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A Literature Review and Hypsometric Analysis to Support Decisions on Trout Management Flows on the Colorado River Downstream from Glen Canyon Dam

Open-File Report 2024-1033
Prepared in cooperation with Ecometric Research Inc.
By: , , , , , and 
https://doi.org/10.3133/ofr20241033

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Executive Summary

Fish stranding has been studied in select rivers worldwide, often with the purpose of determining how to mitigate adverse effects of dam operations on highly valued salmon and trout populations. However, where a reduction in trout population size is desired by resource managers, as is the case downstream of the Glen Canyon Dam on the Colorado River, flow manipulations termed trout management flows (TMFs) may be used to optimize fish stranding and mortality. To inform the design and implementation of potential future TMFs, we reviewed relevant literature to identify key factors that influence fish stranding. We found that key factors were highly interdependent and site-specific, but general trends suggest that down-ramping (decreasing flow) at rapid rates in daytime during the late spring to summer emergence period would lead to stranding of age-0 rainbow trout in shallow shoreline habitat. A hypsometric analysis was then used to predict stranding risk for age-0 rainbow trout in Glen Canyon for a range of TMFs, which incorporated existing bathymetric data and flow and habitat suitability models. Our results indicate that a TMF with a steady high flow ranging from 12,000 to 16,000 cubic feet per second (ft3/s) combined with a minimum flow ranging from 3,000 to 5,000 ft3/s may effectively strand age-0 fish while also minimizing risk to water storage in Lake Powell and other resources. This strategy implemented under normal hydropeaking operations was predicted to lead to a substantive stranding risk when paired with low flows of 5,000 ft3/s, and especially 3,000 ft3/s. However, there remains uncertainty associated with elements of implementing an effective TMF downstream from Glen Canyon Dam. The main uncertainties include (1) the down-ramp rate that maximizes stranding of age-0 trout, (2) the duration of drawdown to maximize stranding mortality while minimizing impact to downstream resources, (3) duration of high flows required for age-0 fish to colonize newly created shoreline habitat (this is only for certain TMF hydrographs), (4) number of repetitions of TMF cycles to minimize compensatory survival response, and (5) recruitment threshold of both rainbow and brown trout populations to trigger TMF implementation.

Suggested Citation

Giardina, M., Korman, J., Yard, M.D., Wright, S., Kaplinski, M., and Bennett, G., 2024, A literature review and hypsometric analysis to support decisions on trout management flows on the Colorado River downstream from Glen Canyon Dam: U.S. Geological Survey Open-File Report 2024–1033, 50 p., https://doi.org/10.3133/ofr20241033.

ISSN: 2331-1258 (online)

Study Area

Table of Contents

  • Introduction
  • Literature Review
  • Hypsometric Analysis
  • Trout Management Flows Implementation and Considerations
  • References Cited
  • Appendix 1
Publication type Report
Publication Subtype USGS Numbered Series
Title A literature review and hypsometric analysis to support decisions on trout management flows on the Colorado River downstream from Glen Canyon Dam
Series title Open-File Report
Series number 2024-1033
DOI 10.3133/ofr20241033
Year Published 2024
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) California Water Science Center, Southwest Biological Science Center
Description Report: viii, 50 p.; Data Release
Country United States
State Arizona
Other Geospatial Colorado River, Glen Canyon
Online Only (Y/N) Y
Google Analytic Metrics Metrics page
Additional publication details