The HFE Page

High-Flow Experimental (HFE) Releases Purpose and Goal The purpose of HFEs is to determine if sandbar building during HFEs exceeds sandbar erosion during periods between HFEs, such that sandbar size can be increased or maintained over several years. LTEMP HFE Protocol As described in the LTEMP ROD, HFEs are experimental in nature and are designed to achieve a better understanding of whether, how, and when to incorporate high releases into future dam operations in a manner that maintains or improves beaches, sandbars, and associated habitat. The LTEMP HFE Protocol establishes a decision-making framework consisting of three components: (1) planning and budgeting, (2) modeling, and (3) decision and implementation. Under the LTEMP, HFE releases are restricted to limited periods of the year when the highest volumes of sediment are most likely available for building sandbars. Sediment-triggered HFEs may be made in spring (March or April) or fall (October or November; Figure 1). Fall extended-duration HFEs range from greater than 96 hr to 250 hr. Spring and fall HFEs that are not extended-duration range from less than 1 hr to 96 hr. Proactive HFEs may be implemented in spring or early summer (April, May or June), and have a duration range up to 24 hr. HFE magnitudes range from 31,500 cubic feet per second (cfs) to 45,000 cfs. The frequency of HFEs is determined by tributary sediment inputs, annual release volumes, resource conditions, and decisions of the Department. Extended-duration fall HFEs are limited to a frequency of 4 times total in the 20-year LTEMP period. HFE Sand Budget Model The LTEMP HFE Protocol uses predictive models to make recommendations for the magnitude and duration of potential HFEs using real-time measurements and models of sand inflow from the Paria River and forecasted hydrologic data to determine whether suitable sediment and hydrology conditions exist for a high-flow experimental release. A sand transport/budget model (Wright et al. 2010) was used to predict the mass of sand that would be transported by an HFE and to estimate if a proposed HFE would transport more or less sand than had been delivered from the Paria River to the Colorado River during the fall accounting period (July 1 to November 30). Only HFE durations that resulted in a “positive sand balance” were considered. Output of the modeling runs provides the initial recommendation for the magnitude and duration of the HFE. However, because modeling only considers a simple range of possible HFE peak magnitudes and durations, the Protocol includes a review of the model output that may modify the recommended HFE to benefit relevant resources. (2018 HFE Tech Team Report)

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Updates Sandbar volume 1990-2018 Rate of post-HFE beach erosion https://www.usbr.gov/uc/progact/amp/twg/2017-01-26-twg-meeting/AR3_Grams.pdf https://www.usbr.gov/uc/progact/amp/twg/2017-01-26-twg-meeting/AR3_Grams.pdf https://www.usbr.gov/uc/progact/amp/twg/2015-06-11-twg-meeting/Attach_02,.pdf https://www.usbr.gov/uc/progact/amp/twg/2016-02-26-twg-meeting/AR02_Grams.pdf 2024 LTEMP SEIS The 2024 LTEMP SEIS adjusted the semiannual sediment accounting period to an annual period (beginning July 1) with the option for a spring or fall HFE release, or both. If a sediment trigger is met, but an HFE release is not implemented in the fall or spring, rollover of sediment into the next accounting period is possible. Implementation of a fall HFE can occur in October or November. Spring implementation could occur from March through June, depending on resource conditions and the potential for implementation of the 2024 LTEMP SEIS cold-water alternatives that include flow spikes. [1] LTEMP Experimental Action: Sediment-Related Experimental Treatments (Table 2-2, pages 11-12) [2] Under Alternative D, the existing HFE protocol was updated and incorporated into the LTEMP process as specified in Appendix P of the FEIS. Changes to the existing protocol were related to implementation of the new HFEs that are included under Alternative D and an B-17 extension of the protocol to the end of the LTEMP period. This new protocol will replace the existing protocol when the LTEMP ROD is issued. Spring and fall HFEs will be implemented when triggered during the 20-year LTEMP period based on the estimated sand mass balance resulting from Paria River sediment inputs during the spring and fall accounting periods, and the dam release pattern during the accounting period. HFE releases will be 1 to 250 hr long and between 31,500 cfs and 45,000 cfs. Depending on the cumulative amount of sediment input from the Paria River during the spring (December 1 through June 30) or fall (July 1 through November 30) accounting periods and the expected accumulation of sand, the maximum possible magnitude and duration of HFE that would achieve a positive sand mass balance in Marble Canyon, as determined by modeling, will be implemented. Sand mass balance modeling will be used to ensure that the duration and magnitude of an HFE are best matched with the mass of sand present in the system during a particular release window. The magnitude and duration of HFEs will not affect the total annual release from Glen Canyon Dam. Reclamation will consider the total water to be released in the water year when determining the magnitude and duration of an HFE. [3] Sediment-Triggered Spring HFEs HFE window: Mar-Apr Up to 96 hrs Could begin after the first two years of LTEMP (start spring 2020), Not in the same water year as an extended-duration (>96 hr) fall HFE Proactive Spring HFEs Triggered by an annual release volume over 10.0 maf HFE window: Apr-Jun Up to 24 hrs Not in the same water year as a sediment-triggered spring HFE or an extended-duration (>96 hr) fall HFE Sediment-Triggered Fall HFEs HFE window: Oct-Nov Up to 96 hrs Extended-Duration Fall HFEs HFE window: Oct-Nov Up to 250 hrs The first test would be limited to 192 hrs No more than four during the 20-year LTEMP period

Links and Information USBR HFE Page GCMRC HFE Page The Sediment Page 2023 Proposal to Amend the High-Flow Experiment Protocol and Other Considerations Environmental Assessment for the Development and Implementation of a Protocol for High-flow Experimental Releases from Glen Canyon Dam, Arizona, 2011 - 2020 Technical Decision Memo: Establishment of Interim Operating Guidance for Glen Canyon Dam during Low Reservoir Levels at Lake Powell Fall HFEs may be connected to the recent increase in brown trout at Lees Ferry. Spring HFEs increase productivity of the aquatic foodbase. Fall HFEs do not appear to affect the long-term composition of the aquatic foodbase and may scour the foodbase prior to the winter non-growing season. HFEs do not appear to directly affect humpback chub or the rainbow trout fishery but there may be indirect affects tied to foodbase and trout production. Sediment Mass Balance for HFE considerations- Model explanation Rapid Response HFE Page Glen Canyon Dam Flow Experiments A 2023 Fall HFE was not conducted for lack of sediment The 2023 Spring HFE A 2022 Fall HFE was not conducted due to the discovery of smallmouth bass in Glen Canyon (1,600,000 mt) A 2022 Spring HFE was not conducted for lack of sediment A 2021 Fall HFE was not conducted due to low reservoir elevations (1,492,000 mt) A 2021 Spring HFE was not conducted for lack of sediment The 2021 Spring Disturbance Flow A 2020 Fall HFE was not conducted for lack of sediment A 2020 Spring HFE was not conducted for lack of sediment A 2019 Fall HFE was not conducted for lack of sediment The 2018 Fall HFE (60h) A 2017 Fall HFE was not conducted for lack of sediment The 2016 Fall HFE A 2015 Fall HFE was canceled due to the discovery of green sunfish in Glen Canyon The 2014 Fall HFE (1,213,000 mt) The 2013 Fall HFE (1,860,000 mt) The 2012 Fall HFE (slow downramp) The 2011 Equalization flows The 2009-11 Fall Steady Flow Experiment The 2008 Spring HFE The 2004 Fall HFE The 2000 Low Steady Summer Flow Experiment (LSSF) The 1997 Experimental Flows The 1996 Spring HFE The 1990-91 Experimental Flows The 1983-86 Floods The 1965 Reservoir Equalization and Channel Cleaning Floods Presentations and Papers 2023 HFE Protocol for Fall 2023 TWG HFE Protocol Motion April 2023 High-Flow Experiment (HFE) Preliminary Results Background Information for "Proposal to Amend the High-Flow Experiment (HFE) Protocol" Preliminary Field Report from the April High-Flow Experiment Proposal to Amend the High-Flow Experiment Protocol and Other Considerations Proposal to Amend the High-Flow Experiment Protocol and Other Considerations April 2023 High-Flow Experiment Preliminary Sandbar Results Preliminary Field Reports from the April High-Flow Experiment Charge to create a process to amend the HFE protocol Overview of Projects A, B, and L and Evaluation of High-Flow Experiments During Aridification Project B Overview and Evaluation of High-Flow Experiments During Aridification 2022 Evaluation of High-Flow Experiments under conditions of low flows and low reservoir elevations The Effects of High-flow Experiments and Dam Releases on Sandbar Erosion and Deposition in Marble and Grand Canyons 2021 Mueller and Grams, 2021, A morphodynamic model to evaluate long‐term sandbar rebuilding using controlled floods in the Grand Canyon: Geophysical Research Letters 2020 HFE Sediment Modeling Ecological Significance of Diminished Spring Freshets Evaluating the Frequency of Triggered Spring High Flow Experiments Assumed in the LTEMP Potential Spring High Flow Experiment – Status of Resources and Experimental Plan 2019 What’s Next? Key Uncertainties and Future HFE Design Presentation The Effects of High-flow Experiments on Sandbar Dynamics Presentation 2018 Geomorphic Changes to the River Channels and Flood Plains of the Colorado River System: The Planned and Unplanned Effects of Water Development High Flow Experiments PPT Discussion about the High Flow Experimental Design PPT GCWC LTEMP comments on springtime HFEs Evaluating the Frequency of Triggered Spring High Flow Experiments (HFEs) Assumed in the Long-Term Experimental and Management Plan PPT Considerations for Seasonal Scheduling of High Flow Experiments PPT Effects of HFEs on Growth and Population Dynamics of Rainbow Trout in Glen Canyon and Mable Canyon PPT Sandbars and Sediment Storage Marble and Grand Canyons: Response to Recent High-flow Experiments and Long-term Trends PPT Mueller et al., 2018, Variability in eddy sandbar dynamics during two decades of controlled flooding of the Colorado River in Grand Canyon: Sedimentary Geology, v. 363, p. 181-199 2017 Sandbars and Sediment Storage in Marble and Grand Canyons: Response to Recent High-flow Experiments and Long-term Trends PPT Boom-and-Bust Cycles in the Population of Rainbow Trout in Glen Canyon and Effect of Fall High Flow Experiments PPT 2016 The Grand Canyon Private Boater’s Association’s (GCPBA) comments regarding the recently concluded High Flow Experiment releases Science Behind High Flow Experiment Planning: From Chasing Storms in the Paria River to Serving Data on the Web Sand Trigger for High-flow Experimental Protocol Introduction of a Motion to TWG Regarding Clarification of the High Flows Protocol for Springtime HFEs: Draft for SCAHG Consideration and Review 2014 Modeling Long Term Effects of HFEs on Trout and HBC Minute 319/Pulse Flow Update on High Flow Experiments Released from Glen Canyon Dam 2013 Earth Magazine 2013 Releasing a flood of controversy on the Colorado River --This article sets the basis for the HFE, provides the history of past HFEs, and discusses the issues. HFE Protocol Decision Process Planning for a Fall HFE High Flow Experiment Update USGS Information and Results from HFE Lessons Learned from the First HFE Protocol Background on HFE Releases and Assessment of Success Background on High Flow Experimental Releases: Implementation Strategy and Assessment of Success 2012 General Science Plan for Monitoring and Research of a High-Flow Experimental Protocol at Glen Canyon Dam White Paper Dated Dec. 22, 2011, and PPT Update on High Flow Experiment PPT News Release Dated May 23, 2012, Subj: Salazar Announces Improvements to Glen Canyon Dam Operations to Restore High Flows and Native Fish in Grand Canyon Creation of DOI Leadership Team to Implement Actions Outlined in the Two Environmental Assessments Implementation of the HFE Protocol with Emphasis on Fall 2012 High Flow Experiment Modeling Process PPT Two Environmental Assessments Updates High-Flow Protocol Environmental Assessment PPT Final Biological Opinion on the Operation of Glen Canyon Dam Including High Flow Experiments and Non-Native Fish Control Memo Executive Summaries from the High-Flow Experiment EA and the Non-Native Fish Control EA 2011 Effects of Three High-Flow Experiments on the Colorado River Ecosystem Downstream from Glen Canyon Dam, Arizona Report on Two Environmental Assessments (EAs): Protocol for High-Flow Experimental Releases EA and Non-native Fish Control EA and PPTs Bureau of Reclamation Updates on Non-native Fish Control Environmental Assessment, High-Flow Protocol Environmental Assessment, and the Long-term Experimental and Management Plan PPT Report on Two Experimental Flow EAs: High-Flow Experimental Releases EA and Non-native Fish Control EA and PPTs Updates on USBR Environmental Documents PPT Briefing Memo, Subject: Summary of upcoming USGS circular on the results of three high-flow experiments released from Glen Canyon Dam, Arizona Circular 1366: Effects of Three High-Flow Experiments on the Colorado River Ecosystem Downstream from Glen Canyon Dam, Arizona USGS Fact Sheet: Three Experimental High-Flow Releases from Glen Canyon Dam, Arizona--Effects on Downstream Colorado River Ecosystem Bureau of Reclamation Updates PPT Sam's Questions: 1)Timing/Magnitude of Paria and LCR Floods?, and 2) Timing/Magnitude of Pre-Dam Colorado River Floods? PPT 2010 High Flow Experimental Protocol Environmental Assessment Update The Effects of Three Glen Canyon Dam High-Flow Experiments (HFE) on the Grand Canyon Ecosystem (HFE Synthesis) High Flow Experiment 2008 High-Flow Experiment at Glen Canyon Dam Benefits Colorado River Resources in Grand Canyon National Park (USGS Fact Sheet 2010-3009) 2008 High Flow Experimental Results PPT Open File Report 2010-1022: Riparian Response to the March 2008 Short-Duration, High-Flow Experiment--Implications of Timing and Frequency of Flood Disturbance on Nonnative Plant Establishment Along the Colorado River Below Glen Canyon Dam (prepared by Barbara Ralston) High Flow Experiment Protocol Development and Initiation of Public Scoping, Federal Register Notice Announcing Scoping, and Process/Schedule; Evaluating Effects of a High-Flow Event on Rainbow Trout Movement in Glen and Marble Canyons, Arizona, by Using Acoustic Telemetry and Relative Abundance Measures Federal Register Notice on HFE Protocol published December 31, 2010 2009 Grand Canyon Monitoring and Research Center Updates Grand Canyon Monitoring and Research Updates: Update on Reporting Schedule for the March 2008 High Flow Experimental Results and corresponding PPT Update on Sediment Inputs and 2008 High Flow PPT Grand Canyon Monitoring and Research Center (GCMRC) Update Water Quality and Sediment, 2008 High Flow Experiment, and Integrated Flow, Temperature, and Sediment Modeling PPT Grand Canyon Monitoring and Research Center updates by Program Managers 1997 The Colorado River in Grand Canyon: How Fast Does It Flow? 1996 Controlled Flooding of the Colorado River in Grand Canyon: The Rationale and Data-Collection Planned 2019 HFE Workshop In lieu of the motion by Recreational Fishing representatives proposed for this meeting, GCMRC has agreed to: (1) conduct a scientific assessment of the effects of past experimental high flows (including powerplant capacity flows) at Glen Canyon Dam on high valued resources of concern to the GCDAMP (i.e., recreational beaches, aquatic food base, rainbow trout fishery, hydropower, humpback chub and other native fish, and cultural resources); and (2) present initial findings in a written summary at the 2019 Annual Reporting Meeting and the March 2019 AMWG meeting for review and discussion. A next step would be for GCMRC to identify experimental flow options that would consider high valued resources of concern to the GCDAMP (defined above), fill critical data gaps, and reduce scientific uncertainties. [4] Extended abstracts from the science presentations given at the HFE Assessment segment of the March 2019 Annual Reporting Meeting 2015 HFE Synthesis Workshop GCDAMP High Flow Experiment Work Shop Introduction Hydrology and Sediment Transport Status and Trends of Sand in Glen, Marble, and Grand Canyons Operations and Hydropower HFE Impacts on Hualapai Lands Sand Resources and Monitoring at Archaeological Sites in Glen and Grand Canyon Big Flood, Small Flood, Spring Flood, Fall Flood: HFE Timing affects foodbase response in Lees Ferry Native and Nonnative Fishes in Glen, Marble and Grand Canyons 2010 HFE Workshop Sand Budget Modeling by Scott A. Wright Hydrologic Modeling by Katrina Grantz Biological Resources by Rich Valdez High Flows in Grand Canyon by Jack Schmidt Effects of the 2008 High Flow Experiment on Abundance, Growth, and Survival Rates of Early Life Stages of Rainbow Trout in the Lees Ferry Reach of the Colorado River by Josh Korman Glen Canyon Replacements and Maintendance by Max Spiker 2011 HFE Protocol EA Appendix A: Federal Register Notice Appendix B: Science Plan Appendix C: Biological Assessment Appendix D: Hydrologic Data Appendix E: Sediment Analysis Appendix F: Methods for Estimating the Impacts on Hydropower at GCD Appendix G: SHPO Letter Power Plant Capacity Flow Tests Habitat Maintenance Flow (HMF) – September 1997 Low Summer Steady Flow: April – September 2000; Included two powerplant-capacity flows, one in May and one in September California power emergencies 2000 - 2001: Included six powerplant capacity flows HFEs and the Colorado River Basin Project Act of 1968 One area that has been a source of recent discussion has been the question of planned high releases from Glen Canyon Dam for such purposes as "beach habitat building flows." The Department expects the AMWG to work and provide its recommendations within the following context. Since the GCPA is clear that it was not intended to modify the compacts or "the provisions of the Colorado River Storage Project Act of 1956 and the Colorado River Basin Project Act of 1968 that govern allocation, appropriation, development, and exportation of the waters of the Colorado River Basin" (GCPA, section 1802(b)), any operational changes under the auspices of the GCPA are clearly subordinate to and must fit within the constraints of those provisions. Historically, there have been differences of legal opinion over some related issues, such as whether releases of water above power plant capacity, if made for authorized purposes, can be considered as not constituting "spills" within the meaning of section 602(a) of the Colorado River Basin Project Act of 1968 and the Operating Criteria implemented pursuant to section 602, and more recently over whether the GCPA "amends" existing law by adding additional authorized purposes for the operation of Glen Canyon Dam. These legal issues have not been finally resolved, but given the limitations provided in the ROD, the Glen Canyon Dam operating criteria, and the 1996 agreement between the Department and the Basin States, it is believed that they have been adequately addressed. [5] Other Stuff Calculating the Cumulative Sand Load for an HFE Determine the amount of sand that has come in from the Paria River during the HFE Accounting Period you are interested in. Go to the Paria River gage at Lees Ferry and check the Cumulative Sand Load box and enter the dates of the HFE Accounting Period. Determine the amount of sand that has been transported out of Marble Canyon during the HFE accounting period by taking the lower bound value of the change in sand storage in Lower Marble Canyon and subtracting it from the lower bound value of the change in sand storage in Upper Marble Canyon. Subtract the amount of sand that has been transported out of Marble Canyon from the amount of sand that has come in from the Paria River and you get the amount of sand Reclamation uses for planning the HFE. Calculating Magnitude and Duration of an HFE Reclamation takes the amount of sand calculated above and subtracts the amount of sand that will be transported out of Marble Canyon between the time of the model run and the HFE. Reclamation then calculates the largest possible volume and duration release from the dam using the Scott Wright sediment transport model that does not result in a negative sand balance between the 30-mile gage and the LCR by the end of the accounting period. How much water can be released at Glen Canyon Dam? 8 generators = 31,500 cfs 4 bypass tubes = 15,000 cfs 2 spillways (require reservoir elevations above 3648') = up to 208,000 cfs How often would an HFE be triggered? (LTEMP Appendix P) Proactive Spring HFEs: 10% of years Sediment-triggered Spring HFEs: 26% of years Sediment-triggered Fall HFEs: 77% of years Extended-Duration Fall HFEs: 25% of years