Forecast Informed Reservoir Operations

FIRO is a reservoir-operations strategy that better informs decisions to retain or release water by integrating additional flexibility in operation policies and rules with enhanced monitoring and improved weather and water forecasts (American Meteorological Society; 2020).

FIRO is being developed and tested as a collaborative effort in the Russian River Basin (Lake Mendocino, Lake Sonoma), the Santa Ana River Basin (Prado Dam, Seven Oaks Dam), the Yuba-Feather River Basins and the Green River (Howard Hanson Dam) that engages experts and stakeholders in civil engineering, hydrology, meteorology, biology, economics and climate from several federal, state and local, universities and others. There is significant interest and support for developing FIRO at other appropriate locations in the Western U.S. and elsewhere.
Overview
Process
News
Projects
FIRO Colloquium
FIRO Workshop

Don Seymour

(Sonoma Water)

F. Martin Ralph

(Center for Western Weather and Water Extremes at Scripps Institution of Oceanography)

Nick Malasavage

(US Army Corps of Engineers)

Michael Anderson

(California State Climate Office, Department of Water Resources)

Chris Frans

(U.S. Bureau of Reclamation)

Michael Dettinger

(CW3E, formerly U.S. Geologic Survey)

Joseph Forbis

(US Army Corps of Engineers)

Alan Haynes

(California Nevada River Forecast Center, NWS)

Joshua Fuller

(National Marine Fisheries Service)

Cary Talbot

(US Army Corps of Engineers)

Robert Webb

(NOAA’s Earth System Research Laboratory)

Patrick Sing

(US Army Corps of Engineers)

Arleen O’Donnell

(Eastern Research Group)

Rob Hartman

(RKH Consulting Services)

Nathan Pingel

(HDR Inc.)

Michael Konieczki

(HDR Inc.)

Jon Rutz

(Center for Western Weather and Water Extremes at Scripps Institution of Oceanography)

Russian River FIRO Fact Sheet

Lake Mendocino One Page Summary

Lake Mendocino FIRO Fact Sheet

Lake Mendocino Work Plan Fact Sheet

Lake Mendocino Full Preliminary Viability Assessment

Lake Mendocino Preliminary Viability Assessment One Page Summary

Russian River

Figure 1. Russian River Watershed with Lake Sonoma (center) and Lake Mendocino (upper watershed).

The Russian River watershed has two major reservoirs, Lake Mendocino (built in 1959), and Lake Sonoma (built in 1983) (Figure 1), both of which are used for water supply and flood risk management. The U.S. Army Corps of Engineers (USACE) is responsible for flood pool releases, and Sonoma Water manages releases from the water supply pool.

The reservoirs are governed by USACE water control manuals (WCMs), which were originally developed without the benefit of modern precipitation and streamflow forecasts. Each WCM specifies reservoir operation according to a guide curve, which dictates water levels during a flood event and water releases soon thereafter to create storage space for the next storm event. Lake Mendocino has a variable guide curve (Fig. 2); the guide curve for Lake Sonoma is a constant value that does not reflect seasonality (Fig. 3).

To address the impacts of climate variability and to help offset the impacts of an over 75% reduction in Eel River diversions, a FIRO viability assessment was completed for Lake Mendocino in 2021. FIRO interim operations (under a USACE-approved major deviation) have resulted in up to 19% higher storage levels compared to the rule curve (Fig 2). In addition to increased storage, FIRO resulted in a deeper, cooler pool that benefits threatened and endangered salmonids and improved flood risk management.

FIRO is a reservoir-operations strategy that better informs decisions to retain or release water by integrating additional flexibility in operation policies and rules with enhanced monitoring and improved weather and hydrological forecasts (American Meteorological Society, cited 2020: Forecast-informed reservoir operations. Glossary of Meteorology).

Figure 2. Lake Mendocino FIRO operations under WCM deviations showed 19% increased storage in 2020.

Based on the positive outcomes from Lake Mendocino, USACE is nearing completion of the WCM update to incorporate FIRO operations, and the Steering Committee was reconstituted to expand FIRO to Lake Sonoma on Dry Creek. In December 2022, Lake Sonoma declined to its lowest level (40% of the total water supply pool) ever recorded, underscoring the need to improve resiliency. FIRO operations under a minor deviation to the WCM during that same water year demonstrated significant benefits, as shown in Fig.3 below:

The ability to mitigate potential impacts of drought through FIRO hinges on accurate forecasts of atmospheric river (AR) storms because they provide roughly half the water supply in just a few storms annually, and yet cause more than 90 percent of all flood damages (Corringham, T.W. Ralph, F.M., Gershunov, A., Cayan, D.R., and Talbot, C.A., 2019: Atmospheric rivers drive flood damages in the western United States. Science Advances, 5, 12, eaax4631, DOI: 10.1126/sciadv.aax4631). Forecast skill for AR storms must be sufficient to ensure adequate lead time to inform dam operators’ decisions whether to release or store water in anticipation of incoming precipitation (or lack thereof). Improving forecast skill can result in greater flexibility over time.

Figure 3. Lake Sonoma Guide Curve, showing significantly increased water storage in WY 2023 with FIRO operations under a minor deviation approved and implemented by USACE.

Figure 4. AR making landfall in the Russian River area. Shading represents integrated water vapor transport, which indicates the strength of the atmospheric river.

The Russian River Steering Committee* is working closely with USACE on the Lake Mendocino WCM update and on the Lake Sonoma FIRO viability assessment, which will be completed in 2026. Upon completion, Sonoma Water and its partners will support USACE in updating the Lake Sonoma WCM to incorporate FIRO operations. To streamline the process, USACE’s Water Manager for the San Francisco District is leading the water resources engineering portion of the viability assessment, so that the work done by the Steering Committee can be used directly in the WCM update rather than conducting a separate analysis, saving time and money.

Lake Sonoma FIRO goals are to:

  • Enhance or maintain flood risk management.
  • Protect fisheries habitat on Dry Creek
  • Improve Lake Sonoma cold water pool reliability for the Don Clausen Fish Hatchery
  • Improve drought resiliency for water supply, environmental, and recreational benefits.
  • Examine the concept of a second outlet from Lake Sonoma to provide regional water supply resiliency

Expansion of FIRO to Lake Sonoma may provide unique opportunities to modify the physical configuration of the system to improve regional resiliency goals to help offset reduced diversions from the Eel River. A potential future project to help mitigate reduced Eel River diversions would be a new second outlet from Lake Sonoma to the Russian River above Dry Creek. Alternative configurations of a second outlet combined with enhanced FIRO strategies will be evaluated in the final viability assessment at a conceptual level. If the Steering Committee determines that a secondary outlet combined with FIRO could improve water supply, flood risk management and/or environmental conditions, further study would be required.

*Russian River Steering Committee: Nick Malasavage, USACE (Co-chair), Marty Ralph, CW3E (Co-chair), Don Seymour, Sonoma Water (Co-chair), Cary Talbot (USACE), Joe Forbis (USACE), Joshua Fuller (NOAA Fisheries), Patrick Sing (USACE), Michael Anderson (California DWR), Alan Haynes (NOAA NWS, CNRFC), Chris Frans (U.S, Bureau of Reclamation), Robin Webb (NOAA OAR)