The U.S. Interior Department is cranking up releases from Glen Canyon Dam this week as part of an ongoing experimental program to replenish downstream sandbars and beaches in the Grand Canyon.
September storms that drenched parts of the West washed bountiful amounts of sediment into two tributaries of the Colorado River below the dam, presenting a wealth of beach-building material that the flood-like high flows are intended to distribute.
The Grand Canyon desperately needs the sediment, which the department says could fill a football field 690 feet deep.
Since the construction of Glen Canyon Dam, which created Lake Powell, the natural transport of nutrient-rich sand and silt into the canyon has been blocked. Instead of nourishing beaches and sandbars and fish spawning grounds, the ruddy bits of eroded Colorado Plateau pile up year after year behind the dam.
That has transformed the canyon ecosystem, making the Colorado colder, clearer and less flood-prone than it was.
Sandbars and beaches that boaters use for camping have disappeared. The river is less hospitable to native fish species such as the humpback chub that depend on murky water to hide from predators.
Federal dam managers tried the first high-flow release in 1996 to redistribute sediment dumped into the Colorado by the Paria and Little Colorado rivers. But the newly deposited sand eroded within a couple of years.
They are now trying more frequent high-flow pulses, triggered by flushes of sediment into the tributaries, to see if the effects will be longer lasting.
The experimental releases, which will continue through 2020, change the rate of water deliveries from Lake Powell to Lake Mead downstream, but not the total volume.
The releases are made through large jet tubes that bypass the dam’s hydroelectric facilities. Managers planned to open the tubes today and close them Saturday morning.