Snowmelt hydrograph separation: Chemical and graphical methods compared

In the semi-arid United States, snowmelt runoff has historically supplied high-quality water for domestic, industrial, and agricultural uses. Yet snowmelt runoff may carry atmospheric and terrestrial pollutants, the fate of which is tied to runoff volume and flowpath. Flowpath information is also required in snowmelt prediction models. In a study conducted at a small mountain watershed near Donner Summit, California, water chemistry and discharge data were gathered to compare chemical and graphical techniques of snowmelt hydrograph separation. From the graphical approach, estimated seasonal baseflow is approximately 12% of total flow. Given measurement uncertainties for discharge and total dissolved solids (TDS), predictions from the two methods agreed fairly well. However, the chemical method estimated seasonal baseflow to be 32% of total flow. This percentage is likely an overestimate, considering the shallow soils and granitic bedrock of the experimental watershed. Overestimation from the seasonal chemical method is attributed to the assumption that baseflow TDS is constant.