Abstract: Concrete dam break generally occurs in a very short period of time. Previous studies seldom consider the process and mode of dam break. According to the structural characteristics of concrete dam and the stress characteristic, we assumed three possible dam break modes, namely, sliding, toppling over, and opening. We examined the hydraulic characteristics of breach under such three modes via physical model test, and compared the test results with empirical transient failure calculation results. Comparison revealed that the calculated values of peak flow rate at breach were higher than test values in general. Among the three break modes, sliding failure witnesses the maximum flow rate with the greatest harm.The results provide guidance for revising empirical formula of dam break by taking into consideration the influence of process and mode of dam break on the hydraulic characteristics of breach.

Key words: concrete dam, dam break modes, sliding break, peak flow rate, hydraulic characteristic