Using SWAT (Soil Water and Assessment Tool) to Evaluate Streamflow Hydrology in a Small Mountain Watershed in the Sierra Nevada, Ca

Hydrological models have been increasingly used for the effect of land cover change and forest management operations on hydrological processes. In the Sierra Nevada, where timber harvest and prescribed fire are commonly employed for forest management, hydrological models have rarely been used, especially in small watersheds. In this research, the SWAT model (Soil Water and Assessment Tool) was used to simulate streamflow on a daily time-step in P301, a small headwater mountain watershed located in the southern Sierra Nevada. The watershed is 1 km2, where about 72% of the land is covered by a dense mixed-conifer forest. SWAT performs satisfactorily with a coefficient of determination (R2) of 0.59 and a Nash-Sutcliffe efficiency value (NSE) of 0.59. This is important to know given the complexity arising from model uncertainty and the intricacies of Sierra Nevada hydrology. Although SWAT performed “satisfactory”, the model still missed two key hydrological processes: the timing of snowmelt and isolated peak flow events. In addition, simulating streamflow on the daily time-step is good for understanding watershed processing and functioning but is not as useful for forest and land management. SWAT will need further model adjustments as well as monthly and yearly water yield estimates in order to be considered for the evaluation of forest management operations in P301.