Stormwater Symposium

Oral

395112 - Testing the Accuracy of Three Empirical Equations for Determining the Effective Impervious Area in Southern California

Wednesday, June 6
4:00 PM - 5:30 PM
Location: Greenway AB
Co-Authors: Rebeka Sultana, Long Beach – California State University, Long Beach; Suzanne Dallman, Long Beach – California State University, Long Beach; Ashmita Sengupta, Costa Mesa – Southern California Coastal Water Research Project; Eric Stein, Costa Mesa – Southern California Coastal Water Research Project

The portion of the Total Impervious Area (TIA) that is hydraulically connected to the storm drainage system is called the Effective Impervious Area (EIA). The remaining portion of the TIA, called the non-Effective Impervious Area, is not directly connected to drainage system and flows onto pervious areas. The use of the TIA percentage instead of the EIA percentage in stormwater modelling and calculations can lead to an over estimate of runoff peak volume discharges, leading to an oversizing of the stormwater drainage system and BMPs. EIA, the more useful parameter for storm system design, cannot be calculated using remote sensing, aerial imagery interpretation, or readily available datasets like TIA. While it can be estimated from time intensive field assessments or empirical equations, the best approach among current EIA assessment methods is to determine the EIA percentage from detailed rainfall-runoff gage data which is not always available in every catchment. For this study, a recessive regression technique using rainfall-runoff gage data is used to calculate the “truth” EIA percentage in five Southern California watersheds. This “truth” EIA percentage is then compared with the EIA percentages from three empirical equations found in the literature to assess the accuracy of the empirical methods. The results of this project will assist engineers and watershed planners in choosing the correct empirical equations to accurately calculate EIA and size storm water capture devices.

Mike Mroczek

Graduate Student
California State University, Long Beach

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Rebeka Sultana

Assistant Professor
California State University, Long Beach

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Suzanne Dallman

Associate Professor
California State University, Long Beach

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Ashmita Sengupta

Modeler
Southern California Coastal Water Research Project

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Eric Stein

Head of Biology Dept
Southern California Coastal Water Research Project

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