A controlled flood along the Colorado River has replenished sandbars and campsites along the Grand Canyon this year.
The Bureau of Reclamation opened the bypass tubes at Glen Canyon Dam in April to release 40,000 cubic feet of water per second for 79 hours, more than doubling the regular flow.
This flood was part of an ongoing environmental mitigation program that began in the 1990s after the Grand Canyon Protection Act was passed. The goal is to mimic the natural annual floods that occurred before the dam was built, which would remake the sandbars and beaches along the river.
The flood moved over 800,000 tons of sediment from the Lees Ferry launch area and deposited new layers on 85% of the beaches monitored by U.S. Geological Survey cameras. While some erosion occurred later in the summer as water was sent downstream to Lake Mead, most beaches saw a net gain in sand this year.
The new sandbars and associated drifts provide thousands of river runners each year with campsites to secure boats and set up for the night. After years of erosion carved gullies into the remaining beaches, guides reported greatly improved conditions this season.
In addition to aiding recreation, the flood supported ecological restoration efforts. The high flow watered newly planted native cottonwoods at Paria Beach without uprooting them, helping the Grand Canyon Wildlands Council’s habitat restoration work.
While beneficial, these floods do incur costs, mainly from lost hydroelectric production when water bypasses the Glen Canyon Dam turbines. Lowering the water level in Lake Powell also risks future power shortages if drought persists and snowmelt cannot replenish the water supply.
However, the floodwaters continue downstream into Lake Mead for storage and use, rather than being truly lost.
Unlike a 2008 spring flood, this year’s event did not appear to increase the young rainbow trout population, which competes with endangered native fish like the humpback chub. Biologists believe differing seasonal timing and changed conditions from drought and warming may explain the varied impacts on trout.
Overall, periodic controlled flooding aims to restore some of the natural dynamics the Grand Canyon ecosystem relied on before the dam’s construction. This year’s flood seems to have succeeded in rebuilding beaches and sandbars along the Colorado River.
However, the long-term costs and benefits will continue being evaluated to strike the right balance.
Cover photo: A high-release experiment floods the Colorado River to benefit the ecosystem downstream in Grand Canyon National Park.