Glen Canyon Dam
Long-Term Experimental and Management Plan

The Long-term Experimental and Management Plan provides a framework for adaptively managing Glen Canyon Dam operations and other management and experimental actions, consistent with the Grand Canyon Protection Act and other provisions of applicable Federal Law.


Current Focus: High-Flow Experiment

In August 2022, it was determined there is sufficient sediment in the Colorado River to trigger a fall High-Flow Experiment. As described in the Long-Term Experimental and Management Plan Record of Decision, HFEs are experimental in nature and are designed to achieve a better understanding of whether, how, and when to incorporate high flow releases into future dam operations in a manner that maintains or improves beaches, sandbars, and associated habitat.

Under the LTEMP ROD, the Department of the Interior may conduct flow-based experiments (HFEs, Bug Flows, Trout Management Flows, and Low Summer Flows) at Glen Canyon Dam when resource conditions warrant and if it is determined that there will not be unacceptable adverse impacts on other resources.

After careful assessment of resources and best available science, it was determined that a fall HFE will not be implemented.

Long-Term Experimental and Management Plan

The U.S. Department of the Interior (DOI), through the Bureau of Reclamation (Reclamation) and National Park Service (NPS) proposes to develop and implement a LongTerm Experimental and Management Plan for operations of Glen Canyon Dam, the largest unit of the Colorado River Storage Project (CRSP). The LTEMP would provide a framework for adaptively managing Glen Canyon Dam operations over the next 20 years consistent with the Grand Canyon Protection Act of 1992 (GCPA) and other provisions of applicable federal law. The LTEMP would determine specific options for dam operations, non-flow actions, and appropriate experimental and management actions that will meet the GCPA’s requirements and minimize impacts on resources within the area impacted by dam operations, commonly referred to as the Colorado River Ecosystem,1 including those of importance to American Indian Tribes.

The LTEMP Environmental Impact Statement (EIS) has been prepared to identify the potential environmental effects of implementing the proposed federal action. In addition, the EIS identifies and analyzes the environmental issues and consequences associated with taking no action, as well as a reasonable range of alternatives to no action for implementing the proposed federal action. The alternatives addressed in this EIS include a broad range of operations and experimental actions that together allow for a full evaluation of possible impacts of the proposed action. DOI, through Reclamation and NPS, has determined these alternatives represent a reasonable range of options that may meet the purpose, need, and objectives (as described below) of the proposed action. These alternatives include a broad range of operations and actions that would accomplish the proposed federal action. This EIS has been developed in accordance with the National Environmental Policy Act of 1969, as amended (NEPA), following implementing regulations developed by the President’s Council on Environmental Quality (CEQ) in Title 40, Code of Federal Regulations (CFR), Parts 1500 to 1508 and DOI regulations implementing NEPA in 43 CFR Part 46.

Glen Canyon Dam Long-Term Experimental and Management Plan EIS Documents

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High Flow Experimental Releases

The last High-Flow Experiment conducted by the Department of the Interior occurred during November 5-8, 2018. The HFE release included a peak flow of approximately 38,100 cubic feet per second for 60 hours (four days including ramping from baseflows to peak release) to move accumulated sediment downstream to help rebuild beaches and sandbars. This HFE release was the first to be conducted under the 2016 LTEMP HFE Protocol. Similar HFE releases were conducted in 2012, 2013, 2014 and 2016 in accordance with the 2011 HFE Environmental Assessment Protocol. The 2018 HFE release provided resource benefits and scientific information to be used in future decision making.

High Flow Experiment at Glen Canyon Dam

HFE releases are triggered based on sediment accumulation in the Colorado River. They are generally driven by storm activity resulting in floods in the Paria River that move sediment over time into the Colorado River. Each year HFE releases are evaluated and when conditions permit can be scheduled within two timeframes: in the spring from March through April and in the fall from October through November, per the 2016 LTEMP. Due to regional weather patterns and other factors, fall HFE releases are expected to be triggered more often than those in the spring. An accounting period for Paria River sediment inputs was determined in the LTEMP; if enough sediment enters the Colorado River from July-November, a fall HFE release may be planned and conducted. Due to logistical and operational constraints, the decision to conduct a fall HFE release is usually made in October rather than at the end of the fall accounting period.

The process for recommending experiments under the LTEMP, which has been used for past experiments, involves outreach to the Glen Canyon Dam Adaptive Management Program partners through regular meetings and additional notification to Tribes inviting consultation. The process also involves coordination to plan for the possible experiment, evaluate the status of resources, and make the technical recommendation whether to conduct an experiment. Ongoing research and monitoring through the Glen Canyon Dam Adaptive Management Program ensures the best science and data are available for making decisions related to flow experiments. The recommendation is then presented to the Department of the Interior for a final decision.

2022 HFE Documents

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Macroinvertebrate Production Flow (Bug Flows) Releases

At the recommendation of the Glen Canyon Dam Planning/Implementation Team (Technical Team), the Secretary's Designee issued a decision to implement experimental macroinvertebrate production flow (Bug Flows) at Glen Canyon Dam. The experiment began on May 1 and continued through August 31, 2022, this concluded the fourth Bug Flow under LTEMP.

aquatic insect eggs on a rock during a bug flow experiment
Midge flies (a non-biting aquatic winged insect) are an important food for fish in the Colorado River. The band of yellow on the rock in this image is midge eggs (family Chironomidae). As part of their life cycle, midge flies lay their eggs along the waterline so that eggs can stay wet before hatching into larvae, which live in the the river until forming a pupae and then hatching as winged insects. If the water level drops, the eggs dry out and do not hatch. Photo provided by Freshwaters Illustrated/USGS.

Bug Flows consist of steady weekend releases from Glen Canyon Dam and normal fluctuating releases during the weekdays. The steady weekend flows are expected to provide favorable conditions for aquatic insects to lay eggs along the Colorado River downstream of Glen Canyon Dam. The minimum flows on weekdays are designed to be similar to flows on the weekends. This flow regime would decrease how dramatically water levels change on the weekends, thus preventing the insect eggs that are laid along the river margins from drying out.

USGS and partners study aquatic insects in the Colorado River downstream of Glen Canyon Dam
USGS and partners study aquatic insects in the Colorado River downstream of
Glen Canyon Dam. Photo provided by Freshwaters Illustrated/USGS.

Technical experts at the U.S. Geological Survey’s (USGS) Grand Canyon Monitoring and Research Center (GCMRC) and Western Area Power Administration (WAPA) have coordinated the design of the experiment to optimize the benefits for insects throughout the Glen, Marble, and Grand Canyons while minimizing negative impacts to hydropower. The purpose of this experiment is to test the effectiveness of Bug Flows for improving insect production, and thus increase the availability of food for desired fish species including the endangered humpback chub (Gila cypha) and rainbow trout (Oncorhynchus mykiss), an important sportfish, as well as terrestrial wildlife like birds and bats.

Bug Flow experiments were implemented at Glen Canyon Dam from May through August for three consecutive years: 2018, 2019 and 2020, but were not implemented in 2021. Findings suggest that the previous Bug Flow experiments may have improved conditions for adult insects, increased the abundance of caddisflies river wide, and increased algae production. In addition, anglers captured more rainbow trout on average during Bug Flows than they did during typical fluctuating flow patterns. Contrary to predictions, no increase in the abundance of midge flies were observed during the first three years of the experiment. Scientists believe that further experimentation, research and monitoring may help to determine whether the Bug Flows experiment benefits native fishes in the Lees Ferry Reach below the Glen Canyon Dam and in the Grand Canyon. This experiment provides scientific information important to future decision-making.

The Glen Canyon Dam Implementation Team will closely monitor the condition of resources during the experiment and may terminate implementation at any time if unanticipated negative impacts are observed or are likely to occur due to ongoing drought and low lake levels.

2022 Macroinvertebrate Production Flow documents

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Last Updated: 11/1/22