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Municipal & Industrial Water Supply Municipal and Industrial (M&I) water supply is only one of several competing uses of water in the Cedar River Watershed. Over the past several decades balancing water resource uses between human use activities and protecting the environment has become more challenging in many watersheds in particular watersheds that have faced tremendous growth such as the Puget Sound Region. With the recent listing of several anadromous fish species under the endangered species act, balancing of resources needs in the watershed has become more challenging by not only including different stakeholders but also requirements to meet federal statutes. M&I water supply issues in the Cedar River Watershed can broadly be divided into two issues, the first is water quality related to how the municipally owned watershed is managed as well as potential impacts from urbanization. The other issue is water quantity as it relates to minimum in-stream flows for the Cedar River and how much flow can be diverted for water supply at different times of the year when considering the needs of fisheries resources and water management needs at the Ballard locks. Seattle Public Utilities operates water supply facilities in the Cedar River Watershed to provide 2/3 of the drinking water for 1.3 million people in the Seattle metropolitan area. (The remaining 1/3 of the water supply is provided through the South Fork Tolt Watershed). The Cedar River municipal Watershed covers 90,546 acres or 141 square miles, of this amount 8,112 acres is not part of the Landsburg drainage sub-basin (used for drinking water supply) 79,452 acres is owned by the City and the remaining 499 acres is owned by private interests. Based on a revision to the City of Seattle’s Comprehensive Plan (1989), the primary use objective of the upper basin is to ensure the supply of high quality water without requiring additional treatment. To support this objective and prevent contamination, unsupervised public access to the watershed is prohibited. Secondary uses of the watershed include protecting existing species, timber harvest, education & research. The upper Cedar River is located in Southeast King County along the west slope of the Cascades. Numerous Rivers drain into Chester Morse Lake (1620 acre) reservoir is regulated by Masonry Dam built in 1916. Masonry pool, immediately west of Chester Morse Lake, serves as an additional impoundment. Water typically passes through Masonry Dam through penstocks driving two turbines. The Cedar River then flows downstream 12 miles to the Landsburg Diversion Dam (river mile 21.9) which was originally built in 1901. At the Landsburg Dam facility, a portion of the river flows is diverted from the Cedar for water supply. The water is screened, disinfected by chlorination, and fluoridated. Water is then conveyed outside of the watershed to Youngs Lake through a tunnel for municipal water uses and industrial uses. The City of Seattle provides the water to residents in the City and to other municipal jurisdictions (26 different purveyors) through contracts. Flows not diverted for water supply continue from Landsburg to Renton and discharge into Lake Washington. Minimum in-stream flows are required at Renton for fisheries resources and for operation of the Ballard Locks. Any water withdrawals from the Cedar River for drinking water purposes will have an effect on instream flows downstream. STAKEHOLDERS PERSPECTIVE: WATER QUALITY The existing water quality in the Cedar River is very high. The water supply system on the Cedar River is one of only a handful in the country that does not have to use filtration. Protection of water quality involves trade-offs of other potential uses of the watershed. The primary variables affecting water quality are temperature, sediment/turbidity and to a lesser extent fecal coliform and microorganisms. Turbidity can be associated with mass wasting, hillslope erosion and road erosion. Some aspects of this water quality variable can be attributed to natural geological processes. However other aspects such as timber harvest and road construction are ones where the stakeholders in the watershed have some control over the impacts. Other timber practices such as clear cutting can impact water quality by creating foraging habitat near water bodies, which can result in a potential source of pathogens and viruses in the water supply. Timber management practices near streams can also have a negative effect on water temperature by eliminating critical stream cover during warmer months. The upper watershed represents potential high value habitat for many species of fish, however allowing anadromous fish above the Landsburg Dam could also lead to water quality degradation. Urbanization of the watershed downstream of the Landsburg diversion has also had negative effects on water quality; these issues are discussed more in the Landuse Issue Paper. The following summarizes the key stakeholders related to water quality.
STAKEHOLDERS PERSPECTIVES WATER QUANTITY Balancing the competing uses of water in the basin is much more complex than water quality issues. The complexity stems in part from the many variables that need to be considered for a M&I water supply system including firm yield, risk and uncertainty of supply, operational flexibility, future needs, water rights and operating costs to mention a few. Municipal and Industrial supply considerations also must factor in water needs for conservation in Lake Washington and usage of the Locks, for navigation, water quality and fish passage. Aside from these human use activities, adequate in-stream flows for anadromous fish below the Landsburg diversion is also critical for a variety of stakeholders. Over the past 20 years there have been a variety of committees and commissions established to help determine how best to manage the trade-offs inherent in water supply. Most recently, and as an outcome of the recently signed Habitat Conservation Plan an interagency Instream Flow Commission was established to implement the Instream Flow Agreement. Signatories on the agreement included the City of Seattle, Washington State Department of Ecology, Washington Department of Fish and Wildlife, US Fish and Wildlife Service and the National Marine Fisheries Service. The Muckleshoot Indian Tribe opted not to sign the agreement, but is a voting member on the Commission. King County and the US Army Corps of Engineers are other stakeholders in the Cedar River Watershed and the larger Lake Washington Basin, but are not voting members on the Commission. The instream flow agreement sets out timing, frequency, ramping rates and withdrawals of firm and non-firm blocks of water that will be followed by the City. Water resource trade-off decisions are made on a continually basis practically for every week of the year.
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