Scientific Investigations Report 2006–5274

Scientific Investigations Report 2006–5274

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Model Parameterization

Initial model parameters were assigned by applying the GIS Weasel (Viger and others, 1998), computing values from measured data, and using parameters from the Methow River Basin precipitation-runoff model (Ely and Risley, 2001; Ely, 2003). A subset of the parameters was adjusted during calibration to achieve a good fit between the simulated and measured or estimated variables, as described in the “Model Calibration and Testing” section of this report.

Using the GIS Weasel, mean slope, aspect, and elevation were assigned to each MRU on the basis of the DEM, soil characteristics were assigned on the basis of the State Soil Geographic (STATSGO) database (U.S. Department of Agriculture, 1994), and the dominant vegetation type and vegetation characteristics were assigned on the basis of National Land Cover Data (NLCD 92) (U.S. Geological Survey, 1992; Vogelmann and others, 2001; fig. 10) and digital maps of United States forest types and density (Powell and others, 1993; Zhu and Evans, 1992). Monthly mean minimum and maximum air-temperature lapse rates were computed from air temperatures for the Omak OMAW AgriMet and Salmon Meadows SNOTEL stations for February 1989 through September 1998. Parameters that represent the mean monthly rainfall or snowfall on each MRU were obtained from values computed with the Parameter-elevation Regressions on Independent Slopes Model (PRISM; Daly and others, 1994 and 2002; Daly and Johnson, 1999) for the climate-normal period of 1971–2000 (Spatial Climate Analysis Service-Oregon State University, 2006). The precipitation-runoff model for this study distributes daily precipitation measured at climate stations across the model area according to the ratios between monthly PRISM values and monthly precipitation at the climate stations and weighted by the inverse of the square of the distance to the climate stations.

The model simulates streamflow for 11 locations (fig. 11) distributed at the mouths of subbasins (nodes 2 through 6), at the mouth of the entire basin (node 11), at points of diversion (nodes 1 and 10), and at three additional locations in lower Salmon Creek (nodes 7 through 9). Node 6, which represents Salmon Creek at the location of Conconully Dam, captures streamflow generated in upper Salmon Creek Basin.

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