Dam Closure Research Articles

Numerical modeling for mining dam cover infiltration design with geosynthetics: A trade off study

In the mining dam closure project, depending on the classification of the tailings, cover systems are used to reduce precipitation infiltration over time, avoiding future environmental impacts associated with metal leaching. Furthermore, reduced infiltration promotes reservoir drainage and therefore improved geotechnical stability. The covering system can be built from different materials, natural or synthetic, or even using waste itself. The main objective of this study is to present the results as a trade-off study of a one-dimensional modeling performed considering 3 configurations of geosynthetic covers, using the SOFTWARE SEEP/W emphasizing the importance and impact of the presence of geosynthetics. Since numerical models constitute an essential tool in the development of engineering projects, computational numerical modeling was carried out using Brazilian climatic parameters from the National Institute of Meteorology in conventional and automatic stations, and historical geotechnical parameters for a structure located in the state of Minas Gerais. Gerais (Brazil). For the comparison of the cover configurations, the thickness and type of the geosynthetic were varied. The results emphasize the importance of studying numerical modeling in the pre-closure design phase, to define a viable, economical and sustainable coverage, and contribute to the use of geosynthetics in this type of application.

The Migration of the Erosion Center Downstream of the Three Gorges Dam, China, and the Role Played by Underlying Gravel Layer

AbstractRivers disrupted by sediment cutoff often experience degradation, but the migration of the erosion center, defined as the location with the greatest degradation rates, has not been thoroughly understood. This paper focuses on the streamwise migration of the erosion center along the ∼400‐km‐long Yichang to Chenglingji reach (YCR) downstream of the Three Gorges Dam (TGD), China. We analyzed channel morphological adjustment based on water, sediment and channel geometry data collected during 2002–2020. Based on the location and time for the occurrence of relatively large channel degradation, a clustering algorithm was used to identify the location of the erosion center. Characteristics and morphodynamic controls of the erosion centers were studied based on the migration of incisional and coarsening waves simulated by a one‐dimensional morphodynamic model for nonuniform sediment. Results show that the erosion center migrated downstream along the Yichang‐Zhicheng reach with gravel‐sand bed during 2002–2012, the migration rate was rapid after the dam closure then decreased with time. After ∼2012, large cascade dams started to operate along the upper Yangtze River, sediment load further decreased and degradation accelerated at the YCR. Correspondingly, the erosion center migrated to the sand‐bedded upper Jingjiang reach with faster rates. The erosion center migrated for a total of over 200 km with an average rate of ∼14 km/yr during 2002–2020. The underlying gravel layer was exposed due to degradation, which enhanced bed coarsening and resulted in the propagation of the erosion center downstream of the TGD.

Morphological resilience at the confluence of a very low discharge creek and a large river (upper Parana, Brazil)

Confluences are important environments within the drainage system for exchanges in energy, sediments, water, and the control of local ecology. Despite the significant advances in the understanding of confluences, the study of the junction of small rivers with very large rivers is still incipient. We present a case study of a confluence bar with an extremely low discharge ratio (Qr = 0.0002) and a high obtuse confluence angle (145°) just downstream of the Porto Primavera Dam, in the Upper Paraná River, Brazil. Our analysis includes bathymetric and sedimentological data from surveys prior to dam closure (1997), and after dam closure (2006, 2018), spanning a total of 21 years. Dam closure reduced the mean water level and suspended sediment load in the Paraná River, as well as controlling the occurrence of natural floods. Although the São Pedro Creek confluence bar has reduced, in terms of spatial area and sediment input, its morphology, sedimentation zones, and hydrodynamics has been preserved during this time frame (1997–2018). The stability of the confluence bar is probably mainly due to the high confluence angle (structural control) that causes high resistance in the Paraná River flow, allowing the generation of a large stagnation flow zone (depositional area). The Upper Paraná River, which is one of the most dammed watersheds in the world, has the São Pedro Creek and other small tributaries as important sediment sources for suspended load, mainly after the Porto Primavera dam construction. The results indicate that the stability of the São Pedro confluence bar is due to the association of the systems involved in the supply of sandy sediment, but mainly due to the obtuse angle, that imposes local conditions of flow and sedimentary circulation necessary for its formation and morphological maintenance.

Characterizing the response of the coastal Rio Grande to upstream damming

Dams are major obstructions to the flow of water and the transport of sediment in rivers. Much work has shown the construction of dams, and storage of sediment in reservoirs, can lead to significant changes in the morphodynamic behavior of alluvial rivers; however, in most cases, the effect of damming has a finite downstream limit as sediment is supplied back to the river through channel bed/bank erosion and/or tributary inputs. Here we present a study of a natural experiment that isolates one source of sediment downstream of a dam – the lower Rio Grande, which has no major tributary inputs of sediment over a ~450 km reach, from Falcon Dam to the coast. Analysis of the morphology and topography of the Rio Grande shows that prior to damming in the 1950s the coastal Rio Grande was a kinematically active channel with large, subaerial point bars. Subsequent to damming, lateral migration of the river shut down and exposed point bars shrunk in size, becoming static and vegetated. Bathymetric survey data show meter-scale incision of the channel bed for hundreds of kilometers downstream of the dam. Entrenchment of the river is also evidenced by the development of steep banks on the inner portions of channel bends. Damming also impacted the interaction between the river and the floodplain, resulting in the formation of persistent gullies incised into the channel banks, suggesting transport of water and sediment is net positive into, not out of, the channel. Based on all of these observations we conclude that the full ~450 km reach of the Rio Grande, from Falcon Dam to the coast, became net degradational following dam closure. We conclude that the presence of such a long degrading reach is caused by the exposure of bedrock in the Rio Grande channel for nearly 100 km downstream of the dam, which, combined with the lack of tributaries, limits downstream sediment supply to the river. Our results provide new insights into the response to damming for rivers with no tributary sediment input and thin alluvial cover, and more broadly to the kinematic and channel geometry responses to a major drop in water discharge and sediment supply for coastal meandering rivers.

Impacts of small dams on the phytoplankton and invertebrates in an Amazonian river

AbstractThe construction of small hydroelectric plants (SHPs) has increased greatly worldwide, and the impacts of these impoundments can cause changes in the aquatic biota. Here, we investigated the ecological attributes (abundance, richness, and species diversity) of three communities (phytoplankton, invertebrates in the water column, and benthos) and the functional groups of phytoplankton, before and after the construction of five SHPs in an Amazonian river. The communities were sampled at two sites, one upstream and another downstream of each dam or construction site, before the dam closure. The dam did not change the limnological factors, and the acid waters and low electrical conductivity, typical of “cerrado” rivers, were characteristic of both the pre‐ and post‐dam phases. For aquatic communities, the phytoplankton abundance increased and the diversity of groups decreased in the post‐dam phase. Regarding the morphology‐based functional groups (MBFG), there was an increase in groups I (small algae with a high surface/volume ratio) and V (phytoflagellates), with a reduction in groups VI (diatoms) and VII (large mucilaginous colonies) in the post‐dam phase. The relative abundance of zooplankton species increased in the post‐dam phase, and the opposite was observed for the benthic community, with reductions in abundance, richness, and group diversity in the post‐dam phase. The structure of the three communities differed between the pre‐ and post‐dam phases, but no difference in communities' similarity was observed between the upstream and downstream sites in both phases. The results show that the change in hydrodynamics, from lotic to semi‐lentic, in the reservoirs of the SHPs, was the main driving force for the alterations in the three communities. For phytoplankton, SHPs are favorable in the sense of decreasing the incidence of algal blooms, particularly of cyanobacteria.

Mechanisms of bar adjustments in the Jingjiang Reach of the Yangtze River in response to the operation of the Three Gorges Dam

Dams alter downstream river flow and sediment regimes, causing significant changes in river morphologies. The middle Yangtze River downstream of the Three Gorges Dam (TGD) has experienced rapid erosion in recent years, and the associated morphodynamic changes have negatively impacted the riverbank stability, navigation waterways and ecological functioning. Earlier studies have analyzed recent channel adjustments in the Yangtze River; however, our understanding of changes in the bar morphodynamics remains incomplete. In this study, we collected and analyzed flow and sediment data (1991–2016) and river bathymetry data (1975–2017) and investigated the mechanisms of bar adjustments along the Jingjiang Reach in the post-TGD period. The results indicate that most steady bars with a higher elevation and better vegetation coverage have experienced lateral erosion, while their elevations have remained stable overall. The unvegetated migrating bars with a lower elevation have experienced severe surficial erosion and area shrinkages. A new assessment method of the dominant discharge range on downstream bars is provided after dam closure. The dominant discharge range that determines bar adjustments corresponds to the flow stages between the submersion of migrating bars (∼12,500 m3/s) and the overtopping of vegetated steady bars (∼27,500 m3/s) in the Jingjiang Reach. A quantitative relationship exists between bar erosion in response to changed dominant discharge regimes and sediment decline. The significant bar erosion after the operation of the TGD can be attributed to the increased flow duration and the sharp decline in the suspended sediment concentration (SSC) of the dominant discharge range, and changes in SSCs play a primary role. The bar area will decrease by ∼0.003 km2 when the annual cumulative duration of the dominant discharge increases by one day and by ∼0.234 km2 when the annual average SSC of the dominant discharge decreases by 0.01 kg/m3. Furthermore, vegetation encroachment and colonization play a positive role in stabilizing bar morphologies and limiting surficial erosion, whereas vegetation soley cannot prevent the lateral erosion of steady bars. These findings suggest that multiple controls of discharge, sediment and vegetation on the evolution of fluvial bars and have important implications for river management and ecological evaluation in response to the operation of large dams.

Limnological characteristics of Lake of the Ozarks (Missouri, USA): long-term assessment following formation of a reservoir series

Jones JR, Obrecht DV, Thorpe AP. 2022. Limnological characteristics of Lake of the Ozarks (Missouri, USA): long-term assessment following formation of a reservoir series. Lake Reserv Manage. XX:XXX–XXX. Impoundment of Truman Lake in 1980 on the Osage River, above Lake of the Ozarks (LOTO), created a reservoir series. This analysis details the changes and processes over the ensuing 35 yr (1980–2014) in this large impoundment dominated by a longitudinal gradient along the mainstem. Temporal variation was determined by hydrology; seasonal mean total phosphorus (TP) ranged between 12 and 58 µg/L at the near-dam location, and hydrologic flushing during summer explained 82% of this variation. After dam closure, mineral suspended solids, attributed to channel scouring of erodible materials in the tailwater reach, declined over time, with a 50% reduction near the dam. Concurrently, organic suspended solids increased by 1 to 4%/yr in mid-reach locations, which indicates greater autotrophic production. Compared with other Missouri reservoirs, algal chlorophyll (Chl) averaged 1.6 times the value predicted from TP. Ratios of Chl:TP have increased over past decades concurrent with an increase in organic suspended solids and expansion of the ultraplankton (<11 µm) fraction of total Chl. Warm and dry conditions are associated with an increase in Chl in the ultra fraction, suggesting climate influence. A comparison with data collected prior to the closure of Truman Dam (1976–1979) provides incontrovertible evidence that light transmission has improved, and both Chl and Chl:TP have increased in LOTO. Formation of a reservoir series resulted in immediate and long-term changes in this major impoundment.

Amplification of downstream flood stage due to damming of fine-grained rivers

River dams provide many benefits, including flood control. However, due to constantly evolving channel morphology, downstream conveyance of floodwaters following dam closure is difficult to predict. Here, we test the hypothesis that the incised, enlarged channel downstream of dams provides enhanced water conveyance, using a case study from the lower Yellow River, China. We find that, although flood stage is lowered for small floods, counterintuitively, flood stage downstream of a dam can be amplified for moderate and large floods. This arises because bed incision is accompanied by sediment coarsening, which facilitates development of large dunes that increase flow resistance and reduce velocity relative to pre-dam conditions. Our findings indicate the underlying mechanism for such flood amplification may occur in >80% of fine-grained rivers, and suggest the need to reconsider flood control strategies in such rivers worldwide.

Temporal and spatial patterns in the shifting of otter diet to invasive prey after river damming

AbstractRiver damming promotes profound changes in aquatic biodiversity, including the facilitation of biological invasions, with subsequent impacts on native communities. The Eurasian otter (Lutra lutra) is a generalist aquatic predator that often incorporates new prey types when they become available. We studied the short‐ and long‐term effects of river damming on the trophic ecology of the otter across a riverine landscape gradient, from the flooded area to upstream tributaries, focusing on the largest artificial lake of Western Europe. Through the analysis of otter feces (spraints), we describe otter diet composition in 14 sites at different distances from the impounded area in three periods: (i) the pre‐filling phase (i.e., lotic conditions); (ii) the immediate filling phase; and (iii) 16 years after the dam closure. The diet of the otter drastically shifted in the short term, from being dominated by native cyprinids to being mainly composed of invasive species of fish and crayfish. In the long term, the number of invasive species consumed by the otter continued to increase while native fish completely disappeared as prey near the reservoir. Presumably, the construction of the dam generated clear spatial gradients of abundances of native and invasive fish species. These patterns arose in the short term but became accentuated in the long term and were mirrored in otter diet composition. Our results demonstrate the potential of otter diet analyses as a surrogate for the impacts of human alterations on aquatic ecosystems, including those of river damming and the associated facilitation of biological invasions.

Applying a Generalized FMEA Framework to an Oil Sands Tailings Dam Closure Plan in Alberta, Canada

Historically, tailings facilities have been designed primarily with consideration of the mine’s active life. This is problematic, as the lifespan of a tailings dam may far exceed the life of the mine. Over time, it is expected that these structures will transform into a mine waste structure and then eventually a landform. In Alberta, Canada, dam owners can submit a decommissioning, closure, and abandonment (DCA) plan and completion reports to apply for the facility to be de-registered as a dam. If successful, the structure would be considered a solid waste structure and may be reclassified and regulated as a mine waste dump. The Alberta Energy Regulator expects DCAs to be accompanied and supported by risk assessments that consider long-term physical failure modes, including failure modes that may not be applicable during operations, in accordance with Manual 019. To help support the process of de-registering a tailings dam, a risk management tool, referred to as a Generalized Failure Modes Effects (G-FMEA) framework, was developed and presented in the Journal of Minerals in the Special Issue Tailings Dams: Design, Characterization, Monitoring, and Risk Assessment. The G-FMEA was designed to be used for assessing risks of an external tailings facility in closure, with the goal of assessing the long-term risk of geotechnical failure to support the process of de-registration. In Alberta, a number of tailings dams are undergoing closure and reclamation activities. This paper applies the developed G-FMEA framework to an oil sands tailings dam in Alberta to demonstrate the application of the framework. The paper assesses two specific failure modes of two different elements, including clogging of the drains and surface erosion of the berm. The failure modes are assessed over different timescales to demonstrate how the consequence, likelihood, and risk rating may change over time. The results of this process are discussed in the context of the potential for the facility to be de-registered as a dam.

Delayed morphological adjustment of the Yellow and lower Wei Rivers upstream of the Sanmenxia dam at multi-temporal scales

The delayed response of channel evolution upstream of dams to base-level changes has not yet been thoroughly understood. In this paper, we studied the delayed response of the morphological adjustment at the middle Yellow and lower Wei Rivers upstream of the Sanmenxia Dam, China, based on data of water volume, sediment load, cross-sectional profiles, and erosion/deposition volumes during 1960–2018. Channel evolution upstream of the dam obviously lagged behind the dynamic pool level fluctuation during the first approximately two decades following dam closure, when retrogressive aggradation/erosion phases were identified. The retrogressive aggradation migrated ∼200 km upstream to the tributary of the Yellow River, i.e., the Wei River. The impact of base-level rise may propagate backwards behind the beginning of the backwater reach, reflecting indirect backwater effects. The dam has been operated by the controlled release of “storing the clear water during nonflood seasons and discharging the turbid water during flood seasons” since 1974, and the reservoir has generally been eroded during flood seasons and aggraded during nonflood seasons. The erosion center was defined as the subreach between two adjacent cross-sections with the greatest erosion rate during the flood season, and the aggradation center was defined as that with the greatest aggradation rate during the nonflood season. The results showed that the erosion/deposition centers migrated towards the dam by ∼50–60 km during 1974–2010 and migrated upstream after ∼2010. The location of the erosion/deposition centers was related not only to the water and sediment conditions and backwater length in the current year but also to these conditions in the previous ∼4 years, reflecting the delayed response of channel adjustment or the cumulative impact of pervious conditions on channel morphology. This study helps to inform future reservoir management and the delayed channel response to base level change caused by different natural and anthropogenic disturbances.

A Failure Modes and Effects Analysis Framework for Assessing Geotechnical Risks of Tailings Dam Closure

Tailings dams remain on site following mine closures and must be designed and reclaimed to meet long-term goals, which may include walk-away closure or long-term care and maintenance. The underperformance of these structures can result in significant risks to public and environmental safety, as well as impacts on the future land use and economic activities near the structure. In Alberta, Canada, the expectation is for a tailings dam to be reclaimed and closed so that it can undergo deregistration. To aid in assessing the risks of underperformance during and after closure, a Generalized Failure Modes and Effects Analysis (G-FMEA) framework was developed to assess the long-term geotechnical risks for tailings dams in Alberta, with the goal of assessing the potential success of a tailings dam closure strategy. The G-FMEA is part of an initiative to enhance closure evaluations in Alberta in a collaborative effort between industry, the regulator, and academia. The G-FMEA incorporates the element of time to account for the evolution of the system, which should be applied at the planning stage and updated continually throughout the life of the facility. This paper presents the developed G-FMEA framework for tailings dams in Alberta, including the developed risk matrix framework.

Chronosequence of morphological change in a stream fish following impoundment

Abstract Water impoundment is among the most prevalent and potent forms of anthropogenic environmental modification worldwide. Flow modification can drive morphological changes in riverine species that persist after dam closure, but little is known about the tempo and trajectory of phenotypic responses to impoundment. Through geometric morphometric analysis of natural history collections from behind Claiborne Lock and Dam (i.e. in Claiborne Lake reservoir) and nearby Chilatchee Creek (Alabama River Basin, Alabama, U.S.A.), we reconstructed multidecadal chronosequences of morphological change in a stream fish (Cyprinella venusta Girard) to characterise phenotypic responses to impoundment and unrestricted flow. We then conducted cross‐correlation analysis of hydrological and morphological time series to determine whether morphological responses to impoundment are consistent with expected outcomes of evolution, phenotypic plasticity, or some combination thereof. We found evidence of marked phenotypic change shortly after impoundment. Within a year of dam closure, individuals from Claiborne Lake exhibited a reduction in head size, an increase in body depth, and a decline in the length of the dorsal fin base, with further responses becoming apparent c. 6 years thereafter. The morphology of individuals from the nearby stream consistently differed from individuals in the reservoir. We found that fish from Chilatchee Creek exhibited gradual directional shifts and morphological fluctuations over time, which differed from patterns of change observed in C. venusta from Claiborne Lake. There also were indications of multidecadal lags at both sites, probably reflecting common responses to periodic climatic variation that were mitigated by site‐specific differences in physiography and ecology. Our findings are consistent with the hypothesis that impoundment can elicit punctuated responses attributable to within‐generational phenotypic change and rapid evolution over as few as two generations. Our findings also indicate that hydrological variation in unrestricted streams can elicit pronounced shifts in body shape, suggesting that space‐for‐time substitutions may not effectively capture the nature of responses to flow modification. Additional investigations based on more extensive and complete chronosequences would further illustrate the value of natural history collections and offer more insight into the mechanistic basis of biotic responses to environmental change.

The influence of changes in flow regime caused by dam closure on channel planform evolution: insights from flume experiments

Constructions of dams influence river courses by cutting off sediment delivery and altering flow regime. We conducted flume experiments to study how sediment starvation, flow deficit and occurrence of series of floods with sediment load influence the evolution of channel planform. Results indicated that reduced flow caused a transition from a braided to incised single-thread planform with remains of inactive channels. The planform resembled rivers suffering from flow reduction caused by dams and constructions of irrigation canals (e.g., Central Platte River, USA). Simulation of series of floods with no sediment delivery caused the formation of an anabranching planform with incised main channel, alluvial islands, and side channels active at high flows. This evolution corresponds to river courses altered by sediment starvation and series of floods (e.g., the lower Drava River, Hungary). Floods with delivery of fines created a single-thread, incised channel with terraces along banks. Such channels are formed by rivers closed by dams, and compensating sediment deficit by sediment load from tributaries and/or floodplains (e.g., the Green River, USA). The flume tests demonstrated how flow and sediment deficit influence river channels and that the potential for restoration strongly depends on possibilities for the activation of sediment supply. However, restoration of pre-dam conditions is often impossible owing to other hydro technical works and land use changes. The highest restoration potential refers to the rivers compensating sediment delivery blocked by dams with tributary and floodplain resources.

Post-wildfire riparian forest recovery processes along a regulated river corridor

Riparian forest recovery was monitored over a 23 km study site that encountered a mixed low to moderate severity wildfire on the floodplain that was followed by a sequence of flows ranging from below bankfull to a 50-year flood on the regulated South Fork Boise River, Idaho, USA. The goals of the study were to examine the dominant mechanisms of post-wildfire riparian forest regeneration along the river corridor in relation to upstream dam operations. Results are put in context with trends occurring in the regulated river system over the past 70 years that exemplify post-impoundment floodplain dynamics. Aerial imagery and field surveys were used to examine trends in geomorphic and forest response related to flow regulation, riparian wildfire, and a 50-year flood. Additionally, a one-dimensional sediment transport model was employed to assess seedling recruitment related to local and reach-scale erosional and depositional processes over a five-year period following the wildfire. A conceptual model is presented to illustrate riparian forest response to the interacting influences of fire severity and flood disturbance to help guide post-wildfire riparian forest management activities.Aerial imagery between 1957 and 2011 shows that flow regulation after dam closure led to channel narrowing of 62% of historic active channel width and an associated increase in floodplain tree density of 59%. This expansion of forest cover on the floodplain was at the expense of seedling recruitment habitat for pioneer species in the Salicaceae family that require bare sediment, light exposure, and access to the shallow groundwater. A 2013 riparian wildfire led to substantial top kill on the floodplain that provided a disturbance for potential seedling recruitment. However, dam releases during average and wet hydrologic conditions led to only 5% of the total observed seedling recruitment in the system occurring on the floodplain due to the limited magnitude of flood disturbances following the burn, highlighting the importance of the sequence of environmental flows immediately following riparian wildfire. Alternatively, 95% of seedling recruitment occurred within the active channel and was directly related to sediment transport processes. Post-wildfire related debris flows were responsible for providing the requisite sediment supply to the channel in an otherwise sediment supply-limited, regulated river system. Resultant sediment deposition was responsible for providing 100% of seedling recruitment habitat in the active channel during dam releases in average hydrologic conditions, whereas deposition accounted for 84% and erosion accounted for 16% of observed recruitment habitat during wet hydrologic conditions.

Hydropeaking Operations of Two Run-of-River Mega-Dams Alter Downstream Hydrology of the Largest Amazon Tributary

© Copyright © 2020 Almeida, Hamilton, Rosi, Barros, Doria, Flecker, Fleischmann, Reisinger and Roland. Large storage dams have widely documented impacts on downstream aquatic environments, but hydroelectric dams with little or no capacity for storage of water inflows (i.e., run-of-river) have received less attention. Two of the world’s largest run-of-river hydropower dams (Jirau and Santo Antonio, Brazil) are located on the Madeira River, the largest tributary to the Amazon River. Here we examine whether the Madeira dams have affected downstream seasonal flood pulses and short-term (daily and sub-daily) flow dynamics. We show that the combined effects of these dams on seasonal flood pulses were modest. However, dam operations significantly increased day-to-day and sub-daily flow variability. The increase in short-term flow variability is largely explained by rapid, short-term variations in river flow caused by fluctuations in energy demand (hydropeaking). Both the magnitude of hydropeaking and the mean absolute day-to-day change in discharge downstream of the dams doubled after dam closure. In addition, the median hourly rate of water level change downstream of the dams was three times higher than upstream. Our findings highlight that even run-of-river dams on very large rivers such as the Madeira—whose average discharge at the dam site is larger than that of the Mississippi River at its mouth—can alter downstream hydrology through hydropeaking. Although little studied in tropical floodplain rivers, hydropeaking by large run-of-river dams may be detrimental to downstream aquatic organisms and human populations that utilize the river for navigation and fisheries.

Closure of Lake Nasser Khores by Different Types of Dams, using Satellite Images

According to the agreement between Egypt and Sudan in 1959 for the full utilization of Nile water arriving Aswan, both countries agreed to build the High Aswan Dam (HAD) in 1964 to get benefits from the water which was flowing to the Mediterranean Sea. Therefore, Lake Nasser, the greatest artificial lake in the world, was created with large areas of shallow depths adjacent to the edges of the lake on both sides according to the topography of the surrounding area namely (khores). These khores increased the surface area; consequently, the estimated evaporation losses reach about 10 BCM/year in average. Reducing evaporation losses from HAD Lake is an option to increase the Egyptian available water resources. Many studies were done in order to partially or completely closure of the Khores, where the surface area of the khores of Lake Nasser is about one third of the total area of the lake, which indicates the effectiveness of its closure in decreasing the evaporation. The objectives of the research are studying the Lake Nasser’s large area khores, evaluating the idea of closing these khores using different types of dams such as earthfill, rockfill and rubber dams, and the consequent saved water. Meanwhile, a preliminary cost study for the different types of dams was done to determine the most suitable dam type. This research used the land sat 4 &amp; 5 at years 1988 and 1999 in order to identify the surface area of the lake for the lowest and highest levels respectively. Also it gets benefit from the data available at Ministry of water Resources and Irrigation (MWRI), such as the Khores bathymetric maps and the evaporation rates of Lake Nasser. The results of the study show that Kalabsha khore is the most optimum for dam closure as its entrance is suitable for dam construction, and at high water levels it has the greatest area thus, reducing the evaporation. It is highly appreciated to use rubber dam either economically or environmentally. The amount of saved water reach about 1.0 Milliard m3 representing 11.11% of the annual total evaporation losses from Lake Nasser, the water saved may reach 1.53 Milliard m3 if the water level reaches 181.52 m for considerable time span.

Response of A Gravel ‐ Bed River To Dam Closure: Insights From Sediment Transport Processes And Channel Morphodynamics

AbstractThis work deals with the impacts of dams on large gravel ‐bed rivers in terms of altering coarse transport regimes and the relationship with river morphodynamics. Using data collected by a tracer ‐based monitoring programme carried out in a 4 ‐km ‐long study sector of the Parma River (Italy), located downstream from a relatively recently established dam, we applied a virtual velocity approach to estimate the coarse bed material load at four river cross ‐sections. Monitoring and calculation results provided new insights into the impacts of the dam on streambed material mobility and the sediment regime over the 17 ‐month calculation period. A longitudinal gradient of effects was observed along the study sector. Sections located closer to the dam are characterized by more evident impacts due to deficits in coarse sediment input from upstream. Sediment mobility here is strongly altered, especially in the highly armoured main channel, and the overall bed material load is extremely low. A partial recovery of sediment dynamics was observed at the sections located further from the dam, where estimates indicate higher sediment yield. The observed longitudinal trend in the coarse sediment transport regime matches the morphology, as the river shifts downstream from a sinuous configuration with alternate bars to a wandering one. The novel insights into alteration of coarse sediment dynamics and the relationship with river morphodynamics are potentially applicable to many other fluvial contexts affected by similar impoundments. © 2019 John Wiley &amp; Sons, Ltd.

Tailings dam closure scenarios, risk communication, monitoring, and surveillance in Alberta

ABSTRACT Tailings dams remain as a part of the landscape in perpetuity following mine closure. As many mines approach closure in the province of Alberta, Canada, it is becoming increasingly important to understand the long-term geotechnical behavior of these facilities and the impact of various loading and environmental scenarios over long time periods. Research surrounding the closure of tailings dams has historically focused on planning for closure, with a limited focus on how the facility may evolve over time. This gap in research has implications for the design and development of policies that adequately account for long-term risk and uncertainty. This paper summarizes key themes identified during interviews conducted with skilled practitioners to leverage their experiences and help fill the knowledge gap surrounding the long-term behavior and policy-making for tailings dams. These include the impact of recent tailings dam failures, long-term monitoring and surveillance, potential closure scenarios, and risk communication.

The impact of a hydroelectric dam on Neotropical fish communities: A spatio‐temporal analysis of the Trophic Upsurge Hypothesis

AbstractWe employed the trophic upsurge hypothesis as an analytical framework to describe the response of Neotropical fish communities to terrestrial inundation associated with river damming. Data were collected for the impact assessment of the Peixe Angical Dam, Tocantins River, Brazil. Monthly surveys were conducted at nine sites (seven upstream, two downstream) from 15 months before to 20 months after dam closure and a follow‐up survey 60–83 months after closure. Fish responses differed in timing and magnitude across sites. In the new reservoir, populations peaked 8–13 months after flooding, demonstrating increases in richness (84 ± 52%), biomass (329 ± 266%) and abundance (681 ± 348%) with the maxima for richness and abundance tending to precede biomass maxima. Populations of all families increased but were greatest for Engraulidae, Hemiodontidae, Serrasalmidae and Characidae, and lower for the benthic catfish: Sciaenidae, Dorididae, Pimelodidae. Downstream populations peaked 5–12 months after closure or showed consistent decline. Five years after dam‐closure richness and abundance were lower compared to predam levels, with populations at all sites demonstrating an ongoing decline. Reservoir creation triggers reproductive recruitment and otherwise pools spatially disparate populations from across the flooded valley. If the rise in richness is largely explained by the increased catchability of species otherwise present prior to flooding, it may be more appropriate to estimate species loss with reference to upsurge data. As peak biomass coincides with declining richness, modelling fisheries production from annually aggregated data may risk overestimating the potential for sustainable harvests. Upsurge–response curves can help identify the timing of critical ecological thresholds for flood‐managed fisheries.