Scientific Investigations Report 2006–5274
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2006–5274
Salmon Creek Basin was subdivided into 179 MRUs (fig. 8) using a tool called the GIS (Geographic Information System) Weasel (Viger and others, 1998) and manually adding separate MRUs for Conconully and Salmon Lake Reservoirs. The GIS Weasel is a computer program that allows easy generation of MRUs and a drainage network (fig. 8) on the basis of a digital elevation model (DEM). The computer program also creates initial model input parameters for each MRU on the basis of a variety of digital geographic data, including soils, land use, and vegetation type and density.
The MRUs and drainage network were delineated according to the same procedures used by Ely and Risley (2001) and Ely (2003) in the precipitation-runoff study of the Methow River Basin. The differences are that, in the current study, a higher-resolution DEM was used for the delineation of the MRUs and drainage network and the selection of different delineation thresholds resulted in generally smaller MRUs and a more detailed drainage network.
The MRUs and drainage network were delineated on the basis of a DEM that had a cell size of 33 ft (10 m) by 33 ft. An initial set of MRUs was generated by considering the range of slopes (fig. 9) and aspects in the basin. This set of MRUs then was subdivided by applying the GIS Weasel two-plane option, which creates separate MRUs on each side of a stream segment. A first-order stream was assumed to drain at least 35,000 DEM cells or an area of 1.35 mi2 (865 acres). The set of MRUs then was subdivided a second time by partitioning the basin into eight equal-elevation bands of 930 ft to account for the large elevation range in the basin. This process created some very small MRUs that then were merged with neighboring, larger MRUs. The merging of MRUs recombined a few MRUs on opposite sides of the streams. The final 179 MRUs range in size from 141 to 1,971 acres and have a mean size of 544 acres. For comparison, the 620 MRUs in the precipitation-runoff study of the Methow River Basin range in size from 596 to 7,370 acres and have a mean size of 1,870 acres.
U.S.
Department of the Interior | U.S. Geological
Survey
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