Scientific Investigations Report 2006–5230
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2006–5230
Climatic and hydrologic conditions in the upper Salmon River Basin generally were below normal (30-year record, 1971–2000 for climatic conditions; long-term means for hydrologic conditions) during water year 2005 (WY05). Monthly snowpack levels were significantly below normal between January 1 and June 1, 2005. The average air temperature during WY05 was slightly higher than the 30‑year average, whereas the average monthly air temperatures were both above and below average. Annual mean streamflows in the basin were significantly below the long-term means, as were monthly mean streamflows.
Average monthly snowpack levels for the Salmon River Basin upstream of Salmon, Idaho, ranged from 34 to 79 percent of normal from January 1 to June 1, 2005. Average snowpack value for this area on April 1, 2005, was 61 percent of normal (Natural Resources Conservation Service, 2006b). The most commonly used snowpack condition indicator is the April 1 value because in most years it is the final value calculated before snowmelt begins.
Measurement sites in the general vicinity of the study sites include Galena Summit (at the headwaters of the Salmon River), Mill Creek Summit (at the headwaters of Yankee Fork), and Morgan Creek (at the headwaters of Morgan Creek). Specific snowpack levels at these sites on April 1, 2005, were: Galena Summit, 79 percent of normal; Mill Creek Summit, 59 percent of normal; and Morgan Creek, 51 percent of normal (Natural Resources Conservation Service, 2006a).
Mean air temperature at Stanley, Idaho, during WY05 was about 1.94ºC (35.5ºF), slightly higher than the 30-year (1971-2000) mean of 1.78ºC (35.2ºF). Mean daily air temperatures generally were higher during July and lower during June, August, and September 2005, than during the long-term (1971–2000) record (fig. 3). Mean monthly air temperatures during the period when snowpack generally accumulates (October through April) were somewhat variable. Mean air temperatures during October, November, and February were below the 30-year mean; those during December, January, March, and April were above the 30-year mean (Western Regional Climate Center, 2006).
Annual mean streamflows at the long-term USGS streamflow-gaging stations on Valley Creek at Stanley (13295000; 65 years of record) and on the Salmon River below Yankee Fork (13296500; 75 years of record) for WY05 were both about 30 percent below the long-term means. Annual mean streamflow at Valley Creek at Stanley was 139 ft3/s compared to the long-term mean of 198 ft3/s; and, the annual mean streamflow at the Salmon River below Yankee Fork was 683 ft3/s, compared to the long-term mean of 970 ft3/s. All monthly mean streamflows for Valley Creek at Stanley were less than the long-term means. Similarly, all monthly mean streamflows at Salmon River below Yankee Fork also were less than the long-term means.
U.S.
Department of the Interior | U.S. Geological
Survey
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