Impact of New Rainfall Patterns on Detention Pond Design

Abstract

A new set of dimensionless rainfall hyetographs has been developed for the state of South Carolina. The new hyetographs show trends similar to those developed recently in other states and in general have milder intensities and lower peak rainfall than the Soil Conservation Service (SCS) rainfall hyetographs. This paper evaluates the impact the new hyetographs have on rainfall runoff and detention pond design and compares the results with those using the SCS hyetographs. Peak discharges for basin runoff were reduced up to approximately 20% of the predicted peak runoff rate using the current SCS hyetographs. Detention pond peak stage was also reduced by 25–50% of the predicted SCS stage. This analysis suggests that design hyetographs should be regularly updated to incorporate recent rainfall data.