Why Do We Flood the Grand Canyon?
The Department of Interior forces 500,000 tons of sediment downstream to create back eddies and beaches, crucial to native fish species, campers and rafters.
At one time, the water from the Colorado River ran all the way to the Pacific Ocean. Then, in 1922, we reached an agreement with seven western states and Mexico to divvy up the water. We built damns on the river and its tributaries. By the 1990s, no water was making it to the ocean.
Millions of people benefited from the reserved water, but sandbars and along with it, fish disappeared.
In the 1990s the Department of the Interior decided to take action. They spent years preparing a strategy for high flows and massive floods along a stretch of the Colorado River in the Grand Canyon to reverse the trend.
Creating New Beaches by Flooding
The strategy is an effort to rebuild habitat by ultimately moving more than 500,000 metric tons of sediment downstream. While sediment used to flow more freely in the canyon, since the building of the Glen Canyon Dam in 1966, the only sediment sources now come from the Little Colorado and Paria rivers. The back eddies and beaches the flooding aims to create are necessary for native fish species, campers and rafters.
The first controlled flood came in 1996. More continued. In 2013, a massive surge of water and sediment from the Glen Canyon Dam took a week to travel through the canyon.
Did the Flooding Work?
At first glance, the floods appeared to have worked, as evidenced by the reappearance of sandy beaches more than 100 miles down from the Glen Canyon Dam; however Jack Schmidt, chief of the U.S. Geological Survey’s Grand Canyon Monitoring Center, points out more research will have to be done to tell for sure. In the past, test floods had unintended repercussions like increasing non-native, predatory trout populations. And, within a year the effects erode.
A 2015 study suggested that we are indeed restoring habitats. Many sandbars have increased in size following each controlled flood, and the cumulative results of the first three releases suggest that sandbar declines may be reversed if controlled floods can be implemented frequently enough.
Related:
Paddle Down the Colorado River Using Google Street View
Rivers in the Grand Canyon Region
Naming the Colorado River
Sources:
eos.org/features/building-sandbars-in-the-grand-canyon