If the ABSCOUR user selects a 2-D model instead of a 1-D model such as HEC-RAS for the hydraulic analysis, Kv should be computed by a different procedure. The 2-D model can be used to measure directly the velocity of flow at the face or toe of the abutment (Vface) and the average flow velocity in the adjacent contracted section. Referring back to equation 1-16a in the H&H Manual, Kv is defined as the ratio of velocity at the abutment face or toe to the mean velocity (Vave) in the adjacent contracted section. Both of these parameters can be measured using the 2-D model. The procedure to calculate Kv is described below:
Select the override option for 2-D flow on the Project Information Card
Step 1 above will open two cells on the Downstream Bridge Data Card:
Enter the calculated/measured flow velocity at the abutment face/toe in the cell designated Vface
Enter the calculated/measured average flow velocity in the adjacent contracted section in the cell designated Vave
The ABSCOUR program will then calculate Kv using Equation 1-16b: