The Marin Municipal Water District will begin pumping water out of Phoenix Lake, a district reservoir seldom used for water supply, starting today, March 1, because of the dry year. MMWD has not used Phoenix for water supply since 1992.
The low rainfall this year means that water storage levels are also low. According to the district, current reservoir storage is less than 61,000 acre-feet, which is about 76 percent of capacity and 86 percent of average for the date. An acre-foot is 325,851 gallons.
Seasonal rainfall at Lake Lagunitas now stands at 18.77 inches, which is well below 50 percent of average rainfall for the date. Seasonal rainfall to date (July through February) of less than 20 inches has occurred 17 times in the 134 years of rainfall records at Lake Lagunitas, most recently in 1991.
Only one year in the last 20 years, during the drought period of 1987-92, have the reservoirs held less water in storage on this date.
MMWD also noted, however, that due to last year’s high rainfall, the district does not expect the reservoir storage levels to drop to the alert stage (50,000 acre-feet on April 1) this year and, therefore, there will be no need for water use restrictions this year.
But, in order to operate the reservoir system in case it continues to be a dry year, MMWD will be pumping out of Phoenix. The pumps will transfer water to the Bon Tempe Treatment Plant, which usually treats water that flows into it from Bon Tempe Lake.
This pumping will continue until March 19 and is expected to transfer approximately 140 acre-feet of water out of Phoenix, which will be lowered by about 10 feet.
Because Phoenix is the second smallest reservoir and downhill from the treatment plant, it is rarely used. It will, however, . The district also spent $500,000 in a new pump and barge for Phoenix Lake in 2010.
According to MMWD, the district is also taking the following steps to mitigate water supply impacts:
• Importing Sonoma County Water Agency (SCWA) water to maintain the water supply reserves in the district’s reservoirs. About 25 percent of the water consumed annually is imported from SCWA.
• Operating the Alpine Lake pumps to pump water from Alpine into Bon Tempe Lake. The goal is to keep Bon Tempe Lake at a high water level, because it is the primary water source for the Bon Tempe Treatement Plant. Due to low rainfall and runoff this year, the Alpine Lake pumps have been operated this winter. Normally these pumps are only operated from late spring through the fall.
• The district is planning to start the Nicasio Lake transfer system as soon as demand increases in the late spring and use this source of water all summer. Water from Nicasio will supplement the water from Kent Lake that is treated by the San Geronimo Treatment Plant, MMWD’s largest treatment plant.
• The district also plans to have the Las Gallinas Water Recycled Water Treatment Plant ready to begin delivering recycled water by mid-March in anticipation of an early start to the irrigation season. Using recycled water for irrigation and other uses decreases demand for potable water.