Deva K. Borah

SWAT Model Background and Application Reviews

Watershed scale hydrologic and nonpoint source pollution models must be thoroughly tested by applying them to watersheds of different sizes and characteristics and from different geographic and geologic locations before using them to assess environmental conditions, evaluate best management practices, and making water resources management decisions. A clear understanding of a model is important for its appropriate use. In an earlier study, eleven watershedscale hydrologic and nonpoint-source pollution models were reviewed: SWAT, HSPF, AGNPS, AnnAGNPS, ANSWERS, ANSWERS-Continuous, PRMS, KINEROS, DWSM, CASC2D, and MIKE SHE, and the mathematical bases of different components of these models were identified and compiled. Among the fully developed hydrologic and nonpoint source pollution models having all the three major components: hydrology, sediment, and chemical, SWAT was found to be one of the promising models for long-term continuous simulations in predominantly agricultural watersheds. Applications of SWAT and a few other promising models, as available in the literature, are currently being reviewed. In this paper, applications of the SWAT model are compiled and discussed, along with a brief background of the model.

AGNPS-based Assessment of the Impact of BMPs on Nitrate-Nitrogen Discharging into an Illinois Water Supply Lake

Abstract The Agricultural Non-Point-Source Pollution (AGNPS) model was used to simulate storm-generated rainfall-runoff and distribution of nitrate-nitrogen (nitrate-N) concentration in the Upper Sangamon River basin draining into Lake Decatur in Decatur, Illinois. This water supply reservoir for the city of Decatur receives water from the 2,400-square-kilometer Lake Decatur agricultural watershed and has high nitrate-N concentrations periodically exceeding the 10 milligram per liter drinking water standard of the U.S. and Illinois Environmental Protection Agencies (USEPA and IEPA). Using monitored and estimated data, the model was calibrated and validated to predict closely-observed runoff volumes and nitrate-N concentrations. Sensitive model parameters were identified. The calibrated model was used to evaluate the effects of different agricultural and watershed management practices (BMPs) for reducing nitrate-N discharge into the lake. Model parameters were identified to represent the BMPs. Model results showed variations of nitrate-N discharge into the lake with respect to different BMPs and BMP applications at different areas of the watershed. The model was found useful in the preliminary evaluations of the BMPs in the Lake Decatur watershed for reducing nitrate-N discharge into the lake. The BMP evaluation approach and the results may be useful to users of the AGNPS model and other non-point-source pollution models. Model limitations must be kept in mind in interpreting the results from this empirically-based model and in using them to solve practical problems.

DWSM – A Dynamic Watershed Simulation Model for Studying Agricultural Nonpoint Source Pollution

DWSM, a Dynamic Watershed Simulation Model has been developed to meet an emerging need of improved models for simulating surface and subsurface runoff, soil erosion, and entrainment and transport of sediment and agricultural chemicals in large agricultural watersheds during severe rainfall events. The model reasonably predicted water and sediment discharges in the 100-km 2 Big Ditch and 251-km 2 Court Creek watersheds in Illinois. Scaling effects on parameters and model results due to alternative subdivision sizes were analyzed on the Big Ditch watershed. Stream segments in the Court Creek watershed were ranked based on their peak flows and sediment yields; and the overland elements were ranked based on unit-width peak flows and unit-width sediment yields from a historical storm instead of a design storm. The rankings were found useful for prioritizing and planning restoration.

Modeling the Big Ditch Watershed in Illinois and Studying Scaling Effects on Water and Sediment Discharges

A Dynamic Watershed Simulation Model (DWSM) was developed at the Illinois State Water Survey to simulate surface and subsurface storm water runoff, propagation of flood waves, soil erosion, and transport of sediment and agricultural chemicals in agricultural and rural watersheds. The hydrology and soil erosion-sediment transport components were tested (calibrated and validated) on the Big Ditch watershed in Illinois, a 100-square-kilometer tributary subwatershed of the Upper Sangamon River basin draining into Lake Decatur. Two different divisions of the watershed, one with coarse subdivisions and the other with fine subdivisions were used in the simulations to investigate scaling effects on parameter values and model results. The fine divisions of the Big Ditch watershed did not add noticeable accuracy to the model results; however, the spatially averaged model parameters were different from the coarse divisions. The overland roughness for the coarse division was one third of the roughness for the fine division whereas the effective lateral saturated hydraulic conductivity was five times of the same, which are all due to the presence of more channel features in the coarse overland segments. The flow detachment coefficient for the coarse divisions was two thirds of its value for the fine divisions due to longer slope lengths in the coarse segments with higher flows and higher erosion potentials.

Hydrologic and Sediment Transport Modeling of Agricultural Watersheds

Dealing with flooding, upland soil and streambank erosion, sedimentation, and contamination of water from agricultural, rural, and urban watersheds, and understanding the underlying natural processes are continued challenges to the environmental hydraulics field and in the management of sustainable water and environmental resources around the world. Watershed simulation models are useful tools to understand and analyze the processes and the problems and help mitigate those through evaluating the effects of land-use changes and best management practices. Developing adequate watershed simulation models and verifying those on real world watersheds with measured and monitored data are challenging. A Dynamic Watershed Simulation Model (DWSM) is being developed at the Illinois State Water Survey to simulate surface and subsurface storm water runoff, propagation of flood waves, soil erosion, and transport of sediment and agricultural chemicals in agricultural and rural watersheds. Different components of the DWSM have been applied to watersheds in Illinois for testing these components and assisting local watershed planning groups in planning restoration projects. Some of the recent progresses made in this ongoing modeling study are presented here. The soil erosion and sediment transport component was tested (calibrated and verified) on the Big Ditch watershed in Illinois, a 100-square-kilometer tributary subwatershed of the Upper Sangamon River basin draining into Lake Decatur. Two different divisions of the watershed, one with coarse subdivisions and the other with fine subdivisions were used in the simulations to investigate scaling effects on the parameter values and the model results.

Hec—5q model applied to a lake system in illinois for water quality evaluations

Abstract The United States Army Corps of Engineers HEC-5Q model was applied to Lake Spring-field and two proposed lakes (Hunter Lake and Lick Creek Reservoir) to be built for supplementing Lake Springfields water. Lake Springfield is the water supply reservoir for the city of Springfield, Illinois. Water from the lake is also used for cooling the citys power plant complex. The model was calibrated and verified on Lake Springfield using monitored data in 1986 and 1988. Eight water quality constituents were simulated. Calibration, verification, and predictions were made only for temperature, dissolved oxygen, nitrate-nitrogen, and phosphate-phosphorus. The calibrated and verified model was used to predict water surface elevations and constituent concentrations in the three lakes, individually and in combination, with meteorological and estimated flow data for a twenty-month period in 1953–1954, the most severe drought of record. The model provided a useful tool in the water quality evaluations of the thre...