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Sara Madison Alger

Utah State University | Graduate Student

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ABSTRACT:

Since the closing of Glen Canyon Dam, the clear waters of the Colorado River have stripped sediment from beaches and sandbars in the Grand Canyon. In an attempt to distribute sand to rebuild beaches, high flow experiments (HFE) have been conducted wherein large releases from Glen Canyon Dam are made over several days. The HFE events are timed to follow the summer/fall monsoon season when sand delivery from the Paria River is typically high given that the Paria is the primary source of sand to the Colorado River in Marble Canyon. Unrelated reservoir operating rules coordinate annual releases from Lake Powell so that the storage contents of Lakes Powell and Mead are equalized. If these “equalization flows” are released when there is relatively little sand supplied from the Paria River, they are likely to erode downstream sandbars, including those created by HFEs. Currently, there is no connection between the operations for reservoir equalization and for implementation of HFEs. Our analysis examines potential changes to the equalization protocols to explore whether equalization flows can be delayed to avoid releases that cause sandbar depletion. Results indicate that delaying equalization in favor of sediment supply results in some inequity for Lakes Powell and Mead, but the imbalance is less than anticipated and less than with no equalization present. Jointly considering sediment supply and equalization could help retain sediment within the Grand Canyon, however, even in years of sand load that meets the threshold for HFE experiments, the sediment supply may not be sufficient to balance out the volumes of equalization flows.

This data resource consists of the files used to support this work. The word document and the power point presentation present the results of this work. The folder CRSS contains two other folders. One folder, 'model' contains a saved version of the Colorado River Simulation System - a model that may be implemented in Riverware. This saved model includes slots corresponding to estimated sediment and slots generated by the implemented ruleset to govern equalization (Sediment Equalization Trigger, Years Without Sediment, 1-yr, 2-yr, 3-yr Equalization Delay). The 'ruleset' folder contains rulesets used in this analysis. There are four rulesets - each corresponding to scenarios run. The folder Data contains R code for running statistical analysis on input sediment data and flow data. The raw input files to run the code are included that correspond to natural flow inputs(obtained from the Bureau of Reclamation) and sand load from the Paria River (obtained from the Grand Canyon Monitoring and Research Center). The Results folder includes 1. a table of Estimated Summer Sandload and 2. a spreadsheet of CRSS results for the various scenarios run along with plots for comparing between them.

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ABSTRACT:

Since the closing of Glen Canyon Dam, the clear waters of the Colorado River have stripped sediment from beaches and sandbars in the Grand Canyon. In an attempt to distribute sand to rebuild beaches, high flow experiments (HFE) have been conducted wherein large releases from Glen Canyon Dam are made over several days. The HFE events are timed to follow the summer/fall monsoon season when sand delivery from the Paria River is typically high given that the Paria is the primary source of sand to the Colorado River in Marble Canyon. Unrelated reservoir operating rules coordinate annual releases from Lake Powell so that the storage contents of Lakes Powell and Mead are equalized. If these “equalization flows” are released when there is relatively little sand supplied from the Paria River, they are likely to erode downstream sandbars, including those created by HFEs. Currently, there is no connection between the operations for reservoir equalization and for implementation of HFEs. Our analysis examines potential changes to the equalization protocols to explore whether equalization flows can be delayed to avoid releases that cause sandbar depletion. Results indicate that delaying equalization in favor of sediment supply results in some inequity for Lakes Powell and Mead, but the imbalance is less than anticipated and less than with no equalization present. Jointly considering sediment supply and equalization could help retain sediment within the Grand Canyon, however, even in years of sand load that meets the threshold for HFE experiments, the sediment supply may not be sufficient to balance out the volumes of equalization flows.

This data resource consists of the files used to support this work. The word document and the power point presentation present the results of this work. The folder CRSS contains two other folders. One folder, 'model' contains a saved version of the Colorado River Simulation System - a model that may be implemented in Riverware. This saved model includes slots corresponding to estimated sediment and slots generated by the implemented ruleset to govern equalization (Sediment Equalization Trigger, Years Without Sediment, 1-yr, 2-yr, 3-yr Equalization Delay). The 'ruleset' folder contains rulesets used in this analysis. There are four rulesets - each corresponding to scenarios run. The folder Data contains R code for running statistical analysis on input sediment data and flow data. The raw input files to run the code are included that correspond to natural flow inputs(obtained from the Bureau of Reclamation) and sand load from the Paria River (obtained from the Grand Canyon Monitoring and Research Center). The Results folder includes 1. a table of Estimated Summer Sandload and 2. a spreadsheet of CRSS results for the various scenarios run along with plots for comparing between them.

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