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Storm flow from first-flush precipitation in stormwater design

TitleStorm flow from first-flush precipitation in stormwater design
Publication TypeJournal Article
Year of Publication2004
AuthorsAhlfeld D. P., Minihane M
JournalJournal of Irrigation and Drainage Engineering
Start Page269
Date Published08/2004
Keywordsprecipitation, Storms, water, Water treatment

Regulations for mitigating nonpoint source pollution from urban areas often include a requirement for treatment of a first-flush depth of stormwater. When the stormwater treatment technology requires specification of a design flow rate, the first-flush depth must be related to a first-flush flow rate. This paper describes a methodology to determine the relation between accumulated storm depth and corresponding flow to a treatment device for small, urban watersheds. The approach uses the rational method under the assumption that the time-of-concentration is small. Intensity–frequency relations, expressed in the form of return periods and associated intensities, were determined using a partial duration frequency analysis of regionalized precipitation data. The results of the method can be used to determine the flow rate to a treatment device that will meet a specified return period for a first-flush depth. The method is demonstrated using 13 years of 15-min data from seven Massachusetts precipitation stations.