Evaluating the transport and fate of nutrients in large scale river basins using an integrated modeling system

Abstract

Watershed management is essential in minimizing riverine and receiving water pollution. No watershed model is currently available that adequately model the large river basin system over long periods of time in a satisfied level of detail. Watershed models must be linked to riverine or other detailed receiving water models in order to adequately represent the intricacies of the physical system under study. Watershed models are used to provide "boundary conditions," both hydrologic/hydraulic and nonpoint source loading fluxes, to the receiving water models. The objectives of this study were to develop an integrated watershed and riverine modeling system using Soil and Water Assessment Tool (SWAT) model and Hydrologic Engineering Center-River Analysis System (HECRAS) model to evaluate the transport and fate of nutrients and water quality impacts in large scale river basins. The SWAT model was constructed for the Upper Mississippi River Basin (UMRB) in an attempt to account for key elements associated with crop production and land use changes. The model was calibrated and validated by using 18 years of observed United States Geological Survey (USGS) streamflow discharge and water quality data. The SWAT model was used to predict flow and nutrient exports from each tributary within the watershed. The results were used as HEC-RAS model's inputs through an interface. The HECRAS model was able to simulate the transport and fate of nutrients and dynamic changes in riverine nutrient concentrations. The integrated SWAT and HEC-RAS modeling system provides a systematic approach to modeling nonpoint nutrient sources, transport, and fate in a large scale river basin. The modeling system can be used to predict downstream water quality impacts with land use changes and assess the effectiveness of different watershed management practices whether directed toward nutrient source supply or abatement.