Loon Lake (California)

In 1884, Loon Lake Dam was constructed to provide summer and autumn water supply to Georgetown Ridge for mining.[2] It was owned and operated by the Georgetown Divide Water Co. whom used it for irrigation and as a canal system from Gerle Creek to Georgetown Ridge. In 1943, E. F. Sullivan of the Bureau of Reclamation proposed that Loon Lake be used for matters of power generation. In 1948, the Georgetown Divide Public Utility District (GDPUD) applied for appropriative rights from the State of California to appropriate 260,000 acre-feet of water from the American River basin. This was in order to divert water through Loon Lake and Gerle Creek for purposes of irrigation, stock-watering and domestic use.[3]

Originally, the Georgetown Divide Public Utility District (GDPUD) had obtained appropriative water rights from the State Water Resources Control Board. Also, GDPUD exercised pre-1914 rights for diversion of water from several tributaries of Pilot Creek in the South Fork American River. The Georgetown Divide Water Company and other water companies invested that included Sierra Pacific Power Company, Loon Lake Water and Power Company, California Water Company and the Pilot Creek Water Company claimed pre-1914 rights in the South Fork Rubicon and Pilot Creek drainages for years prior to the 20th century. These rights included storage in Loon Lake, diversion from South Fork Rubicon River, Gerle Creek and Pilot Creek and all its tributaries. The water storage in Loon Lake was diverted and re-diverted into a canal system which eventually made its way from the South Fork Rubicon drainage into Pilot Creek drainage.[4]

A deed was signed in 1952 by GDPUD, whom paid for the rights and operation of all facilities in the Georgetown service area and the Georgetown Divide Water Company that included Loon Lake, diversions from Rubicon and Onion Creek to all Pilot Creek watersheds and diversions. Between the years of 1940 and 1950, Sacramento Municipal Utility District (SMUD) was interested in obtaining rights to facilities of the GDPUD in the South Fork Rubicon River watershed that included Loon Lake, for development of SMUD's Upper American River Project (UARP). In 1961, an agreement was made between SMUD and GDPUD and the associated rights to the South Fork Rubicon watershed were turned over. The pre-1914 water rights of the facilities in the Upper Rubicon watershed were also turned over to SMUD in the written deed. SMUD then applied for appropriative water rights in the Upper Rubicon watershed which included Loon Lake, diversions into Loon Lake and diversions out of the South Fork Rubicon basin into Silver Creek.[4]

Loon Lake Reservoir is the name used by SMUD. This development consists of a 1.6 mile long tunnel that diverts water from the Buck Island Lake to the Loon Lake Reservoir. Loon Lake Dam consists of a side channel spillway adjacent to the main dam, an auxiliary dam, and an earthfill dike. Another component, the Loon Lake Powerhouse, is an underground power generator that is located more than 1,000 ft (300 m) below the Loon Lake Reservoir and has a tunnel that runs from the powerhouse to the Gerle Creek Reservoir. Energy is conveyed using two transmission lines (69 kilovolts each) which share towers: one runs between Loon Lake and Robbs Peak switchyards and the other runs between Loon Lake and Union Valley switchyards.[6]

SMUD uses the UARP to generate electricity. This also serves to safeguard the reliability of the electrical transmission system SMUD operates. The Balancing Authority of Northern California, in which SMUD operates, is the zone that it balances power and interchanges with other power grids. The Loon Lake, Ice House and Union Valley Reservoirs provide about 90% of the total UARP water storage during the peak winter and spring snowmelt seasons. In the mid-summer the reservoirs let out water storage to generate more power when energy demand is greatest. The Rubicon and Buck Island Reservoirs capture and divert water into Loon Lake to produce the power it generates.[6] The storage at Loon Lake typically follows an annual cycle of increasing reservoir elevation in the spring and the highest point in the summer months. From the power generation over summer, the reservoir gradually lowers and allows for recharge in winter months and again storage to begin in spring. This annual cycle allows for a fluctuation of around 36 feet water elevation.[7]

An appendix to the 2014 California Water Quality Certification[8] requires SMUD to mitigate certain effects of Loon Lake on the environment. These are associated with geologic, aquatic and terrestrial resources of the former ecosystem, that is, as it was prior to the completion of the current dams. The presence of the lake also induces recreational visitation. Some of these impacts include: varying water level, modified streamflow patterns affecting aquatic life communities, aesthetic resources, and human pathogen concentration due to recreation.