Assessment of Depression Impact on Runoff Characteristics Using GIS Technique

Abstract

Depression is a storage volume that could be filled prior to runoff. It might be used as a rectification parameter to adjust runoff volumes and peak discharges. GIS tools are used to extract depressions and calculate their characteristics (volumearea) and to pick the corresponding catchments and estimate their characteristics from DEM. In this work, HEC-HMS is used as a step to calculate runoff using three approaches to assess the impact of presence of depressions on runoff from three points of view; outlet location, runoff volume and peak discharge downstream the depression. First approach neglects the presence of depression. Second approach accounts depression in study but assuming one outlet with width equal to one cell size and lastly the third approach is as same as second approach but multi outlets are used with different widths and levels. The last approach gives more realistic value for runoff volume and peak discharge as it accounts volume of water stored in depression and represents the outflow from depression in an accurate way.