Sunrise light on a grove of tufa towers emerging from the water of Mono Lake with soft green and dusty-red wild grasses in the foreground, Canada geese in the shallow water with reflections of the rocky towers, and desert hills in the distance.

Grant Lake Reservoir spills

On Saturday July 3rd, Grant Lake Reservoir began spilling for the second time since the year 2000–it also spilled in 2006 after filling up in 2005.

Inflow is dropping as the melting snow runs out, although the warm weather is melting higher elevation snow, which could maintain high inflow for a few more days. Outflow is declining as well after peaking this morning at about 460 cfs (cubic feet per second). The spill peaked at 171 cfs on Thursday and Friday last week, but LADWP was still increasing the flow in the MGORD (Mono Gate One Return Ditch) until this morning. LADWP installed pumps at the spillway in order to ensure it would meet its normal year peak flow requirement of releasing at least 380 cfs for five days followed by 300 cfs for seven days. If the reservoir hadn’t spilled, pumping 30 cfs plus the maximum safe flow in the MGORD of 350 cfs would have met the requirement.

The peak flow above the reservoir was 500 cfs last week when Southern California Edison (SCE) released a controlled spill from Gem Lake. This was the highest flow above Grant since 1998 and 2006. When combined with the 150 cfs diverted from Lee Vining Creek, the peak inflow to Grant Lake Reservoir was about 650 cfs.

Blocks of concrete slow down the water racing down the Grant Lake Reservoir spillway. Photo by Greg Reis.
Blocks of concrete slow down the water racing down the Grant Lake Reservoir spillway. Photo by Greg Reis.

Lee Vining Creek, Walker Creek, Parker Creek, and numerous smaller streams had a primary peak flow on June 7th, after a warm week melted a well-above-average snowpack. Mill Creek peaked on June 29th after Lundy Lake Reservoir filled and spilled. Rush Creek has more reservoir storage, which is why its peak flow is so much later than the other creeks–because it took longer for the reservoir to fill. Mono Lake will continue rising during the Rush Creek peak flow–it has already risen over a quarter of a foot since June 1st and is currently rising about an inch a week!