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Restoring Rivers by Restoring Flooding

By Brian Richter, National Geographic

2278 days ago   Article ID# 1467050
Original URL


Nature Conservancy

NEW YORK, NEW YORK (National Geographic) - The Army Corps of Engineers is making floods.

It’s true. I’ve seen them doing it. They’ve been doing it for years. And it’s a very good thing for fish, frogs, mussels, wetlands, and local communities that depend on the bounty of healthy river systems and estuaries for their livelihoods and economies.

As part of a decade-long partnership called the Sustainable Rivers Project, the Corps and The Nature Conservancy are collaborating in eight river basins across the U.S. to modify dam operations for the benefit of downstream river and estuary health. In five of those basins – the Savannah River in Georgia and South Carolina, the Green River of Kentucky, the Bill Williams River of Arizona, the Big Cypress Bayou of Texas, and the Willamette River in Oregon – the Corps is releasing ‘designer floods’ from their dams.

You may be surprised to learn that floods can be good for people and nature. That’s not what you hear from a media fixated on death and destruction — and to be sure, big floods like last year’s on the Mississippi provide plenty of those stories.

But river scientists hold a different – or at least a more balanced — perspective of floods.

In muddy, raging floodwaters they see regeneration and growth. They see fish migrating and spawning, wetland plants and floodplain forests regenerating, aquatic habitats being formed and reshaped, and essential nutrients being carried into coastal estuaries during floods to nourish food chains and fisheries.

Floodplains and estuaries are the most productive ecosystems on Earth but their health and productivity depend entirely upon a good flood every now and then.

The more than 50,000 large dams built on the world’s rivers have been quite effective in dampening or completely eliminating all but the biggest floods. The aquatic life in dammed rivers has suffered greatly. Nearly 40% of US fish species are imperiled or extinct, and dams are a leading cause.

That’s why the Corps of Engineers, historically the biggest dam-builder in the U.S., is now in the business of making floods. They do it by intentionally releasing large volumes of water from their dams at specific times of the year to reinvigorate river ecosystems in a carefully controlled manner that promises maximum ecological benefit while avoiding damage to structures, roads, and farms.

Water Management for the 21st Century

The Sustainable Rivers Project epitomizes both the innovation and the novel partnerships that will be required to reduce conflicts and competition over water in coming decades.

In an editorial published last year in the Journal of Water Resources Planning and Management, two of my Nature Conservancy science colleagues and the director of the Corps’ Institute for Water Resources wrote: “The challenge of the 21st century is to make the most effective use of our legacy capital investment in water infrastructure by adjusting its design and operation to meet the needs of today and tomorrow.”

The authors pointed out that most of the Corp’s 600+ dams are more than 50 years old. Over that time period more than 300 million people were added to the U.S. population, and the values that Americans hold with respect to rivers have changed dramatically. In essence, we want to be supplied with water, electricity, and flood control but we also want fishing, wildlife-viewing, and beauty in our rivers.

Yet the Corps’ rule books – called “water-control plans” – for operating this water infrastructure have seldom been revisited or rewritten since the day the dams were built. The Sustainable Rivers Project presents an opportunity to take a fresh look.

If At First You Don’t Get It Right….

Scientists involved in ecosystem management often talk about the likelihood of surprises and the need to be ready to adaptively adjust your strategy when things don’t turn out the way you expected.

We were reminded of that philosophy on a beautiful sunny day on the Savannah River in March 2004.

As the Corps prepared to release its first-ever eco-flood, a crowd of curious onlookers was buzzing with excitement along the riverbanks. TV news reporters were busily interviewing the gathered dignitaries, including Lt. General Carl Strock, who was soon to take the helm of the Corps as Chief of Engineers. He was joined by business-suited executives of The Nature Conservancy for a milestone event in the then-nascent partnership.

The design of the flood released that day – its size, its timing, its duration – had been carefully designed over the course of more than a year with input from nearly 50 scientists and other technical experts. We wanted to enable young fish to swim into flooded swamps on the floodplain where they could grow more quickly. We wanted to disperse the seeds of bald cypress, tupelo, and other native hardwood trees throughout the floodplain so that they could better reproduce naturally; the riverside forest hadn’t been regenerating for decades since the upstream dams were built.

Perhaps most importantly we wanted to provide a water pulse to stimulate endangered sturgeon to migrate upstream to their spawning shoals.

Out on the Savannah River, boatloads full of fish biologists tuned their transmitters for signs of the sturgeon that had been implanted with tiny radio tags so that their movements could be tracked during the flood.

As the frothy brown water of the flood of dreams came rushing downstream, we could see a look of bewilderment in the faces of the biologists. One yelled from his boat to a colleague within earshot, “What’s going on?!”

The sturgeon, instead of making a lover’s dash for the upstream shoals, had turned downstream.

One of the biologists dropped his face into his hands in anguish. The water released from the bowels of Thurmond Dam upstream was way too cold and the sturgeon had literally gone frigid. You could almost hear the distraught biologist say it: “Duh.”

We’re Getting Better Every Year

Our first flood experiment on the Savannah, and virtually every other attempt to provide ecologically beneficial releases from dams such as the well-publicized flood releases in the Grand Canyon, have taught us a great deal (hint: wait until the water warms up in the reservoir before flushing it downstream). What matters is that we keep trying, and we’re getting better.

Nature Conservancy scientists have taken the lessons learned from the Savannah and other SRP experiences to far-distant rivers like the Rio Patuca in Honduras and the Yangtze in China.

Since the Big Disappointment on the Savannah, river scientists around the world have documented many important successes in their dam-release experiments: increased native fish spawning in the Colorado River in the Grand Canyon below Glen Canyon Dam; expansion of wetland and riparian vegetation on the Bill Williams River in Arizona; increases in fishery production and waterfowl breeding on the Senegal in Mauritania; decreases in non-native predatory fish in the San Juan of Utah.

The list is long, and it gets longer every year.

Copyright 2018 National Geographic   (Copyright Terms)
Updated 2278 days ago   Article ID# 1467050

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