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• 11. [Article] Patterns and processes of sediment transport following sediment-filled dam removal in gravel bed rivers

  Dam removal is increasingly viewed as a river restoration tool because dams affect so many aspects of river hydrology, geomorphology, and ecology; but removal also has impacts. When a dam is removed, ...

  Citation × Citation Citation Abstract Copy Title: Patterns and processes of sediment transport following sediment-filled dam removal in gravel bed rivers Author: Stewart, Gregory B. Dam removal is increasingly viewed as a river restoration tool because dams affect so many aspects of river hydrology, geomorphology, and ecology; but removal also has impacts. When a dam is removed, sediment accumulated over a dam’s lifetime may be transported downstream; and the timing, fate and consequences of this sediment remain some of the greatest unknowns associated with dam removal. In this thesis, I develop a conceptual model for erosion and deposition following removal of sediment-filled dams in mountain streams, and use field studies to document actual change. The data show that reservoir erosion in mountain rivers is likely to occur by knickpoint migration, with 85% of stored sediment being released during a single storm event in two field studies, at shear stresses less than that required for mobilization of the median surface particle size. Coarse sediment is predicted to deposit close to the dam with channel aggradation decreasing exponentially with increasing distance downstream, although some channel features are shown to have a greater propensity for aggradation than others. Field studies show that turbidity associated with dam removal and reservoir erosion may decrease hyporheic exchange, but gravel deposition (e.g., 470 m3 of gravel from Dinner Creek Dam) has the potential to more than offset that decrease, and increased hyporheic exchange is shown to reduce diurnal temperature change. Macroinvertebrate density and taxa richness did not respond to dam removal itself, but rather with time-lagged reservoir erosion. Following reservoir erosion, macroinvertebrate density recovered quickly, although longterm taxa community composition appears to be altered. On the Sandy River, field measurements of shear stress and patterns of sediment deposition following cold lahars were used as an analog to predict the fate of fine sediment, which is likely to deposit far from the dam. Results show that the Sandy River has little capacity for fine sediment storage in pools above RK 6.4 (~ 42 kilometers below Marmot Dam) at discharges associated with reservoir sediment releases. Taken as a whole, this paper illustrates a complex suite of process that may accompany removal of sediment-filled dams in mountain rivers. Title: Patterns and processes of sediment transport following sediment-filled dam removal in gravel bed rivers Author: Stewart, Gregory B. Dam removal is increasingly viewed as a river restoration tool because dams affect so many aspects of river hydrology, geomorphology, and ecology; but removal also has impacts. When a dam is removed, sediment accumulated over a dam’s lifetime may be transported downstream; and the timing, fate and consequences of this sediment remain some of the greatest unknowns associated with dam removal. In this thesis, I develop a conceptual model for erosion and deposition following removal of sediment-filled dams in mountain streams, and use field studies to document actual change. The data show that reservoir erosion in mountain rivers is likely to occur by knickpoint migration, with 85% of stored sediment being released during a single storm event in two field studies, at shear stresses less than that required for mobilization of the median surface particle size. Coarse sediment is predicted to deposit close to the dam with channel aggradation decreasing exponentially with increasing distance downstream, although some channel features are shown to have a greater propensity for aggradation than others. Field studies show that turbidity associated with dam removal and reservoir erosion may decrease hyporheic exchange, but gravel deposition (e.g., 470 m3 of gravel from Dinner Creek Dam) has the potential to more than offset that decrease, and increased hyporheic exchange is shown to reduce diurnal temperature change. Macroinvertebrate density and taxa richness did not respond to dam removal itself, but rather with time-lagged reservoir erosion. Following reservoir erosion, macroinvertebrate density recovered quickly, although longterm taxa community composition appears to be altered. On the Sandy River, field measurements of shear stress and patterns of sediment deposition following cold lahars were used as an analog to predict the fate of fine sediment, which is likely to deposit far from the dam. Results show that the Sandy River has little capacity for fine sediment storage in pools above RK 6.4 (~ 42 kilometers below Marmot Dam) at discharges associated with reservoir sediment releases. Taken as a whole, this paper illustrates a complex suite of process that may accompany removal of sediment-filled dams in mountain rivers. Close

• 12. [Article] Development and decommissioning of small dams : analysis of impact and context

  Management of small dams may have profound implications for the health and integrity of small rivers and freshwater diversity. Global indicators suggest future growth in the small hydropower sector, particularly ...

  Citation × Citation Citation Abstract Copy Title: Development and decommissioning of small dams : analysis of impact and context Author: Kibler, Kelly Maren Management of small dams may have profound implications for the health and integrity of small rivers and freshwater diversity. Global indicators suggest future growth in the small hydropower sector, particularly in developing countries. As a renewable energy source, it is often presumed that small hydropower entails fewer and less severe negative externalities than those associated with development of larger hydropower facilities. However, as very little study exists investigating the cumulative effect of small‐scale hydrodevelopment on ecological and social systems, limited data is available to substantiate this assumption. To enhance understanding of small hydropower effects, I present a comprehensive comparison of biophysical consequences of small and large hydropower stations in Nujiang Prefecture, Yunnan Province, China. My comparison indicates that cumulative ecological effects of small hydropower development may equal or exceed those associated with development of large hydropower. Because negligible adverse effects are anticipated, small hydropower projects often are characterized by reduced project oversight, streamlined permitting processes, relaxed requirements for environmental impact assessment and mitigation, and increased opportunity for international support relative to large hydropower projects. Outcomes from my comparison of small and large hydropower stations in Nujiang Prefecture and synthesis of available study from diversion‐design facilities suggest that current policies allowing less rigorous standards of impact assessment for the small hydropower sector should be reevaluated. Further study is necessary to optimize management that minimizes the consequences of small hydropower and to create effective policies encouraging low‐impact development of renewable energy sources. With regard to decommissioning of small dams, the restoration potential of small rivers impounded by reservoirs filled with coarse sediment may outweigh the likelihood of detrimental dam‐removal effects. After removal of the Brownsville Dam from the Calapooia River, Oregon, aquatic habitats directly below the dam became more heterogeneous over the short term, while changes further downstream were virtually undetectable. As the Brownsville Dam stored coarse rather than fine sediments, outcomes following removal differ from results of many prior dam removal studies. As current conceptual ideas of dam removal effects are largely informed by study of low‐gradient systems transporting finer sediments, I propose a refined conceptual model describing downstream geomorphic processes following small dam removal when upstream fill is dominated by coarse sediments. Dam removal monitoring studies challenge many basic assumptions of conventional experimental designs and data analysis techniques, thus the quality of information available to aid decision making may often be questionable or misleading. To assist managers in undertaking dam removal monitoring, I also discuss assets and limitations of monitoring and analysis options available for dam removal studies, with emphasis on selecting a rigorous experimental design and determining significance of results. Title: Development and decommissioning of small dams : analysis of impact and context Author: Kibler, Kelly Maren Management of small dams may have profound implications for the health and integrity of small rivers and freshwater diversity. Global indicators suggest future growth in the small hydropower sector, particularly in developing countries. As a renewable energy source, it is often presumed that small hydropower entails fewer and less severe negative externalities than those associated with development of larger hydropower facilities. However, as very little study exists investigating the cumulative effect of small‐scale hydrodevelopment on ecological and social systems, limited data is available to substantiate this assumption. To enhance understanding of small hydropower effects, I present a comprehensive comparison of biophysical consequences of small and large hydropower stations in Nujiang Prefecture, Yunnan Province, China. My comparison indicates that cumulative ecological effects of small hydropower development may equal or exceed those associated with development of large hydropower. Because negligible adverse effects are anticipated, small hydropower projects often are characterized by reduced project oversight, streamlined permitting processes, relaxed requirements for environmental impact assessment and mitigation, and increased opportunity for international support relative to large hydropower projects. Outcomes from my comparison of small and large hydropower stations in Nujiang Prefecture and synthesis of available study from diversion‐design facilities suggest that current policies allowing less rigorous standards of impact assessment for the small hydropower sector should be reevaluated. Further study is necessary to optimize management that minimizes the consequences of small hydropower and to create effective policies encouraging low‐impact development of renewable energy sources. With regard to decommissioning of small dams, the restoration potential of small rivers impounded by reservoirs filled with coarse sediment may outweigh the likelihood of detrimental dam‐removal effects. After removal of the Brownsville Dam from the Calapooia River, Oregon, aquatic habitats directly below the dam became more heterogeneous over the short term, while changes further downstream were virtually undetectable. As the Brownsville Dam stored coarse rather than fine sediments, outcomes following removal differ from results of many prior dam removal studies. As current conceptual ideas of dam removal effects are largely informed by study of low‐gradient systems transporting finer sediments, I propose a refined conceptual model describing downstream geomorphic processes following small dam removal when upstream fill is dominated by coarse sediments. Dam removal monitoring studies challenge many basic assumptions of conventional experimental designs and data analysis techniques, thus the quality of information available to aid decision making may often be questionable or misleading. To assist managers in undertaking dam removal monitoring, I also discuss assets and limitations of monitoring and analysis options available for dam removal studies, with emphasis on selecting a rigorous experimental design and determining significance of results. Close

• 13. [Article] Jake Place Spring Symposium Presentation - Danielle Reynolds

  Many western river systems have become degraded or incised over time due to grazing, agriculture, impoundments, and extermination of beaver. Restoration efforts are looking to more natural solutions aimed ...

  Citation × Citation Citation Abstract Copy Title: Jake Place Spring Symposium Presentation - Danielle Reynolds Author: Reynolds, Danielle Many western river systems have become degraded or incised over time due to grazing, agriculture, impoundments, and extermination of beaver. Restoration efforts are looking to more natural solutions aimed at reconnecting streams to their original floodplain. Beavers were the original ecosystem engineers in Northwest America. They built dams, which held back water and sediment forcing stream channels in various directions, thus providing a mechanism for heterogeneity of fluvial processes and fish habitat. Restoration ecologists are looking to the beaver dam as a multifunctional tool aimed at reversing the anthropogenic effects of stream degradation. Baseline research was conducted at the Jake Place to provide important data and determine locations for beaver dam analogues. Important fluvial parameters such as pool to riffle ratios, historic floodplain areas and stream gradients were gathered for comparison after beaver dams were constructed. Five artificially installed beaver dam analogues were constructed in 2016 on the South Fork of the Crooked River. Dam porosity diminished in the weeks following installation, likely due to holes filling with aquatic vegetation, meaning fish passage may have to occur over or around the structures or during high flows. Following the 2017 spring flood event, two of the five beaver dam analogues had withstood the high flows and are functioning well, the other three dams did not withstand the event. Future work will include measuring sediment aggradation, success of riparian plantings, beaver activity, geomorphology, and fish passage. Title: Jake Place Spring Symposium Presentation - Danielle Reynolds Author: Reynolds, Danielle Many western river systems have become degraded or incised over time due to grazing, agriculture, impoundments, and extermination of beaver. Restoration efforts are looking to more natural solutions aimed at reconnecting streams to their original floodplain. Beavers were the original ecosystem engineers in Northwest America. They built dams, which held back water and sediment forcing stream channels in various directions, thus providing a mechanism for heterogeneity of fluvial processes and fish habitat. Restoration ecologists are looking to the beaver dam as a multifunctional tool aimed at reversing the anthropogenic effects of stream degradation. Baseline research was conducted at the Jake Place to provide important data and determine locations for beaver dam analogues. Important fluvial parameters such as pool to riffle ratios, historic floodplain areas and stream gradients were gathered for comparison after beaver dams were constructed. Five artificially installed beaver dam analogues were constructed in 2016 on the South Fork of the Crooked River. Dam porosity diminished in the weeks following installation, likely due to holes filling with aquatic vegetation, meaning fish passage may have to occur over or around the structures or during high flows. Following the 2017 spring flood event, two of the five beaver dam analogues had withstood the high flows and are functioning well, the other three dams did not withstand the event. Future work will include measuring sediment aggradation, success of riparian plantings, beaver activity, geomorphology, and fish passage. Close

• 14. [Article] Geomorphic and Ecological Disturbance and Recovery from Two Small Dams and Their Removal

  This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by the Public Library of Science. The published article can be found at: http://www.plosone.org/.

  Citation × Citation Citation Abstract Copy Title: Geomorphic and Ecological Disturbance and Recovery from Two Small Dams and Their Removal Author: Tullos, Desirée D., Finn, Debra S., Walter, Cara This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by the Public Library of Science. The published article can be found at: http://www.plosone.org/. Title: Geomorphic and Ecological Disturbance and Recovery from Two Small Dams and Their Removal Author: Tullos, Desirée D., Finn, Debra S., Walter, Cara This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by the Public Library of Science. The published article can be found at: http://www.plosone.org/. Close

• 15. [Article] Dam removals and downstream bar-pool morphology

  Bar-pool morphology in rivers can provide vital habitat to aquatic species, notably salmonids, which require gravel riffles to bury eggs and pools for hydraulic and cold-water refuge. In some cases, the ...

  Citation × Citation Citation Abstract Copy Title: Dam removals and downstream bar-pool morphology Author: Zunka, John Page Purnell Bar-pool morphology in rivers can provide vital habitat to aquatic species, notably salmonids, which require gravel riffles to bury eggs and pools for hydraulic and cold-water refuge. In some cases, the erosion and subsequent deposition of coarse sediment downstream of a dam removal can modify habitat by inundating bar-pool structure, filling pools, and homogenizing the channel bed. To assess extents and durations of geomorphic impacts of dam removals, project managers may devote significant resources to detailed one-dimensional numerical modeling studies and requisite data collection, but the manner in which these width-averaged sediment inundation depths are expressed laterally and interact with pre-existing morphology is not considered. We address the uncertainty associated with the lateral impacts of sediment pulses by presenting and evaluating a conceptual framework for both visualizing dam removal data and explicating hypotheses describing the response of cross-channel bed relief to changing sediment thicknesses. Within this conceptual framework, we examine, using data from two dam removals in Oregon, the hypothesis whereby bed relief in a cross-section is formed and initially increased by sediment deposition and subsequently diminished during continued deposition. Results suggest that the conceptual framework is a useful means for visualizing dam removal data and effectively captured the different behaviors and changing morphologies observed in the cross-sectional data at each field site. Although there was some data that the hypothesis did not describe sufficiently, the confirmation of the general trends of the hypothesis in much of the data make it a good starting point for estimating the range of responses to dam removal of alluvial channels that exhibit bar-pool morphology and developing more physically detailed and site specific hypotheses. Title: Dam removals and downstream bar-pool morphology Author: Zunka, John Page Purnell Bar-pool morphology in rivers can provide vital habitat to aquatic species, notably salmonids, which require gravel riffles to bury eggs and pools for hydraulic and cold-water refuge. In some cases, the erosion and subsequent deposition of coarse sediment downstream of a dam removal can modify habitat by inundating bar-pool structure, filling pools, and homogenizing the channel bed. To assess extents and durations of geomorphic impacts of dam removals, project managers may devote significant resources to detailed one-dimensional numerical modeling studies and requisite data collection, but the manner in which these width-averaged sediment inundation depths are expressed laterally and interact with pre-existing morphology is not considered. We address the uncertainty associated with the lateral impacts of sediment pulses by presenting and evaluating a conceptual framework for both visualizing dam removal data and explicating hypotheses describing the response of cross-channel bed relief to changing sediment thicknesses. Within this conceptual framework, we examine, using data from two dam removals in Oregon, the hypothesis whereby bed relief in a cross-section is formed and initially increased by sediment deposition and subsequently diminished during continued deposition. Results suggest that the conceptual framework is a useful means for visualizing dam removal data and effectively captured the different behaviors and changing morphologies observed in the cross-sectional data at each field site. Although there was some data that the hypothesis did not describe sufficiently, the confirmation of the general trends of the hypothesis in much of the data make it a good starting point for estimating the range of responses to dam removal of alluvial channels that exhibit bar-pool morphology and developing more physically detailed and site specific hypotheses. Close

• 16. [Article] Spillway Staging and Selective Sediment Deposition in Sand Storage Dams

  Rainfall scarcity and variability present serious challenges to water security for many rural communities throughout the world's drylands. Sand dams--weirs built across ephemeral or seasonal rivers--provide ...

  Citation × Citation Citation Abstract Copy Title: Spillway Staging and Selective Sediment Deposition in Sand Storage Dams Author: Viducich, Jonathan M. G. Rainfall scarcity and variability present serious challenges to water security for many rural communities throughout the world's drylands. Sand dams--weirs built across ephemeral or seasonal rivers--provide an appropriate water harvesting and storage option for many regions. The structures quickly fill with sediment during rainy season flow events and store water underground in interstitial pores, thereby limiting evaporation, contamination and the prevalence of disease-carrying vectors. The size of deposited sediment particles largely determines sand dam effectiveness; fine materials do not transmit or yield usable quantities of water under a dam's modest head conditions. Many researchers and practitioners propose building sand dams in stages to limit capture of fine particles. I apply field and remotely-sensed data and statistical analysis to evaluate hypotheses about the catchment and reach-scale conditions required to optimize sediment deposition. I also use the results of unsteady HEC-RAS flow models to quantify the sensitivity of sedimentation processes to spillway height. The results of the statistical analyses show a negative correlation between mean catchment slope and median particle size collected by sand dams. Modeled results indicate that sedimentation is relatively more sensitive to variations in spillway height than to changes in the hydrograph, especially when a dam is short. However, sensitivities to a given modeled parameter vary by site. Based on the results, I recommend that the need for spillway staging be evaluated on a site-by-site basis, accounting for costs and expected benefits, and that designs incorporate progressively taller stages. Title: Spillway Staging and Selective Sediment Deposition in Sand Storage Dams Author: Viducich, Jonathan M. G. Rainfall scarcity and variability present serious challenges to water security for many rural communities throughout the world's drylands. Sand dams--weirs built across ephemeral or seasonal rivers--provide an appropriate water harvesting and storage option for many regions. The structures quickly fill with sediment during rainy season flow events and store water underground in interstitial pores, thereby limiting evaporation, contamination and the prevalence of disease-carrying vectors. The size of deposited sediment particles largely determines sand dam effectiveness; fine materials do not transmit or yield usable quantities of water under a dam's modest head conditions. Many researchers and practitioners propose building sand dams in stages to limit capture of fine particles. I apply field and remotely-sensed data and statistical analysis to evaluate hypotheses about the catchment and reach-scale conditions required to optimize sediment deposition. I also use the results of unsteady HEC-RAS flow models to quantify the sensitivity of sedimentation processes to spillway height. The results of the statistical analyses show a negative correlation between mean catchment slope and median particle size collected by sand dams. Modeled results indicate that sedimentation is relatively more sensitive to variations in spillway height than to changes in the hydrograph, especially when a dam is short. However, sensitivities to a given modeled parameter vary by site. Based on the results, I recommend that the need for spillway staging be evaluated on a site-by-site basis, accounting for costs and expected benefits, and that designs incorporate progressively taller stages. Close

• 17. [Article] Characterizing community impacts of small dam removal : a case study of the Brownsville Dam

  Emerging river policy has launched small dam removal as a viable option to meet the ecological and social demands for river restoration. As small dam removals gain precedence as a policy tool in river ...

  Citation × Citation Citation Abstract Copy Title: Characterizing community impacts of small dam removal : a case study of the Brownsville Dam Author: Elston, Denise E. Emerging river policy has launched small dam removal as a viable option to meet the ecological and social demands for river restoration. As small dam removals gain precedence as a policy tool in river restoration projects there exists a glaring gap in the social considerations, in particular how small dam removals may affect existing community conditions. In order to determine the community impacts that may result, a case study of the Brownsville Dam Removal, in Brownsville Oregon was investigated to address two questions: 1) how has the Brownsville Dam removal affected the social and economic conditions of the community and 2) what indicators can be used to characterize and monitor the impacts. Twenty-nine semi-structured interviews were conducted with four community affiliations: 1) Canal Company members; 2) Calapooia Watershed Council members; 3) City Officials; and 4) community residents. A participatory social impact assessment (SIA) approach was used to validate existing and/or emergent impacts and indicators. The semi-structured interviews assisted in the development of a matrix of impacts and indicators specific to small dam removal. The local impacts and indicators were operationalized and measured. Findings suggest that the social and economic impacts when distributed across the community are minimal in this case of small dam removal. Because local data availability is limited, it was determined that the traditional social impact assessment framework can be vastly improved through the engagement of the community. This research further suggests that when collaboration is extended beyond a unidirectional flow of information (which is often the case in a traditional SIA), issues and concerns are open to deliberation in a non-threatening arena. The Calapooia Watershed Council served as the forum through which the residents of Brownsville were able to enhance their participation in decision making. This also contributed to a learning process that in the end furthered the community's understanding of the dynamic physical changes to the Calapooia River as well as their capacity to solve complex decisions. The case also demonstrated that collective learning is a reflective process of adjustment to the changing circumstances in which the community came to perceive, interpret, and act upon their interest. With a growing number of collaborative partnerships of watershed based management, distinguishable by their decentralized, participatory engagement of stakeholders, it may be likely that these place-based mechanisms will become the nexus to the successful coordination of small dam removal deliberation in the future. Title: Characterizing community impacts of small dam removal : a case study of the Brownsville Dam Author: Elston, Denise E. Emerging river policy has launched small dam removal as a viable option to meet the ecological and social demands for river restoration. As small dam removals gain precedence as a policy tool in river restoration projects there exists a glaring gap in the social considerations, in particular how small dam removals may affect existing community conditions. In order to determine the community impacts that may result, a case study of the Brownsville Dam Removal, in Brownsville Oregon was investigated to address two questions: 1) how has the Brownsville Dam removal affected the social and economic conditions of the community and 2) what indicators can be used to characterize and monitor the impacts. Twenty-nine semi-structured interviews were conducted with four community affiliations: 1) Canal Company members; 2) Calapooia Watershed Council members; 3) City Officials; and 4) community residents. A participatory social impact assessment (SIA) approach was used to validate existing and/or emergent impacts and indicators. The semi-structured interviews assisted in the development of a matrix of impacts and indicators specific to small dam removal. The local impacts and indicators were operationalized and measured. Findings suggest that the social and economic impacts when distributed across the community are minimal in this case of small dam removal. Because local data availability is limited, it was determined that the traditional social impact assessment framework can be vastly improved through the engagement of the community. This research further suggests that when collaboration is extended beyond a unidirectional flow of information (which is often the case in a traditional SIA), issues and concerns are open to deliberation in a non-threatening arena. The Calapooia Watershed Council served as the forum through which the residents of Brownsville were able to enhance their participation in decision making. This also contributed to a learning process that in the end furthered the community's understanding of the dynamic physical changes to the Calapooia River as well as their capacity to solve complex decisions. The case also demonstrated that collective learning is a reflective process of adjustment to the changing circumstances in which the community came to perceive, interpret, and act upon their interest. With a growing number of collaborative partnerships of watershed based management, distinguishable by their decentralized, participatory engagement of stakeholders, it may be likely that these place-based mechanisms will become the nexus to the successful coordination of small dam removal deliberation in the future. Close

• 18. [Article] Trends in streamflow above and below dams across the Columbia River basin from 1950 to 2012 : assessing sub-basin sensitivity

  Climate change, combined with population growth, is expected to exacerbate water scarcity globally. In the Columbia River basin (CRB), streamflow is managed for multiple objectives with a network of dams ...

  Citation × Citation Citation Abstract Copy Title: Trends in streamflow above and below dams across the Columbia River basin from 1950 to 2012 : assessing sub-basin sensitivity Author: Hammond, John C. (John Christophe) Climate change, combined with population growth, is expected to exacerbate water scarcity globally. In the Columbia River basin (CRB), streamflow is managed for multiple objectives with a network of dams and reservoirs distributed throughout the basin that may mitigate climate change effects on water scarcity. This study quantified trends in daily streamflow from 1950-2012 in 28 pairs of gages above and below dams in the CRB, including the U.S. and Canada. Each gage pair consisted of an above-dam gage that is primarily forested and has little apparent human disturbance and minimal flow regulation or diversions, combined with a below-dam gage immediately downstream of a major dam and reservoir. Monthly streamflow and precipitation for a total of 59 sites was correlated with monthly indices of the Pacific Decadal Oscillation (PDO), the Northern Pacific Index (NPI), the Pacific North America pattern (PNA), and the 700-millibar wind speeds (u700) using Pearson's r. Long-term trends and patterns in daily streamflow and climate data were estimated using linear regression, the Mann-Kendall test, and wavelet analysis. Streamflow was generally weakly correlated with NPI, PNA, and PDO, while positively correlated with upper elevation wind speed at low elevations during wet months. Fewer than half of above-dam gages in the CRB have experienced increasing trends in daily streamflow from mid-March to the beginning of May over the period 1950 to 2012, whereas a majority has experienced decreasing trends from the middle of May to the middle of October. These trends in above-dam basins are consistent with trends expected from climate change, but they also may be affected by legacies of past forest harvest or wildfire. Below dams, reservoir management appears to have overwritten the signal of earlier snowmelt, except in the Boise sub-basin, but long-term declines in late summer flows were evident at half of below-dam sites. Declining summer flows below dams were attributable to a variety of factors, including changes in reservoir management as well as reservoir management that propagates signals from above dam catchments, such as climate change or forest-harvest legacy effects on streamflow. There have been very few significant changes in annual flow volume throughout the basin, and these streamflow trends represent a small percentage of annual flow volume; thus, observed trends appear to be shifts in timing rather than shifts in the annual water balance. The magnitude of 60-yr declines in late summer flow in above-dam catchments represents only a few percent of annual yield, and much less than the storage capacity of the dams, but these long-term changes may be quite important for water yield during the late summer low-flow period. These findings are relevant for strategies to adaptively manage water resources in light of the ongoing planning for renegotiation of the U.S.-Canada Columbia River Treaty. Title: Trends in streamflow above and below dams across the Columbia River basin from 1950 to 2012 : assessing sub-basin sensitivity Author: Hammond, John C. (John Christophe) Climate change, combined with population growth, is expected to exacerbate water scarcity globally. In the Columbia River basin (CRB), streamflow is managed for multiple objectives with a network of dams and reservoirs distributed throughout the basin that may mitigate climate change effects on water scarcity. This study quantified trends in daily streamflow from 1950-2012 in 28 pairs of gages above and below dams in the CRB, including the U.S. and Canada. Each gage pair consisted of an above-dam gage that is primarily forested and has little apparent human disturbance and minimal flow regulation or diversions, combined with a below-dam gage immediately downstream of a major dam and reservoir. Monthly streamflow and precipitation for a total of 59 sites was correlated with monthly indices of the Pacific Decadal Oscillation (PDO), the Northern Pacific Index (NPI), the Pacific North America pattern (PNA), and the 700-millibar wind speeds (u700) using Pearson's r. Long-term trends and patterns in daily streamflow and climate data were estimated using linear regression, the Mann-Kendall test, and wavelet analysis. Streamflow was generally weakly correlated with NPI, PNA, and PDO, while positively correlated with upper elevation wind speed at low elevations during wet months. Fewer than half of above-dam gages in the CRB have experienced increasing trends in daily streamflow from mid-March to the beginning of May over the period 1950 to 2012, whereas a majority has experienced decreasing trends from the middle of May to the middle of October. These trends in above-dam basins are consistent with trends expected from climate change, but they also may be affected by legacies of past forest harvest or wildfire. Below dams, reservoir management appears to have overwritten the signal of earlier snowmelt, except in the Boise sub-basin, but long-term declines in late summer flows were evident at half of below-dam sites. Declining summer flows below dams were attributable to a variety of factors, including changes in reservoir management as well as reservoir management that propagates signals from above dam catchments, such as climate change or forest-harvest legacy effects on streamflow. There have been very few significant changes in annual flow volume throughout the basin, and these streamflow trends represent a small percentage of annual flow volume; thus, observed trends appear to be shifts in timing rather than shifts in the annual water balance. The magnitude of 60-yr declines in late summer flow in above-dam catchments represents only a few percent of annual yield, and much less than the storage capacity of the dams, but these long-term changes may be quite important for water yield during the late summer low-flow period. These findings are relevant for strategies to adaptively manage water resources in light of the ongoing planning for renegotiation of the U.S.-Canada Columbia River Treaty. Close

• 19. [Article] Frequency and magnitude of bedload transport downstream of the Pelton-Round Butte Dam Complex, lower Deschutes River, Oregon

  A first-order approximation is made of the frequency and magnitude of bedload transport downstream of the Pelton-Round Butte Dam Complex, lower Deschutes River, Oregon with implications for salmonid spawning ...

  Citation × Citation Citation Abstract Copy Title: Frequency and magnitude of bedload transport downstream of the Pelton-Round Butte Dam Complex, lower Deschutes River, Oregon Author: Fassnacht, Heidi A first-order approximation is made of the frequency and magnitude of bedload transport downstream of the Pelton-Round Butte Dam Complex, lower Deschutes River, Oregon with implications for salmonid spawning habitat. Field measurements of channel hydraulics, geometry, and particle size were combined with one-dimensional hydraulic and bedload transport models to determine the streamflow needed to move the channel bed material and to predict how much material would move once bedload transport was initiated. Inflows and outflows from the Dam Complex, and the predicted bedload carried by each, were compared to evaluate the effect of the Dam Complex on downstream discharge and bedload transport. Predicted critical discharges were equaled or exceeded very infrequently during the 72-year streamflow record. In addition, discharges capable of transporting bed material exceeded threshold conditions by very little. This has resulted in low predicted rates and amounts of bedload transport over the period of record. The Pelton-Round Butte Dam Complex was found to slightly increase the magnitude of flood peaks and associated predicted bedload transport for post-dam transport events exceeding threshold transport conditions. An exception to this pattern was the effect of the Dam Complex on the flood of December 1964, the second largest flood on record. This large flood occurred under unique circumstances -- while the reservoir of Round Butte Dam was filling for the first time. Since none of the transport events that occurred after the reservoir finished filling were affected by the Dam Complex in the same way as the 1964 event, the influence of the Complex on the 1964 flood is considered unique. The two largest floods on record (1964 and 1996), despite their relatively large sizes with respect to all other recorded flood events, did not cause major morphological changes to the lower Deschutes River. This observation, along with other independently derived information, supports the conclusion that the lower Deschutes is a very stable river. Title: Frequency and magnitude of bedload transport downstream of the Pelton-Round Butte Dam Complex, lower Deschutes River, Oregon Author: Fassnacht, Heidi A first-order approximation is made of the frequency and magnitude of bedload transport downstream of the Pelton-Round Butte Dam Complex, lower Deschutes River, Oregon with implications for salmonid spawning habitat. Field measurements of channel hydraulics, geometry, and particle size were combined with one-dimensional hydraulic and bedload transport models to determine the streamflow needed to move the channel bed material and to predict how much material would move once bedload transport was initiated. Inflows and outflows from the Dam Complex, and the predicted bedload carried by each, were compared to evaluate the effect of the Dam Complex on downstream discharge and bedload transport. Predicted critical discharges were equaled or exceeded very infrequently during the 72-year streamflow record. In addition, discharges capable of transporting bed material exceeded threshold conditions by very little. This has resulted in low predicted rates and amounts of bedload transport over the period of record. The Pelton-Round Butte Dam Complex was found to slightly increase the magnitude of flood peaks and associated predicted bedload transport for post-dam transport events exceeding threshold transport conditions. An exception to this pattern was the effect of the Dam Complex on the flood of December 1964, the second largest flood on record. This large flood occurred under unique circumstances -- while the reservoir of Round Butte Dam was filling for the first time. Since none of the transport events that occurred after the reservoir finished filling were affected by the Dam Complex in the same way as the 1964 event, the influence of the Complex on the 1964 flood is considered unique. The two largest floods on record (1964 and 1996), despite their relatively large sizes with respect to all other recorded flood events, did not cause major morphological changes to the lower Deschutes River. This observation, along with other independently derived information, supports the conclusion that the lower Deschutes is a very stable river. Close

• 20. [Article] Is dam development a mechanism for human security? Scale and perception of the Grand Ethiopian Renaissance Dam on the Blue Nile River in Ethiopia and the Xayaburi Dam on the Mekong River in Laos

  Human security is a framework related to the stability and sustainability of political, environmental, economical, and socio-cultural areas of concern. Water resources around the world are under increased ...

  Citation × Citation Citation Abstract Copy Title: Is dam development a mechanism for human security? Scale and perception of the Grand Ethiopian Renaissance Dam on the Blue Nile River in Ethiopia and the Xayaburi Dam on the Mekong River in Laos Author: Veilleux, Jennifer Corinne Human security is a framework related to the stability and sustainability of political, environmental, economical, and socio-cultural areas of concern. Water resources around the world are under increased pressure from increased development, growing populations, pollution, and global climate change. Large-scale dam development while still popular for political and economic development reasons, has been found to result in costs that outweigh benefits in environmental and socio-cultural sectors. This research assesses the human security impacts from dam development at three scales: the international river basin, the nation-state, and the local affected communities. Human security includes aspects of political, environmental, economic, and socio-cultural sectors. A combination of quantitatively-derived parameters from global indices and field-generated qualitative interviews and observations are employed to understand how perceptions of impacts change dependent on scale and sector. Two case studies are analyzed to capture three scales of human security impacts from dam development: the Grand Ethiopian Renaissance Dam on the Blue Nile River in Ethiopia and the Xayaburi Dam on the Mekong River in Laos. A new human security measurement is developed to consider qualitative aspects of interview data in order to compare the human security stability of very secure, secure, slightly insecure, and insecure to the global indexes. Comparisons between case studies, scales, and methods are drawn. Differences between human security and human development are highlighted. The conclusions are that human security impacts due exist from dam development, but are of a different magnitude depending upon scale, sector, and perception, as well as the datasets used for analysis. For the international scale, I combined publicly available datasets Human Development Index (HDI), Human Security Index (HSI), and the Transboundary Freshwater Dispute Database Basin Country Units (TFDDBCU) to create GIS based maps of watershed development and security ranking. For the national scale I analyzed information provided through official documents, websites, and field interviews. For the local scale I conducted empirical observation and field interviews in local communities. I conclude that the best measurement of human security is from a combination of scale, sector, and perception using qualitative and quantitative context and data for measurement. Title: Is dam development a mechanism for human security? Scale and perception of the Grand Ethiopian Renaissance Dam on the Blue Nile River in Ethiopia and the Xayaburi Dam on the Mekong River in Laos Author: Veilleux, Jennifer Corinne Human security is a framework related to the stability and sustainability of political, environmental, economical, and socio-cultural areas of concern. Water resources around the world are under increased pressure from increased development, growing populations, pollution, and global climate change. Large-scale dam development while still popular for political and economic development reasons, has been found to result in costs that outweigh benefits in environmental and socio-cultural sectors. This research assesses the human security impacts from dam development at three scales: the international river basin, the nation-state, and the local affected communities. Human security includes aspects of political, environmental, economic, and socio-cultural sectors. A combination of quantitatively-derived parameters from global indices and field-generated qualitative interviews and observations are employed to understand how perceptions of impacts change dependent on scale and sector. Two case studies are analyzed to capture three scales of human security impacts from dam development: the Grand Ethiopian Renaissance Dam on the Blue Nile River in Ethiopia and the Xayaburi Dam on the Mekong River in Laos. A new human security measurement is developed to consider qualitative aspects of interview data in order to compare the human security stability of very secure, secure, slightly insecure, and insecure to the global indexes. Comparisons between case studies, scales, and methods are drawn. Differences between human security and human development are highlighted. The conclusions are that human security impacts due exist from dam development, but are of a different magnitude depending upon scale, sector, and perception, as well as the datasets used for analysis. For the international scale, I combined publicly available datasets Human Development Index (HDI), Human Security Index (HSI), and the Transboundary Freshwater Dispute Database Basin Country Units (TFDDBCU) to create GIS based maps of watershed development and security ranking. For the national scale I analyzed information provided through official documents, websites, and field interviews. For the local scale I conducted empirical observation and field interviews in local communities. I conclude that the best measurement of human security is from a combination of scale, sector, and perception using qualitative and quantitative context and data for measurement. Close