by Carl Gowan
Four 10,000-pound barges manufactured by Bay Ship & Yacht Company in Alameda—one for Phoenix Lake and three for Alpine Lake—were delivered to MMWD earlier this month. The barges will be used to support a replacement pump in Phoenix Lake and two replacement pumps in Alpine Lake.
Phoenix Lake and Alpine Lake are both part of the district’s seven-reservoir system. The reservoirs store rainfall runoff from the Mt. Tamalpais Watershed and provide 75 percent of our water supply.
The Phoenix Lake barge will be installed this year. When needed, Phoenix Lake water is pumped up to Bon Tempe Lake and then treated at the Bon Tempe Treatment Plant. Due to the high pumping cost associated with the high lift to Bon Tempe Lake (approximately 600 feet), Phoenix Lake water is held as a reserve water supply for use in unusually dry years.
Historically, the district had a 100-hp (horsepower) pump installed on a barge in Phoenix Lake. However, the pump and barge were retired from service a few years ago as both were at the end of their useful lives. The new barge, along with a new pump and floating pipeline, will replace the old equipment.
The Alpine Lake barges will be installed next spring. Two of the barges will support two new 200-hp vertical turbine pumps while the third barge will support a valve manifold for the pumps. The two new pumps will replace the existing 400-hp submersible pump, which transfers water from Alpine Lake to Bon Tempe Lake so it can be sent to the Bon Tempe Treatment Plant for treatment. The new barge-mounted pumps will be installed in a deeper part of the lake, allowing the district to draw from water that is currently inaccessible.
These projects are part of a series of planned operational improvements designed to yield more water from the reservoir system. The other projects include the construction of an additional untreated water pipeline to facilitate the direct transfer of Lake Nicasio water to Kent Lake, and the replacement of an existing pump station in Corte Madera to increase the amount of water that can be supplied from the Ross Valley to southern Marin. All told, in the event of a drought, these improvements could increase the sustainable water supply yield of the reservoir system by about 1,000 acre-feet.*
*One acre-foot is 325,851 gallons, or enough water to supply three MMWD households for one year.