The two dimensional potential flow pattern around a rectangular abutment was used for evaluating the velocity distribution across the contracted section. A study of the velocity distribution in this constricted section (3, 4) applying the principles of potential flow revealed that the ratio of the velocity at the toe of the abutment to the mean velocity of the flow in the contracted section can be approximated by the following equation:
kv = 0.8(q1/q2)1.5 + 1Where:
This equation was developed considering flow through a simple contraction, where the unit discharge of the approach section is less than that in the contraction, q1 < q2.
The values of kv should be limited to the range of values between 1.0 and 1.8. If the computed value is less than 1.0, use a value of 1.0; if the computed value is greater than 1.8, use a value of 1.8.