During the 2021 runoff year (April 1, 2021–March 31, 2022), the Los Angeles Department of Water & Power (DWP) was allowed to export up to 16,000 acre-feet of stream diversions from the Mono Basin because Mono Lake was above 6380 feet above sea level on April 1, 2021. Yet, only 13,300 acre-feet of water was taken, consistent with the low reservoir requirements in DWP’s water licenses, which were amended last year by the California State Water Resources Control Board.
The new licenses contain an overall minimum level of 11,500 acre-feet of storage for Grant Lake Reservoir, with a minimum of 20,000 acre-feet for July–September. On March 15 of this year, dropping levels in Grant forced DWP to curtail surface water exports and on April 4, Grant came within 36 acre-feet of the minimum level. This summer it will remain below the 20,000 acre-foot summertime minimum, with similar conditions as the 2015 drought year.
Prior to the new licenses, low Grant levels were supposed to limit surface water exports; however, those limitations had never stopped DWP’s exports before. DWP’s 1996 Grant Lake Operations & Management Plan specified a 12,000 acre-foot minimum operating level for Grant, but DWP decided that exports trumped that plan in 2008–2009 and 2015–2016. In both instances, the reservoir dropped below 12,000 acre-feet, which resulted in dust storms around the reservoir as well as high turbidity and warm temperatures in the water released to Rush Creek, both of which are detrimental to fish.
Reservoir recreation, fish health, and air and water quality aren’t the only resources impacted by low Grant levels. When Grant is below 11,500 acre-feet of storage, water flows released from Grant into Rush Creek are reduced to match the inflow upstream of the reservoir in order to prevent additional reservoir declines. As of early May, Grant is just above this level, and could drop below it with low runoff. Rush Creek could be low enough that stream temperatures could rise to lethal levels for trout. April precipitation was a little above average at high elevations, and this disastrous situation is looking less likely, but it will still be a challenging year for fish in Rush Creek.
This post was also published as an article in the Summer 2022 Mono Lake Newsletter. Top photo by Arya Harp.