UC Davis

This study developed a hydrological model for the Upper Trinity Watershed in California. The Upper Trinity Watershed consists of the portion of the Trinity Watershed upstream of Lewiston Dam and contains both Lewiston and Trinity Lakes. The Upper Trinity Watershed is an important source of water supply in California. Lewiston Lake is used for inter-basin water transfer to the Central Valley region of California for agriculture and municipal use. The watershed model was developed using the Watershed Environmental Hydrology Hydroclimate Model (WEHY-HCM). WEHY-HCM was previously developed over many years in the Hydrological Research Laboratory at UC Davis. WEHY-HCM is a physically-based, numerical, integrated, and distributed modeling system and integrates atmospheric, snowmelt, surface and subsurface flow, and hydraulic processes. WEHY-HCM combines physical equations with spatial relationships and observations such as land use/cover, soil type, and digital elevation model datasets. The primary model output in this study is the streamflow into the Trinity Lake reservoir. The model was calibrated using water years (Oct 1st-Sept 30th) 1997-1999 and was validated using water years 2000-2006. In order to calibrate this model, a program was developed using the evolutionary optimization algorithm differential evolution. The results show that a physically-based, integrated, distributed model is an accurate and effective method for hydrological modeling for the Upper Trinity Watershed. While calibration using a sophisticated algorithm can produce acceptable model results, it was comparable to that obtained by manual calibration in other studies. Automated calibration can produce time savings compared with a manual calibration approach.