Use of an Agricultural Non-Point Source pollution model to assess impacts of development and management practicies [sic] in an urban watershed

Abstract

A Geographical Information System (GIS) linked to a Non-Point Source (NPS) model are being used to predict the effectiveness of storm water management strategies and examine the impact of proposed land use changes on Total Maximum Daily Load (TMDL) attainment. This study tests a methodology for analyzing land use changes and management using GIS analyses of impervious surfaces and AGricultural Non-Point Source (AGNPS) pollution modeling in an approximate 1100 acre urban watershed located in East Baton Rouge Parish (EBRP), Louisiana. The GIS analyses of Total Impervious Area (TIA) quantified increases in urbanization and provided land use data utilized in AGNPS modeling in a small urban watershed which also included a natural swamp park. AGNPS modeling was executed in several different scenarios to predict changes in NPS loadings associated with increases in TIA, its subsequent management and Digital Elevation Model (DEM) grid cell size. Data was processed and edited using ArcView (3.2) and GeoMedia (6) GIS systems. The test watershed underwent significant urbanization in the 8 years between 1996 and 2004, causing an increase in quantity and decrease in quality of subsequent runoff, and these created measurable impacts in the swamp park. Predictions of sediment, erosion and runoff were compared for each scenario year. Management practices were also simulated. TIA increased by 8.47 % from 1996 to 2004 and pavement counted for the greatest increase. Differences in Average Annual Outputs (AAOs) for 5m and 25m DEMs varied greatly with 5m simulations providing less in sediment erosion, load, yield, and runoff. The differences in simulations based on TIA assignment in 5m also varied from those based on TIA. Changes in AAOs based on the increase in TIA and the implementation of permeable pavements resulted in a maximum reduction of 43%, 8%, 3% and a 1% reduction in erosion yield, runoff, load and erosion respectively. Urbanization of the BSW is still continuing today and now has even greater imperviousness. The proposed methodology might be adopted by planners and managers to forecast water quality and storm water management implications of proposed projects on downstream TMDL attainment.