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TUD Water Source Details

The unique TUD water system makes water conservation by our customers more important this year than ever before.

Tuolumne County is close to both Don Pedro and New Melones Reservoirs and although there is ample water in each, Tuolumne Utilities District (TUD) does not have access to water contained within them.

In a good year, those Reservoirs hold over 4.4 million acre feet of water. However, TUD does not have pumping facilities, pipelines, water contracts, or rights to the water in those Reservoirs. All of which would be a monumental cost to establish.

Additionally, TUD’s water system does not operate anything like your typical valley city, such as the City of Modesto, Stockton, or Sacramento. Each of those communities has access to significant groundwater out of extensive ground water aquifers. Only 5% of TUD’s water comes from ground water wells. Instead, TUD must rely on a relatively small reservoir system shared with hydroelectric generation and recreation at Pinecrest Lake and are subject to the whims of nature.

So where then does TUD get its water?

Our water supply comes from the South Fork Stanislaus River and is stored in Lyons and Pinecrest Reservoirs, which combined, hold approximately 25,000 acre feet of water. This water is delivered to TUD under a contract with Pacific Gas and Electric (PG&E) and our average annual demand is approximately 18,000 acre feet.

These Reservoirs are owned and operated by PG&E for hydroelectric power generation. Lyons Reservoir is very small and can hold up to about two months of summertime supply. Later in the season, Lyons Reservoir is supplemented with water from Pinecrest Lake. Each year, Pinecrest Lake fills and spills however, this year conditions are so dry, it appears that both Reservoirs will just fill to capacity where normally, the river would spill much longer and later into the spring and summer.

With some of the state’s largest Reservoirs (Don Pedro and New Melones) on the county’s western boundary and brimming with water, it can be difficult to explain to TUD customers that we may be facing drought conditions this summer. Compound this with statements from state and federal water managers about how much “carry over” storage they have in these large Reservoirs and how water deliveries will only slightly be affected by the drought, and we have a recipe that makes it difficult to understand why TUD may need to conserve water this year.

In a normal year, both Pinecrest and Lyons will fill to the spill point and overflow (uncontrolled) from about May through June. The storage volume then normally supports all uses of the water for the remainder of the year. This year, the concern has been whether there was even enough water to fill the Reservoirs first, and now, the runoff may be very early creating an unusual reliance on stored water in Pinecrest much earlier this summer than normal.

As stated before, TUD does not own or operate Pinecrest Lake or Lyons Reservoir; PG&E does. Every year in the fall by design, the water level in Pinecrest Lake is drawn down for hydroelectric generation as well as to provide storage capacity for flood water, winter precipitation and snowmelt runoff. This water year however was truly an anomaly, as most weather predictions were for a very wet winter similar to last year. Early storms in October led PG&E and TUD to believe all forecasts were correct, until we experienced extremely dry months in November and December in which precipitation levels were near the lowest on record like occurred in 1976/77.

At the end of December, PG&E and TUD began planning ways to hold back as much water in Pinecrest as possible in the event that dry conditions continued. PG&E began voluntarily slowing its water flows from Pinecrest which reduced the amount of hydroelectric power they could produce By January 20, 2012, PG&E had voluntarily shut down its local hydroelectric facilities in order to maximize water storage in Pinecrest for TUD’s uses this summer and fall. PG&E cooperation has resulted in a steadily increasing storage volume in both Reservoirs. The snow and precipitation that occurred between March 16 and March 19, 2012 has improved the outlook, but there is still very little snow melt runoff expected and we are still very concerned about water availability this summer and in the event we have another dry year next year.

This year, more than ever before, TUD needs the cooperation from our customers to reduce water consumption. Please view our website at, for more information on how to reduce water consumption and please consider taking advantage of the Tuolumne County Masters Gardener’s program to help make your landscape water efficient.