A new footbridge to the gate house at Moccasin Reservoir means SFPUC staff no longer need to row a boat to the tower and crank a nearly 100-year-old gate valve by hand when they need to increase or decrease the amount of water in the reservoir. New upgrades will allow SFPUC staff to open and close gate valves remotely, without having to set foot, or boat, on the reservoir.
Built in 1930, the Moccasin Reservoir, located in the quiet Tuolumne County town of Moccasin, is one of the smallest in the SFPUC’s vast water-delivery system. Moccasin Reservoir impounds water released from the Moccasin Powerhouse before entering pipelines that deliver water to the Bay Area.
A severe rainstorm on March 22, 2018 sent a surge of water and debris down several creeks into Moccasin Reservoir. It overwhelmed the Moccasin Creek Diversion Dam upstream from the reservoir and threatened to overwhelm Moccasin Dam. SFPUC crews were able to lower the water level but some equipment sustained damage and a large amount of rock, sand and wood debris had to be removed. SFPUC crews completed extensive repairs and the reservoir was returned to service in June 2019, supporting water reliability for the SFPUC’s 2.7 million customers.
Additional work is taking place this summer and fall to replace the nearly 100-year-old gate valve and install a debris boom (aka log boom) to manage debris. Contractors drained the reservoir and demolished the aging motor actuator, shaft and knife gate. The replacement process is nearly complete, and a new actuator is being installed to allow for remote operation via a Supervisory Control and Data Acquisition (SCADA) system. A debris boom will reach across the width of the reservoir to manage and divert floating debris such as logs, etc.
The new section of footbridge connecting the existing gate tower bridge to the shore of Moccasin Reservoir means the row boat won’t be used as often. SFPUC staff no longer need to crank the gate valve open or closed by hand, a job that can take quite a bit of time and muscle. It is safe to bet staff will enjoy having remote control when the next heavy rain storm starts filling the reservoir.
The work is scheduled to be completed in mid-October 2019.