Upstream Water Sources Establish Background Water Quality Sample Clauses

Upstream Water Sources Establish Background Water Quality. The water quality of the Reservoir is primarily influenced by the water quality arriving from upstream sources. The Reservoir is a run-of-the-river reservoir of approximately 8,235 surface acres at 100,000 cfs (maximum 9,860 acres at flood flows). Its 43-mile length is second longest among mid-Columbia River reservoirs behind Xxxxx Xxxx Lake, created by Chief Xxxxxx Xxx. However, due to its narrow width, the Reservoir is one of the smallest in total volume of the seven mid-Columbia River reservoirs. The average depth is approximately 42 feet, with a maximum depth of about 180 feet. The water retention rate varies from less than one day at high flows to over three days at low flows, and averages about 1.8 days. This is a very low retention rate for a reservoir, but typical of other mid-Columbia run-of-the-river reservoirs that have similarly low water retention rates when compared to storage projects (Xxxxxx, 1993). The source water for Reservoir is the Xxxxx Reservoir, which receives flow from Chief Xxxxxx Xxx (Lake Xxxxx Xxxxx) and the Methow and Okanogan Rivers. The primary influence on water quality from Lake Xxxxx Xxxxx is the limnology of Lake Roosevelt, which is formed by Grand Coulee Dam. Lake Roosevelt is a major storage reservoir with a mean retention time of well over one month. The operation of Lake Roosevelt has a major influence on not only water quality, but biotic qualities of downstream reservoirs such as the supply of phytoplankton and zooplankton stocks (Xxxxxxx et al., 1985; Xxxxxx et al., 1981).