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# Interior Region 7 • Upper Colorado Basin

Encompassing all or parts of Arizona, Colorado, Idaho, Nevada, New Mexico, Texas, Utah and Wyoming

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            - Glen Canyon Dam Adaptive Management Program
            - Long-Term Experimental and Management Plan

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# 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.

Key Content                  - Long-Term Experimental and Management Plan
                  - High Flow Experimental Releases
                  - Macroinvertebrate Production Flow (Bug Flows) Releases

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## Current Focus: High-Flow Experiment

On March 29, 2024, Reclamation and the Grand Canyon Monitoring and Research Center determined that there is not sufficient sediment to support implementing an HFE at Glen Canyon Dam during the Spring 2024 planning window; therefore, an HFE will not be tested this Spring. This determination is based on the best available sediment and streamflow data and sand budget modeling to date. The determination that no HFE has been triggered this spring is made in accordance with the process for sediment related experiments described in the Glen Canyon Dam LTEMPROD.
                  - Insufficient Sediment to Trigger Implementation of a Spring 2024 High Flow Experiment at Glen Canyon Dam Notification Memo **Link is to a PDF file

**In-Depth**
                  - Bug Flow experiment to be conducted this summer under the Glen Canyon Dam Long-Term Experimental and Management Plan

### Related Projects & Facilities

                  - Colorado River Storage Project
                  - Glen Canyon Unit
                  - Glen Canyon Dam Operations
                  - Glen Canyon Dam Adaptive Management Program

### Related Links

                  - Grand Canyon Monitoring and Research Center **
                  - Grand Canyon Monitoring and Research Center – High Flow Experiments page **
                  - Predicted Shorelines for High Flows on the Colorado River **
                  - Grand Canyon National Park **
                  - Grand Canyon National Park – 2018 High Flow Experiment page **
                  - Glen Canyon National Recreation Area **

## 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

              - Record of Decision for the Glen Canyon Dam Long-Term Experimental and Management Plan Final Environmental Impact Statement
              - Glen Canyon Dam Long-Term Experimental and Management Plan Final Environmental Impact Statement

Return to Top **

## High Flow Experimental Releases

The last High-Flow Experiment conducted by the Department of the Interior occurred during April 24-27, 2023. Water releases from the dam during the 3-day spring flow experiment were as high as 39,500 cubic feet per second (cfs). High sediment loads in Marble Canyon and favorable hydrology conditions were present to support a spring experiment based on the analysis considered under the Long-Term Experimental and Management Plan, which allows for high-volume dam releases for sediment conservation. Five HFEs have been conducted since the High Flow Experiment Protocol was initiated in 2012. Those HFEs occurred in November 2012, 2013, 2014, 2016 and 2018. This was the first spring release implemented under the protocol.

### 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.

#### 2023 HFE Documents

              - Notification of Decision to Implement a Spring Flow Experiment at Glen Canyon Dam **Link is to a PDF file
              - HFE Spring 2023 Notification Letter **Link is to a PDF file

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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.

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. 

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

              - Press release
              - Technical Recommendation Report **Link is to a PDF file
              - Approval Memo **Link is to a PDF file

Return to Top **

*Last Updated: 4/10/24*

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