. Consider a simple two-layered bioretention facility designed with two soil layers with different characteristics. As water enters the facility at the top, it infiltrates into the soil based on the modified Green Ampt equation (Equation 1). The water then moves through the top soil layer at the computed rate, determined by Darcy's and Van Genuchten's equations. As the soil approaches field capacity (i.e., gravity head is greater than matric head), we can determine when water will begin to infiltrate into the second layer (lower layer) of the soil column. This occurs when the matric head is less than the gravity head in the first layer (top layer). 173 Appendix E Santa Margarita Region Hydrology Model Guidance – June 2013 Since the two layers have different soil characteristics, water will move through the two layers at different rates. Once both layers have achieved field capacity then the layer that first becomes saturated is determined by which layer is more restrictive. This is determined by using Darcy's equation to compute flux for each layer at the current level of saturation. The layer with the more restrictive flux is the layer that becomes saturated for that time step. The next time step the same comparison is made. The rate and location of water discharging from the soil layer is determined by the discharge conditions selected by the user. There are four possible combinations of discharge conditions: 1. There is no discharge from the subsurface layers (except for evapotranspiration). This means that there is no underdrain and there is no infiltration into the native soil. Although this discharge condition is unlikely, we still need to be able to model it. 2. There is an underdrain, but no native infiltration. Discharge from the underdrain is computed based on head conditions for the underdrain. The underdrain is configured to have an orifice. (It is possible for the orifice to be the same diameter as the underdrain.) With a maximum of three soil layers determining head conditions for the orifice is complicated. Each modeled layer must overcome matric head before flow through the underdrain can begin. Once matric head is overcome by gravity head for all of the layers then the underdrain begins to flow. The flow rate is determined based on the ability of the water to move through the soil layers and by the discharge from the orifice, whichever is smaller. Head conditions are determined by computing the saturation level of the lowest soil layer first. Once the lowest soil layer is saturated and flow begins, then the gravity head is considered to be at the saturation level of the lowest soil layer. Once the lowest soil layer is saturated completely then the head will include the gravity head from the next soil layer above until gravity head from all soil layers is included. Gravity head from ponding on the surface is included in the orifice calculations only if all of the intervening soil layers are saturated. 3. There is native infiltration but no underdrain. Discharge (infiltration) into the native soil is computed based on a user entered infiltration rate in units of inches per hour. Specific head conditions are not used in determining infiltration into the native soil. Any impact due to head on the infiltration rate is considered to be part of the determination of the native soil infiltration rate. Because it is possible to have a maximum of three soil layers, each modeled layer must overcome matric head before infiltration to the native soil can begin. Once matric head is overcome by gravity head for all modeled layers, then infiltration begins at a maximum rate determined either by the ability of the water to move through the soil layers or by the ability of the water to infiltrate into the native soil, whichever is limiting. 174 Appendix E 4. Santa Margarita Region Hydrology Model Guidance – June 2013 There is both an underdrain and native infiltration. Underdrain flow and native infiltration are computed as discussed above. However, there is one other limitation to consider. In the case where the flow through the soil layer is less than the sum of the discharge through the underdrain and the native infiltration, then the flow through the soil layer becomes the limiting flow and must be divided between the native infiltration and the underdrain. This division is done based on the relative discharge rates of each. Note that wetted surface area can be included in the discharge calculations by adding the infiltration through the wetted surface area to the lower soil layer and the upper surface layer individually. This is done by computing the portion of the wetted surface area that is part of the upper surface layer and computing the infiltration independently from the portion of the wetted surface area that is part of the lower soil layers. There are several equations used to determine water movement from the surface of the bioretention facility, through the soil layers, and into an underdrain or native infiltration. The water movement process can be divided into three different zones: 1. 2. 3. Surface ponding and infiltration into the top soil layer (soil layer 1) Percolation through the subsurface layers Underdrain flow and native infiltration 175 Appendiix E Santa Margaritta Region Hydroology Model Guiidance – June 20013 m Greeen Ampt equ uation (Equaation 1) contr trols the infilltration rate into the top The modified soil lay yer: ( )(d ) f K 1 F (E Equation 1) f = soil surface inffiltration ratee (cm/hr) soiil porosity off top soil layeer soiil moisture coontent of topp soil layer sucction head att the wettingg front (cm) F= soiil moisture content c of the top soil lay yer (cm) d= surrface ponding g depth (cm)) K= hyd draulic cond ductivity based on saturaation of top ssoil layer (cm m/hr) K (relaative hydrau ulic conductiv vity) can be computed uusing the folllowing Van Genuchten approx ximation equ uation: (Eqquation 2) ng with multtiple subsurfface soil layeers. The K vvalue used inn A few issues arise when dealin p soil layer. Infiltration into the uppper soil layerr Equatiion 1 must be computed from the top must not n exceed th he lesser of the t maximum m percolatio n rates for each of the sooil layers. Finally y, the rate off percolation n of the top laayer may bee reduced beccause the layyer or layerss beneatth the top lay yer cannot acccept the perrcolation fluux because of existing saaturation levels. 176 Appendix E Santa Margarita Region Hydrology Model Guidance – June 2013 Water storage and movement through the three subsurface layers will be computed using Darcy’s equation as shown below: q K h z (Equation 3) Where: q = Darcy flux (cm/hr) K = hydraulic conductivity of the porous medium (cm/hr) h = total hydraulic head (cm) z = elevation (cm) The total head, h, is the sum of the matric head, , and the gravity head, z: h z . (Equation 4) Substituting for h yields: q K d ( z ) . dz (Equation 5) 177 Appendiix E Santa Margaritta Region Hydroology Model Guiidance – June 20013 Hydrau ulic conducttivity and matric m head vary v with soiil moisture ccontent. Theese values ccan be com mputed by solving the Van V Genuchtten's equatioon (Equationn 6) for bothh values. Noote that 0 when th he soil is saturated. (Equation 6) Effectiive saturatio on (SE) can be computeed using thee following Van Genuchhten equatioon: (Equation 7) Ignorin ng z (elevatiion head) ressults in h = hm h (matric hhead). Evapotranspiration n is an imp portant com mponent of tthe bioretenntion facilityy's hydrologgic processses. Evapottranspiration n removes water w from bbioretention surface ponnding and tthe soil column c duriing non-sto orm periodss. The rooutine will satisfy pottential evappotranspiiration (PET T) demands in the same sequence s as iimplementedd in HSPF: 1. 1 2. 2 3. 3 Water available a fro om vegetatio on interceptioon storage Water available a fro om surface ponding Water available a fro om the biorettention soil llayers (top laayer first) 178 Appendix E Santa Margarita Region Hydrology Model Guidance – June 2013 Water will be removed from vegetation interception storage and surface ponding and the bioretention soil layers (starting at the top layer) down to the rooting depth at the potential rate. Water is taken from the soil layers below the rooting depth based on a percentage factor to be determined. Without this factor there will be no way to remove water from below the rooting depth once it becomes completely saturated. 179