Use of geology in NWSRFS calibrations; Nisqually River, Mt. Ranier, Washington

Subsurface geology, rock types, and glacial processes greatly influence hydrogeologic processes. Good geologic understanding can create better insights for the initial estimation and subsequent adjustment of parametersof the Sacramento Soil Moisture Accounting (SAC-SMA) and SNOW-17 models of the National Weather Service's River Forecast System (NWSRFS). Geologic information is readily available from the Roadside Geology series or US Geological Survey Geologic maps.The Nisqually River near National, Washington, is divided into four areas in NWSRFS. The Lower area, filled by glaciofluvial sediments, displays a subdued hydrologic response. This geological information translates as deep SAC-SMA tension-water and free-water parameter boxes which indicate high porosity and permeability, plus significant baseflow; low SAC-SMA REXP and ZPERC values suggest rapid percolation; and low SAC-SMA UZK values mean slow recessions. The Middle and Upper areas feature massive volcanic flows which are hydrologically flashy.The Glacial area shows a glacial peak flow by August. SNOW-17 model parameters show a glacier covering 40% of a volcanic terrain. The NWSRFS Water Balance operation incorporates mass balance analyses (eg., Accumulation Area Ratio) showing glacial growth or recession. The Nisqually glacier shows a 3% decline.