Difference between revisions of "A 2021 Fall HFE"

Revision as of 16:57, 20 October 2021

High Flow Experiment- 2021

2021 Fall High Flow Experiment Snapshot

The PI Team has worked over the past several weeks to evaluate existing data and coordinate the potential implementation of an HFE. The PI Team evaluated the latest data from agency experts, and considered multiple issues in making its recommendation, as summarized below. The PI Team arrived at this recommendation after several weeks of PI Team conference calls, and after receiving feedback from Adaptive Management Program stakeholders. The Secretary of the Interior and/or her Designee will consider the recommendation of the PI Team, but retains sole discretion to decide how best to accomplish operations and experiments in any given year pursuant to the 2016 LTEMP ROD and other binding obligations for Glen Canyon Dam. The PI Team incorporated the most current science and data and considered multiple issues with agency experts, as summarized below, in making this final recommendation.

192-hour Extended Duration Fall HFE

The PI Team arrived at this recommendation after several weeks of PI Team conference calls, and after receiving feedback from Adaptive Management Program stakeholders. By consensus, the PI Team is opposed to recommending that the Department implement a 192-hour extended duration HFE in fall 2021. The PI Team identified the following resource concerns associated with a 192-hour extended duration fall HFE: challenges and risks associated with reallocating a large volume of water (415 kaf) while meeting hourly, daily and monthly operating objectives identified in the LTEMP ROD and consistent with a 7.48 maf annual release pattern; uncertainties and risks associated with exacerbating low reservoir elevations (e.g. additional days below 3,525 ft, lower annual minimum); the strain on the already low status for the Basin Fund as projected by WAPA; and potential impacts to non-native fish, including increased brown trout immigration to Lees Ferry and increased risk of fish entrainment at lower reservoir elevations. PI Team members highlighted uncertainties regarding Glen Canyon Dam’s ability to reliably and effectively deliver water and generate power when pool elevation drops below 3,525 ft. Further, a highly anticipated spring HFE, if triggered, would be prohibited from occurring in the same water year as an extended duration HFE.

60-hour Fall HFE

Technical representatives were divided in the assessment of a shorter duration 60-hour HFE, having evaluated the alternative for its ability to reduce negative resource impacts while still providing sufficient benefit to the sediment resource in terms of learning and effectiveness. The majority of representatives on the PI Team are opposed to recommending that the Department implement a 60-hour HFE this fall, several members support recommending that the Department implement a 60-hour duration HFE this fall, and two members (WAPA and AGFD) have abstained from making a recommendation. PI Team representatives opposed to a 60-hour HFE include all seven Basin States (AZDWR, CA, CO, NM, UT, WY, NV), UCRC, and Reclamation. Those opposed to implementing a shorter duration HFE this fall indicated that the reduced duration did not sufficiently address all unacceptable adverse impacts to resources identified above (low pool elevation, Basin Fund status). They also expressed concern that potential benefits to the sediment resource would not outweigh potential adverse impacts. PI Team members again highlighted uncertainties regarding Glen Canyon Dam’s ability to reliably and effectively deliver water and generate power when pool elevation drops below 3,525 ft.

Those that support or that do not oppose implementation of a 60-hour HFE include BIA, NPS, USGS, and USFWS. PI Team members in favor of an HFE cited the much-needed sediment resource benefits from a fall HFE and included this option as a potential compromise for the Leadership Team to consider that addresses both concerns expressed while still providing benefits to sediment (predicted +30% sandbar size in November 2021 relative to October 2021). They also noted that, in LTEMP, fall HFEs were predicted to be conducted frequently (~3 out of every 4 years) and it has been three years since the most recent HFE (fall 2018) was triggered and implemented, such that this HFE would rebuild some of the beaches that were lost during this time. GMCRC noted that sandbar benefits from a 60-hour HFE would likely be greater in Marble Canyon, but would result in sandbar deposition throughout Marble Canyon and Grand Canyon. It was noted that maintaining camping beaches is important for the LTEMP sediment resource goal. Also noted is the potential for improved legacy of sandbar increases resulting from a fall HFE (predicted +20% sandbar size in April 2022 relative to October 2021) due to relatively low winter flows consistent with the 7.48 maf annual release pattern planned for Lake Powell in Water Year (WY) 2022. The GCMRC highlighted the learning value of implementing an HFE in November 2021 in that it would contribute to addressing, 1) the long-term question about the cumulative effect of multiple HFEs over the 20-year period of the LTEMP, and 2) questions about the potential combined effects of HFEs and riparian vegetation management for sand storage in aeolian dunefields covering archaeological sites. Although the best available science indicates a fall HFE may result in small benefits to undesired non-native species, these effects were highly uncertain (see rainbow trout section below) or the marginal impact was expected to be small (see brown trout section). Thus, expert opinion among fishery biologists was that a 60 hour fall HFE would not substantively increase risk to endangered and native fishes in Grand Canyon above the existing level of risk. Media:2021.09.28 - FINAL TechReport - Fall 2021 HFE Recommendation.pdf

Sediment Conditions

Winter Accounting Period

• Paria input (Jul 1 to Nov 30):
• Evacuated from Upper Marble Canyon (Jul 1 to Nov 30, lower bound) =
• Evacuated from Lower Marble Canyon (Jul 1 to Nov 30, lower bound) =
• Available for Fall HFE:

SUPPORTING DOCUMENTS

• FINAL Tech Report - Fall 2021 HFE Recommendation

COMPLIANCE

CONCERNS

ADDITIONAL

A November 2021 High Flow Experiment is being considered by the Glen Canyon Dam Planning and Implementation Team. In early October, the Secretary of the Interior (or her Designee) will decide whether to implement a fall HFE following careful consideration of the Team's technical recommendation.

Under the 2016 Long-Term Experimental and Management Plan Record of Decision, HFE releases are triggered by substantial sediment accumulation in the Colorado River below Glen Canyon Dam. Monsoonal flooding in the Paria River near Lees Ferry moves sediment into the Colorado River, where its accumulation is carefully monitored by the U.S. Geological Survey. When implemented, high flows carry and redistribute the sediment throughout the canyon above the typical high-water mark.

Per the 2016 ROD, HFEs releases can occur either in the spring from March through June (spring HFE), or in the fall from October through November (fall HFE). If enough sediment enters the Colorado River from July to November, a fall HFEs release can be implemented. The decision to conduct a fall HFE release is usually made in October based on sediment accumulation, as well as a variety of other resource conditions.

No HFEs were conducted in calendar year 2019 or 2020, though a Spring Disturbance Flow was implemented in March 2021. The Department of the Interior conducted the most recent HFE release from Glen Canyon Dam on 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-up 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. [1]