Instantaneous water surface and bed scour profiles using video image analysis

Abstract

In steady open-channel flow, the use of a conventional point gauge to obtain the water surface profile yields reasonably accurate results. However, in unsteady and quasi-steady flows, the point gauge is not of much use. Furthermore, in flow fields where there is significant bed scour, it is often of interest to the hydraulic engineer to obtain the instantaneous bed scour profile during the scouring process. In most quasi-steady flows involving bed scour, the water surface profile continuously readjusts itself in response to the changes in the bed profile. To carry out a proper analysis of the entire flow field, it is necessary to obtain both the instantaneous water surface and the corresponding bed scour profiles. The development of a nonintrusive video image analysis procedure to simultaneously obtain the water surface and bed scour profiles in a two-dimensional flow field is presented in this paper. A computer program entitled PROSCAN has been developed to extract the water surface and bed scour profiles from digitized video images of the flow field. The use of PROSCAN is demonstrated by obtaining the instantaneous water surface and bed scour profiles for a two-dimensional flow field downstream of a sluice gate.Key words: image analysis, software development, water surface profile, bed scour profile, scour dynamics.