Calculation formula and coefficient analysis of dam breach discharge based on surface velocity

Abstract

In previous studies, a new formula Qout=Cdg−1B‾us3 was proposed to estimate the discharge of a breaching dam based on water flow surface velocity. To determine the range of the discharge coefficient Cd and the optimal application position in an actual dam breach event, this paper used experimental and statistical methods for further investigation. First, the sensitivity and influencing factors of the new discharge coefficient were discussed. Second, the distributions of the surface velocity in the x and y directions and the resultant velocity along the breach width direction were analyzed, and the spatial and temporal distributions of maximum surface velocity and average surface velocity were compared. Third, the surface velocities of four sections were substituted into the new flow formula, and the range of the new discharge coefficient was analyzed using regression fit. Finally, the correctness of the value range of the new flow formula was verified by inverting Tangjiashan landslide dam data. The results indicate that the influence of the calculated section position (Froude number) was less than that of the average flow velocity coefficient k2 on the discharge coefficient. Based on the maximum surface velocity, the flow formula can be approximately transformed to Qout=Cdg−1B‾(βums)3. The reasonable ratio of the average surface velocity to the maximum surface velocity in the formula was 0.550≤β≤0.749, and the discharge coefficient falled within 0.373≤Cd≤0.645.