title: Modeling the Contributions of Glacial Meltwater to Streamflow in Thunder Creek, North Cascades National Park, Washington
Creators: name: Chennault, Jay W.
Publisher: name: Western Washington University
Year: 2004

description: <p>In regions where glaciers occur, like the North Cascades, glacial meltwater is a vital component of rivers and streams. Glacial meltwater can also be critical for hydroelectric and municipal purposes. A concern for water resources managers is that glaciers in the North Cascades have been shrinking. The glacier ice coverage of Thunder Creek watershed, the most heavily glaciated basin in the North Cascades, has dropped from approximately 22.5 % to 12.8 % since the Little Ice Age (LIA) maximum (ca. 1850). Glacial meltwater contributions to Thunder Creek are of interest because the creek serves as a tributary to Diablo Reservoir, which is one of three reservoirs on the Skagit River maintained by Seattle City Light for hydroelectric power production. In this study, I use the Distributed Hydrology Soils Vegetation Model (DHSVM) to evaluate the effects of glacial retreat on summer stream discharge in Thunder Creek. DHSVM is a physically based model that simulates a water and energy balance at the scale of a digital elevation model (DEM). GIS maps of topography (DEM), the watershed boundary, soil type, soil thickness, vegetation, and a flow network define the characteristics of a watershed. The input meteorological requirements for DHSVM include time-series data representing air temperature, humidity, wind speed, incoming shortwave radiation, incoming longwave radiation and precipitation. These data were compiled from recent historical records of local weather stations, except for longwave radiation, which was estimated. I calibrated and validated DHSVM for water years 1998-2002 to seasonal snow accumulation and melt at Thunder Basin SNOTEL and North Klawatti Glacier using two-hour time steps and a 50-meter pixel size. I also calibrated and validated the model to hydrographs measured at the U. S. Geological Survey (USGS) gauging station at Thunder Creek. DHSVM was then used to assess the influence that modern glaciers have on streamflow in Thunder Creek. The model was also used to estimate streamflow with LIA and 1958 glacial conditions as well as glacial conditions at 50, 100, 150, 300 and 500 years in the future based on current rates of glacial retreat. Results of the modeling indicate the percentage of late summer streamflow in Thunder Creek from glacial meltwater varied annually from 0.6% to 56.6% in water years 1998 through 2002. The timing of the initiation of glacial meltwater in the simulated Thunder Creek hydrograph varied from June 13 to July 26. Glacier melt also had a greater effect on streamflow during warm and dry years rather than cool and wet years. LIA glacial meltwater simulations produced between 6.1% and 63.4% more total late summer runoff than from the 1998 glaciers due to an increase in glacier area. In contrast, future glacier meltwater simulations produced systematically less runoff as the watershed was deglaciated. Simulation results suggested that within 100 years, total August and September streamflow in Thunder Creek could decrease more than 30% due to shrinking glaciers.</p>