Dams fragment streams and rivers, with >14,000 in New England alone, and have the potential to significantly alter the physical, chemical, and biological characteristics of lotic systems. For example, dams can alter temperature and dissolved oxygen (DO) regimes, which can, in turn, affect species distributions, whole system metabolism, and nutrient processing rates. Moreover, changes in temperature signal life history cues (e.g., emergence, egg-hatching, migration) for many species of aquatic organisms, and present another avenue for dams to alter biotic communities. Despite the prevalence of small dams in the landscape and their potential significant impacts on temperature and DO, dams have not been well-studied and published impacts vary widely across sites. Given the variation in impact, I sought to quantify the impacts of small dams to stream temperature and DO, and to determine the drivers of inter- and intra-site variation in response. To accomplish this, I deployed 160 continuous temperature data loggers at 30 small, surface-release dams in Massachusetts. The majority of sites (61%) had higher temperatures downstream of the dam compared to upstream and most (85%) experienced decreasing temperatures with increasing distance downstream of the dam, such that the warmest temperatures were located closest to the dam. At approximately half of the temperature sites, flow had a homogenizing effect on temperatures throughout the study reach, whereby impacts were more pronounced (e.g., more warming, faster decay rates) under periods of low flow than under high flow conditions. Magnitude of warming varied greatly among sites, and this variation was explained best by landscape position and reservoir volume, with dams in smaller watersheds and with larger reservoir volumes experiencing greater warming magnitudes. Forest cover, dam height, and the presence of an auxiliary spillway best predicted the downstream temperature decay rate, with temperatures cooling fastest downstream of shorter dams in forested basins that did not have an auxiliary spillway. I used continuous DO loggers upstream, within the impoundment, and downstream of 12 dams to identify dam impacts to DO. Most sites experienced lower DO (66%) within the impoundment compared to upstream; however, 58% of the sites showed no difference in diel ranges between these reaches. The effect of dams on downstream DO was mixed, with increases, no change, and decreases relative to upstream condition; however, the majority of sites (58%) experienced a suppressed downstream diel range relative to upstream. The upstream slope, basin size, and dam height drove the impoundment response, such that dams with steeper upstream reach slopes, located in smaller basins, and with shorter dam heights experienced the greatest decreases in impoundment DO relative to upstream. Differences between downstream and upstream DO were best explained by upstream slope and impoundment volume, whereby sites with steeper upstream reaches and larger volumes of water within the impoundment experienced the largest decreases in downstream DO when compared to upstream reaches. These results may help managers prioritize dam removal at sites where a dam is having larger and more negative (e.g., elevated temperatures, decreased DO) impacts, and therefore where the greatest benefits should occur following restoration.

Post-dam removal geomorphologic adjustment of a stream channel has been documented in the scientific literature at watershed, hillslope, and laboratory scales. Hillslope-scale studies in channel cross sections are most common and add significant value in the dam-removal literature. This study examines geomorphic stream channel adjustment following dam removal at the hillslope scale under natural climatic conditions. A sedimentfilled silt fence dam (1 m tall, 12.65 m wide) was removed in three stages, and the width and depth of the upstream developing channel was monitored at six transects for 15 months. Headcut retreat and changes in channel sinuosity were also recorded. After the silt fence dam was removed, channel development was initiated by headcut formation, which migrated upstream at a rate of 4 cm/d for about 10 months and then gradually reached attenuation. The channel progressed through four distinct stages: Stage 1 (Initial conditions); Stage 2 (Downcutting)-wide, shallow, meandering channel incised to a maximum depth of 0.52 m, and sinuosity decreased; Stage 3 (Floodplain development)-upon reaching base level, surface runoff began to meander within the channel, widening it through bank slumps and erosion; and Stage 4 (Quasi-equilibrium)-channel development reached dynamic (quasi-) equilibrium with only minor widening at downstream transects (maximum width of the incised channel reached 0.46 m), accompanied by sediment aggradation. The stages of upstream channel development and headcut retreat pattern in this study are consistent with the findings of other studies at the laboratory and watershed scales, indicating that channel development after dam removal is scale independent.

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In recent years, the United States has seen a high demand for dam rehabilitation projects as most dam infrastructure has started to reach or exceed the expected life span of 50-70 years. Rehabilitation projects can be very expensive, however, and the funding options for dam owners are limited. To raise awareness, organizations such as ASDSO and the Virginia DCR release cost estimates every few years to encourage more investment in dam infrastructure. Unfortunately, many cost estimates have been made with limited data and outdated methodologies. This research collects a new sample of cost data for Virginia dam rehabilitation projects and uses it to assess key factors for cost estimating. Factors such as height, drainage area, hazard classification, and ownership type were used to make regression models that predict the cost of addressing Virginia's non-compliant dams. This study estimates that approximately $300 million is needed to address Virginia's 98 deficient high hazard, local government owned dams and that $122 million of that estimate is need for SWCD dams alone. / Master of Science / Dam rehabilitation refers to the repair, removal, or upgrade of an existing dam structure. Rehabilitation projects are done when dams start to exceed their intended life span (approximately 50-60 years) or when policy makers change the required safety standards. The demand for dam rehabilitation has been increasing for the past several years as more and more dams are being identified as unsafe, but the available funding for rehabilitation projects is limited and competitive to obtain for dam owners. To raise awareness, dam safety agencies release cost estimates every few years to encourage government leaders and the general public to take action. However, these estimates need to be taken with caution as they are often made with limited data availability and outdated methodologies. This research collects a new sample of cost data for Virginia dam rehabilitation projects that have occurred in the last 15 years. Dam characteristics such as height, watershed size, downstream risk potential, and ownership type were used to form equations that predict the cost of addressing Virginia's non-compliant dams. This study estimates that approximately $300 million is needed to address Virginia's 98 deficient high hazard, local government owned dams and that $122 million of that estimate is need for Virginia's Soil and Water Conservation District dams alone.

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This thesis explores landscape's framing role in memorialization through a discussion of southeastern United States mill villages. This paper moves the preservation discussion from the architectural realm of an isolated textile mill building to the scale of the landscape encompassing the entire infrastructure of mill life. The beginning of the 20th century witnessed the transformation of the piedmont region of South Carolina from a farmland of sharecroppers to the cotton textile center of the nation. This rapid industrialization altered rolling landscape and winding creeks into a series of mill villages and dammed waterways connecting larger cities of neighborhood mills. The beginning of the 21st century is witnessing another transformation, the shuttering of those mills because of globalization and a trend toward adaptive reuse into luxury apartments. While this form of preservation rescues a portion of the deteriorating memory infrastructure, it threatens to distort or erase the unique relationship between mill and mill village by romanticizing mill life and brushing over the complex history of labor present in those spaces. The landscape reveals that the mills channeled not only human labor, but also the work force of nature through dams regulating waterways. Like the social restructuring of the mills, this restructuring of nature had impacts: disturbed ecologies, toxic sedimentation, and altered waterways. Investigation proceeds through a research and design process. Research includes creating a spatial data set of the mills in the South Carolina piedmont region from a list in the 1930 edition of Clark's directory of southern textile mills. This mapping along with watershed analysis determines a specific mill site for intervention along a waterway where dams have impaired the natural ecology. The design explores the potential of revising or removing the mill dam, a piece of memory infrastructure, and wrestles with the balance of preservation and ecological restoration. / Master of Landscape Architecture

L’Orge est une petite rivière de plaine fortement segmentée, du bassin parisien. En 2010, elle comptait en moyenne un clapet tous les kilomètres sur sa partie aval. Pour rétablir la continuité écologique du cours d’eau, le Syndicat de l’Orge efface progressivement ces ouvrages. L'objet de cette thèse est le suivi biogéochimique, hydro-sédimentaire et écologique d'un bief de l’Orge de 6 km où 3 clapets consécutifs ont été effacés.Les hauteurs d’eau dans la rivière ayant baissé, des bancs de vase ont été mis à l'air. Ces banquettes de sédiments subissent des séquences d’inondation/exondation au rythme des crues. Les transformations de l’azote et du soufre y sont particulièrement actives et dynamiques. Cependant, les faibles flux d’eau échangés (modélisation) limitent l’impact des banquettes sur la rivière. Des processus intenses de précipitation/solubilisation des sulfates, liés aux variations des niveaux d’eau, ont une importance non négligeable sur la dégradation de la matière organique et la production d’ammonium dans la banquette.La capacité de transport de sédiments de la rivière a fortement évolué suite aux effacements, ce qui se traduit par l’apparition d'une granulométrie plus grossière en fond de lit. Ont été évalué la nouvelle vitesse de transit des particules charriées et le temps nécessaire pour atteindre un nouvel équilibre du lit et des espèces biologiques qui y vivent. Les indicateurs biologiques montrent que les effacements améliorent l’habitabilité de la rivière.Ces suivis montrent l’impact positif des effacements de barrage sur une rivière de plaine, même si un suivi dans la durée reste nécessaire pour confirmer les évolutions mises en évidence. / Orge is a lowland river from Seine’s watershed, France. In 2010, Orge River was highly segmented with on average one dam (< 2m) every kilometer in downstream part. To restore the ecological continuity of the river, the “Syndicat de l’Orge” gradually removes these little dams. The purpose of this thesis is the monitoring of hydro-morphology, biogeochemistry and ecological of a section of 6 km of Orge where 3 consecutive dams have been removed in spring 2010.After the water level decrease, some previously drowned sediment deposits appear along the river bank. These sediment banks are frequently inundated by high flows. Nitrogen and sulfate processes are very intense onto these banks. However, a model shows that water fluxes limited biochemical impact of sediment banks on the river. Intense precipitation/solubilization sulfate processes, link with water level variations, have a significant importance on organic matter degradation and ammonium production in sediment banks.The sediment transport capacity of the river has changed significantly after dam removal. It results in an increase of the maximum transportable diameter of the river, leading to the appearance of a coarser bed in-situ. It was possible to evaluate the new transit speed of particles carried along and highlight the time required to reach a new equilibrium of the bed and the biological species that live there. Biological indicators show that removals enhanced the livability of the river.All these studies show the positives impacts of dam removal on a lowland river, even if a monitoring in time is still needed to confirm the first developments highlighted here.

Dada a importância estratégica das barragens no Brasil e à disputa de interesses, o descomissionamento dessas estruturas é um assunto inevitável a ser discutido. Um conjunto de casos de descomissionamento de outros países é apresentado e ilustra de maneira abrangente essa questão pouco discutida e ainda não legislada no Brasil. Uma metodologia para avaliação da necessidade de descomissionamento com base no potencial de risco oferecido foi proposta e aplicada aos barramentos constantes do Cadastro de barragens das bacias PCJ, no estado de São Paulo. Apesar de a metodologia não poder ser aplicada em sua total extensão devido à insuficiência de dados do cadastro, é possível perceber quando algumas barragens encontram-se descuidadas, sem nenhum tipo de monitoramento podendo ser elegíveis para escomissionamento. / Due to the importance of dams in Brazil and to different interests, dam decommissioning is an unavoidable issue to be discussed. Some examples of dam removal in some countries are presented to generally elucidate this subject that still hasnt been acknowledged, neither legislated in Brazil. A methodology for evaluation of decommissioning demanding, based on the potential risk offered by dams has been set up and tested over a few dams that are constituent of a data basis of dams of Piracicaba-Capivari-Jundiaí (PCJ) basins, in São Paulo state. Despite the fact that the methodology couldnt be used at its full length due to lack of field data, it has been realized when some dams of the data basis are most despised, recklessly maintained and are contestant for decommissioning.