Photo LADWP Tinemaha Runoff

LADWP Crews Successfully Manage Over 325 billion gallons of Water Flowing from Historic Eastern Sierra Snowpack

LADWP developed a detailed water operation plan to maximize the beneficial use of the runoff water for its operations, customers, and environmental responsibilities, and reduce impacts to public and private property throughout the Owens Valley region.

LOS ANGELES (August 3, 2023) – On April 1, 2023, the Los Angeles Department of Water and Power (LADWP) announced a record snowpack of 296% of normal for the Eastern Sierra making 2023 one of – if not the largest – snowpack year on record in California, eclipsing other big water years like 1952, 1983, 2017, and surpassing the Department’s 1969 record that measured at an estimated 270% of normal.

In wet years, there is more than four times as much water along the LA Aqueduct than in dry years. This year’s record snowmelt translates into managing 1 million acre-feet of water along the LA Aqueduct which is equivalent to filling about 493,617 Olympic-sized pools with water.

The peak of the runoff season—the period in which temperatures rise and the snow melts–usually lasts from May to June. This year’s impressive snowpack and the volume of water that it translates into pushed the season to August and possibly into early September.

“In light of lessons learned during the 2017 and 2019 wet year events, LADWP took immediate steps to prepare for the decidedly high runoff this year,” said Anselmo Collins LADWP Senior Assistant General Manager of Water System. “LADWP was able to successfully maximize aqueduct flows and water spreading throughout the Owens Valley, strategically manage reservoir levels, and expeditiously protect Owens Lake dust mitigation infrastructure, all while performing day-to-day operations, prioritizing human health and safety, and maintaining its environmental responsibilities.”

The dramatic winter storms brought heavy amounts of precipitation to the Eastern Sierra Nevada and Southern California. During the extreme March rain-on-snow event, an uncovered concrete section of the LA Aqueduct near Olancha was breached requiring the expertise of about 75 LADWP personnel working around the clock to make repairs. The LA Aqueduct breach and subsequent damage from the storms expedited LADWP runoff work.

Crews repaired diversion structures to better ready spreading grounds (an area that holds surface water long enough to let it sink into the soil); restored and cleaned ditches that receive runoff water by removing vegetation and blockages; and shored up areas of Owens Lake to minimize the expected damage rising water levels pose to dust mitigation infrastructure.

In anticipation of the high runoff and in preparation for a worst-case scenario, LADWP Aqueduct Operations also readied all spreading grounds for use. During a normal water year, LADWP utilizes only productive spreading grounds for a brief period of time during peak runoff – this year both non-productive and productive spreading grounds were used.

The Laws and Big Pine spreading grounds, which are the most productive, were in use by early spring. The second most productive spreading grounds off of the creeks from Tinemaha Reservoir to the Haiwee Reservoir complex, just South of Lone Pine, needed extensive preparation work by personnel as they also suffered damage during the March flooding event.

Laws spreading grounds near Upper McNally Canal.The Tinemaha Reservoir spilled substantially in 1969, so LADWP Water Operations installed a siphon system in May 2023 to increase the capacity of outflow water from Tinemaha Dam and prevent spilling the reservoir.

During the peak of runoff in wet water years, the LA Aqueduct system and all spreading operations combined are completely maximized and excess water is then released to Owens

The historic nature of the 2023 winter storms and likely massive runoff prompted Mayor Karen Bass of the City of Los Angeles to issue an Emergency Declaration to allow LADWP to take immediate steps to protect infrastructure and aid in managing flood waters.

Taking lessons learned from 2017, LADWP personnel installed temporary and permanent defensive measures at and near Owens Lake to manage any rush of flood water onto the dry lakebed and to best protect the environment and existing investments in dust mitigation infrastructure.

“From March through July only 100,000 acre-feet of runoff of the projected 180,000 acre-feet has made its way to Owens Lake, resulting in the lake level rising by 3 feet,” said Collins. “As a result of our effective preparation work and extraordinary efforts, we are past the peak runoff period and the Aqueduct system has held up seeing minimal damage, and with the majority of Owens Lake flood protection measures installed this year now providing permanent protection for the future.”

Examples of protective measures taken at Owens Lake:

• Placement of additional riprap (large stones) armor on approximately 14.5 miles of berm slopes that are adjacent to the brine pools to help strengthen the berms and prevent erosion due to wave and wind action.
• Repaired roads and performed general earthwork.
• Removed critical electrical equipment in low-elevation areas, and installed temporary protection measures for key electrical and mechanical facilities by placing temporary barriers, gravel, and sandbags.
• Installation of seven monitoring stations and cameras to track flood water in real-time.

LADWP placed additional gravel armor on approximately 14.5 miles of berm slopes that are adjacent to the brine pool to help strengthen the berms and prevent erosion.

The LADWP Water Operations Aqueduct Division effectively calculated how to lower reservoir elevations to create more storage space for runoff­ water. The staff also figured out to efficiently move water through almost 2,000 miles of canals and open ditches adjacent to the Owens River to replenish local groundwater aquifers while supplying LA with Aqueduct water in place of purchased water and pumped water wherever possible.

Photo LADWP Upper McNally 2023 Spreading

Also as a result of the unprecedented water year, LADWP hydrographers scheduled additional snow surveys in June and July for the first time in the Department’s recorded history to better understand the rate of snowmelt to inform runoff conditions.

“The hot temperatures in the Owens Valley since the 4^th of July holiday weekend increased the flows in the creeks and waterways along the Eastern Sierra,” said Adam Perez, LADWP LA Aqueduct Manager. “Fortunately much of the region experienced a long cool spring and a cooler than expected beginning of summer, which delayed the arrival of the runoff and allowed our crews additional time to prepare the Aqueduct system,” Perez added.

LADWP’s Communications and Corporate Strategy Division and Water Operations Division worked together to produce a dedicated runoff webpage and waterway safety messaging in both print and digital media throughout the summer months. To help provide guidance and a big-picture view of the anticipated severity of the runoff, officials from Inyo County and LADWP hosted a preparedness meeting for the community in early spring, and LADWP communications staff actively participated in the Inyo County joint incident command communications group.

LADWP, Inyo County, Mono County, Inyo Sheriff, Southern California Edison, Caltrans and other land agencies worked together to share public messages on waterway and recreation safety during the runoff season.

Even though many of the creeks and streams have passed their peak flows, the expectation is that water will continue to flow fast into the late summer. LADWP still recommends avoiding recreation next to swift-moving waterways and suggests enjoying one of the many lakes and ponds that are located along the Eastern Sierra such as Buckley Ponds in Bishop or Klondike Lake.

“The flows have been manageable and associated damage resulting from the runoff has been minor, however, we are not 100 percent out of the woods in addressing the record-breaking snowpack and resulting runoff, but Mother Nature has been kind to the community along the Eastern Sierra,” said Perez.

LADWP personnel will continue to actively work through September managing the high flows and sediment build-up in the waterways from this year’s extremely wet year.

LADWP manages approximately 315,000 acres of City-owned land in the Eastern Sierra for the primary purpose of providing water and power supply for the City of Los Angeles and the towns in Inyo and Mono Counties. LADWP in the Eastern Sierra is utilizing leading technologies in water, environmental, and cultural resource management to support a water supply vision that is ‘water strong’, resilient, sustainable, reliable, and equitable well into the next century.

 PEAK RUNOFF BY THE NUMBERS