Expect to see the arroyos in Pleasanton drying up this month after the Zone 7 water agency shut off all releases to save limited supplies for delivery to customers.
Artificial releases to Arroyo Mocho were reduced March 21 from 9 cubic feet per second (cfs) to 6 cfs, and on Arroyo Del Valle from 5 cfs to 4 cfs. They were ramped down further last week and on March 27 were shut off completely. A residual flow was expected to last for three to five days, but some stretches dried up before others.
Zone y representatives said that due to the continuing drought emergency, it is being forced to conserve every drop coming into the Livermore-Amador Valley from the State Water Project.
Over the past week, the California Department of Water Resources (DWR) gradually reduced flows to the local arroyos that normally help replenish the local groundwater basin.
During normal rainfall years, Zone 7 releases some of its imported State Water Project supplies down the arroyos to augment natural flows. This water is Sierra snowmelt that has been captured by the State Project in Lake Oroville and then conveyed through the Delta to be exported to other parts of the state, including the Livermore-Amador Valley.
Water in the arroyos seeps into the groundwater basin and this percolated water replenishes the groundwater basin and helps maintain ground water quality.
But these are unprecedented times, Zone 7 said. The state is in a third consecutive dry year, and calendar year 2013 was the worst on record in many parts of California, including here in Zone 7's service area. There is almost no snow in the Sierras to melt and re-fill Lake Oroville. In January, there were declarations of both state and local drought emergencies.
DWR has set a 0% allocation for State Project water this year. That means that Zone 7 will have to rely on stored or unused water from last year, which was also dry.
In response, Pleasanton residents and businesses have been asked to reduce water use by at least 20%. As the dry year continues, this number is likely to increase. Using drinking water for outdoor watering may not be possible this summer.
By gradually reducing releases into the arroyos over a week's time, instead of immediately, Zone 7 hoped to mimic the drying-out period that would happen naturally in a low rainfall year. The idea is to make release reductions slowly, consistent with a natural rain event, to allow species to adjust as well as possible.