The October 2007 removal of Marmot Dam, a 14.3-m-tall dam on the Sandy River in northwestern Oregon storing approximately 730,000 m3 of impounded sediment, provided an opportunity to study short- and long-term geomorphic effects of dam removal. Monitoring reservoir morphology during the two years following dam decommissioning yields a timeline of reservoir channel change. Comparison of a pre-dam survey in 1911 with post-removal surveys provides a basis from which to gage the Reservoir Reach evolution in the context of pre-dam conditions. Analyses of time-lapse photography, topographic surveys, and repeat LiDAR data sets provide detailed spatial and temporal documentation of a release of sediment from the reservoir following dam removal. The majority of morphologic changes to the reservoir largely took place during the first few days and weeks following removal. Channel incision and widening, along with gradient changes through the Reservoir Reach, exhibit diminishing changes with time. Channel incision rates of up to 13 m/hr and widening rates of up to 26 m/hr occurred within the first 24 hours following breaching of the coffer dam. Although channel position through the Reservoir Reach has remained relatively stable due to valley confinement, its width increased substantially. The channel reached an average width of 45 m within two weeks of breaching, but then erosion rates slowed and the channel width reached about 70 to 80 m after one and two years, respectively. Diminishing volumes of evacuated sediment were measured over time through quantitative analysis of survey datasets. About 15 percent of the initial impounded sediment was eroded from the Reservoir Reach within 60 hours of breaching; after one and two years, 50 and 58 percent was eroded, respectively. Grain-size analysis of terraces cut into reservoir fill following dam removal show that bed material coarsened over time at fixed elevations and vertically downward as the channel incised. Overall, these findings indicate valley morphology and local in-channel bedrock topography controlled the spatial distribution of sediment within the reservoir reach while variability in river discharge determined the timing of episodic sediment release. Changes within the Reservoir Reach shortly after dam removal and subsequent evolution over the two years following removal are likely attributable to 1) the timing and intensity of flow events, 2) the longitudinal and stratigraphic spatial variations in deposit grain-size distributions initially and over time, and 3) the pre-dam topography and existing valley morphology.

No description available.

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. / Graduation date: 2010

Dams play an important role in our society, but their negative impacts on aquatic ecosystems have led to a need for conservation efforts to mitigate the negative effects. In some instances, dam removal has been suggested to be the most economically and ecologically beneficial restoration method to improve longitudinal connectivity. This, however, has increased the need of more research about the effects dam removal have on aquatic ecosystems, since the outcomes of this restoration method can be unpredictable. In this study, I investigated ecological impacts of dam removals in Swedish inland waters. I collected field data from five different lakes in Värmland and Dalarna, two lakes with dam removal in 2017/2018 and three without. I studied how dam removal affected different trophic levels of the aquatic ecosystem, where I predicted that a top-down effect would increase abundances of piscivorous European perch (Perca fluviatilis) and zooplankton, but decrease phytoplankton, whereas a bottom-up effect would lead to increases in biomass at all trophic levels (with most pronounced effects on nutrient concentration). If both top-down and bottom-up effects would operate in parallel, all the above mentioned effects could occur. I also predicted that if dam removal affected the fish community, there would be a change in species diversity and fish biomass. Moreover, if perch demography was affected, there would be a change in perch length and abundance of different age classes. To investigate this, I collected data on fish, plankton, nutrients (P, N), DOC, pH and conductivity in the five lakes and compared this with already existing historical data using a BACI design. Two-way ANOVAs were used to study the effects of dam removals on these variables. There were not enough historical data on P concentration or zoo-and phytoplankton to be analyzed statistically. I did, however, conduct correlation analyses with zoo- and phytoplankton. Contradictory to my prediction, the results showed no effect of dam removal on fish biomass or diversity, water chemistry or perch demography in the studied lakes. There was, however, a statistically significant effect of time on Tot-N, with lower values after the years of 2017/2018 (regardless of dam removal). There were also some differences between the lakes in species diversity, concentration of Tot-N, potentially piscivorous perch and perch length. The outcomes of dam removal are unpredictable, as are the expected time-lapse of the effects, which means that changes may yet occur in the studied lakes. Knowledge about ecosystem responses to dam removal enables managers to better predict the effects of dam removal, and thereby facilitate decision makings related to this restoration method. / Dammar spelar en viktig roll i vårt samhälle, men deras negativa påverkan på akvatiska ekosystem har ökat behovet av bevarandeinsatser för att minska de negativa effekterna. I somliga fall har dammutrivning föreslagits vara den mest ekonomiskt och ekologiskt gynnsamma bevarandemetoden för att förbättra longitudinell konnektivitet. Detta har dock ökat behovet av mer forskning gällande dammutrivningars effekter på akvatiska ekosystem, eftersom utfallen av denna bevarandemetod kan vara oförutsägbara. I denna studie undersökte jag dammutrivningars ekologiska effekter i svenska inlandsvatten. Jag samlade data i fält från fem olika sjöar i Värmland och Dalarna, två sjöar med dammutrivningar under 2017/2018 och tre utan. Jag undersökte hur dammutrivning påverkade olika trofiska nivåer i det akvatiska ekosystemet, med förväntningarna att en top-down-effekt skulle öka abundansen av fiskätande abborre (Perca fluviatilis) samt djurplankton, men minska växtplankton, medan en bottom-up-effekt skulle leda till ökad biomassa inom samtliga trofiska nivåer (men med mest effekter på näringskoncentration). Om både top-down- och bottom-up-effekter skulle verka parallellt kunde samtliga ovanstående nämnda effekter förekomma. Jag förväntade även att om dammutrivning påverkade fisksamhället skulle det ske en förändring i artdiversitet och fiskbiomassa. Därtill bör en effekt på demografi hos abborre leda till förändringar i abborrlängd- och abundans i olika åldersklasser. För att undersöka detta samlade jag in data över fisk, plankton, näringsämnen (P, N), DOC, pH och konduktivitet i de fem sjöarna och jämförde detta med redan existerande historiska data med en BACI design. Tvåvägs-ANOVAs användes för att studera effekterna av dammutrivningar på dessa variabler. Det fanns inte tillräckligt med historiska data över P-koncentration eller djur- och växtplankton för att analyseras statistiskt. Jag utförde dock korrelationsanalyser med djur- och växtplankton. I kontrast till min förväntan visade resultaten ingen effekt av dammutrivning på fiskbiomassa- eller diversitet, vattenkemi eller demografi hos abborre i de studerade sjöarna. Det var däremot en statistiskt signifikant effekt av tid på Tot-N, med lägre värden efter 2017/2018 (oberoende av dammutrivning). Det var även en del skillnader mellan sjöarna i artdiversitet, koncentration av Tot-N, potentiellt fiskätande abborre samt abborrlängder. Utfallen av damutrivningar är oförutsägbara, och detsamma gäller tidsintervallet för effekterna, vilket innebär att det fortfarande kan ske förändringar i de studerade sjöarna. Kunskap om ekosystemrespons till dammutrivning möjliggör för förvaltare att lättare bedöma effekter av dammutrivningar, och underlättar därav beslutsfattning relaterat till denna bevarandemetod.

Vattenkraftverk utgör vandringshinder för den akvatiska faunan i vattendrag. Den vandrande fisken hindras från att nå sina lekområden vilket har lett till ett minskat bestånd. Omprövningen som ska ske av vattenkraften i Sverige kommer att ställa högre krav på miljöanpassningar och bevarandet av ekologin. Elbristen i Europa har lett till en paus av omprövningen. Pausen möjliggör för att få ytterligare kunskap kring utförandet av restaureringsarbetet innan implementeringen. Studiens syfte var att identifiera vilka utmaningar och möjligheter som finns med restaureringsarbetet av vattenkraft, både ur ett socialt och ekologiskt perspektiv. Metoden utgjordes av ett flertal intervjuer med personer som för studien hade relevant kunskap. Resultatet visar på att det finns möjligheter och utmaningar inom samarbete, finansiering och restaurering. Slutsatsen av studien var att omprövningen är en grund till förbättrat arbete som bidrar med tydligare riktlinjer för samarbete, en miljöfonden som kan finansiera miljöanpassningarna och att restaureringsåtgärder faktiskt kommer implementeras. Utmaningarna som identifierades var konflikten mellan olika intressen, den varierande effektiviteten av en fiskväg och kostsamma miljöanpassningar. En utrivning ger snabba positiva förändringar och kan också därför anses vara den mest effektiva miljöanpassningen. Slutligen, restaurering av vattendrag är värdefullt för den akvatiska faunan. / Hydroelectric power plants constitute migration barriers for the aquatic fauna in watercourses. The migrating fish are prevented from reaching their spawning areas, which has led to a reduced stock of fish. Omprövningen of hydropower in Sweden will place higher demands on environmental adaptations and the preservation of ecology. The electricity shortage in Europe has led to a pause of omprövningen. The pause makes it possible to gain additional knowledge about the execution of the restoration work before the implementation. The purpose of the study was to identify which challenges and opportunities exist with the restaureation of watercourses with hydropower, both from a social and ecological perspective. The method consisted of several interviews with people who had relevant knowledge for the study. The results showed that there are opportunities and challenges with cooperation, financing and restoration. The conclusion was that the omprövning contributes with possibilities such as clearer guidelines for cooperation, the environmental fund that can finance the environmental adaptations and that restoration measures will actually be implemented. The identified challenges were conflicts between different interests, the varying efficiency of a fish passage and financing the expensive adaptations. A removal produces rapid positive change and can therefore be considered the most effective environmental adaptation. Finally, restoration of watercourses is valuable for the aquatic fauna.