Characterisitics of check dam scour hole by free over‐fall flow

Abscract

Protection works are needed downstream of hydraulic structures for safety. They are designed primarily based on the shapes and sizes of scour holes. It is a fundamental to find the relationships among the characteristic factors of scour holes. Two types of sandy soils, including uniform and graded distributions, are used to simulate the bed material downstream of the weir phenomena due to free over‐fall flows. The experimental observations are compared with the theoretical results. It is found that all the shape factors, C_b, C_s and C_i are function of the Drop number N_d and the relative diameter G. It is shown that for the stable scour hole the characteristic coefficients of shape factors, C_sb (=C_s -C_b )≥1, C_is (=C_i -C_s )≥1. Also, for the stable scour hole, the volume factor A_s ≥π/2. The results also indicate that the ratio of the length of the stable scour hole L_i -L_b to the maximum scour depth y_s varies from 2.5 to 5.0.

Key Words:

• scour hole
• free over‐fall flow
• Drop number

Notes

Correspondence addressee