Photograph courtesy Peter Esselman, University of Michigan
Senior Advisor for Sustainable Hydropower, the Nature Conservancy
How can we know what a river needs to stay healthy when scientists have never studied that river?
That was our challenge on the Patuca River, the longest river in Honduras, and to date still running wild. But with a hydropower dam to be built within a few years, finding a way to answer this question was an urgent matter.
In 2006, the Honduran government approved a hydroelectric dam on this previously undammed river. Downstream of the proposed dam site stretches the largest wilderness in Central America, home to thousands of indigenous people living in dozens of communities along the Patuca. Because the people and ecosystems downstream depends on the vitality of the river, the government asked the Nature Conservancy to help it understand how the river could remain healthy.
As a scientist with the Conservancy, I work to identify the conditions that rivers require to remain healthy. We call these conditions “environmental flows,” a clinical term that simply describes a way to understand, measure, and articulate the dynamic features that make a river a river.
Throughout the year a river’s flow often varies dramatically from very low to very high. The periods of high flow can signal fish to migrate and spawn, connect the river to nearby wetlands, and deliver soil and nutrients to the floodplain. Scientists ask: How much water is needed in a river to perform these essential functions? At what time of year, and for how long?
Defining these environmental flow needs—and communicating them to the people who manage rivers and dams—is critical for maintaining healthy rivers in the face of all that society expects from them, including drinking water, navigation, electricity, fish, and recreation.
To determine environmental flows, scientists usually mine existing studies and data, deploy sophisticated tools and models, and synthesize the expert judgment of researchers and managers who are intimately familiar with the river in question.
But how can environmental flows be defined for rivers that lack all of these sources of scientific information and expertise? That was the challenge we faced on the Patuca.
With the dam’s initial design and other preparations well under way, we knew we had a small window of time to propose recommendations that could be incorporated into the dam’s operating plans. To compound the challenge, we had a modest budget and quickly learned that there were essentially no existing sources of data, studies, or scientific expertise.
Seeking a way forward, we soon realized that the people with the most at stake with any change in river flows—the indigenous communities—were also the people who could best answer questions about how the Patuca River really worked.
In collaboration with Honduran government agencies, we organized a boat tour of the Patuca. The expedition consisted of Honduran scientists and engineers and Pete Esselman, a fish biologist from the University of Michigan the Conservancy hired for this project.
Traveling in long dugout canoes, the expedition stopped at 11 communities along the river. At each, Dr. Esselman and the other scientists interviewed fishers, farmers, and boat drivers about how they used the river. They asked questions about which fish they caught and the crops they planted and how river levels—with flows varying dramatically across the year—influenced these activities.
Community members also drew maps depicting their homes, farm fields, and fishing spots. They then added lines representing the river levels at different times of the year. For example, the October river flow was shown to inundate bean fields, and the farmers noted that moderate flooding at that time of year, with the consequent depositing of nutrient-rich soil, was associated with ample harvests the following year.
From these maps and interviews we also learned how small floods at the beginning of the rainy season triggered spawning migrations for fish and how extreme low flows, exacerbated by excessive sedimentation in the river caused by land clearing upstream, impeded navigation.
We combined the information gleaned from the communities with hydrological analyses to develop a set of environmental flow recommendations for the Patuca River and then, with a simple spreadsheet model, demonstrated how the dam could effectively produce both hydropower and the recommended flow levels.
Translating these recommendations into the dam’s operating plans was cut short when the dam’s funding suddenly collapsed in 2009. However, we’ve now learned a great deal more about the Patuca and how the people who live along its banks depend upon it. This project also provided an example of how environmental flow recommendations can be developed for rivers with limited resources and scant existing information.
The loss of the dam’s funding also allows those who care about the Patuca to take a deep breath and to ask bigger questions about how to best balance the need for more energy with the values of free-flowing rivers. Although environmental flows can help maintain downstream ecosystems, they cannot address all the impacts from a dam. For example, high dams can block fish migrations, and some fish may require the habitat above a dam to spawn successfully. In terms of a dam’s environmental impact, the selection of where to locate a dam can be the most important decision. Now that the rush to harness the Patuca’s energy has momentarily paused, the Honduran government, scientists, and communities have a chance to consider a broader set of alternatives to determine how best to achieve sustainable energy development.
Jeff Opperman works for the Nature Conservancy to promote ecologically sustainable water management in river basins with hydropower infrastructure. Through this work, Jeff has provided strategic and scientific assistance to environmental flow assessments for several rivers in the U.S. and for the Patuca River in Honduras. Jeff serves on the governing board of the Low Impact Hydropower Institute and on the Technical Advisory Committee of the California Energy Commission’s Instream Flow Assessment Program. He also works to advance floodplain conservation and restoration and recently served on an Independent Review Panel that provided recommendations for floodplain management to California’s Department of Water Resources. Prior to joining the Conservancy, Jeff coordinated watershed assessment and riparian restoration projects, developed workshops and educational materials on stream management for landowners, and served as a consultant on environmental policy for foundations and conservation organizations.
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