Importance of Short Duration Rainfall Intensities

Abstract

Flood flows and water quality in the Southwest are roust dramatically influenced by short, intense rainstorms. Runoff from these storms has been modeled with some success. One key element that has often been overlooked, however, is the importance of intra-storm rainfall distribution on runoff response. Actual storms were modeled for small experimental watersheds in the Southwest using different time increments of intra-storm rainfall. Increments of 5 minutes or less proven satisfactory for accurate hydrograph simulation. As increments became longer than 5 minutes, the ability to simulate actual hydrographs became increasingly difficult. Increments of 30 minutes or longer proved unacceptable for most storms. Hydrologic models must be sensitive to short time increments of intra-storm rainfall to accurately predict peak flows in the Southwest. Watershed treatments will be more cost-effective if their design considers intense bursts of intra-storm rainfall in addition to total storm volume.