Using Large-Scale Flow Experiments to Rehabilitate Colorado River Ecosystem Function in Grand Canyon: Basis for an Adaptive Climate-Resilient Strategy

Authored by: Theodore S. Melis , William E. Pine , Josh Korman , Michael D. Yard , Shaleen Jain , Roger S. Pulwarty

Water Policy and Planning

Print publication date:  June  2016
Online publication date:  June  2016

Print ISBN: 9781482227970
eBook ISBN: 9781482227987
Adobe ISBN:

10.1201/b19534-21

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Abstract

Adaptive management of Glen Canyon Dam is improving downstream resources of the Colorado River in Glen Canyon National Recreation Area and Grand Canyon National Park. The Glen Canyon Dam Adaptive Management Program (AMP), a federal advisory committee of 25 members with diverse special interests tasked to advise the US Department of the Interior, was established in 1997 in response to the 1992 Grand Canyon Protection Act. Adaptive management assumes that ecosystem responses to management policies are inherently complex and unpredictable, but that understanding and management can be improved through monitoring. Best known for its high-flow experiments intended to benefit physical and biological resources by simulating one aspect of pre-dam conditions—floods—the AMP promotes collaboration among tribal, recreation, hydropower, environmental, water, and other natural resource management interests. Monitoring has shown that high flow experiments move limited new tributary sand inputs below the dam from the bottom of the Colorado River to shorelines, rebuilding eroded sandbars that support camping areas and other natural and cultural resources. Spring-time high flows have also been shown to stimulate aquatic productivity by disturbing the river bed below the dam in Glen Canyon. Understanding of the responses of nonnative tailwater rainbow trout (Oncorhynchus mykiss) and downstream endangered humpback chub (Gila cypha) to dam operations has also increased, but this learning has mostly posed surprise adaptation opportunities to managers. Since reoperation of the dam to Modified Low Fluctuating Flows in 1996, rainbow trout now benefit from more stable daily flows and high spring releases, but possibly at a risk to humpback chub and other native fishes downstream. In contrast, humpback chub have so far proven robust to all flows, and native fish have increased under the combination of warmer river temperatures associated with reduced storage in Lake Powell and a systemwide reduction in trout from 2000 to 2006, possibly due to several years of natural reproduction under limited food supply. Uncertainties about dam operations and ecosystem responses remain, including how native and nonnative fish will interact and respond to possible increased river temperatures under drier basin conditions. Ongoing assessment of operating policies by the AMP’s diverse stakeholders represents a major commitment to the river’s valued resources, while surprise learning opportunities can also help identify a resilient climate-change strategy for co-managing nonnative and endangered native fish, sandbar habitats, and other river resources in a region with already complex and ever-increasing water demands.

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