Reduction of Urban Runoff Peak Flows by Ponding

The methods used and advantages which can be obtained by incorporating the concept of roof-top ponding and short-term on-site detention storage into the design of urban storm drainage facilities are described. By limiting the rate of runoff from flat roofs and other applicable flat areas to predetermined rates, the peak rate of runoff to the receiving storm drainage system can be reduced. On-site detention ponding can also be used to reduce peak runoff rates. These techniques have been used to advantage in the Denver region to minimize the impact of new developments on the storm drainage system. Effective design of ponding and detention features requires careful analysis of regional rainfall characteristics. Because storage volumes are relatively small and the runoff hydrographs involved have short time bases with steep peaks, it is necessary to consider fully the magnitude-frequency relationship and intensity-duration characteristics of rainfall as well as its geographic distribution.