Abutment Scour Computation: Step 2. Development of Model Cross-sections
- Select the two cross-sections required to run the ABSCOUR program:
- one section at the upstream approach section (Section 1) as defined by the water surface profile model, normally WSPRO or HEC-RAS,
- one section under the bridge at the downstream end of the bridge, Section 2.
- Convert the actual cross-sections to ABSCOUR model cross-sections for the subareas of the left overbank, main channel and right overbank.
Represent each subarea as a rectangle having a width and average depth. Obtain the top width (T) and flow area (A) of each subarea from the output
tables of the water surface profile model. Compute the average depth of flow or hydraulic depth for each subarea as yave = y1 = A/T.
- Modify section 1 and 2 as necessary to reflect field conditions. The model assumes an ideal one-dimensional flow pattern with a straight channel.
The occurrence of a bend would affect the flow distribution in the reach of the stream under study. The user has the option of selecting a unit
discharge different from that computed by the program if the site under study varies somewhat from the assumptions used in the model.
The flow width under the bridge must extend to the abutment. If it does not reach the abutment, the program will not compute abutment scour.
Click here to see the sketch for sections
Click here to the the profile through the bridge