The San Francisco Public Utilities Commission (SFPUC) manages the dam and reservoir at Cherry Lake as part of the Hetch Hetchy water system. That overall system provides water to 2.6 million customers in the San Francisco Bay Area. Due to the failure of one of the four release valves (in the dam) last winter, the SFPUC is undertaking a major replacement project for the failed valve and two other high flow release valves that are estimated to be at the end of their operating capacity. To do the needed work, Cherry Lake must be drained down to a “minimum pool.” These photos taken in mid-September show that the lake seems greatly drained when seen from one side, but a view from the dam shows that a huge amount of water was still to be drained over further weeks in order to lower the lake.
The planned draining of the reservoir was complicated by this year’s tremendous snowpack and run-off that filled the Lake in June and July. Starting in mid-July, dam operators began releasing significant flows downstream into Cherry Creek in order to get Cherry Lake down to the minimum pool so that repair work can be started in October and can hopefully be completed by mid-November before the arrival of major fall storms.
Cherry Lake normally stretches from the dam north for more than three miles to the point where Cherry Creek flows out from the Emigrant Wilderness into the reservoir. Especially during the summer, the Lake is popular for boating, fishing, and quiet recreation. This year, due to the repair project, motorized boat access was restricted starting in early September, and recreational access below the dam is restricted to ensure public safety. The diminished reservoir will still have sufficient fresh water to sustain fish and good water quality. A pumping system will be utilized to send water from the minimum pool through temporary piping over the dam to discharge flows into the creek below the dam.
