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With blue skies above, white capped rapids below and the cliffs of the Grand Canyon on either side, Chris Konrad and a team of scientists spent two days rafting the Colorado at the speed of…sand?
Which is just the right pace to find out why endangered fish species are losing their homes, and beaches for outdoor recreation within the canyon are disappearing.
Konrad, a river scientist working jointly with The Nature Conservancy and the U.S. Geological Survey, took part in an experiment to learn more about the way dams are affecting the Grand Canyon.
Nature.org: What were you looking for during your trip down the Colorado?
Chris Konrad: We were trying to learn more about the disappearing sand bars in the canyon. Losing these sand bars means fewer beaches for people to use and dwindling habitat for fish species like the endangered humpback chub.
Historically, the Colorado River carried millions of tons of sand every year that built sand bars. But Arizona's Glen Canyon dam traps 90 percent of the sand supply to the Grand Canyon. Without an upstream source of sand to replace what the river carries away, beaches and shallow water habitats are slowly fading away.
Water managers are releasing high volumes of water from the dam as an experiment to mimic the natural phenomenon of building up the river banks. My colleagues at the USGS Grand Canyon Monitoring and Research Center invited me to join in one of their monitoring experiments to see if this method is working.
Nature.org: Why did you move so slowly down the river?
Chris Konrad: Because we stopped every 30-45 minutes to take samples of the water column — an arm-muscle-building exercise that involved cranking an 80 pound sampler by hand.
While our boatman tried to hold us in place against the rapids, each of us took turns carefully lowering and raising the sampler. Crank too slowly and the sampler filled up before making its entire trip through the water column. Hit the bottom with the sampler and it blew the whole sample. The steady tick-tick-tick of a metronome kept us on track.
We didn’t see too much during those two days — just the fantastic scenery, some science camps and a few recreational rafters and kayakers who lucked out in catching the high flow conditions that are rarely seen these days. We worked into the evening then camped out on the riverbank, pretty exhausted by the long day.
Nature.org: So is the releasing of water from the dam working to replenish some of the lost sand?
Chris Konrad: Preliminary results of this experiment show that more sand bars have been deposited further down the Colorado than in previous experiments, but we still have questions — namely, how long those sand bars will last.
Nature.org: Tell us more about dams — it sounds like they can really change a lot about a river.
Chris Konrad: Dams change rivers profoundly, but the effects go well beyond the river to floodplains, riparian areas and beyond.
Take the cottonwood tree. In the spring, these trees depend on flooding rivers to carry their seeds to places that are wet enough to germinate. Then seedlings rely on a river’s naturally gradual flow changes so they can take root.
Cottonwoods can have a difficult time along rivers that have been altered by dams, where stream flow fluctuates artificially to generate power or where large amounts of water are released for downstream irrigation demands in the summer. Their seeds may not reach a place to grow or young seedlings may be swept away in dam releases.
When dams store water, they change the way a river works. Dams can:
- Alter the seasonal timing of stream flow, which can impact plants and animals whose lifecycles are tied to natural flow patterns;
- Restrict the movement of sediment, which plants, fish and other life forms depend on, as well as the migratory path of species like salmon.
- Affect water quality — notably river water temperature. Changes in water temperature act as cues for a range of species, from insects to the fish. A dam’s disruption of these natural temperature patterns causes species to become far less successful in critical activities such as finding food and reproducing.
Nature.org: Rivers are clearly important. What are the biggest challenges to conserving them and maintaining their natural flows?
Chris Konrad: Rivers have always been important to people.
And the services they provide us — from drinking water to transportation to energy generation — are a result of natural stream flow patterns. But when we try to manage a river for only one of these services, like building a dam to store water, we lose the total package that a river provides when it flows its natural course.
We need to take a hard look at how we can manage river ecosystems for all of the services that they provide.
Also, we’re still trying to figure out how to manage water effectively for biodiversity in rivers, floodplains and estuaries. This is an area where scientific collaboration between the Conservancy and USGS makes a lot of sense — both organizations are dedicated to learning how precious water resources can be used most effectively for conservation.
Nature picture credits (top to bottom, left to right): Photo © Chris Konrad (Grand Canyon); Photo © Yao Yin (Chris Konrad).
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