Jay Jasperse and Marty Ralph: Piloting Forecast-Informed Reservoir Operations at Lake Mendocino

Jay Jasperse and Marty Ralph: Piloting Forecast-Informed Reservoir Operations at Lake Mendocino

A panorama of Lake Mendocino in Northern California.

Many western reservoirs are operated under strict water level rules that are intended to ensure that they have the necessary capacity to control storm water and prevent floods. However, it stands to reason that as our understanding of and capacity to forecast those storms improves, those long-standing rules can be made more responsive to actual conditions, with the result that more water can be stored for use during dry periods. The effort to do this is known as forecastinformed reservoir operations (FIRO). One groundbreaking FIRO effort occurred at the U.S. Army Corps of Engineers’ Lake Mendocino reservoir, which is operated for water conservation and water supply purposes by Sonoma Water. In this interview, Jay Jasperse of Sonoma Water and Dr. F. Martin “Marty” Ralph of the Center for Western Weather and Water Extremes (CW3E) at the Scripps Institution of Oceanography at the University of California, San Diego (UCSD) tell us about the grassroots beginnings of their cooperation, the new management practices being implemented based on their project, and how the process is creating a better model for the future.

Municipal Water Leader: Please tell us about your backgrounds and how you came to be in your current positions.

Jay Jasperse: I am the chief engineer and director of groundwater management at Sonoma Water, where I oversee engineering, capital projects, and water resources planning. I am also the cochair, along with Marty, of the Lake Mendocino FIRO steering committee. Marty and I helped initiate the project approximately 6 years ago.

Sonoma Water is a California special act district that provides water supply, flood control, and wastewater services to Sonoma County and other parts of the northern Bay Area. Among our responsibilities is water resource management. We are the local sponsor of the federal projects that are owned and operated by the Army Corps on the Russian River in Northern California. One of those federal projects is Lake Mendocino, which is the site of our FIRO project. The Army Corps’ San Francisco District manages the reservoir’s flood risk, and Sonoma Water operates it for water conservation and water supply purposes.

Marty Ralph: I am a meteorologist by training, but I have spent time around hydrologists, so in a way, I’m a hydro meteorologist. After working at the National Oceanographic and Atmospheric Administration (NOAA) for 21 years in Boulder, Colorado, I moved to UCSD in 2013 to build its capabilities to work on Western water-related challenges. Put simply, my job as a scientist is to help improve weather forecasts. I do that by understanding the storms that produce the rain that becomes our water supply or creates floods. I founded the CW3E at UCSD’s Scripps Institution of Oceanography to pursue this work. Scripps is a worldwide leader in oceanographic science and climate science, and it is the perfect home for our new center, which will build on its deep knowledge of ocean and climate and culture of linking science to solutions. Working with Jay at Sonoma Water and with the Army Corps to explore the possibility of using forecasts to help reservoir operators at Sonoma Water’s facilities was one of the sentinel projects that launched CW3E. Atmospheric rivers (ARs) are another major focus of our center.

Municipal Water Leader: When did the FIRO concept become viable and why? Was it because of a better understanding of the AR phenomenon?

Jay Jasperse: Marty and I started working together on hydrometeorological programs when he was at NOAA. It soon became clear that ARs were fundamental to our operations and critical to effective water management and operations. As it became clear that ARs were the signature precipitation event that ought to drive water management decisions, Sonoma Water made it a priority to better understand them and to look for ways to better manage both the flood control and the water supply issues that these extreme events produce.

Several components of the Army Corps were involved in this effort. Initially, we worked with the Lake Mendocino reservoir operators in the Army Corps’ San Francisco District. However, the involvement expanded to other offices of the agency. Three of NOAA’s line offices—the National Weather Service, the Office of Atmospheric Research, and the National Marine Fisheries Service (NMFS)—were key partners. The NMFS helped us evaluate the potential benefits of FIRO for ecosystems and species, especially the salmonid species in the Russian River system. The California Department of Water Resources and the state climatologist, Mike Anderson, have also been partners from the beginning of this endeavor. We also engaged with the scientists who work on climate and hydrology issues at the U.S. Geological Survey and the Bureau of Reclamation.

Marty Ralph: Several advances contributed to the development of FIRO at Lake Mendocino. Around 2008, there was a recognition that action was needed to help imperiled salmon populations recover. There were also several years of intensive research on extreme weather on the West Coast. Specifically, in the 2010–2012 time frame, there was a recognition that AR storms were the key to West Coast water supply and flooding. In 2013, I started the CW3E and was able to build on Scripps’s reputation and capabilities to work with the Army Corps and Sonoma Water to develop the FIRO concept and the resources it would require. To add two other dimensions, Sonoma Water has a history of innovation. It was already working with scientists to understand the hydrology and the geology of the watershed.

In its early days, a lot of people were skeptical of this idea, because precipitation forecasts were not considered reliable. However, we believed that a better understanding of AR events in the West could help to manage water flows throughout the region. The scope of effort and the technical steps required to develop and evaluate FIRO were laid out in 2014–2015 in the form of a work plan representing the technical requirements and strategies. Major funding to pursue parts of the work plan was provided beginning in October 2015. Finally, in 2016, the Army Corps’ engineering manual was revised for the first time, incorporating the option for Sonoma Water to consider forecasts in the day-to-day operations of the reservoir.

Municipal Water Leader: Why was Lake Mendocino the reservoir where FIRO was piloted?

Marty Ralph: In 2012, the Army Corps released water from Lake Mendocino in the wintertime, as it is mandated to do. After this release, we experienced one of the driest periods on record over a span of 14 months. Some key people in the Army Corps, Marty, and I looked at that experience and wondered whether there was something we could have done to improve the outcome. Was there information that we could have brought to bear on our management decisions? It became clear that if forecasts of ARs had been accurate enough, the Army Corps could have made an active decision to hold back some of the water that was released based on dated rule curve requirements. If a big AR storm that threatened to create a flood had approached, there would have been time to release it.

Jay Jasperse: One of the key factors that motivated work on Lake Mendocino was a sharp reduction of inflows into it from a nearby river. The reservoir’s water supply operations have been especially difficult since around 2006, when diversions from the nearby Eel River into the reservoir were significantly reduced. Water has been diverted from the Eel River since 1908, and the reservoir was built in the late 1950s with the assumption that the same amount of water would continue to be diverted to the Russian River and Lake Mendocino. However, since 2006, diversions from the Eel River have decreased by about 57 percent, resulting in an average reduction of total inflow to the reservoir of approximately 40 percent. This rapid change in water supply put everything off kilter, and we are still struggling to manage the reservoir to provide adequate water supply. Those conditions were right for a FIRO solution.

Municipal Water Leader: How did the Lake Mendocino FIRO project progress?

Marty Ralph: At an interagency Russian River workshop in early 2014 at Sonoma Water, I launched the idea of a FIRO project. The Army Corps participants were on board. One of the action items from that meeting was for Jay and me to form a steering committee. This led to the first FIRO workshop, which was held at the Seaside Forum at Scripps in summer 2014. The FIRO steering committee and a group of other experts came together and developed the technical FIRO work plan, which was finalized the following summer.

The creation of a detailed technical work plan led naturally to a collaboration with the relevant Army Corps research entity, the Coastal and Hydrology Lab at the Engineer Research and Development Center, which ultimately provided the primary funding for executing major portions of the work plan. That work plan spent 2 years in a preliminary viability assessment (PVA); the remainder of the 5 years focused on the final viability assessment (FVA).

Initially, we launched the FIRO project with the intention of it being a research study that would generate a paper report over the course of 5 years; there would be no change in how the reservoir was operated as we developed the concept and explored its viability. When the 2 years of PVA finished in 2018, the results were so encouraging that the Army Corps requested the proposal of a major deviation to Lake Mendocino’s water control manual that would allow its operators to consider the forecast in their day-to-day reservoir operations decisions.

A major deviation requires a rigorous review, and it was suggested that the grassroots committee itself be the entity to submit the formal major deviation request. Our committee authored, prepared, and submitted the request to the Army Corps, and it was reviewed for over a year. Ultimately, the Army Corps approved the deviation a week before the beginning of the new water year. Were it not for the approval, the Army Corps would have been required to release several thousand acre-feet of water to open the space normally required for flood control purposes. Instead, it was possible to retain that water at least into the winter. That approval began a 2‐year trial run, during which the reservoir operated based on the FIRO effort.

Jay Jasperse: We received our first major deviation in the 2019 water year, a wet year in which we experienced flooding. Using FIRO tools, the operators were able to successfully navigate the high-flow conditions experienced during that winter and spring. By contrast, 2020 was the third driest of the 127 years on record. We essentially relived the 2013 water year that originally motivated us to develop

the FIRO program at Lake Mendocino. We had the early storms followed by a dry winter and spring, but this time we were able to use FIRO to achieve a much better result than we did in 2013. Using FIRO increased our storage by 19 percent over what we would have had if we had operated under the historic rule curve. This was a significant success.

Even though we have completed the FVA, we are hoping that we can continue to operate and learn more about FIRO operations over the next 5 years as we work with the Army Corps to formally update the water control manual to include the FIRO strategy. As the strategy must be carefully thought out and crafted, we expect this next step to take several years.

Lake Mendocino, pictured here in 2019.

Marty Ralph: We are happy to report that FIRO worked just as we thought it would. In January, the reservoir was at its normal, expected level of about 68,000 acre-feet. In a relatively dry winter, there were enough storms to moisten the soil that by mid-January, when two ARs hit over a week or two, they partially filled the reservoir’s empty space, the flood pool, by about 11,000 acre-feet up to about 80,000 acre-feet. Normal operations would have required operators to drain the reservoir back to 68,000 acre-feet instead of keeping it at roughly 80,000. The major deviation allows the operator to monitor the forecast on a daily basis for the rest of the winter. With no big ARs on the horizon, that water was not released. By the middle of March, the water that normally would have been released was still in the reservoir and became part of the water supply for the summer during this exceptionally dry year. It was a remarkable success story.

Municipal Water Leader: Is there anything else you want to add about the findings of the FVA?

Jay Jasperse: A lot of good work from the FVA focusing on the practicality and feasibility of FIRO is now being implemented. FIRO 1.0, as we call it, was analyzed based on current technology and scientific capabilities in the FVA. However, we want to anticipate the growth path for future iterations of FIRO. Future research and collaboration between researchers and operators will identify and leverage new technology, science, and forecasting skills. We do not have to wait 20 years to figure out how to take the last 20 years of advances and incorporate them into FIRO.

Marty Ralph: As forecasts get better, the range of options for reservoir operations will increase. The FIRO concept is being tested now at a couple of other reservoirs of different sizes, climates, purposes, and operating complexities. Expanding the exploration of FIRO viability to other reservoirs and continuing to develop the FIRO concept are the primary next steps. Research into landfalling ARs and the precipitation and runoff they cause will enable greater flexibility in future reservoir operations here at Lake Mendocino and in other locations where ARs are the dominant storm type.

Municipal Water Leader: Based on this trial and others like it, will there be overall changes to the Army Corps’ regulations or manuals?

Jay Jasperse: The Army Corps’ San Francisco District, which operates Lake Mendocino, is starting to update its water control manual to include FIRO.

Marty Ralph: The engineering regulation that allows for forecast information underpins all this innovation. Each reservoir has its own water control manual, and the FIRO effort helps explore whether it is viable to consider more flexible operations in each reservoir based on skillful forecasts. If it is viable, then the water control manual could be modified to adopt the appropriate level of flexibility. The vision is that FIRO helps do the homework to allow for updates in those water control manuals.

Municipal Water Leader: Where else is FIRO being piloted?

Marty Ralph: Because of the grassroots effort I described, Lake Mendocino’s was the first FIRO pilot study. The next to have its viability assessment come online was Prado Dam on the Santa Ana River in Southern California. AR storms are the main player there as well. We partnered with Orange County Water District (OCWD) and the Army Corps’ Los Angeles District on that project. Prado Dam is in a big urban area, unlike Lake Mendocino, which is located in a relatively rural area of Sonoma. The distance from the reservoir to the ocean is also shorter. The reservoir is used primarily for flood control, and after a storm, it normally keeps only a small amount of water, which is used to recharge groundwater. We are looking into whether some extra water could be kept after a storm long enough to be recharged into the groundwater that OCWD maintains. The PVA is nearly completed and looks promising; we are about to start the FVA process.

The next FIRO viability assessment combines two reservoirs, Yuba Water Agency’s New Bullards Bar Dam in the northern Sierra on the west side of the Sierra Nevada and the nearby Oroville Dam, which is operated by the California Department of Water Resources. Both are fed by the Yuba and Feather Rivers, and combined, they hold nearly 5 million acre-feet of water. We have formed a FIRO steering committee for the Yuba-Feather system, have nearly finished creating the work plan, and have started the PVA.

Jay Jasperse: In the case of the Yuba-Feather system, there is also a parallel effort to look at updating the water control manual. For Lake Mendocino, it was sequential: We started with FIRO and then turned to the water control manual update. At Yuba-Feather, they are running in parallel and are being coordinated.

The next effort is being initiated in the Seattle area at the Howard Hanson Dam, where we are working with the Northwest District of the Army Corps.

Marty Ralph: FIRO is potentially applicable in many other locations across the nation. However, our forecast abilities vary a lot when it comes to extreme precipitation. Thunderstorms, which are the primary source of flooding in parts of the country, are pretty tough to predict. It looks like ARs may have the best inherent predictability, but there is work to be done to explore whether we have the skills to forecast tropical cyclones or big convective storms in the Midwest, the Southeast, and Texas well enough to enable FIRO in those parts of the country. That is being researched.

Municipal Water Leader: Is there anything you would like to add?

Jay Jasperse: While we have talked a lot about the technical aspects of FIRO and the engineering aspects of reservoir operations, I cannot emphasize enough the importance of the steering committee’s efforts. The initial partnership was able to successfully establish a multiagency, multidisciplinary steering committee. There are research scientists, fisheries biologists, reservoir managers, and water supply managers among our ranks. Leveraging our diverse experience and skill sets helped us to realize this accomplishment at Lake Mendocino.

Marty Ralph: I agree with that sentiment wholeheartedly. The building of trust through the formation of the steering committee was key because the different parties have different interests and priorities. The steering committee created a shared vision of what could be achieved, underpinning the whole effort’s success. That is something our committee members have often noted.

Jay Jasperse is the chief engineer and director of groundwater management at the Sonoma Water Agency. He can be reached at jay.jasperse@scwa.ca.gov.

Marty Ralph is a hydrometeorologist and the founding director of the Center for Western Weather and Water Extremes at the Scripps Institution of Oceanography at the University of California, San Diego. He can be reached at mralph@ucsd.edu.