Reservoir reoperation for fish ecosystem restoration

March 26th, 2012

Dr. Yi-Chen E. Yang, University of Massachusetts & Dr. Ximing Cai, University of Illinois

Reservoirs have traditionally been designed for human purposes such as water supply, flood control, hydropower generation and recreation. Recently, environmental and ecological concerns, especially for fish communities since they are at the top of the aquatic food web, have brought up the possibility of reservoir reoperation; which is to revise reservoir operation rules to achieve a balance between the original purposes of a reservoir and the emerging ones, especially the restoration of natural flow regimes. However, reservoir reoperation may jeopardize the original objectives of the reservoir. Thus, determining how to resolve the conflict between the new (ecological) and original (human) objectives presents a critical question for reservoir reoperation.

Traditionally, a minimum water release from a reservoir is set to satisfy the downstream ecosystem flow requirement. Although this is the easiest and perhaps the most practical way, it may not be effective given the flow regime requirement for all downstream fish communities. Recently, the concept of ‘minimum water release’ has been replaced with the concept of ‘recovering natural flow regimes’ for downstream ecosystems1. In addition, fish community models that reflect how fish population structures change under different flow conditions can provide useful information for reservoir managers when incorporating ecosystem restoration into reservoir operations.

In a recent study2, we examined the practicalities of adding an ecological objective to the operation of Lake Shelbyville, a reservoir situated on the Kaskaskia River in east-central Illinois (Figure 1). This reservoir is operated by the U. S. Army Corps of Engineers (USACE) and has a total storage of 1,035,900 acre-ft. The current operation rules of the reservoir follow the USACE Lake Shelbyville water control plan3 and the primary objectives are: (1) reduction of flood-induced agricultural damage; (2) enhancement of recreational opportunities.

An ecological-hydrologic relationship between flow conditions and fish communities at the site was first identified using a fish community model4. The fish community model uses a data mining approach to link hydrological indicators with the fish diversity index. This model can be used to predict the possible fish diversity under different flow conditions.

A multi-objective optimization model was then developed to optimize the operation rules for two objectives: minimizing flood damage; and maximizing fish diversity for the downstream ecosystem, using daily inflows. The multi-objective genetic algorithm (MOGA) was used to solve this two-objective optimization problem. Meanwhile, a Monte Carlo simulation was conducted to handle the uncertainty involved in reservoir inflows. The modelling results were used to assess the impact of adding the ecological objective to the primary objective of the reservoir.

The objective values from the MOGA optimal solutions were compared to those taken from historical records (Figure 2a). Most of the historical results are close to non-inferior solutions, except for a couple of years with large floods (i.e. 1996 and 2002). In these cases, the historical releases resulted in much higher economic losses than the optimal releases based on the revised operation rules.

Figure 2b displays the solutions with total losses of less than $1 million within a year. The results of two particular years, which represent the optimum solutions with the given historical data in 20 years, are shown with triangles. Point A represents the solution of minimum economic loss and Point B represents the solution of maximum fish diversity over 20 years. Both points A and B are close to the x-axis (with low economic losses), which shows that the historical operations were dominated by the economic objective.

The MOGA optimal solutions reduce extreme flooding events although they may slightly increase flooding losses incurred during less severe events. The ecological objective leads to a reduction of the maximum allowable water release and an increase of the minimum water release. In general, adding the ecological objective to Lake Shelbyville’s operation does not jeopardize the primary flooding control objective and also improves downstream fish habitats. The robustness analysis through Monte Carlo simulations showed that the optimized operation rules are sensitive to water levels; the biased representation of the role of water level in the reservoir release function can cause the bias of water release from its optimal value.

Our study presents a method to improve conventional reservoir operation rules with consideration of both ecological and economic objectives. The method represents a possible alternative for reservoir managers to consider for future reservoir operation.

References:

1. Richter, B.D., Mathews, R., Harrison, D.L. and Wigington, R. (2003), ‘Ecologically sustainable water management: managing river flows for ecological integrity’, Ecological Applications, Vol. 13, No. 1, pp. 206-224.

2. Yang, Y. C. E. and Cai, X. (2011), ‘Reservoir Reoperation for Fish Ecosystem Restoration Using Daily Inflows – A Case Study of Lake Shelbyville’, Journal of Water Resources Planning and Management, Vol. 136, No. 6, pp. 470-480.

3. U.S. Army Corps of Engineers (USACE) (2008), Upper Mississippi River Basin Kaskaskia River Basin, Illinois Lake Shelbyville – Appendix A to Master Reservoir Regulation Manual, St. Louis District.

4. Yang, Y.C.E., Cai, X. and Herricks, E.E. (2008), ‘Identification of hydrologic indicators related to fish diversity and abundance: A data mining approach for fish community analysis’, Water Resources Research, Vol. 44, No. W04412, doi:10.1029/2006WR005764.

Dr. Yi-Chen E. Yang is a postdoctoral research scientist in the Department of Civil and Environmental Engineering at the University of Massachusetts, Amherst. He obtained his doctoral degree from University of Illinois at Urbana-Champaign in 2010. Dr. Yang can be contacted at yceyang@engin.umass.edu. Dr. Ximing Cai is Associate Professor in Ven Te Chow Hydrosystems Laboratory, Department of Civil and Environmental Engineering at University of Illinois, Urbana-Champaign. Dr. Cai can be contacted at xmcai@illinois.edu. The article is based on an original piece of research published in the Journal of Water Resources Planning and Management titled, ‘Reservoir Reoperation for Fish Ecosystem Restoration Using Daily InflowsCase Study of Lake Shelbyville‘.

The views expressed in this article belong to the individual authors and do not represent the views of the Global Water Forum, the UNESCO Chair in Water Economics and Transboundary Water Governance, UNESCO, the Australian National University, or any of the institutions to which the authors are associated. Please see the Global Water Forum terms and conditions here.