Download Chapter 5_FlowSimulation

Royal Haskoning
Triwaco User's Manual
Translation of model parameters
For the definition of the upper boundary condition Triwaco uses the so-called top systems together with line
elements or rivers. The top system parameters are distributed parameters, defined in each node of the grid
and represent the node's influence area. The river parameters, representing line elements, are defined in
each river-node and are valid for an area equal to the length of the river stretch multiplied by the river width,
which is generally considerably smaller than the river-node's influence area.
In ModFlow the upper boundary condition is defined for cells belonging to the uppermost layer, regardless of
the fact whether the boundary condition represent a distributed parameter or a line element. The area
represented is accounted for in the conductance parameter (Cond).
The following ModFlow packages are used to define the upper boundary condition:
Code
RCH
GHB
Package
Recharge package:
General Head Boundary
Input parameter
RECH
Cond
HBND
[L3/T]
Q = Cond * (HBND - HCELL)
DRN
RIV
dimension
[L/T]
[L2/T]
[L]
Drain package
HDRAIN
[L]
Q = Cond * (HBND - HCELL)
Q=0
Cond
{HCELL > HBND}
{HCELL
HBND}
[L2/T]
[L3/T]
River Package
RBOT
[L]
HRIV
[L]
Cond
{HCELL > RBOT}
{HCELL
RBOT}
[L2/T]
[L3/T]
Q = Cond * (HRIV - HCELL)
Q = Cond * (HRIV - RBOT)
Where in Triwaco a distinction can be made between an infiltration and a drainage situation, the GHB, DRN
and RIV package do not differentiate between these two situations. The conductance is supposed to be a
constant, regardless of the prevailing condition. Therefore, the upper boundary condition in Triwaco, be it a
top system or a river, is translated into a combination of the ModFlow boundary packages mentioned. The
precipitation excess or groundwater recharge is simulated using the RCH package.
The conductance of the GHB or RIV package is based on the infiltration resistance of top system or river,
whereas the conductance of the DRN package is based on the drainage resistance. Thus, the program
runMFfli will interpret the top system and river information and generate the corresponding ModFlow
packages:
Triwaco Top system
Precipitation excess
RP1
IR = 1
IR = 2
Controlled water level
RP1
Hydraulic resistance Drainage resistance RP2
RP3
IR = 4
Not yet fully functional
RP1 - RP13
IR =11
Precipitation excess
RP1
Hydraulic resistance
RP2 RP3 RP4
Drainage resistance
RP5
Infiltration resistance
Controlled water level
River
River water level
HRx
River width Drainage resistance
RWx
Infiltration resistance
CDx
CIx
ModFlow packages
RCH
GHB
GHB and DRN
GHB and DRN or RIV and DRN
5 Execution of Groundwater Flow Simulations: FLAIRS and MODFLOW-36