DWP draws down Grant Lake

The Los Angeles Department of Water and Power (LADWP) began diverting water from the Mono Basin on April 1, with the intent of taking the entire year’s allotment by the beginning of May. According to the Mono Lake Committee, this will drop the Grant Lake Reservoir level by six feet before summer even starts.

After decades of litigation, the California State Water Resources Control Board’s 1994 Decision regulated the amount of water LADWP can take from the Grant Lake reservoir and tributary streams based on the water level of Mono Lake. Due to this year’s April 1 (the start of the runoff year) reading, LADWP is only allowed to divert 4,500 acre feet from the Mono Basin, as opposed to the 16,000 acre feet it has been exporting every year since 1997.

Although LADWP can legally take their water allotment anytime between April 1 and March 31 each year, diverting the water this early in the year, “is not the best way of operating for this dry drought year, and that’s unfortunate,” said Geoff McQuilkin, Executive Director of the Mono Lake Committee. “Certainly they are allowed to get the water they are authorized to get and that’s important for [Los Angeles], but when you take it and how fast you take it is an important consideration for how the reservoir is affected.”

As of April 1, the surface area of Grant Lake measured at 700 acres, as opposed to 1,091 acres when full. LADWP began diverting 100 cubic feet per second, or roughly 200 acre feet per day on the evening of April 1, with projections to take all 4,500 acre feet by the end of the month. The Mono Basin snowpack measured at 14 percent of average on the first of April, which translates to a 19 percent of average runoff forecast for April through September as the snow melts. 22 percent is the runoff forecast for Rush Creek specifically.

“There is some inflow of water entering the reservoir, via Rush Creek, however water also has to be released to provide flow in Rush Creek downstream. With these factors and the export considered, the Committee projects a net drop of six feet in the level of Grant Lake by the end of the month,” McQuilkin said. “Once Grant Lake Reservoir reaches a low point, it will probably stay around the minimum storage level of 11,500 acre-feet until next winter precipitation begins.”

McQuilkin said the largest issue isn’t diverting the water but the timing of that diversion, which could adversely affect summer boating and recreation at Grant Lake, and potentially the Rush Creek fishery. “The general guidelines that already exist would point towards doing a slower export in the late summer or fall. Then you minimize the temperature and recreation problems and LA gets their water,” he said. “As a starting point that’s what you would expect and they chose to do something else.”

LADWP said it is diverting the water in April, “to accommodate inspection, maintenance, and repair” of the Mono Craters Tunnel, which hasn’t been done for 15 years. Depending on the extent of maintenance, the tunnel could be closed for much of the runoff year.

LADWP insists that the Mono Basin exports will be in accordance with the Water Board Decision, but that water from Mono Basin is crucial to offsetting the limited resources throughout the state, given that the snowpack and runoff this year will be the worst in recorded history.

“LADWP took extra steps to properly study and to ensure that the early delivery will not have adverse environmental impacts to Grant Lake, Mono Basin streams, and the Owens River,” said Amanda Parsons, PR Representative for LADWP. “Results of modeling to evaluate temperatures was performed and found that taking the exports early in the runoff year will not have any detrimental effect on the fishery.”

Mark Drew, the Director of the Sierra Program at CalTrout, said the effects of the early drawdown are yet unknown and that extensive monitoring, in addition to the existing LADWP modeling and analysis, would be “prudent.” He said there is concern that the early diversions could affect the water quality and temperature in Rush Creek, adversely affecting the fishery. A monitoring system would allow LADWP to stop diversions within 24 hours if needed.

“I understand and can appreciate the need to exercise the DWP water rights, especially in a dry year, but we would encourage the Department and others to consider potential effects on Rush Creek and even the Upper Owens,” Drew said. “It’s a balancing act between distributing water to people in Los Angeles and the environmental impacts of such diversions.”

A lot of this is unavoidable, given the statewide drought, McQuilkin concluded. “But part of it is a question of timing and considering all the different functions the reservoir has besides storing water for the aqueduct.”