Event Title

Gravel Mobility in Regulated Rivers: Assessment and Issues in Planning Environmental Flows (Cconnected to the iUtah EPSCoR Effort)

Presenter Information

Suzanne Walther

Location

ECC 303/305

Event Website

http://water.usu.edu/

Start Date

4-4-2012 1:30 PM

End Date

4-4-2012 1:50 PM

Description

A relatively new approach to management of regulated rivers, particularly for salmon in the Pacific Northwest, is the use of environmental flows -- the management of dam releases to restore some elements of the pre-dam hydrograph to improve habitat (Risley et al., 2010). Several important criteria exist for environmental flows in salmon restoration including flows that will mobilize and clean spawning gravels, and flow-sediment supply combinations that will maintain channel morphology and bed characteristics. Understanding sediment size distributions and mobility on a river is instrumental in defining environmental flows. This paper presents the results on the discharge needed to move the D50 grain size on gravel bars on the lower McKenzie River, Oregon. We calculated the return interval of the discharge to evaluate the potential for mobility and achieve the stated management goals. Results show that the D50 of all of the bars are mobilized with 2-year to 5-year flows. However, uncertainties make simple, straight-forward recommendations difficult. We use field data, hydraulic modeling, and stream flow records to discuss the results and the issues involved in assessment with respect to their importance in environmental flow considerations.

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Apr 4th, 1:30 PM Apr 4th, 1:50 PM

Gravel Mobility in Regulated Rivers: Assessment and Issues in Planning Environmental Flows (Cconnected to the iUtah EPSCoR Effort)

ECC 303/305

A relatively new approach to management of regulated rivers, particularly for salmon in the Pacific Northwest, is the use of environmental flows -- the management of dam releases to restore some elements of the pre-dam hydrograph to improve habitat (Risley et al., 2010). Several important criteria exist for environmental flows in salmon restoration including flows that will mobilize and clean spawning gravels, and flow-sediment supply combinations that will maintain channel morphology and bed characteristics. Understanding sediment size distributions and mobility on a river is instrumental in defining environmental flows. This paper presents the results on the discharge needed to move the D50 grain size on gravel bars on the lower McKenzie River, Oregon. We calculated the return interval of the discharge to evaluate the potential for mobility and achieve the stated management goals. Results show that the D50 of all of the bars are mobilized with 2-year to 5-year flows. However, uncertainties make simple, straight-forward recommendations difficult. We use field data, hydraulic modeling, and stream flow records to discuss the results and the issues involved in assessment with respect to their importance in environmental flow considerations.

https://digitalcommons.usu.edu/runoff/2012/AllAbstracts/53