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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, continues on next page FMA NEWS
