Environmental Engineering Reference
In-Depth Information
Chapter 8
Watershed Scale Physically Based Water
Flow, Sediment and Nutrient Dynamic
Modeling System
Billy E. Johnson, Zhonglong Zhang and Charles W. Downer
Abstract Non-point source (NPS) runoff of pollutants is viewed as one of the
most important factors causing impaired water quality in freshwater and estuarine
ecosystems and has been addressed as a national priority since the passage of the
Clean Water Act. To control NPS pollution, state and federal agencies developed a
variety of programs that rely heavily on the use of watershed management in
minimizing riverine and receiving water pollution. Watershed models have
become critical tools in support of watershed management. Lumped, empirical
models such as HSPF do not account for spatial heterogeneity within subwater-
sheds and the simulations of the actual processes are greatly simplified. This
chapter describes a distributed water flow, sediment and nutrient dynamic mod-
eling system developed at U.S. Army Engineer Research and Development Center.
The model simulates detailed water flow, soil erosion, nitrogen (N) and phos-
phorus (P) cycling at the watershed scale and computes sediment transport across
the landscape, nutrient kinetic fluxes for N and P species. The model consists of
three distinct parts: (1) watershed hydrology, (2) soil erosion and sediment
transport, and (3) nitrogen and phosphorus transport and cycling. The integrated
watershed model was tested and validated on two watersheds in Wisconsin
(French Run and Upper Eau Galle Watersheds). The model performed well in
predicting runoff, sediment, nitrogen and phosphorus. This chapter presents the
model development and validation studies currently underway in Wisconsin.
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