Modernizing Reservoir Operation

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Goals for the Manual Updates: Efficient Use of Reservoir Storage in line with USACE Water Control Management Mission

Oroville and New Bullards Bar are owned and operated by the California Department of Water Resources (DWR) and Yuba Water Agency (YWA), respectively. Each was built for multi-purpose functions including flood control, water supply, power generation, recreation, and conservation. Oroville and New Bullards Bar are operated as a system for flood control, considering the objective flow at the Yuba-Feather River confluence and downstream. The water control manuals developed by SPK contain data and information about the facilities and watersheds and prescribe flood operation for the dams. SPK developed the water control manuals at the time of construction. The Oroville and New Bullards Bar water control manuals were published in 1970 and 1972, respectively. Since then, physical changes to the facilities have occurred or are planned, including recovery of the flood control outlet spillway and armoring of the emergency spillway at Oroville Dam after the 2017 incident when the spillways were damaged, and the addition of a secondary spillway at New Bullards Bar Dam, which is in design and will increase the release capability of the dam at lower reservoir pool elevations. Furthermore, the existing water control manuals consider storage available at Marysville Reservoir, which was never built. In updating the flood operation rules within the water control manuals, SPK’s goal is to prescribe efficient operation that continues to meet USACE’s water control management mission, as described in Engineer Regulation 1110-2-240: •Operate in accordance with authorized purposes and applicable laws. •Maintain the structural and operational integrity of the project. •Avoid risk to public health and safety, life, and property. •Strike a balance among the use of water storage for multiple authorized purposes.

Current Reservoir Operation Lacks Flexibility to Leverage Forecasts

Currently, the amount of space in Oroville and New Bullards Bar reservoirs allocated for flood control varies seasonally, based on established precipitation and runoff patterns. During the summer, the reservoirs are allowed maximum storage for water supply and environmental purposes. In the fall they are drawn down gradually, as necessary to provide maximum flood space for the winter when flood risk is highest. In the spring, the reservoirs are gradually refilled. In addition, at Lake Oroville, the flood storage required depends on ground saturation represented by a “wetness index.” When flood space is encroached at the reservoirs, the water control manuals dictate that operators must evacuate flood space as quickly as possible without exceeding objective flows downstream or maximum rates of change in release magnitude. Although effective, the current operation rules lack flexibility to fully leverage forecasts in determining the use of flood storage space and the magnitude of releases. They also account for storage at Marysville Reservoir that is not available.

Opportunity for Modernization: Use of Current Forecast Technology

Advancement of forecast skill over the past 50 years presents the opportunity to explicitly incorporate probabilistic inflow forecasts into reservoir operation rules. For example, if the forecast shows a large event approaching,

MODERNIZING RESERVOIR OPERATION: USACE SACRAMENTO BEGINS UPDATE OF 50-YEAR-OLD OROVILLE AND NEW BULLARDS BAR WATER CONTROL MANUALS CONTINUED

reservoir releases can be made gradually in advance of peak inflow to more reliably and optimally attenuate peak outflow downstream, yielding greater flood control benefits. Conversely, in the spring, if no storms are forecast, runoff can be safely stored, yielding additional water supply reliability benefits. “The water control manuals from the ‘70s were based on hydrologic conditions and the state of technology at that time,” Greg Kukas, SPK Hydrology and Hydraulics Branch Chief, said. “We can now use forecast technology to make safe reservoir decisions long before water hits the ground.” SPK’s 2019 update of the Folsom Dam water control manual demonstrated this capability. SPK developed forecast-based operation rules for Folsom Dam that consider 1-, 2-, 3-, and 5-day forecast inflow volume to determine use of variable flood space and magnitude of releases. The Folsom water control manual update was the first water control manual to explicitly incorporate inflow forecasts into reservoir operation rules. A Folsom-like, forecast-based approach may be formulated for Oroville and New Bullards Bar. The operation would determine the following: Given the current storage and forecasted inflow, how much does the reservoir need to be evacuated below the maximum level, and at what rate, to meet desired objectives given estimated likelihoods of occurrence? Other alternative strategies incorporating use of forecasts may also be developed. Alternative development will require an iterative approach, where potential environmental effects and stakeholder concerns are identified, and the alternatives are tested and refined to yield performance within constraints. The operational flexibility provided by FIRO can minimize tradeoffs between optimal flood operation and operation for other authorized purposes.

Collaborative Partnership: The YubaFeather Forecast-Informed Reservoir Operation Program

SPK has partnered with the Yuba-Feather ForecastInformed Reservoir Operation (FIRO) Program for the Oroville and New Bullards Bar water control manual updates. The FIRO Program is a multiagency effort including participation by SPK, the USACE Engineer Research and Development Center, the National Weather Service California Nevada River Forecast Center, DWR, YWA, the Scripps Institution of Oceanography Center for Western Weather and Water Extremes, and others.

Similar to the “forecast-based operation” implemented at Folsom Dam, FIRO is “a reservoiroperations 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,” as defined by the American Meteorological Society (2021). The goals of the FIRO Program are closely related to the water control manual updates. The FIRO Program seeks to demonstrate the viability of FIRO at Oroville and New Bullards Bar dams, conduct research for future applications of FIRO, and identify investment opportunities over time to enhance FIRO. The FIRO Program includes research on atmospheric rivers, which generally fuel California’s largest storms (Dettinger et al. 2011).

This parallel effort presents the opportunity for close collaboration with the water control manual updates, marrying research and development with operations to develop the most effective solution for yielding public benefits.

Initial Project Accomplishments: CrossAgency, Cross-Program Planning

During the first year of the water control manual updates, SPK has laid the foundation for a successful project. SPK has focused on coordinating with the dam owners, DWR and YWA, and the FIRO Program. SPK has developed several management plans that reflect this coordination on project goals and objectives, analysis tasks, and schedules. SPK has also begun reviewing existing studies to leverage analyses already done for the Yuba-Feather watershed and filling information gaps. SPK is currently establishing flood risk management performance baselines resulting from existing operations and historical conditions.

In addition, SPK is planning its approach to environmental compliance. It is expected that SPK will work with DWR and YWA to develop joint National Environmental Policy Act/California Environmental Quality Act (NEPA/CEQA) documentation for each dam.

Path Forward: Collaborative Alternative Development

In 2021 and 2022, SPK will expand stakeholder outreach and begin to develop new alternative sets of release rules, with input from the FIRO Program analysis. Key items that will be addressed are:

•What are the flood risk management objectives for each dam? •How should performance against flood risk management objectives be measured? •Do operation alternatives provide resilience to climate change? •Besides enhancing flood control benefits, can operation alternatives enhance water supply

reliability or other benefits? •What potential environmental effects are of concern? •Pending additional funding, the end products of the effort will include: •A comprehensive engineering report describing alternative development and performance for each dam. •NEPA/CEQA documentation for each dam. •An updated water control manual for each dam that includes selected alternatives, reflects current data and information, and meets current USACE guidance. •An updated Sacramento River Basin Master

Manual of Reservoir Regulation (1959), to which the water control manuals are an appendix, that reflects current data and information and meets current USACE guidance. SPK plans to complete both water control manual updates by the end of 2024 in time for planned completion of New Bullards Bar secondary spillway construction.

References

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American Meteorological Society (2021). “Glossary of Meteorology.” https://glossary.ametsoc.org/wiki/Forecastinformed_reservoir_operations. Accessed Feb. 2021. Dettinger, M. D., Ralph, F. M., Das, T., Neiman, P. J., & Cayan, D. R. (2011). Atmospheric rivers, floods and the water resources of California. Water, 3(2), 445-478.

Authors

Joe Forbis: Chief, Water Management Section, U.S. Army Corps of Engineers, Sacramento District Jenny Fromm: Lead Water Manager, Water Management Section, U.S. Army Corps of Engineers, Sacramento District Donna Lee: Senior Project Manager, HDR Engineering, Inc. Nathan Pingel: Principal Hydrologic Engineer, HDR Engineering, Inc.

FMA BOARD AGENCY REPORT NOAA/NWS

Alan Haynes, Hydrologist in Charge, California Nevada River Forecast Center

Super Dry Water Year With Low Runoff Expected

Precipitation since the beginning of the Water Year (October 1st, 2020) has been very low over California and Nevada, with most areas receiving less than 50% of average (see Fig. 1). Precipitation deficits over the main water supply regions of Northern California, such as the coastal mountains, around Lake Shasta and the Northern Sierra, measure in the tens of inches, with some areas seeing departures greater than 40 inches for the water year so far.

Figure 1. The left panel shows the average water-year precipitation (since Oct. 1, 2020) to date (as of May 3rd, 2021). The middle panel shows observed water-year precipitation to date and the right panel shows the departure from average water-year precipitation to date.

The low amounts of precipitation this year also resulted in a low snowpack, which is expected to mostly melt off before June, with much of the runoff soaking into parched soils. Cumulative two-year runoff on the four rivers that comprise the Sacramento River Index (Sacramento, Feather, Yuba and American Rivers) is forecast to be near record low levels, second only to the 1976-1977 water years (see figure 2). By the end of the 2021 Water Year, the twoyear projected flow accumulation is forecast to be around 15.9-17.0 MAF, ranking WY2020-2021 drier than the WY2014-2015 accumulated flow. The average annual volume of water is 18.2 MAF; so essentially, we’ve lost over an entire year of runoff.