Hydroelectric power is often touted as clean energy, but this claim is true only in the narrow sense of not causing air pollution. In many places, such as the U.S. East Coast, hydroelectric dams have damaged the ecological integrity of nearly every major river and have decimated runs of migratory fish.
This need not continue. Our rivers can be liberated from their concrete shackles, while also continuing to produce electricity at the site of former hydropower dams. How might that occur? A confluence of factors — the aging of many dams, the advent of industrial-scale alternative energy sources, and increasing recognition of the failure of traditional engineering approaches to sustain migratory fish populations — raises fresh possibilities for large rivers to continue to help provide power and simultaneously to have their biological legacies restored.
The answer may lie in “sharing” our dammed rivers, and the concept is straightforward. Remove aging hydroelectric dams, many of which produce relatively small amounts of electricity and are soon up for relicensing. When waters recede, rivers will occupy only part of the newly exposed reservoir bottoms. Let’s use these areas as a home for utility-scale photovoltaic (PV) and wind power installations, and let’s employ the existing power line infrastructure to the dams to connect the new solar and wind power facilities to the grid.
This vision both keeps the electricity flowing from these former hydropower sites, while helping to resurrect once-abundant fish runs, as has recently happened in Maine.
Fish access has a dismal record
More than a half-century of modern attempts to allow fish to traverse what often are sequences of dams that block access to their historical spawning reaches in eastern U.S. rivers presents a dismal record. Highly unnatural conveyances such as fish ladders are often only marginally helpful to fish on their upstream spawning runs, which is one reason why some migratory fish runs have fallen as much as five orders of magnitude.
Take Atlantic salmon, a revered game and food fish that once may have numbered a half million in U.S. rivers. In 2014, fewer than 400 attempted to reach their New England spawning grounds. Such relic populations are often protected from harvest, yet are still not meaningfully restored.
No other action can bring ecological integrity back to rivers as effectively as dam removal. Yet such efforts may come at the cost of a loss of hydropower. And so what many hoped would be a precedent-setting breaching of the Edwards Dam on Maine’s Kennebec River in 1999 — which had yielded only 3.5 megawatts of power — has not been followed by the dismantling of other, higher-wattage dams on the East Coast.
Yet the efficacy of dam removal to restore migratory fish was shown in the Kennebec after the Edwards Dam fell; for the first time in more than a century and a half, alewives, a species of herring, were able to access an upriver tributary, the Sebasticook. Within just a few years the Sebasticook’s run of alewives swelled from nonexistent to almost three million, supporting scores of bald eagles and an “alewife festival” that celebrates the Sebasticook’s extraordinary renewal.
Start by breaching aging dams
In “sharing” a river more equitably between energy production and its ecological imperatives, the critical step would be the breaching of existing dams. Though that may seem improvident — if not downright radical — it is important to remember that many of these concrete walls are middle-aged or older and will be reaching their life expectancies in the coming decades. Deteriorating dams are a serious public safety concern — one likely to increase as climate change generates more frequent and intense storms.
We believe the compelling ecological and impending structural reasons for dam removals should be considered in light of the rapidly evolving national energy landscape, and that together they signal exciting possibilities for a dramatically improved stewardship of major rivers. Fortunately, traditional hydropower facilities already offer the real estate that lies under reservoirs and existing electrical transmission lines that could be used by renewable energy sources.
In breaching a dam and draining a reservoir, substantial areas of land could become available for new uses. Take the Conowingo Dam in Maryland, for example. The Conowingo is the largest of four hydroelectric dams on the lower 55 miles of the Susquehanna River and sits only nine miles above the head of Chesapeake Bay. Its 572-megawatt capacity is fed by a 9,000-acre reservoir that also serves as an emergency water supply for Baltimore, and provides water for cooling intakes at the nearby Peach Bottom nuclear plant. The pool is also used by recreational boaters and fishers.
If the Conowingo Dam were removed, this would free up more than enough area to replace the lost hydroelectric generation with power from solar parks along the former reservoir bottom, and to allow for other land uses, such as creation of fringing wetlands and forests.
For comparative scale, California’s new 392-megawatt Ivanpah Solar Electric Generating System has three units occupying 3,500 acres. More sun shines on the Mojave than in the mid-Atlantic region, but according to the National Renewable Energy Laboratory calculator, acre for acre, the Conowingo region should support 76 percent of the power-generating capacity of the desert. Thus, about three-quarters of the river bottom would need to be in solar to match the output of Ivanpah.
One other issue facing the Conowingo Dam removal would be the sediments behind the dam that would need to be stabilized. The reservoir itself is close to capacity, and current plans are to dredge the pool, at an estimated cost of $48 million to $267 million annually. Those who are concerned for the ecological health of the Chesapeake Bay fear that if the dam is removed, millions of tons of sediment, enriched with nutrients and (potentially) toxic substances, could pour into the bay. But sediment stabilization is routinely done in dam removals and could be safely accomplished with careful design and engineering.
What about pushback from local residents?
Finally, what of the pushback by those who cherish the status quo? Few local residents were alive when the Conowingo Reservoir began filling in 1928, so the big pool is their cultural heritage. Surely any such drastic change would be hotly debated in many forums. But only a small number of houses exist on the 29 miles of shoreline that would be affected if the reservoir were removed.
The same issues were faced in the debates about removing mainstem dams in the Penobscot River in Maine, and eventually a consensus emerged there. Preservation of power generation (diverted to smaller tributaries) was important to closing the deal, and will likely be important in other cases. And although man-made reservoirs have their aficionados, rivers often have more of them — the scores who appreciate the fishing, paddling, and nature watching they provide. One study showed large economic benefits from the Edwards Dam removal.
And what about the nuclear plant and Baltimore’s emergency water supply? The Peach Bottom plant could install water-miserly, closed-cycle cooling towers, and Baltimore could still withdraw water from the Susquehanna in an emergency.
There are other potential tools available to help share rivers. Any remaining backwater ponds could be outfitted with floating solar panel arrays, as used successfully in Japan. Also, because reservoirs are nestled in valleys, in some instances the surrounding ridges might host wind turbines. Though combined alternative energy sources such as these might alone make up or exceed the original hydropower lost, “run of the river” hydropower — in which only a portion of the current is routed through turbines — could also contribute. But, critically, while generating some hydropower, the river’s mainstem would remain free-flowing, opening the way for resurgent fish migrations.
On the Penobscot River, the precedent of restoring a major river while maintaining equivalency of energy production was recently accomplished. This was done by increasing hydroelectric generation capacity on a set of tributaries while reopening the mainstem channel through dam removals and more effective fishways — thus returning nearly 1,000 miles of river habitat to eleven species of sea-run fish, including Atlantic salmon, sturgeon, and river herring.
Other once biologically productive New England rivers now clogged with multiple dams — such as the Kennebec, Merrimack, Connecticut, and Housatonic — could be prime candidates for some of these new ways of thinking about the future of rivers.
We need a dramatically different vision
Other innovative approaches could also be explored. The previously submerged but newly available riverfront property might be sold or transferred for conservation easements or for parks or even environmentally sensitive residential development. The revenue from these sales could be used for solar or wind projects in other promising but underutilized locations, such as landfills and urban brown fields.
A discussion of new strategies is timely because we are about to double-down on the flawed status quo. The Federal Energy Regulatory Commission will be evaluating many East Coast hydro dams for relicensing within the next few years — licensing that would lock in the failed fish passage paradigm for as much as an additional half-century.
As two conservation biologists who study rivers, we believe it’s time to explore a dramatically different vision. It may be that hydro companies should not continue to act as the gatekeepers for what could otherwise be healthy rivers brimming with life. Certainly, society requires electrical power, and rivers already are part of our grid. The way forward just may be to share a river more equitably between renewable energy production and its natural ecology.
Karin Limburg is a professor of environmental biology at SUNY’s College of Environmental Science and Forestry. John Waldman is a Queens College professor of biology. This post was originally published at Yale Environment 360.