That’s what makes rivers so valuable — both for fish and for energy.
A river is the concentrated water of a whole region as rain and snow across an entire basin becomes runoff, is funneled into cataracts, creeks and canyons, and collected into the narrow ribbon of a river channel (narrow in a relative sense — even a river channel several kilometers wide is incredibly narrow compared to its basin which may be hundreds of thousands of square kilometers in area).
Fishes use these concentrated pathways to move throughout a river basin—a fluvial highway network—their travel driven by shifting patterns of resource availability and water conditions. The highway network allows migratory fishes to access habitat types and capture productivity from throughout much of a river basin, rather than being restricted to the food and conditions of one place.
Hydropower also relies on these same concentrated pathways. Water is the “fuel” for hydropower and the river basin does all the work of delivering fuel to the power plant, with topography and gravity working together to shepherd far-flung water molecules into a concentrated pathway of power.
That’s what happens when the fish traveling the narrow ribbons collide with the structures designed to harness the concentrated pathways.
A recent paper in Science highlights this confrontation. In a Policy Forum article, Texas A&M fish biologist Kirk Winemiller and several dozen colleagues (including The Nature Conservancy’s Paulo Petry) describe the looming confrontation between hydropower and fish in three of the world’s great river basins: the Amazon, Congo, and Mekong.
Together, these basins hold one-third of world’s fish species, much of them endemic, along with some of the most important freshwater fish harvests in the world (with migratory fish generally representing the majority of harvests). Currently, these basins contain relatively few dams, but Winemiller et al. report that 450 hydropower dams are under construction or in the planning pipeline for the three basins. They review the multiple ways that dams cause losses of fish species and productivity—not just as barriers to migration but also by changing the flow patterns of a river, such as by capturing and storing the flood pulse that otherwise causes downstream rivers to swell, connecting the narrow ribbon of a river channel to the vast and productive floodplains that flank it.
Winemiller et al. suggest that project-level environmental review and mitigation cannot adequately produce balanced solutions between a basin’s ability to produce both fish and energy. Ultimately, they say, what is needed is “Integrative, strategic planning…applied at the basin scale, with the goal of finding balance between tapping hydropower potential and sustaining key natural resources.” The authors emphasize the importance of site selection and comparing alternative configurations for dam development.
Last year, The Nature Conservancy released a report that explored this recommended approach. In The Power of Rivers we produced analyses that demonstrate the potential benefits of integrative and basin-scale planning, examining alternative spatial configurations of dams within river basins and quantifying the tradeoffs between generating energy and maintaining free-flowing rivers.
For example, we compared 30 different configurations of how hydropower could be developed in Mexico’s Coatzacoalcos River basin. Several of these alternatives would develop between 70% and 80% of the basin’s total hydropower capacity (a high level because development almost never reaches 100%). We found that several of these high development scenarios would disconnect almost 70% of the basin’s channel network, leaving only 400 kilometers in a connected and free-flowing condition. However, other scenarios that avoided the dams which had the biggest impacts on connectivity could achieve the same energy generation but would disconnect only 30% of the channel network, meaning 70% (or 1,000 km) of the basin’s river channels could remain connected and free-flowing (Figure 1).
These results, and similar results from two other river basins, illustrate the clear benefit of moving beyond project-level planning, review and mitigation and toward understanding the cumulative impacts, tradeoffs, and opportunities that are revealed by considering an entire basin or system – an approach we call “Hydropower by Design.”
The benefits of widespread application of this approach could be huge. In The Power of Rivers we drew on a global database of planned dams (compiled by Christiane Zarfl and colleagues at the Leibniz-Institute of Freshwater Ecology and Inland Fisheries) and ran hundreds of thousands of scenarios for developing hydropower in river basins around the world, comparing business-as-usual development with “Hydropower by Design” scenarios.
Our results found that for the same level of energy development—a level that approached global projections for hydropower by 2050—Hydropower by Design scenarios could maintain 100,000 more kilometers of river in a free-flowing condition worldwide compared to business-as-usual approaches.
Finding solutions to achieve this potential for more balanced outcomes is urgent. Global hydropower capacity is projected to roughly double in the next few decades. In our report we calculated that if all the planned dams were built that there will be a global reduction in free-flowing rivers (river segments not affected by dams through fragmentation or flow alteration) of more than 300,000 kilometers, with dramatic declines in the river basins highlighted by Winemiller et al (Figure 2).
While hydropower development will always have impacts, the results in our report, along with analyses such as those by Ziv et al. for the Mekong, show that dramatically improved outcomes are possible through application of system-scale planning.
In many ways, the technical challenge is relatively easy. Aligning decision making around potential balanced solutions is far harder. For that we’ll need to go beyond concentration and confrontation and add one more word to the fish-energy vocabulary list.
There will always be a need for campaigns against dams with unacceptably high impacts. But, for conservation organizations, campaigns alone will not produce the widespread changes needed to achieve more balanced outcomes at a global scale. For that, we also need to work directly with those who plan, fund, build and operate hydropower dams and find collaborative solutions.
The Nature Conservancy is working in range of places, with diverse partners, to promote the kind of system-scale analyses and planning recommended by Winemiller et al. In Mexico, we are working with the Federal Commission for Electricity and other partners on basin-scale approaches to hydropower planning that balance energy generation with maintaining environmental and social resources. In Gabon we are collaborating with government agencies and providing them tools and methods to compare hydropower development scenarios to help them achieve their ambitious goals for both renewable energy expansion and conservation of ecosystems. With the International Hydropower Association and stakeholders from finance, government, industry and civil society we helped write the Hydropower Sustainable Assessment Protocol to provide a standardized tool for evaluating the relative sustainability of a hydropower project or system.
Achieving more balanced outcomes through system-scale planning won’t be easy, due to a lack of regulatory examples and structures, sector inertia and complexity, and political hurdles. These challenges are compounded in trans-boundary river basins such as the Amazon and Mekong. But based on the rate of hydropower expansion and where it’s happening—concentrated in basins where rivers support high biological diversity and are most closely linked to rural livelihoods and food sources—solutions are urgently needed. Science can point to better potential pathways, but only collaborative problem solving can deliver on that potential.