Field Test on Conversion of Natural Watershed into Kinematic Wave Rectangular Plane

Abstract

Conversion of a natural watershed into its equivalent kinematic wave rectangular plane has long been a concern in the practice of storm water numerical simulations. Based on the principles of mass and energy, the actual watershed and its virtual kinematic wave plane can be related by the watershed shape factor that involves the waterway length and slope and watershed area. In this study, two dimensionless watershed shape functions are derived to use parabolic function and trigonometric sine curve for watershed conversion. These two watershed shape functions produce good agreements with the maximum overland flow length method for hypothetical square watersheds. Also, these two watershed shape functions are able to reproduce similar kinematic wave plane widths as reported in a calibrated model. Furthermore, in this study, these two watershed shape functions are tested by nine observed rainfall events and three levels of modeling details. These 54 case studies reveal that the parabolic shape function consistently produces better agreements with the observed runoff hydrographs. Also, it is concluded that a model with more drainage details results in higher peak flows. On the contrary, a model with a low resolution tends to decrease the peak flow because of the significant surface detention volume spread in the overland flow.