The analysis of USGS gage data in the Skagit River basin resulted in the
delineation of 5 hydrologic regions. Flood flows in the lower elevation regions
(regions 1 and 2) are primarily a response to storm precipitation. Peak flows in these
regions occur in fall and early winter, with 50-year peak flows of about 165 cfs/mi2
and 255 cfs/mi2, respectively. In the higher elevation regions (regions 3, 4, and 5),
much of the storm precipitation falls as snow in fall and winter, resulting in annual
hydrographs that tend to be dominated by peak flows in spring. The 50-year peak
flow estimates in these regions are 245, 170, and 80 cfs/mi2, respectively.
Regions 1 (lower valley) and 5 (Ross Lake area) have the lowest average
annual precipitation with less than 90 inches per year. However, average basin
elevations are less than 2000 feet in region 1, and over 4000 feet in region 5. Regions
3 and 4 (Mount Baker and Glacier Peak areas) have the highest average annual
precipitation at more than 120 inches per year, and have average basin elevations
above 3500 feet. Region 2 is a transition area both in terms of rainfall and elevation,
with average annual precipitation between 60 and 100 in/yr, and average basin
elevations ranging from 2000 to 3500 feet
Beechie, T. J., 1992. Delineation of Hydrologic Regions in the Skagit River Basin. Skagit System Cooperative, La Conner, WA. pp. 39.
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