Mountainous Watershed Modeling with WEHY-HCM: A Case Study from Trinity Watershed in California

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 interbasin 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 is a physically based, numerical, integrated, and distributed modeling system. WEHY-HCM integrates atmospheric, snowmelt, surface and subsurface flow, and hydraulic processes. The model combines physical equations with spatial relationships and observations such as land use/cover, soil type, and digital elevation model data. The primary model output in this study is the streamflow at the watershed outlet that is available for water supply diversion and other purposes. The model was calibrated using water years (October 1st–September 30th) 1997–1999 and was validated using water years 2000−2006. Calibration was conducted 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.