Low-Water Point Chosen for Maintenance of Pumps : Aqueduct: Shutdown won’t produce a net gain in supplies but will briefly relieve some of the pressure on Lake Oroville, officials say.

State officials chose a particularly low-water point in California’s prolonged drought to shut down the pumps carrying northern water south across the Tehachapis last week in order to perform routine maintenance.

The action will not produce a net gain in water supplies, but it will briefly relieve pressure on heavily drawn Lake Oroville, the State Water Project’s major storage reservoir, state officials said.

They said with water supplies at low levels nearly everywhere, engineers decided now was the best time to shut down the Edmonston pumping plant in the Tehachapi Mountains to examine and repair equipment. Since the 1976-77 drought, the pumps have been shut down three times, officials said, usually at low-flow periods that normally occur at other times of the year.

The shutdown began Wednesday and was expected to last about two weeks. The water loss to Southern California will be made up by increasing releases from southern storage reservoirs. Water flows into the pumps from the California Aqueduct, which carries water south from the Sacramento-San Joaquin Delta.

“This was an operations decision,” state Water Resources Director David N. Kennedy said. “There was no water allocation policy involved.

“Clearly there is a problem because of the drought. (But) we didn’t look it as a drought management situation but as a week-to-week operating situation,” he added.

However, Kennedy and Metropolitan Water District of Southern California officials indicated that unless substantial rainfall occurs within the next few weeks, the possibility of cutbacks in existing water allocations will be examined.

Currently, Lake Oroville holds less than half of its normal volume for this time of year. To coincide with the shutdown of the Edmonston pumps, previously reduced releases from Oroville feeding into the delta were further cut from 5,000 cubic feet per second to 3,000, officials said.

Further cutbacks are unlikely, however, because fresh water from Oroville must keep flowing at a rate sufficient to prevent intrusion of sea water from San Francisco Bay into the ecologically delicate delta, particularly during periods of high tide.

Water from Oroville and elsewhere in the northern mountains collects in the delta and then either flows into the sea or into the vast California Water Project. But the delta itself is suffering a water shortage and is hard-pressed to export water to the south.

“If we had plenty of water in the delta, we would be pumping it (over the Tehachapis),” Kennedy said. “Given the fact there isn’t, and the maintenance has to be done, (we decided) to get the work done and be back in operation shortly.”

In the meantime, the MWD will draw increased amounts of water from relatively small reservoirs like Castaic and Silverwood in Southern California. However, these storage sites have a limited capacity and cannot be tapped for long periods without exhausting them.

Richard Balcerzak, MWD assistant general manager, said if substantial storms fail to occur in the next couple of weeks, a previously approved 10% reduction in MWD allocations might be bypassed in favor of a 17% cut. The cut would be effective Feb. 1.