Event Title

Concurrent Sessions A: Dam Removal II - Physical and Biological Responses to Dam Removal: Evidence Against Small Dam Removal as an Ecological Disturbance

Location

Construction & Engineering Hall, Oregon State University

Start Date

25-6-2013 1:30 PM

End Date

25-6-2013 1:50 PM

Description

Managers and the public both regularly express concern regarding biological consequences of the pulse release of sediment associated with dam removal. However, limited field data exists against which concerns regarding biophysical responses to and recovery from dam removals can be evaluated. Thus, this study documents an investigation of responses to small dam removal, with emphasis on the parallel concept of disturbance in geomorphology and ecology of rivers. This presentation includes results from analysis of field observations at the Brownsville Dam, Calapooia River (height = 2.5 m, D50 = 59 m) and the Savage Rapids Dam, Rogue River (height = 12 m, D50 = 8 m). Field surveys of channel topography and substrate and benthic macroinvertebrates were conducted in an upstream-downstream BACI study design. Analyses investigated how disturbance-related attributes of the physical channel (grain size and variability, bed stability, bed complexity) and benthic macroinvertebrate community (species richness, functional traits) changed over space and time. It was hypothesized that commonly-observed changes in the physical channel (i.e. reduction in bed complexity, changes in the size and mobility of bed material) following the sediment pulse would lead to reduction in species richness and a transition to functional traits affiliated with sediment disturbance (i.e. short lived, rapid reproduction, tolerant of mobile beds). Furthermore, evidence of physical and ecological disturbance was expected to be greater at the Brownsville Dam site than at Savage Rapids Dam, where a less stable, more variable bed and a lower erosional efficiency on the Calapooia River was expected to generate a greater sensitivity to the sediment pulse.

Results illustrate that variability in the channel and biological community over the study period were driven by different factors: While the sediment pulse was the dominant force influencing geomorphic variability across the study periods, annual variability in hydrology was the dominant force in establishing variability in the benthic macroinvertebrate community. In fact, the data offer little evidence of substantial impact of the sediment pulse on the invertebrate communities. Rates of recovery of the channels appears to be driven more by post-removal hydrology than by sensitivity of the channel to the sediment pulse.

Comments

DESIREE D. TULLOS is a licensed engineer and associate professor in the Department of Biological and Ecological Engineering, Oregon State University, Corvallis. Dr. Tullos joined the faculty at Oregon State University in 2005. Her research areas include ecohydraulics and environmental fluid mechanics, river engineering, morphology, and restoration, systems analysis of water resources management, and habitat, hydraulic, and hydrodynamic modeling. Current research includes a) Channel and biological responses to river restoration and engineering, including dam removal, engineered log jams, and dam reoperation, b) Impacts of dam operations on flood risk reduction, water supply, hydropower generation, and environmental requirements, c) Analysis of uncertainty in water resources modeling, d) Effects of hydropower development strategies in China, India, and Nepal e) turbulence and kinematics of flow around dense vegetation, and f) Sediment management in reservoirs. She received her B.S. in civil engineering from the University of Tennessee, Knoxville, and her MC.E. in civil engineering and Ph.D. in biological engineering from North Carolina State University, Raleigh.

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Jun 25th, 1:30 PM Jun 25th, 1:50 PM

Concurrent Sessions A: Dam Removal II - Physical and Biological Responses to Dam Removal: Evidence Against Small Dam Removal as an Ecological Disturbance

Construction & Engineering Hall, Oregon State University

Managers and the public both regularly express concern regarding biological consequences of the pulse release of sediment associated with dam removal. However, limited field data exists against which concerns regarding biophysical responses to and recovery from dam removals can be evaluated. Thus, this study documents an investigation of responses to small dam removal, with emphasis on the parallel concept of disturbance in geomorphology and ecology of rivers. This presentation includes results from analysis of field observations at the Brownsville Dam, Calapooia River (height = 2.5 m, D50 = 59 m) and the Savage Rapids Dam, Rogue River (height = 12 m, D50 = 8 m). Field surveys of channel topography and substrate and benthic macroinvertebrates were conducted in an upstream-downstream BACI study design. Analyses investigated how disturbance-related attributes of the physical channel (grain size and variability, bed stability, bed complexity) and benthic macroinvertebrate community (species richness, functional traits) changed over space and time. It was hypothesized that commonly-observed changes in the physical channel (i.e. reduction in bed complexity, changes in the size and mobility of bed material) following the sediment pulse would lead to reduction in species richness and a transition to functional traits affiliated with sediment disturbance (i.e. short lived, rapid reproduction, tolerant of mobile beds). Furthermore, evidence of physical and ecological disturbance was expected to be greater at the Brownsville Dam site than at Savage Rapids Dam, where a less stable, more variable bed and a lower erosional efficiency on the Calapooia River was expected to generate a greater sensitivity to the sediment pulse.

Results illustrate that variability in the channel and biological community over the study period were driven by different factors: While the sediment pulse was the dominant force influencing geomorphic variability across the study periods, annual variability in hydrology was the dominant force in establishing variability in the benthic macroinvertebrate community. In fact, the data offer little evidence of substantial impact of the sediment pulse on the invertebrate communities. Rates of recovery of the channels appears to be driven more by post-removal hydrology than by sensitivity of the channel to the sediment pulse.