Effective Impervious Area in Urban Runoff Modeling

Simulated results from many urban runoff models are sensitive to the value used for impervious area. This paper explores the use of effective impervious area versus total impervious area for input to these models. Total impervious areas may be appropriate for black-box models but not for deterministic models. Potential problems of using total impervious area in deterministic models include that (1) runoff volumes and peak flows may be substantially overestimated for ungaged watersheds, (2) simulated changes in runoff due to increasing intensity of land use are likely to be smaller if total impervious area is used rather than effective impervious area, and (3) overestimates of infiltration parameters are likely if the model is calibrated using total impervious area and measured runoff data. Impervious-area data collected from 19 urban watersheds in the Denver metropolitan area showed strong relationships between effective impervious area, total impervious area, and land use.