Low Impact Development Applications in Urban Watersheds: Efficacy Evaluation by Imperviousness Connctivity Estimations
Published: 08 June 2015 by MDPI AG in 8th Conference of the International Forum on Urbanism (IFoU) session True Smart & Green Urban Design and Visions
Abstract: Although recent studies have emphasized the benefits of Low Impact Development (LID), the influence of LID on impervious surface connectivity to downstream drainage has not yet been fully investigated by using quantitative measurements. Some previous studies have attempted to measure correlates between discharged stormwater volume and the directly connected impervious areas (DCIA), a fraction of the impervious area that is hydraulically connected to downstream drainage by a piped route. They found that DCIA could be a more accurate predictor of urban development impacts on stream ecosystems than is the total impervious area. This study measured the DCIA of urban watersheds in the Energy Corridor District, Houston, Texas, where rapid urbanization and increasing impervious surfaces have caused urban stream degradation during the past decades. This study primarily prioritized land use into four types based on the contribution of hypothetically implemented LID facilities to DCIA reduction for each land use. Stormwater infrastructure and impervious cover data were analyzed using Geographic Information Systems. Sutherland's equations taken from Sutherland, R.C. (1995) were utilized to compute DCIA at the parcel level. The results were 1) a greater value of current DCIA in commercial areas than in residential areas (single family houses 40%, multi-family houses 64%, big box retails 77%, scattered small-scale retails 71%); 2) a significant reduction of DCIA for all land uses after hypothetically implementing LID applications (reduction rates ranged from 6.4% to 52.2%); and 3) the greatest change of DCIA in big box retail areas with pervious pavement and vegetated swale installation. The results will contribute to determining which land use type is of higher priority in implementing source-control stormwater infrastructure and providing local governments with a better index to calculate drainage fees, which are currently imposed on property owners based on total impervious area.
Keywords: impervious surface connectivity, directly connected impervious area (DCIA), Low Impact Development (LID), stormwater management, the Energy Corridor District (ECD)