A very dry summer continuesAugust 12th, 2012 by Greg, Information & Restoration Specialist
This summer is turning out to be drier than expected. Preliminary data for April–July show Lee Vining Creek runoff is about 1,000 acre-feet short of the 17,900 acre-feet (53% of average) forecast, Rush Creek runoff about 2,000 acre-feet short of the 23,400 acre-feet (49%) forecast, and Parker Creek runoff about 600 acre-feet short of the 3,400 acre-foot (62%) forecast. Only Walker Creek appears to be on target with its 1,300 acre-foot (42%) prediction—notably the lowest forecast of the four creeks.
The preliminary data is inconclusive, but it appears that Walker Creek dropped below 2 cfs at the end of July. This is apparently a 33-year low for July. Our daily data goes back to 1980, and it has never dropped below 2 cfs in July. Parker Creek, a stream with about twice as much annual runoff, as well as it having the Kuna Glacier at its higher headwaters, has never gotten below 10 cfs in July. Preliminary data shows Parker Creek running at 9 cfs on July 20th—perhaps a new July record as well? This was also the first year (aside from during a couple of recent flow studies) since the early 1990s that DWP diverted Parker and Walker creeks into the aqueduct. These creeks were not diverted in 2007 (another dry year), although the approved plan is to divert them in dry years when no peak flows are required and their water makes up for less diversions from Rush and Lee Vining creeks. This means that less of the 16,000 acre-feet of annual water export needs to come out of Grant Lake Reservoir storage in dry years. If they were not diverted, this water eventually would come out of Rush Creek. Under the new Stream Ecosystem Flow recommendations, these creeks will not be diverted (as has been the management scheme until this year), and the water will be used to augment Rush Creek below their confluence, meaning slightly less Rush Creek water will be released at Grant Dam (making it all balance).
Interestingly, at the peak of the Parker Creek diversions in July, more water was diverted from Parker Creek than Lee Vining Creek—perhaps another first?
In the Summer 2012 Mono Lake Newsletter, I stated that I expected Grant Lake Reservoir to spill this summer. It turns out I was wrong. Due to lower inflows than expected, it peaked at 94% of capacity, 2,600 acre-feet short of the lip of the spillway in late May. We knew about seismic concerns resulting in a drawdown order keeping Waugh Reservoir half full and Gem Lake Reservoir ten feet below spill, and the lining of Agnew Dam keeping that reservoir empty. But we hadn’t anticipated SCE shutting down its Rush Creek power plant for maintenance. SCE resumed operation of its Rush Creek power plant on July 23rd for the first time since May, resulting in an eight-fold increase in the flow of Rush Creek (over two days) where it enters Grant Lake Reservoir downstream of the power plant. As a result, Grant Lake Reservoir has been slowly rising since July 24th. It is now 90% full.
Rainfall also continues to be paltry in this very dry year. At the end of April, Lee Vining had received 47% of average precipitation since last October. This declined to 43% at the end of July. From May through July, only 0.14 inches fell in Lee Vining (about 10% of the average), 0.29 inches at Cain Ranch, 0.24 inches at Gem Lake, and 0.4 inches at Ellery Lake. Finally last weekend some rain fell, at a rate that could result in an average August if it keeps up the rest of the month. There is a chance of showers for the next seven days!
This past spring, Mono Lake dropped faster than expected: A tenth of a foot more than the April and May forecasts, and it dropped twice as fast as was predicted in June. July’s drop was at the rate predicted, resulting in an August 1st lake level 0.4 feet lower than the forecast: it stood at 6383.0 feet above sea level. This drop of 1 foot since April 1st is faster than the 0.8 foot drop for the same period in 2007, which was a drier year. In 2007 the lake dropped another foot by early October, and this year’s forecast is for another foot drop by November 1st. Mono Lake should end the calendar year about where it was in 2009 and 2010, before the wet year of 2011.
The Climate Prediction Center predicts a warmer than average August, meaning more of the same—unless we get rain!