Environmental hedging: A theory and method for reconciling reservoir operations for downstream ecology and water supply

Abstract

Building reservoir release schedules to manage engineered river systems can involve costly trade‐offs between storing and releasing water. As a result, the design of release schedules requires metrics that quantify the benefit and damages created by releases to the downstream ecosystem. Such metrics should support making operational decisions under uncertain hydrologic conditions, including drought and flood seasons. This study addresses this need and develops a reservoir operation rule structure and method to maximize downstream environmental benefit while meeting human water demands. The result is a general approach for hedging downstream environmental objectives. A multistage stochastic mixed‐integer nonlinear program with Markov Chains, identifies optimal “environmental hedging,” releases to maximize environmental benefits subject to probabilistic seasonal hydrologic conditions, current, past, and future environmental demand, human water supply needs, infrastructure limitations, population dynamics, drought storage protection, and the river's carrying capacity. Environmental hedging “hedges bets” for drought by reducing releases for fish, sometimes intentionally killing some fish early to reduce the likelihood of large fish kills and storage crises later. This approach is applied to Folsom reservoir in California to support survival of fall‐run Chinook salmon in the lower American River for a range of carryover and initial storage cases. Benefit is measured in terms of fish survival; maintaining self‐sustaining native fish populations is a significant indicator of ecosystem function. Environmental hedging meets human demand and outperforms other operating rules, including the current Folsom operating strategy, based on metrics of fish extirpation and water supply reliability.

Climate-informed environmental inflows to revive a drying lake facing meteorological and anthropogenic droughts

“…The high water stress even during wet periods underscores the prevalence of a chronic anthropogenic drought. To cope with this situation, investigating an 'environmental hedging' approach guided by hydrologic and biologic forecasting (Adams et al 2017) may offer a practical strategy to facilitate progress towards ecological recovery of the lake while meeting human demands within the constraints of basin scale water availability and ecological functions of Lake Urmia.…”

Using river temperature to optimize fish incubation metabolism and survival: a case for mechanistic models

“…In summary, the models illustrated here highlight the importance of characterizing the biological and spatial/temporal details of fish early life growth and survival when developing temperature control programs for managed river systems. Characterizing and modeling biological responses for target species such as winter-run Chinook is essential for achieving efficient reservoir operations (Adams et al 2017).…”

Assessing the Potential of Agricultural Reservoirs as the Source of Environmental Flow

“…Reservoirs play an important role for water resources management by helping store rainwater received from their drainage areas and regulate downstream streamflow. Reservoir operation can alter downstream flow regimes and ecosystems [1][2][3]. Sustainable water resources management requires reservoirs to support both anthropogenic activities and the environment; however, the hydrological and social complexity involved in reservoir decision-making processes makes it challenging to optimize the trade-off between multiple water use objectives [1,4,5].…”

“…Reservoir operation can alter downstream flow regimes and ecosystems [1][2][3]. Sustainable water resources management requires reservoirs to support both anthropogenic activities and the environment; however, the hydrological and social complexity involved in reservoir decision-making processes makes it challenging to optimize the trade-off between multiple water use objectives [1,4,5]. Various reservoir operation models and strategies have been developed to guide reservoir-river management, but there is still substantial room for improvement in balancing between reservoirs' roles as the sources of water for agricultural water use and the environmental flow (EF) [1][2][3]6,7].…”