#ColoradoRiver: @USGS scientists hope to bolster aquatic insects below #GlenCanyonDam to fatten up trout #COriver

Glen Canyon Dam

From the Associated Press via The Cortez Journal:

Researchers with the U.S. Geological Survey are hoping a monthslong experiment to release low, steady flows of water from Glen Canyon Dam will give the eggs that bugs lay just below the water’s surface a better chance at survival. It starts this weekend…

Scientists are anticipating a 26 percent increase in black flies and midges by next summer, and the eventual return of bigger bugs seen in other stretches of the Colorado River that largely have disappeared from a prized fishery known as Lees Ferry. When insects thrive, so do fish, bats, birds and other predators, scientists say.

Insects attach their eggs to hard surfaces like rocks, wood or cattails near the river’s shore. Fluctuations in the water for hydropower create artificial tides that can expose the eggs and dry them out.

If they’re not back underwater within an hour, they die, said Jeff Muehlbauer, a research ecologist with the Geological Survey.

The so-called bug flows are part of a larger plan approved in late 2016 to manage operations at Glen Canyon Dam, which holds back Lake Powell. The plan allows for high flows to push sand built up in Colorado River tributaries through the Grand Canyon as well as other experiments with the flow that could help non-native trout.

“It’s an ongoing endeavor to understand first, what’s the status of all these different resources — the fish, the sandbars, the cultural resources — and then making adjustments based on how the ecosystem is changing,” John Hamill said, a volunteer with Trout Unlimited who helped work on the plan.

The flows won’t change the amount of water the U.S. Bureau of Reclamation must deliver to three states and Mexico. The lower water levels on the weekend would be offset by higher peak flows during the week, the agency said. Still, hydropower is expected to take a $335,000 hit.

From USBR (Marlon Duke):

The Department of the Interior will conduct the first experimental flow at Glen Canyon Dam since implementing its Long-Term Experimental and Management Plan (LTEMP) in 2016. The goal is to provide enhanced habitat for the lifecycle of aquatic insects that are the primary food source for fish in the Colorado River.

Experiments under LTEMP consist of four flow regimes: high flows, bug flows, trout management flows, and low summer flows. Collaborative discussions among technical experts resulted in a decision to begin this first experiment on May 1 and continue through August 31, 2018. It will slightly modify the schedule and flow rates of water releases from Lake Powell through Glen Canyon Dam, Arizona. The normally scheduled monthly and weekly release volumes will not be affected.

Flows during the experiment will include steady weekend water releases with routine hydropower production flows on weekdays that include normal hourly changes in release rates. Those steady weekend flows are expected to provide favorable conditions for aquatic insects to lay and cement their eggs to rocks, vegetation, and other materials near the river’s edge. Steady weekend flows will be relatively low, within four inches of typical weekday low water levels. It is unlikely casual recreational river users will notice the changes in water levels.

“Experiments like these are an important tool as we continue to work collaboratively to balance the need to deliver water and power resources with our obligation to actively preserve and protect the river system through Glen, Marble, and Grand canyons,” said Dr. Timothy Petty, Assistant Secretary for Water and Science. “We expect this experiment will positively benefit crucial insect populations, which will benefit the entire ecosystem while limiting the impact on other resources and Colorado River users.”

The decision to conduct this experiment was based on input from a collaborative team, including Department of the Interior agencies—Bureau of Reclamation, National Park Service, U.S. Geological Survey, U.S. Fish and Wildlife Service, Bureau of Indian Affairs—the Department of Energy’s Western Area Power Administration, six consulting American Indian Tribes, and all seven of the Colorado River Basin States. Before proceeding with these experiments, experts determined there would be no unacceptable adverse impacts on other resource conditions. Technical experts with the Department of the Interior have coordinated the experiment’s design to optimize benefits to the aquatic ecosystem throughout the Grand Canyon while meeting all water delivery requirements and minimizing negative impacts to hydropower production.

Insects expected to benefit from this experiment are an important food source for many species of fish, birds, and bats in the canyon. Beyond expected resource benefits, this experiment will also provide scientific information that will be used in future decision making.

For more information about flow volumes, please visit the following websites:

Hydrograph at Lees Ferry: https://www.gcmrc.gov/discharge_qw_sediment/station/GCDAMP/09380000

Lake Powell 40-day data (elevation, storage, inflows, and releases): https://www.usbr.gov/rsvrWater/rsv40Day.html?siteid=919&reservoirtype=Reservoir

The Bug Flow release pattern for May: https://www.usbr.gov/uc/water/crsp/studies/images/BugFlowExp-May2018.png

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