Abstract: In order to determine the range of discharge coefficient values during the dam break process of a landslide dam, based on the water flow surface velocity, a formula for estimating dam-break discharge was proposed, five sets of flume experiments were conducted and the mathematical regression method was utilized to study the flow coefficient during the dam failure process of the dam. The research results show that the longitudinal development of the breach is primarily characterized by layered scouring, with the inclination angle of the scouring surface gradually decreasing and the scouring rate firstly increasing and then decreasing. The discharge of the breach is influenced by multiple factors, such as the height of the dam body and the ratio of the dam body's height to the thickness along the direction of water flow at the bottom. The novel approach of estimating the breach discharge based on surface flow velocity is found to be feasible and highly accurate, with the coefficient Cd of the new outflow formula ranging from 0.19 to 0.43.

Key words: water conservancy engineering; landslide dam; discharge coefficient; dam failure process; surface velocity; dam-break discharge

摘要： 为确定堰塞坝溃坝过程流量系数的取值范围，基于水流表面流速估算溃口流量的公式，通过5组水槽试验并用数学回归方法对堰塞坝溃坝过程的流量系数进行了研究。研究结果表明：溃口纵向发展以层状冲刷为主，冲刷面倾角逐渐降低，冲刷速率先快后慢；溃口流量受多种因素影响，如坝体高度、坝体高度与坝体底部沿水流方向厚度比值等；基于表面流速计算溃口流量这一全新思路是可行且具有较高准确性，新流量公式系数Cd取值介于0.19~0.43。

关键词: 水利工程；堰塞坝；流量系数；溃坝过程；表面流速；溃口流量