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

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.

[1]  Chris J. Johnson,et al.  Temperature and Flow Effects on Migration Timing of Chinook Salmon Smolts , 2009 .

[2]  Charles S. Revelle,et al.  Optimizing Reservoir Resources: Including a New Model for Reservoir Reliability , 1999 .

[3]  J. Stedinger,et al.  Water resource systems planning and analysis , 1981 .

[4]  Michael J. Sale,et al.  An approach to optimizing reservoir operation for downstream aquatic resources , 1982 .

[5]  Henriette I. Jager,et al.  Thinking outside the channel: Timing pulse flows to benefit salmon via indirect pathways , 2014 .

[6]  J. Lund,et al.  Optimal Flood Pre-Releases—Flood Hedging for a Single Reservoir , 2015 .

[7]  R. Sparks,et al.  THE NATURAL FLOW REGIME. A PARADIGM FOR RIVER CONSERVATION AND RESTORATION , 1997 .

[8]  L. Blaney,et al.  Water Resources Control Board , 1995 .

[9]  R. Vogel,et al.  Relations among storage, yield, and instream flow , 2007 .

[10]  R. Sparks,et al.  The Natural Flow Regime , 2006 .

[11]  Maynard M. Hufschmidt,et al.  11. Resource Systems by Simulation Analyses , 1962 .

[12]  M. Bayazit,et al.  Effects of hedging on reservoir performance , 1990 .

[13]  William W.-G. Yeh,et al.  Reservoir Management and Operations Models: A State‐of‐the‐Art Review , 1985 .

[14]  Dong Wang,et al.  Assessment of the flow regime alterations in the middle reach of the Yangtze River associated with dam construction: potential ecological implications , 2016 .

[15]  J. Lund,et al.  Optimal Hedging and Carryover Storage Value , 2004 .

[16]  Hal E. Cardwell,et al.  Designing Instream Flows to Satisfy Fish and Human Water Needs , 1996 .

[17]  Henriette I. Jager,et al.  Designing Optimal Flow Patterns for Fall Chinook Salmon in a Central Valley, California, River , 2003 .

[18]  Richard M. Vogel,et al.  An Optimization Approach for Balancing Human and Ecological Flow Needs , 2005 .

[19]  J. Lund,et al.  FISH HABITAT OPTIMIZATION TO PRIORITIZE RIVER RESTORATION DECISIONS , 2012 .

[20]  M. Bradford.  Comparative review of Pacific salmon survival rates , 1995 .

[21]  Daniel P. Loucks,et al.  Reliability, resiliency, and vulnerability criteria for water resource system performance evaluation , 1982 .

[22]  M. Freeman.  Environmental Flows: Saving Rivers in the Third Millennium. , 2013 .

[23]  G. A. Thomas,et al.  Restoring Environmental Flows by Modifying Dam Operations , 2007 .

[24]  W. V. Winkle,et al.  Modelling the linkages between flow management and salmon recruitment in rivers , 1997 .

[25]  Jay R. Lund,et al.  Operating Rule Optimization for Missouri River Reservoir System , 1996 .

[26]  C. Harman,et al.  Optimizing dam release rules to meet environmental flow targets , 2005 .

[27]  Francesco Gallerano,et al.  Multi-objective analysis of dam release flows in rivers downstream from hydropower reservoirs , 2012 .

[28]  Ximing Cai,et al.  Hedging rule for reservoir operations: 2. A numerical model , 2008 .

[29]  David E. Rosenberg,et al.  Hydro-economic models: concepts, design, applications, and future prospects. , 2009 .

[30]  R. Tharme.  A global perspective on environmental flow assessment: emerging trends in the development and application of environmental flow methodologies for rivers , 2003 .

[31]  John G. Williams.  Central Valley Salmon: A Perspective on Chinook and Steelhead in the Central Valley of California , 2006 .

[32]  J. Wayland Eheart,et al.  Reservoir management to balance ecosystem and human needs: Incorporating the paradigm of the ecological flow regime , 2006 .

[33]  John W. Labadie,et al.  Optimal Operation of Multireservoir Systems: State-of-the-Art Review , 2004 .

[34]  V. Klemeš.  Value of information in reservoir optimization , 1977 .

[35]  J. Choo.  Potential ecological implications of human entomophagy by subsistence groups of the Neotropics , 2008 .

[36]  Ximing Cai,et al.  Hedging rule for reservoir operations: 1. A theoretical analysis , 2008 .

[37]  Ximing Cai,et al.  Reservoir Reoperation for Fish Ecosystem Restoration Using Daily Inflows—Case Study of Lake Shelbyville , 2011 .

[38]  N. LeRoy Poff,et al.  The ecological limits of hydrologic alteration (ELOHA): a new framework for developing regional environmental flow standards , 2007 .