Charles W. Downer

More efficient PEST compatible model independent model calibration

This article describes some of the capabilities encapsulated within the Model Independent Calibration and Uncertainty Analysis Toolbox (MICUT), which was written to support the popular PEST model independent interface. We have implemented a secant version of the Levenberg-Marquardt (LM) method that requires far fewer model calls for local search than the PEST LM methodology. Efficiency studies on three distinct environmental model structures (HSPF, FASST, and GSSHA) show that we can find comparable local minima with 36-84% fewer model calls than a conventional model independent LM application. Using the secant LM method for local search, MICUT also supports global optimization through the use of a slightly modified version of a stochastic global search technique called Multi-Level Single Linkage [Rinnooy Kan, A.H.G., Timmer, G., 1987a. Stochastic global optimization methods, part I: clustering methods. Math. Program. 39, 27-56; Rinnooy Kan, A.H.G., Timmer, G., 1987b. Stochastic global optimization methods, part ii: multi level methods. Math. Program. 39, 57-78.]. Comparison studies with three environmental models suggest that the stochastic global optimization algorithm in MICUT is at least as, and sometimes more efficient and reliable than the global optimization algorithms available in PEST.

Watershed Scale Physically Based Water Flow, Sediment and Nutrient Dynamic Modeling System

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 subwatersheds and the simulations of the actual processes are greatly simplified. This chapter describes a distributed water flow, sediment and nutrient dynamic modeling system developed at U.S. Army Engineer Research and Development Center. The model simulates detailed water flow, soil erosion, nitrogen (N) and phosphorus (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.