Using Airborne Snow Observatory distributed snow water equivalent to predict seasonal inflow volumes and inform management decisions at the Hetch Hetchy Reservoir

Abstract:

Traditionally, estimates of seasonal streamflow volumes have been determined using statistical relationships to precipitation and snow depth measurements taken at widely spaced while geographically clustered gauges. While strong statistical relationships have been identified in some locations, these relationships are susceptible to breaking down during extreme conditions such as droughts or extremely wet years. The Airborne Snow Observatory (ASO) is a program where airplane mounted lidar is used to create snow-on and snow-off DEMs, yielding distributed estimates of snow water equivalent at the catchment scale. These estimates allow us, for the first time, to compare basin wide snow water equivalent to seasonal streamflow volumes. At the Tuolumne River basin in Yosemite National Park, Sierra Nevada Mountains, California, the ASO estimates of basin wide SWE are shown to be tightly correlated to seasonal streamflow volumes. These estimates are further improved when combined with precipitation measurements. These estimates appear to be more robust than traditional statistical methods, and have been used to improve predictions of inflows at the Hetch Hetchy Reservoir, the primary water source for the City and County of San Francisco and surrounding areas.