Environmental Engineering Reference
In-Depth Information
Chapter 10
Evaluating the Transport and Fate
of Nutrients in Large Scale River Basins
Using an Integrated Modeling System
Zhonglong Zhang and May Wu
Abstract Watershed management is essential in minimizing riverine and
receiving water pollution. No watershed model is currently available that ade-
quately 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 (HEC-
RAS) 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 HEC-
RAS 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
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