Abstract

A dynamic watershed simulation model (DWSM) is under development at the Illinois State Water Survey (ISWS) using physically based governing equations to simulate propagation of flood waves, entrainment and transport of sediment, and all commonly used agricultural chemicals for agricultural and rural watersheds. The hydrology component of the model was developed, tested, and reported on earlier (Borah et al., 1998). Using data collected earlier by the ISWS, it was tested on the 925-square-mile Upper Sangamon River basin, which drains into Lake Decatur. During the current study period (April 1998 - March 1999), detailed data on flow, sediment, and water quality (specifically, nitrate-nitrogen, phosphate-phosphorus, atrazine, and metolachlor concentrations) were collected at the Big Ditch station, draining a 38-square-mile subwatershed of the Lake Decatur watershed, during the spring 1998 storm events. The data were analyzed to develop relationships of pollutant concentrations with water discharge. Two different hydrologic algorithms of the DWSM were tested on the Big Ditch subwatershed using the monitored data. The DWSM was expanded to simulate soil erosion and sediment transport in a watershed, and tested on the Big Ditch subwatershed using the monitored data. The study provides new relations of constituent concentrations with water flow, and the model provides an advanced tool for engineers, scientists, and public policy makers working on land use and groundwater protection issues in floodplain areas.