Rui Hui

Risk‐based planning analysis for a single levee

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Optimal Pre-storm Flood Hedging Releases for a Single Reservoir

Flood hedging reservoir operation is when a pre-storm release creates a small flood downstream to reduce the likelihood of a more damaging but uncertain larger flood in the future. Such pre-storm releases before a flood can increase reservoir storage capacity available to capture more severe flood flows, but also can immediately increase downstream flood damage and reduce stored water supply. This study develops an optimization model for pre-storm flood hedging releases and examines some necessary theoretical conditions for optimality, considering hydrologic uncertainty from flood forecasts and engineering uncertainty from flood failures. Theoretically, the ideal optimality condition for pre-storm flood hedging releases is where the current marginal damage from the hedging release equals the future expected marginal damage from storm releases. Additional water supply losses due to pre-storm releases tend to reduce pre-storm flood hedging releases. The overall flood damage cost to be minimized must be a convex function of pre-storm hedging releases for flood hedging to be optimal. Such convexity is determined by the overall flood risk together with the probability distribution of storm forecasts. Increasing the convexity of the failure probability function can induce more pre-storm hedging release. Categorized by flood risk likelihood downstream, forecasted storms that are large, but not yet overwhelming flood management systems, drive optimal flood hedging operation. A wide range of near-optimal hedging releases is observed in numerical examples, providing options for more rational water resources management decisions.

Flood Storage Allocation Rules for Parallel Reservoirs

AbstractOptimal operating policies have been derived for reservoirs in series and in parallel for various purposes, but little formal analysis has been done for flood operation of parallel reservoirs. For flood management, parallel reservoir releases should be managed together to reduce downstream peak flow and minimize flood damage. The optimal allocation of total available flood storage capacity among parallel reservoirs should have each reservoir’s flood storage allocation providing the same incremental reduction to downstream flood flows. This approach is developed mathematically and applied for deterministic and probabilistic inflows. The applicability and effectiveness of these derived flood storage allocation rules are demonstrated by the case study of Oroville Reservoir and New Bullards Bar Reservoir in California’s Sacramento River Basin with a single historical 1997 flood and an uncertain storm.

Optimal Flood Pre-Releases—Flood Hedging for a Single Reservoir

Hedging for flood reservoir operations involves making releases in advance of a storm to make additional storage capacity available in the reservoir, as a way of reducing the probability of more severe flooding. Such pre-releases can involve the likely loss of water which would have value for water supply and might also involve pre-releases large enough to create small floods or small increases in downstream levee failures under some conditions. This paper explores some sufficient theoretical conditions needed for flood hedging to be optimal. In all cases, a necessary condition for flood hedging is that the overall expected damage from flood pre-release decisions is convex. The convexity in flood risk can arise from convex levee failure probability function, convex flood damage functions, and the probability distribution of possible storms. Extremely large storms that overwhelm the systems, and small storms that are handled relatively easily, do not encourage flood hedging operations. The likelihood of intermediate storms that are large but not overwhelming, where the additional flood storage capacity from pre-releases is likely to reduce overall flood damage, drives the optimality of flood hedging pre-releases operations. The ideal theoretical condition for optimal flood hedging is that current marginal damages from pre-releases equal future marginal expected damages from later storm releases.

Developing a water-energy-GHG emissions modeling framework: Insights from an application to California's water system

Abstract Integrating processes of water and energy interdependence in water systems can improve the understanding of the tradeoffs between water and energy in management and policy. This study presents a development of an integrated water resources management model that includes water-related energy use and GHG emissions. We apply the model to a simplified representation of Californias water system. Accounting for water demands from cities, agriculture, environment and the energy sector, and combining a surface water management model with a simple groundwater model, the model optimizes water use across sectors during shortages from an economic perspective, calculating the associated energy use and electricity generation for each water demand. The results of Californias water system show that urban end-uses account for most GHG emissions of the entire water cycle, but large water conveyance produces significant peaks over the summer season. Different policy scenarios show the significant tradeoffs between water, energy, and GHG emissions.