Experimental Investigations of Partial-Breach Dam-Break Flows

This paper presents experimental results on partial-breach dam-break flows. Three-dimensional (3D) flood waves resulting from an instantaneous breach of a dam are experimentally investigated by combining different measurement techniques. The dam-break flow is initiated by quickly lifting a gate separating a reservoir and a downstream dry basin. Three different initial upstream water depths are considered. The study utilizes the digital particle tracking velocimetry (DPTV) technique for measuring the free-surface velocity and water depth. Stereoscopic configuration of two high definition video cameras recording the movement of hollow plastic balls enabled measurement of the 3D velocity field and the water-surface elevation in the near field. The pressure head is measured by pressure transducers at various locations. Ultrasonic velocity profilers (UVP) are used to obtain velocity profiles in the emptying reservoir. A simple nondimensional relationship for the variation of water-surface elevation in the upstream reservoir is presented. The following observations are made: (1)the maximum value for the nondimensional speed of the front wave is close to 1.0; (2)the ratio of surface velocity front wave propagation speed in the lateral direction to that in the downstream direction is almost 1:3; (3)the water depth is greater than the pressure head near the gate and less than the pressure head downstream of the gate due to water surface curvature effect; and (4)normalized velocity profiles in the upstream reservoir under different initial heads show a satisfactory collapse.