Dam Removal

By trapping sediment in reservoirs, dams interrupt the continuity of sediment transport through rivers, resulting in loss of reservoir storage and reduced usable life, and depriving downstream reaches of sediments essential for channel form and aquatic habitats. With the acceleration of new dam construction globally, these impacts are increasingly widespread. There are proven techniques to pass sediment through or around reservoirs, to preserve reservoir capacity and to minimize downstream impacts, but they are not applied in many situations where they would be effective. This paper summarizes collective experience from five continents in managing reservoir sediments and mitigating downstream sediment starvation. Where geometry is favorable it is often possible to bypass sediment around the reservoir, which avoids reservoir sedimentation and supplies sediment to downstream reaches with rates and timing similar to pre‐dam conditions. Sluicing (or drawdown routing) permits sediment to...

The vast majority of dams in the US, and thus the majority of those removed, are small structures that are governed primarily by state and local institutions. Important differences between large and small dams suggest that the existing work on the governance of large dam removals should not be expected to explain decisions about small dam removals. It is, for example, unclear which policies and organisations drive dam removals when there is no direct federal nexus. It is also unclear how the relevant policies and organisations shape the local decision-making process and how the design of the decision-making process influences stakeholder opinions on the decision to remove the dam. The objective of this study is thus to characterise and evaluate the governance that has driven recent decisions to remove small dams. A modified version of Ostrom’s Institutional Analysis and Development framework was applied to two dam removal case studies, that of the Beeson-Robison Dam in Oregon and th...

The foundations of river restoration science rest comfortably in the fields of geology, hydrology, and engineering, and yet, the impetus for many, if not most, stream restoration projects is biological recovery. Although Lane's stream balance equation from the mid-1950s captured the dynamic equilibrium between the amount of stream flow, the slope of the channel, and the amount and calibre of sediment, it completely ignored biology. Similarly, most of the stream classification systems used in river restoration design today do not explicitly include biology as a primary driver of stream form and process. To address this omission, we cast biology as an equal partner with geology and hydrology, forming a triumvirate that governs stream morphology and evolution. To represent this, we have created the stream evolution triangle, a conceptual model that explicitly accounts for the influences of geology, hydrology, and biology. Recognition of biology as a driver leads to improved understanding of reach-scale morphology and the dynamic response mechanisms responsible for stream evolution and adjustment following natural or anthropogenic disturbance, including stream restoration. Our aim in creating the stream evolution triangle is not to exclude or supersede existing stream classifications and evolutionary models but to provide a broader "thinking space" within which they can be framed and reconsidered, thus facilitating thought outside of the alluvial box.

Cette étude présente une estimation de la valeur économique totale (VET) des biens et services marchands de la ressource en eau dans le delta de l’Ouémé en l’unité monétaire. Les données utilisées sont collectées dans le mois d’Avril 2021 avec 797 pour le compte de l’agriculture, 500 pour le compte de la pêche et 138 pour le compte de l’élevage. En somme, la valeur d’utilisation économique totale des biens et services marchands liés à l’agriculture, la pêche et l’élevage de la ressource en eau du delta de l’Ouémé est de cent quarante millions cent quatre-vingt-trois mille cent quatre-vingt-onze virgule soixante cinq franc cfa (140.183.191,65). Cette valeur est nécessaire pour l’introduction des approches intégrées de planification et de valorisation des ressources agricoles, animales
et halieutiques dans le delta de l’Ouémé.

Accurate estimation of suspended sediment in rivers and reservoirs is fundamental for water resources management, reservoir sustainability, flood risk assessment, river morphology studies, and the operational safety of hydraulic infrastructure. Conventional sediment sampling techniques, while reliable, are often labor-intensive, discontinuous, and limited in capturing the high spatial and temporal variability of sediment transport. Suspended sediment transport directly influences river dynamics, reservoir storage loss, and water quality, making the development of advanced, continuous monitoring systems essential. In recent decades, Acoustic Doppler-Based Technologies Acoustic Doppler Current Profilers (ADCPs), Acoustic Doppler Velocimeters (ADVs), and Acoustic Doppler Meters (ADMs) have emerged as robust tools for estimating Suspended Sediment Concentration (SSC) and flux. By exploiting acoustic backscatter intensity calibrated against sediment properties, these instruments enable non-intrusive, real-time, and highresolution measurements across river cross-sections. Advances in signal processing, beam geometry, and multi-frequency acoustic systems have further enhanced the accuracy of SSC estimation, particularly in distinguishing particle size distributions and concentration levels. Integration with geostatistical techniques and machine learning models has strengthened predictive capability, while coupling ADCP velocity profiles with sediment rating curves allows comprehensive quantification of sediment load, bridging the gap between point-scale measurements and basin-scale sediment budgets. Operational adoption of acoustic techniques is expanding among river basin agencies, dam operators, and hydropower developers, supporting decision-making for sediment management strategies, desiltation planning, and infrastructure protection. Implementation frameworks emphasize robust calibration with physical samples, optimized deployment strategies (fixed stations, boat-mounted systems, or tethered platforms), and seamless integration with existing hydrological and digital monitoring networks. Challenges such as acoustic signal attenuation under very high sediment loads, particle composition variability, and site-specific calibration requirements remain, but international case studies confirm that acoustic approaches deliver cost-effective, continuous, and actionable sediment data compared to traditional methods. This paper synthesizes the scientific advances, methodologies, and field applications of Acoustic Doppler techniques for suspended sediment monitoring. It outlines an implementation framework and proposes a Standard Operating Procedure (SOP) for field deployment. The case studies from India and abroad, the paper highlights operational advantages, limitations, and pathways for integrating acoustic approaches into long-term sediment management and dam safety frameworks. By addressing technical challenges and emphasizing best practices, the study provides a roadmap for transitioning river sediment monitoring from manual, periodic sampling to continuous, adaptive, and data-driven systems in the context of climate variability and increasing anthropogenic pressures.

Dam removal is often proposed as way to restore ecological integrity to rivers and streams, but ecological responses to dam removals are poorly understood, especially for downstream benthic communities. We examined the responses of benthic macroinvertebrate and algal assemblages in downstream reaches to the removal of a small, run-of-river dam on Manatawny Creek, Pennsylvania. Benthic macroinvertebrates, algae, and habitat characteristics were monitored upstream and downstream of the dam for 4 mo before removal, 3 mo after partial removal (i.e., when the impoundment was largely eliminated but sediment remained trapped behind the remaining structure), and 12 mo after complete dam removal. Macroinvertebrate density, algal biomass, and diatom species richness declined significantly downstream of the dam following complete dam removal, but overall assemblage structure (as indicated by Nonmetric Multidimensional Scaling ordinations) downstream remained similar to upstream control sites throughout the study for both invertebrates and diatoms. Downstream impacts occurred only after the dam structure had been completely removed and sediments had been transported downstream from the former impoundment by high flows. Biotic impacts persisted for the duration of the study (12 mo after complete removal). Our results and other studies of dam removal suggest that downstream sedimentation following dam removal can reduce densities of macroinvertebrates and benthic algae and may reduce benthic diversity, but for small dams such impacts may be relatively minor and will usually be temporary.

To advance the science of dam removal, analyses of functions and benefits need to be linked to individual dam attributes and effects on downstream receiving waters. We examined 7550 dams in the New England (USA) region for possible tradeoffs associated with dam removal. Dam removal often generates improvements for safety or migratory fish passage but might increase nitrogen (N) flux and eutrophication in coastal watersheds. We estimated N loading and removal with algorithms using geospatial data on land use, stream flow and hydrography. We focused on dams with reservoirs that increase retention time at specific points of river reaches, creating localized hotspots of elevated N removal. Approximately 2200 dams with reservoirs had potential benefits for N removal based on N loading, retention time and depth. Across stream orders, safety concerns on these N removal dams ranged between 28% and 44%. First order streams constituted the majority of N removal dams (70%), but only 3% of those were classified as high value for fish passage. In cases where dam removal might eliminate N removal function from a particular reservoir, site-specific analyses are warranted to improve N delivery estimates and examine alternatives that retain the reservoir while enhancing fish passage and safety.

Human disturbance induces significant geomorphic changes to river systems. In eastern Australia, land‐use practices such as clearance of forests and riparian vegetation, and removal of wood from channels in the 19th and 20th centuries induced widespread geomorphic impacts. However, since the 1970s, there has been a noticeable shift in the geomorphic condition of many rivers in eastern New South Wales (NSW). This transition to a recovery trajectory reflects a reduction in land‐use pressures and improved farming practices on the one hand and adoption of recovery enhancement approaches to river conservation and rehabilitation by management authorities on the other. Monitoring and tracking changes in condition by state government agencies involves identifying when geomorphic recovery is occurring so that decision‐support frameworks can determine whether river management is required, where, when, and how much to intervene to enhance river recovery and when to opt‐out of management becaus...

The aim of this study was to determine if Arase dam gate removal and flushing elevated concentrations of any trace elements in Kuma River and Yatsushiro Bay sediments or caused riverine environmental change. The Arase dam gate on the Kuma River was opened in April 2010. Surface and bottom sediments were compared using 10-cm-long cores (2011) and two grain size fractions. Surface sediment data from 2002, 2012, and 2013 from the Kuma River and Yatsushiro Bay were also compared. The sediments were analyzed using XRF for 23 elements, and the grain size analysis was done. The short core surface and bottom sediments do not show major chemical changes, and therefore, may not represent post-and pre-dam sediments. Results based on 2011 samples show that the removal of the Arase dam gates in 2010 has been geoenvironmentally beneficial due to the decrease of environmentally related trace elements Pb and Zn in 2013. However, a slight increase in the levels of Cr, Cu, Zr, and Nb in 2013 indicate...

The successful completion of any project entails extraordinary planning, patience, cooperation, and collaborative hard work involving many individuals. Sustaining American Indian consultation partnerships that involve research, fieldwork, analysis, report writing, and mitigation meetings requires careful planning, patience, coordination, and cooperation among the numerous individuals involved in government-to-government consultation programs on the Nevada Test and Training Range and on the Nevada Test Site. This report represents the integrated efforts of two federal agencies, 18 American Indian entities, and many individuals who have collaborated at multiple levels in order to allow this project to germinate. We wish to express our sincere appreciation towards the people who have contributed to this project's success. This study and related studies conducted over the past ten years could not have been undertaken without the participation of numerous Indian elders and cultural experts who took the time away from their jobs, families, and other commitments, sometimes traveling great distances, to share with us their traditional knowledge, stories, beliefs, and worldviews, often about sensitive topics. We extend our thanks to those people who shared their stories in person as well as in written form. With apologies at the outset for anyone we may have inadvertently omitted, it is with profound gratitude and respect that we acknowledge the following Indian people: Pat Alpers,

À partir de terrains d’étude variés, aux Nords comme aux Suds, permettant de situer le propos dans différents contextes historiques, culturels et linguistiques, l’objectif du colloque « Collectifs : mémoires, discours, territoires » est de comprendre comment la notion de « collectif » permet d’appréhender des enjeux de société contemporains, globaux, dans une perspective comparative. Il s’agit d’étudier comment cette notion est construite, interprétée et remobilisée, dans des actions visant à faire émerger des solidarités. De même, l’enjeu est d’évaluer dans quelle mesure les « collectifs », formés, organisés, servent de levier à la création de légitimités et de projets politiques territorialisés. Ainsi, le colloque cherchera à déterminer comment les articulations entre « mémoires », « discours » et « territoires », permettent aux collectifs d’émerger, de se structurer et d’engager des changements sociaux observables dans l’espace.

Strategies for filling the Grand Ethiopian Renaissance Dam and implications for downstream water resources are analyzed using a river basin planning model with a wide range of historical hydrological conditions and increasing coordination between the co-riparian countries. The analysis finds that risks to water diversions in Sudan can be largely managed through adaptations of Sudanese reservoir operations. The risks to Egyptian users and energy generation can be minimized through combinations of sufficient agreed annual releases from the Grand Ethiopian Renaissance Dam, a drought management policy for the High Aswan Dam, and a basin-wide cooperative agreement that protects the elevation of Lake Nasser.

Overstreet, and Laurel Stratton Garvin (USGS) provided technical content and methodological advice to inform the monitoring approaches. Heather Bervid and Gabriel Gordon (USGS) assisted with manuscript preparation. We thank Terrence Conlon (USGS) for comments and discussions that shaped our thinking and the structure of this report. Acknowledgments .

Coastal erosion outpaces land generation along many of the world's deltas and a significant percentage of shorelines, and human-caused alterations to coastal sediment budgets can be important drivers of this erosion. for sediment-starved and erosion-prone coasts, large-scale enhancement of sediment supply may be an important, but poorly understood, management option. Here we provide new topographic measurements that show patterns and trends of beach accretion following the restoration of sediment supply from a massive dam removal project. River sediment was initially deposited in intertidal-to-subtidal deltaic lobes, and this sediment was reworked by ocean waves into subaerial river mouth bars over time scales of several months. these river mouth bars welded to the shoreline and then initiated waves of sediment accretion along adjacent upcoast and downcoast beaches. Although the downcoast shoreline has a high wave-angle setting, the sedimentation waves straightened the downcoast shoreline rather than forming self-organized quasi-periodic instabilities, which suggests that simple coastal evolution theory did not hold under these conditions. combined with other meganourishment projects, these findings provide new understanding of littoral responses to the restoration of sediment supplies. Coastal erosion and flooding hazards along the world's shorelines pose risks to human settlements, infrastructure and natural resources 1-3 . The rates of sediment supply to coasts and the movement of coastal sediment will govern whether coastal settings accrete or erode and are, therefore, integrally related to coastal hazards 4 . Rivers are an important source of sediment to many coastal settings, and humans can increase or decrease these supplies through watershed modifications and river engineering . Many rivers throughout the world have been dammed to provide water supplies, flood control, and hydroelectric power, which have had the unintended consequences of reducing fluxes of sediment to the coast . Because river mouths and deltas are inherently dynamic landforms from the variability of river sediment supply with time as well as other hydrologic and oceanographic factors 7,9,10 , erosion of these systems can be pronounced where river sediment is intercepted by dams, such as documented for the Nile, Yangtze, Mekong, Ebro and other Mediterranean deltas . Given these coastal challenges, there is growing interest in supplementing or restoring sediment inputs to coastal systems to reduce erosion and flooding. Although dredging and beach nourishment has become routine along many developed shorelines , there is increased urgency to conduct and understand innovative, large-scale projects that have the potential to reverse deficits in coastal sediment budgets and improve coastal resilience . The removal of the Elwha and Glines Canyon Dams from the Elwha River, Washington, USA initiated an unprecedented ecosystem and sediment restoration for a river with nearly a century of reduced sediment supply (Fig. ). Built in 1912 and 1927, these two hydroelectric dams were originally constructed to be 32 m and 64 m in height and with 10 million m 3 and 50 million m 3 storage capacities, respectively, but they did not allow fish passage for salmonids returning to spawn in the watershed. The removal of these dams, which began in 2011, can be considered the largest dam removal project to date, because it resulted in the tallest dam intentionally removed and the greatest sediment release from a dam removal project . Before dam removal began in 2011, approximately 30 million tonnes (Mt) of sediment was deposited in the river's reservoirs [we use units of mass for sediment, owing to its conservation and the documented variability in sediment bulk density throughout the Elwha system 20 ]. The grain size of these reservoir sediments were found to be approximately 63% coarse (sand, gravel and cobble) and 37% silt and clay by mass 25 . Sediment capture by the reservoirs resulted in downstream reductions in sediment supply that caused measurable changes in the morphology and rates of change in the fluvial and coastal landforms . For example, reduced sediment supplies to the downstream river resulted in coarsening of much of the river bed to an armored, cobble substrate 27 . At the

Small surface-release dams are prevalent across North American watersheds and can alter stream flow, thermal regimes, nutrient dynamics, and sediment transport. These dams are often implicated as a cause of negative water quality impacts—including reduced dissolved oxygen (DO)—and dam removal is increasingly employed to restore natural stream processes and improve DO. Published impacts of small dams on DO vary widely across sites, and even less is known about the extent and timescale of DO recovery following removal. Therefore, we sought to quantify the effects of small dams and dam removal on DO and determine the dam, stream, and watershed characteristics driving inter-site variation in responses. We deployed continuous data loggers for 3 weeks during summer months in upstream (reference), impoundment, and downstream reaches at each of 15 dammed sites and collected equivalent data at 10 of those sites following dam removal. Prior to dam removal, most sites (60%) experienced a decre...

Extending from the area of tidal influence, including the riparian zone, out to 30 meters Mean Lower Low Water (MLLW) depth, the Elwha nearshore provides migration corridor, rearing, and spawning habitat for federal and state listed species including the following: bull trout, chinook salmon, coho salmon, steelhead, eulachon, longfin smelt, surf smelt, and Pacific sand lance.

Over the lifetime of a dam several measures are usually taken in order to assure the stability and the performance of the dam. In this case a hydropower dam in Northern Sweden is in need of dam safety measures. The question arose, what consequences there might be when such measures are performed. In order to estimate these effects, simulations have been carried out in the finite element programme PLAXIS 2D. Thereby, the deformations and the stability of the dam for the planned work can be evaluated. The performed simulations are based upon previously conducted research at Luleå University of Technology, where soil parameters in the investigated dam were identified by a method of inverse analysis. Three sections have been analysed: A, B and C. In section A increasing pore water pressure has been observed at the downstream side of the dam. Thereby it has been concluded that a new drainage system is needed; new trenches of large size are to be excavated. In section B new toe berms are planned, due to the requirement that the dam should be able to divert leakage without erosion occurring at the dam toe. This contains soil material that might degrade when stresses are increased, with intensified deformations as a consequence. In section C a new berm is to be constructed, before this can be conducted an excavation is performed at the toe of the dam. The results have shown deformations of an acceptable magnitude and factors of safety that indicate conditions for the planned dam safety measures. Numerical values of deformations and factors of safety can be utilised as an attempt to establish alarm values for the stability of the dam. The finite element method is a useful tool for this kind of evaluation.

Dam removal in the United States is becoming a common practice for stream restoration as these structures age, climate driven precipitation patterns change, and ecological uplift becomes desirable. Yet in highly urbanized watersheds, these dams may operate as retention basins removing pollutants and mitigating hydrological change. While elimination may be ecologically and economically advantageous, sediment and pollutant removal processes may be better protective of water quality and damaging flooding. In Central Virginia, we compared a watershed split between an urbanized subwatershed (>20% impervious surface encompassing 37.8% of the total watershed land surface) flowing through a 18 Ha reservoir with a rural subwatershed (<5% impervious encompassing 63.2% of the total watershed land surface) located in the James River and Chesapeake Bay watersheds. This reservoir is scheduled for removal in the near future. Comparisons of data suggest that while portions of the urbanized watershed are degraded, this condition is not reflected at the confluence where water quality more closely resembles the rural and minimally impervious subwatershed. This conclusion was further strengthened from data collected following an unexpected dam overtopping in August 2018 where the reservoir was temporarily drained because of safety concerns. After the draining, water quality reversed with the confluence resembling the urbanized rather than the rural subwatershed. Most significantly, water quality flowing into the James River quickly and significantly shifted from a good to a degraded condition. This case study suggests reservoirs in highly urbanized watersheds may serve as critical water quality improvement structures and removal as part of a stream restoration strategy must be carefully considered.

Dam removal in the United States is becoming a common practice for stream restoration as these structures age, climate driven precipitation patterns change, and ecological uplift becomes desirable. Yet in highly urbanized watersheds, these dams may operate as retention basins removing pollutants and mitigating hydrological change. While elimination may be ecologically and economically advantageous, sediment and pollutant removal processes may be better protective of water quality and damaging flooding. In Central Virginia, we compared a watershed split between an urbanized subwatershed (>20% impervious surface encompassing 37.8% of the total watershed land surface) flowing through a 18 Ha reservoir with a rural subwatershed (<5% impervious encompassing 63.2% of the total watershed land surface) located in the James River and Chesapeake Bay watersheds. This reservoir is scheduled for removal in the near future. Comparisons of data suggest that while portions of the urbanized watershed are degraded, this condition is not reflected at the confluence where water quality more closely resembles the rural and minimally impervious subwatershed. This conclusion was further strengthened from data collected following an unexpected dam overtopping in August 2018 where the reservoir was temporarily drained because of safety concerns. After the draining, water quality reversed with the confluence resembling the urbanized rather than the rural subwatershed. Most significantly, water quality flowing into the James River quickly and significantly shifted from a good to a degraded condition. This case study suggests reservoirs in highly urbanized watersheds may serve as critical water quality improvement structures and removal as part of a stream restoration strategy must be carefully considered.

Dam removal is often proposed as way to restore ecological integrity to rivers and streams, but ecological responses to dam removals are poorly understood, especially for downstream benthic communities. We examined the responses of benthic macroinvertebrate and algal assemblages in downstream reaches to the removal of a small, run-of-river dam on Manatawny Creek, Pennsylvania. Benthic macroinvertebrates, algae, and habitat characteristics were monitored upstream and downstream of the dam for 4 mo before removal, 3 mo after partial removal (i.e., when the impoundment was largely eliminated but sediment remained trapped behind the remaining structure), and 12 mo after complete dam removal. Macroinvertebrate density, algal biomass, and diatom species richness declined significantly downstream of the dam following complete dam removal, but overall assemblage structure (as indicated by Nonmetric Multidimensional Scaling ordinations) downstream remained similar to upstream control sites throughout the study for both invertebrates and diatoms. Downstream impacts occurred only after the dam structure had been completely removed and sediments had been transported downstream from the former impoundment by high flows. Biotic impacts persisted for the duration of the study (12 mo after complete removal). Our results and other studies of dam removal suggest that downstream sedimentation following dam removal can reduce densities of macroinvertebrates and benthic algae and may reduce benthic diversity, but for small dams such impacts may be relatively minor and will usually be temporary.

L’objectif de cet article est de mettre en évidence les liens entre la gestion intégrée des ressources en eau et l’approche de l’économie sociale. Cette étude a examiné les retombées positives d’un programme provincial néobrunswickois d’amélioration des systèmes de fosses septiques dirigé par des associations de bassin versant du littoral acadien (sud du golfe Saint-Laurent) entre 2003 et 2007. Tout d’abord, le contexte théorique permet de situer les concepts de gestion par bassin versant, de gestion intégrée des ressources en eau et d’économie sociale. Par la suite, une analyse des perceptions des retombées environnementales, économiques et sociales résultant de l’administration du programme provincial est effectuée grâce à une recherche partenariale participative, des entrevues et des groupes de discussion. Les conclusions de cette étude mettent en valeur la contribution de ces associations à l’économie sociale, au développement durable et à la gestion intégrée au Nouveau-Brunswick.

After the removal of two large, long-standing dams on the Elwha River, Washington, the additional load of sediment and wood is expected to affect the hydrology of the lower river, its estuary, and the alluvial aquifer underlying the surrounding flood plain. To better understand the surface-water and groundwater characteristics of the river and estuary before dam removal, several hydrologic data sets were collected and analyzed. An experiment using a dye tracer characterized transient storage, and it was determined that the low-flow channel of the lower Elwha River was relatively simple; 1-6 percent of the median travel time of dye was attributed to transient-storage processes. Water data from monitoring wells adjacent to the main-stem river indicated a strong hydraulic connectivity between stage in the river and groundwater levels in the flood plain. Analysis of temperature data from the monitoring wells showed that changes in the groundwater temperature responded weeks or months after water temperature changed in the river. A seepage investigation indicated that water from the river was moving into the aquifer (losing reach) between 1.7 and 2.8 kilometers from the river mouth. Surface-water measurements and temperature and salinity data collected throughout the estuary helped to characterize the magnitude and nature of water movement in and out of the estuary. Salinity and stage sensors positioned in the estuarine network showed a strong surface-water connection between the river and estuary waters east of the river. In contrast, there was a weaker connection between the river and estuarine water bodies west of the river.

After the removal of two large, long-standing dams on the Elwha River, Washington, the additional load of sediment and wood is expected to affect the hydrology of the lower river, its estuary, and the alluvial aquifer underlying the surrounding flood plain. To better understand the surface-water and groundwater characteristics of the river and estuary before dam removal, several hydrologic data sets were collected and analyzed. An experiment using a dye tracer characterized transient storage, and it was determined that the low-flow channel of the lower Elwha River was relatively simple; 1-6 percent of the median travel time of dye was attributed to transient-storage processes. Water data from monitoring wells adjacent to the main-stem river indicated a strong hydraulic connectivity between stage in the river and groundwater levels in the flood plain. Analysis of temperature data from the monitoring wells showed that changes in the groundwater temperature responded weeks or months after water temperature changed in the river. A seepage investigation indicated that water from the river was moving into the aquifer (losing reach) between 1.7 and 2.8 kilometers from the river mouth. Surface-water measurements and temperature and salinity data collected throughout the estuary helped to characterize the magnitude and nature of water movement in and out of the estuary. Salinity and stage sensors positioned in the estuarine network showed a strong surface-water connection between the river and estuary waters east of the river. In contrast, there was a weaker connection between the river and estuarine water bodies west of the river.

, et al.. A : Dynamique fluviale : Flux hydriques, sédimentaires et chimiques et Géormorphologie-B : Biocénoses aquatiques : Suivi des flux migratoires de poissons par Hydroacoustique (DIDSON) et Caractérisation biologique et toxicologique de la population de poissons dans la retenue de Vezins [Rapport d'étape annuel 2014-Programme Sélune Phase pré-arasement]. [Rapport de recherche] Agence de l'Eau Seine-Normandie. 2015, pp.96. hal-03378202

Dam removal is often proposed for restoration of anadromous salmonid populations, which are in serious decline in California. However, the benefits of dam removal vary due to differences in affected populations and potential for environmental impacts. Here, we develop an assessment method to examine the relationship between dam removal and salmonid conservation, focusing on dams that act as complete migration barriers. Specifically, we (1) review the effects of dams on anadromous salmonids, (2) describe factors specific to dam removal in California, (3) propose a method to evaluate dam removal effects on salmonids, (4) apply this method to evaluate 24 dams, and (5) discuss potential effects of removing four dams on the Klamath River. Our flexible rating system can rapidly assess the likely effects of dam removal, as a first step in the prioritization of multiple dam removals. We rated eight dams proposed for removal and compared them with another 16 dams, which are not candidates for removal. Twelve of the 24 dams evaluated had scores that indicated at least a moderate benefit to salmonids following removal. In particular, scores indicated that removal of the four dams on the Klamath River is warranted for salmonid conservation. Ultimately, all dams will be abandoned, removed, or rebuilt even if the timespan is hundreds of years. Thus, periodic evaluation of the environmental benefits of dam removal is needed using criteria such as those presented in this paper. Keywords Dam effects Á Pacific salmon Á Steelhead Á Climate change Á Klamath River Á Mediterranean environments Electronic supplementary material The online version of this article (

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Water is the essential resource to maintain all existing communities on the earth and its scarcity will have various direct and indirect impacts on each and every life forms of ecosystem [1]. But it is very unfortunate that this life saving natural resource is not uniformly distributed in all over the planet by season or else by location [2]. And the boom comes in the present era on worldwide due to dam projects and its developmental activities will complex it manifolds because the dam projects have many positive and negative impacts on human life and its related environment [3]. The positive impacts of the dam projects include that they mitigate the demand of drinking water at appropriate time and durability; it regulates environmental flow regimes, and have a major role in the growth and development of human civilization and overall development of the world’s metropolitan cities, its industrialization as well as in agriculture practices [4]. The need and demand of water is ever in...

We review and build on a growing literature assessing small dam removal outcomes to inform future dam removal planning. Small dams that have exceeded their expected duration of operation and are no longer being maintained are at risk of breach. The past two decades have seen a number of small dam removals, though many removals remain unstudied and poorly documented. We summarize socioeconomic and biophysical lessons learned during the past two decades of accelerated activity regarding small dam removals throughout the United States. We present frameworks for planning and implementing removals developed by interdisciplinary engagement. Toward the goal of achieving thorough dam removal planning, we present outcomes from well-documented small dam removals covering ecological, chemical, and physical change in rivers post-dam removal, including field observation and modeling methodologies. Guiding principles of a dam removal process should include: (1) stakeholder engagement to navigate the complexity of watershed landuse, (2) an impacts assessment to inform the planning process, (3) pre-and post-dam removal observations of ecological, chemical and physical properties, (4) the expectation that there are short-and long-term ecological dynamics with population recovery depending on whether dam impacts were largely related to dispersion or to habitat destruction, (5) an expectation that changes in watershed chemistry are dependent on sediment type, sediment transport and watershed landuse, and 6) rigorous assessment of physical changes resulting from dam removal, understanding that alteration in hydrologic flows, sediment transport, and channel evolution will shape ecological and chemical dynamics, and shape how stakeholders engage with the watershed. Keywords Dam removal Á Small dams Á Run-of-river dams Á Low-head dams Á Impoundment Á Channel evolution Á River restoration

Terrestrial wildlife species are important yet often overlooked taxa in the recovery of ecosystems following dam removal. Their presence can shape ecosystem recovery, signal restoration of ecosystem function, and influence food web dynamics and nutrient transfer. We used camera traps to examine seasonal use of two former reservoir beds and an upstream reference reach by the mammalian community following the removal of two large dams on the Elwha River, Washington, USA. For certain taxa, we compared current species use to data collected prior to dam removal. Camera traps revealed use by at least fifteen mammal species, including but not limited to American black bear (Ursus americanus), Columbian black-tailed deer (Odocoileus hemionus columbianus), Roosevelt elk (Cervus elaphus roosevelti), puma (Puma concolor), coyotes (Canis latrans), bobcats (Lynx rufus), and snowshoe hares (Lepus americanus). Coyotes were found mostly lower in the watershed outside the Olympic National Park boundary, while other species were distributed throughout the restoration area. We did not see major differences in species composition between the restoration areas and the upstream reference reach, though number of detections across study reaches differed for most species. Unlike previous findings, black bears were observed across all seasons in this study, suggesting a shift in seasonal use since dam removal. Full restoration of the terrestrial wildlife community could take decades to unfold, but early patterns demonstrate rapid establishment and use by wildlife on new riparian surfaces that are expected to continue to evolve with restoration of fish and vegetation communities.

6 Galeries de déviation et crues artificielles Les lacs de retenue bloquent le passage des matériaux charriés. Cela conduit à des déficits de charriage en aval, qui se répercutent négativement sur l'état écologique et morphologique des cours d'eau. Il est possible d'accroître la disponibilité des sédiments et d'atténuer ces déficits en construisant des galeries de déviation et en déclenchant des crues artificielles. Exemples à l'appui, la fiche 6 explique en quoi consistent ces deux mesures et décrit leurs effets sur l'écologie et la morphologie des eaux.