| Abstract/Description or Keywords |
This multi-phase study was initiated in 2005 to examine concerns regarding low flows in the Deadman River. Knowledge that one reach has been known to go dry intermittently, high fisheries values, and a desire to maintain natural instream flows and fish habitat, have provided both the motivation and the funding for this study. This phase of the work included gathering streamflow data at the outlet of Snohoosh Dam and along the river downstream to the mouth. Key findings include: -The original rating curve for the Snohoosh Dam weir (that translates water levels into streamflow rates) is no longer accurate, and had in fact changed with a gauge replacement in 1980 and again during the flood of 1990. Three rating curves have been developed to make the data collected over the past 30 years useable and meaningful, -The inaccurate rating curve resulted in less water was being released from the dam than was originally intended to meet all downstream needs (at times it is only 1/2 of the intended flow rate), -Even with the reduced outflow from the dam, the target flows downstream of the last intake were being met during the 2006 summer and fall seasons. 2006 was not an exceptionally wet or dry year ("near normal"). Several irrigation intakes were not in use and this helped to maintain higher instream flows. Full use of all irrigation licenses during a very dry year would leave the instream flow much lower near the mouth, -A "dry section" on the old Docksteader property has much lower flows than elsewhere along the river as water naturally sinks into valley bottom sediments and resurfaces farther downstream. This section had only a very low flow during irrigation season and was completely dry during portions of Oct / Nov 2006 with a documented fish kill after flows were reduced following the end of irrigation season. This "dry section" could occur naturally, but can be exacerbated by irrigation withdrawals or low releases from the dam, -While the 2006 operation of the dam has met its stated target flows there may be a need to refine the operation during dry years with full irrigation use, or to attempt to keep and "dry section" wetted during short periods of low flow to avoid fish kills. |
