Modeling The Effect of Depression Areas on Outflow Hydrograph

Abstract

The value of runoff peak discharge of any basin is the most important hydrological parameter that should be calculated accurately in order to determine the suitable protection strategy and perform suitable design for any proposed hydraulic structures. There are many factors affecting the runoff peak discharge; meteorological factors (mainly rainfall characteristics) and basin morphological characteristics such as size, slope, land cover, shape, soil type, and depression/surface storage. This research discusses the reduction factors affecting the peak values due to the existence of depressions/surface storage along the watershed main stream using 2D hydrodynamic modeling approach. In this research, the analysis has considered different characteristics of the depressions with respect to the location, return period and depression area as categorized by NRCS (1975). The analysis results of this research have been compared with the adjustment factors for ponding and swamp areas developed by NRCS (1975). The research showed that the peak reduction may reach 90% of the watershed original peak flow if the depression is located along the watershed main stream and at its lower part with depression area equals to 20% of watershed area. The research revealed that, The lower locations along the main stream are the most effective on reducing peak flow values and there is a proportional relation between depression area and the reduction percentage. The results showed that the watershed shape factor is one of the most important factors that should be taken into account when investigating the effect of depression on peak flows; as it may change the reduction factors globally.