Officials commemorate revised water control manual for Lake Mendocino in Oct. 22 ceremony
By Lauren Fimbres Wood, Scripps Institution of Oceanography
Leaders from the U.S. Army Corps of Engineers (USACE), Sonoma County Water Agency (Sonoma Water), UC San Diego’s Scripps Institution of Oceanography Center of Western Weather and Water Extremes (CW3E) and California Department of Water Resources (DWR) entered a new era in reservoir operations today with the signing of updates to the water control manual for Coyote Valley Dam and Lake Mendocino.
The revised manual redefines the operating rules around flood control schedules for the first time in the dam’s 66-year history by incorporating the principles of modern-day forecast-informed reservoir operations, or FIRO, to enhance the facility’s dual mission of flood risk management and water supply security.
“Before this update, we would inevitably be required to release water to give airspace to the dam for the next storm regardless of the upcoming weather,” said Nick Malasavage, Operations & Readiness Division chief for the USACE San Francisco District. “FIRO allows us to be informed by the forecast and make better decisions.”
U.S. Representative Jared Huffman, who represents California’s Second Congressional District, praised the achievement and its national importance.
“Today is a great day in the advancement of drought management, flood control, and fish habitat. With this update, operations will be based on the latest science instead of outdated guesswork. FIRO’s approach is leading the industry and will ensure more sustainable water supplies – something that’s more urgent than ever in our changing climate,” said Rep. Huffman. “I was proud to work in Congress to not only expand FIRO nationwide, but to have the pilot project start right here in Mendocino County. Congratulations to Sonoma Water and to the Army Corps of Engineers on this important partnership that made this all possible!”
Since the Corps completed construction of Coyote Valley Dam in 1959, the water control manual has been updated just twice in its existence – once in 1986, when the City of Ukiah’s hydroelectric power plant was installed, and in 2011, in order to define minimum flow capacity required to maintain downstream aquatic habitats. But with each of these versions, the flood control schedules remained unchanged, until FIRO procedures were evaluated and tested through temporary planned deviations to Lake Mendocino’s Water Control Manual.
“FIRO is now inherently bound into our operating rules,” said Malasavage.
Led by the Lake Mendocino FIRO Steering Committee comprised of members representing USACE, Sonoma Water, Scripps CW3E, National Oceanic and Atmospheric Administration, and California DWR, FIRO was first applied to the dam operations at Lake Mendocino in 2017. The program’s goals have been to gain valuable observational data, advance modern-day forecasting technology, apply them to water management decisions, and to eventually update the 1950s-era water control manual for Coyote Valley Dam. The revised water control manual allows for an additional 11,650 acre-feet of water storage into the flood control space at USACE discretion when forecast and advanced decision support tools indicate that it is safe to do so.
Initial FIRO assessments ran virtual trials of the program using modeling, forecasts and hindcasts. The success of the virtual trials led to operators receiving USACE-approved deviations. FIRO was then demonstrated successfully at Lake Mendocino during the course of two very different water years—Water Year 2019 was a relatively wet year, while Water Year 2020 was the third driest year over a 127-year record. In both years, FIRO increased water storage and managed flood risks. In Water Year 2020, FIRO enabled a 19 percent increase in water storage, totaling more than 11,000 acre-feet. These findings were shared in a multi-agency viability assessment.
“Our ability to accurately forecast incoming storms has improved dramatically in recent years. Using this new capability to improve how to efficiently protect communities from flooding and save water for droughts is critical to preparing for California’s hotter and drier future,” said DWR Director Karla Nemeth. “Lake Mendocino has been the first of many such efforts across California to guide new reservoir operations across the state, and we’re delighted to celebrate in Sonoma County Water Agency’s success.”
Along the U.S. West Coast, atmospheric rivers, weather phenomena that transport large amounts of water vapor in the sky, are the dominant weather phenomenon that can deliver massive amounts of precipitation or create drought in their absence. Forecasting the landfall location and how strong they will be is challenging with traditional sources of meteorological data such as weather satellites, which often cannot measure the key patterns of water vapor, wind and temperature within atmospheric rivers.
Advances in forecasting atmospheric rivers have been enabled by CW3E’s Atmospheric River Reconnaissance Program, a research and operations partnership that collects data on these storms from Air Force and NOAA “Hurricane Hunters,” as well as a network of drifting buoys across the Pacific Ocean and land-based observations. These observations and state-of-the-art weather models tailored to atmospheric river forecasting have significantly improved forecast reliability of precipitation amounts and landfall location.
“The implementation of FIRO takes advantage of strong skill in predicting atmospheric river storms,” said Marty Ralph, research meteorologist and founding director of CW3E. “This skill is founded upon, and has been recently improved upon, through scientific knowledge, specialized observations, advanced weather models and custom forecast tools. This marks a major milestone to implement science-based decision support tools to inform water management, reduce flood hazards and increase water availability. These enable society to better deal with the large swings between drought and flood that are characteristic of this region.”
Sonoma Water is the local cost-sharing partner for Lake Mendocino and determines the amount of water released from the reservoir when levels are in the water supply pools. The lake depends on annual rainfall as well as diversions from the Potter Valley Project to fill. Lake Mendocino is a key drinking water source for approximately 650,000 people in Mendocino, Sonoma and Marin counties. Releases from the lake are essential for meeting minimum instream flow requirements in the Russian River and providing critical habitat for threatened Chinook salmon and steelhead trout.
“Updating the water control manual to include FIRO is a historic step for the watershed,” said Lynda Hopkins, chair of the Sonoma Water Board of Directors and Sonoma County Board of Supervisors. “Since FIRO viability studies began at Lake Mendocino, these innovative techniques have saved water equivalent to a second Lake Mendocino without pouring a single ounce of concrete, providing critical reliability to water users downstream.”
Over the past three years, FIRO has saved nearly 30,000 acre-feet of water in Lake Mendocino. Lake Mendocino is one of two major reservoirs which supports a complex drinking water system for more than 600,000 residents in portions of Sonoma and Marin counties, including 150,000 residents in the upper Russian River watershed, such as residents in the Ukiah Valley that receive water under contract from the Mendocino County Russian River Flood Control and Conservation District.
About FIRO
Forecast Informed Reservoir Operations (FIRO) is a flexible water management approach that uses data from watershed monitoring and improved weather forecasting to help water managers selectively retain or release water from reservoirs for increased resilience to droughts and floods. FIRO applies emerging science and technology to optimize water resources and adapt to climate change without costly changes to infrastructure. Learn more about FIRO at Lake Mendocino by visiting: https://www.sonomawater.org/firo
