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 outlet design

The Los Angeles Aqueduct diversion dam on Lee Vining Creek was upgraded 15 years ago in order to better deliver mandated flows to the long-suffering creek. Now progress is moving quickly to apply a substantially larger fix to achieve required restoration flows on Rush Creek, Mono Lake’s largest tributary.

A pair of 12-foot-tall Langemann gates will be installed in the Grant Lake Reservoir spillway to allow peak restoration flows in Rush Creek. Photos by Arya Degenhardt.
A pair of 12-foot-tall Langemann gates will be installed in the Grant Lake Reservoir spillway to allow peak restoration flows in Rush Creek. Photos by Arya Degenhardt.

Thanks to the Mono Basin Stream Restoration Agreement negotiated by the Mono Lake Committee with the Los Angeles Department of Water & Power (DWP), along with our friends at the California Department of Fish & Wildlife and CalTrout (see Fall 2013 Mono Lake Newsletter), a new facility will be constructed at Grant Lake Reservoir to overcome the limitations of DWP’s existing WWII-era infrastructure.

Based on details reviewed at an early spring engineering design meeting in Los Angeles, the new facility will utilize the same Langemann gate technology as the Lee Vining Creek improvements—but with more and bigger gates.

At the meeting, which was part of the Agreement’s communication procedures, DWP staff showed that the facility is well on the way from concept to reality. The overall plan is to deepen the existing reservoir spillway to allow the controlled release of water via a pair of 12-foot-tall variable-position gates. Core samples have been drilled, geotechnical data analyzed, and engineering drawings are now at what the engineers call 30% completion. Design finalization is scheduled for 2016, with construction to follow in 2017 and 2018.

In addition to the outlet construction work, measures will be taken to shore up the existing ditch that supplies water to Rush Creek. While that ditch is far too small to carry the needed wet-year peak flows, it will be used simultaneously with the new gates to achieve flows in Rush Creek of at least 750 cubic feet per second in the wettest of years. Excavated material from the spillway will be used to reinforce and raise the outer ditch wall. The remainder of the material will be placed into an old excavation pit that dates back to the original Grant Dam construction.

The Committee is pleased that the Grant Outlet provisions of the Stream Restoration Agreement are moving forward toward full implementation. While engineering and construction challenges still lie ahead, modernization of DWP’s Mono Basin infrastructure will bring the aqueduct into the 21st Century, providing the capacity to meet stream and fishery restoration goals simultaneously with providing for the needs of Los Angeles residents.

Progress on new DWP water license

Revision of DWP’s official water licenses, in order to incorporate the provisions of the 2013 Mono Basin Stream Restoration Agreement, continues to move forward, with formal action likely by the California State Water Resources Control Board in late summer.

Progress has been slow, but unavoidably so because to take action the State Water Board also needs DWP’s design and environmental documentation for the Grant Outlet in hand. That design work is substantial and has proceeded relatively quickly, meaning that the schedule laid out in the Agreement is being followed and that Rush Creek is moving closer to the day when its fish, birds, meandering channels, and streamside forests will experience the promised restorative flows of water.

This post was also published as an article in the Summer 2015 Mono Lake Newsletter.