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Ecol Appl. 2020 Jan;30(1):e02005. doi: 10.1002/eap.2005. Epub 2019 Oct 18.

Designing flows to enhance ecosystem functioning in heavily altered rivers.

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Department of Fish, Wildlife and Conservation Biology and the Graduate Degree Program in Ecology, Colorado State University, 1474 Campus Delivery, Fort Collins, Colorado, 80523, USA.
Department of Biology and Graduate Degree Program in Ecology, Colorado State University, Fort Collins, Colorado, 80523, USA.
Institute for Applied Ecology, University of Canberra, Bruce, Australian Capital Territory, 2617, Australia.
Department of Civil and Environmental Engineering, Colorado State University, Fort Collins, Colorado, 80523, USA.
USDA Forest Service, National Stream and Aquatic Ecology Center, 2150 Center Ave, Fort Collins, Colorado, 80526, USA.
Corona Environmental Consulting, 357 McCaslin Blvd, Louisville, Colorado, 80027, USA.
U.S. Geological Survey, Fort Collins Science Center, 2150 Center Ave., Fort Collins, Colorado, 80526, USA.
The Nature Conservancy, 2424 Spruce St., Boulder, Colorado, 80302, USA.
Department of Bioagricultural Sciences and Pest Management, Colorado State University, 1177 Campus Delivery, Fort Collins, Colorado, 80523, USA.


More than a century of dam construction and water development in the western United States has led to extensive ecological alteration of rivers. Growing interest in improving river function is compelling practitioners to consider ecological restoration when managing dams and water extraction. We developed an Ecological Response Model (ERM) for the Cache la Poudre River, northern Colorado, USA, to illuminate effects of current and possible future water management and climate change. We used empirical data and modeled interactions among multiple ecosystem components to capture system-wide insights not possible with the unintegrated models commonly used in environmental assessments. The ERM results showed additional flow regime modification would further alter the structure and function of Poudre River aquatic and riparian ecosystems due to multiple and interacting stressors. Model predictions illustrated that specific peak flow magnitudes in spring and early summer are critical for substrate mobilization, dynamic channel morphology, and overbank flows, with strong subsequent effects on instream and riparian biota that varied seasonally and spatially, allowing exploration of nuanced management scenarios. Instream biological indicators benefitted from higher and more stable base flows and high peak flows, but stable base flows with low peak flows were only half as effective to increase indicators. Improving base flows while reducing peak flows, as currently proposed for the Cache la Poudre River, would further reduce ecosystem function. Modeling showed that even presently depleted annual flow volumes can achieve substantially different ecological outcomes in designed flow scenarios, while still supporting social demands. Model predictions demonstrated that implementing designed flows in a natural pattern, with attention to base and peak flows, may be needed to preserve or improve ecosystem function of the Poudre River. Improved regulatory policies would include preservation of ecosystem-level, flow-related processes and adaptive management when water development projects are considered.


NEPA policy change; algae; aquatic insects; channel geomorphology; climate change; designed flow regime; fish; hydrology; modeling; probabilistic Bayesian Network model; riparian community; water development


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