Download FINAL APPENDIX A WITH PICTURES C REVISED

PART 2: GUIDELINES FOR APPLYING THE ABSCOUR
PROGRAM
(See Part 1 for a Table of Contents)
I. INTRODUCTION
Available technology has not developed sufficiently to provide reliable scour estimates at
abutments for all possible site conditions. The policies and guidance in the abutment
scour program ABSCOUR and in Chapter 11 of the SHA Manual of Hydraulic and
Hydrologic Design have been developed with this consideration in mind.
The ABSCOUR program provides for considerable flexibility in the input format and the
computations to permit the user to model field conditions. However, the user should
make a critical review of all scour computations, using ABSCOUR for sensitivity
analyses of input factors, to evaluate whether the answers obtained are reasonable. Part 2
guide has been written to assist the user in this evaluation.
The user assumes all responsibility for any decisions or actions taken as a result
of the use of this program.
Please note that definitions used and references cited refer back to the text in Part 1.
The discussion on abutment scour in the FHWA HEC-18 Manual (Reference 1) explains
why the early abutment scour equations developed from laboratory flume studies are
generally not reliable for predicting scour at abutments. The essence of this discussion is
that a rectangular flume with a constant depth and velocity of flow across the width of the
flume does not accurately model the field conditions of a channel and its flood plain;
consequently, the equations developed from these lab studies generally predict
conservative estimates of scour.
In the last several years, various researchers have begun to model “compound channels”
to reproduce more accurately the field conditions of a channel and its flood plain.
Information from these studies has been used to develop the ABSCOUR software
program. The background on the development of the logic and the equations used in the
ABSCOUR analysis is presented in Part 1 of this Appendix. The Engineer is encouraged
to read and understand this information as well as the information in Part 2, Users Guide,
before using the ABSCOUR computer program.
In addition to calibrating the ABSCOUR 9 methodology with information obtained from
flume studies conducted by the FHWA, ABSCOUR 9 was calibrated using information
from the USGS database of abutment scour measurements of bridges in South Carolina
(See the discussion in Part 1 of this Appendix)
The ABSCOUR program is an expanded application of Dr. Emmett Laursen‟s live bed
contraction scour equation as presented in the FHWA HEC-18 Manual, with certain
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