Search

Xixiayuan Reservoir, as a counter-regulating reservoir of Xiaolangdi Reservoir, plays an important role in regulating the unsteady flow of Xiaolangdi Reservoir. Since the operation of Xixiayuan Reservoir, the reservoir has shown a continuous trend of siltation. It is of great significance to study the siltation removal capacity of Xixiayuan Reservoir. Based on the measured water and sediment data of Xixianyuan Reservoir from 2011 to 2022, this paper made an in-depth analysis of the sediment discharge process and influencing factors of Xixianyuan Reservoir over the years. The research results show that the sediment discharge of Xixianyuan Reservoir is affected by multiple factors such as the reservoir operation mode and the conditions of incoming water and sediment. The sediment delivery ratio of the reservoir is significantly affected by the variation coefficient of discharge along the flow and the sediment discharge in the reservoir, and the sediment discharge ratio is significantly positively correlated with the variation coefficient of discharge along the flow and negatively correlated with the sediment discharge in the reservoir. The empirical formula of sediment discharge is established by regression analysis, with the coefficient of determination of 0.79, and the fitting effect is good. [ABSTRACT FROM AUTHOR]

Sedimentation processes in reservoirs can jeopardize their functionality and compromise dam safety. Climate change and associated hydrologic uncertainty are introducing additional stressors to US reservoirs, and data-driven indicators of climate impacts on upstream soil erosion and reservoir sedimentation processes are crucial to evaluate their aggradation and life expectancy. The US Army Corps of Engineers developed the Enhancing Reservoir Sedimentation Information for Climate Preparedness and Resilience (RSI) system to consolidate historical information of elevation-capacity surveys. However, the multiple surveying technologies, protocols, and computational analysis methods used over the service life of reservoirs can impact the quality of reservoir survey data in the RSI system. The objective of this study was to develop a methodology to detect anomalous records and identify multivariate relationships between historical sedimentation data for 184 US reservoirs and associated watershed variables. For this purpose, unsupervised machine learning techniques including principal component analysis (PCA), autonomous anomaly detection, and Kolmogorov–Smirnov and Efron anomaly detection were assembled in an anomaly detection protocol that led to the detection of 20 reservoirs with anomalous records. The variables contributing most to anomaly detection were related to elevation characteristics (watershed and channel slopes, and minimum elevation), precipitation (maximum and cumulative monthly precipitation), dam properties (time since dam completion and initial trap efficiency), and curve number (CN). PCA results indicated that reservoirs in the Mediterranean California ecoregion, although experiencing substantial extreme precipitation events, had small basin areas and CN values that reflected in small capacity losses, contrasting with larger capacity losses found at reservoirs in the Great Plains and Eastern Temperate Forests ecoregions. The developed anomaly detection protocol represents a powerful tool for the analysis and monitoring of this large and heterogeneous data set with the potential of providing reliable information on the impacts of historical climate and watershed properties on erosion and sedimentation processes in US reservoirs. Practical Applications: The US Army Corps of Engineers created the Reservoir Sedimentation Information (RSI) system to compile historical reservoir elevation-capacity data collected using various measurement protocols, instruments, and analysis methods. These differences in data collection and analysis methods, in addition to any human error, can result in anomalies that require detection and correction before the dissemination of the data set for further usage. Data anomalies are values that deviate from normal or expected patterns. Apparent erroneous data, related to duplicate records or increases in reservoir capacities, can be flagged through a preliminary analysis. However, the detection of anomalies in an automated and fully data-driven way represents a powerful tool for the maintenance and monitoring of this large and heterogeneous data set. A depurated RSI data set is a potential major data source for large-scale and long-term studies related to sedimentation rates and suspended solid loads in freshwater systems due to the spatial and temporal scale of its records. This kind of data set will allow the development of effective management plans for reservoir operation, maintenance, and upstream erosion control as well as enabling the indirect monitoring of suspended sediment loads in freshwater systems at a nationwide scale. [ABSTRACT FROM AUTHOR]

Naumure Multipurpose Project (NMP) featuring a 169 m high Concrete Face Rock Filled Dam (CFRD) is the proposed reservoir project in the West Rapti River with an installed capacity of 218.34 MW. Most of the rivers in Nepal carry significant sediment loads that will consequently catalyze reservoir sedimentation. This phenomenon prevails as the primary factor in reducing reservoirs useful life, making ineffective for both flood control and hydroelectricity generation. Ultimately, such process of sedimentation has adverse impacts on projects economic feasibility and long-term sustainability. Therefore, the objective of this research was to examine the expected sediment deposition pattern in the NMP reservoir throughout its operational period by employing 1D HEC-RAS model to simulate the sedimentation process. The model was simulated for 10, 20, 30, 40 and 50 years. Yang's equation as a sediment transport function, Active layer as a bed sorting method and Toffaleti as a fall velocity method were best suited for the river reach. The delta deposition was formed between 11 km and 22 km upstream of the dam region in the Jhimruk river, with the sediment deposition depth reaching peaks of about 23 m, 38 m, 39 m, 41 m and 49 m in 10, 20, 30, 40 and 50 years, respectively. Similarly, the delta deposition was formed between 13 km and 33 km upstream of dam region in the Madi river, with the sediment deposition depth reaching peaks of about 47 m, 62 m, 60 m, 68 m and 75 m in 10, 20, 30, 40 and 50 years respectively. Headcutting of delta deposition occurred between 20 and 30 year due to high flood during low stage of reservoir. Furthermore, the study revealed that about 6.22%, 11.61%, 15.94%, 22.96% and 25.65% of the storage capacity of NMP reservoir will be depleted in 10, 20, 30, 40 and 50 years respectively. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the critical suction velocity required for lifting sediment off the bed under hydrosuction. Flow characteristics below the suction pipe under unbound and bound conditions were studied experimentally and numerically, and the effects of various parameters on the critical suction velocity, such as suction pipe diameter, suction discharge, suction inlet height, and sediment size, were investigated. The results showed all the parameters significantly affect the critical suction velocity, with suction inlet height being the most influential. Unbound and bound conditions yielded divergent flow characteristics beneath the suction pipe, revealing distinct flow patterns. Interdependency among the parameters affecting critical suction velocity have been studied statistically, and empirical relations are developed to compute the critical suction velocity, its resultant centerline velocity, and the associated flow profile. A proposed relation for critical suction velocity showcased a ±10% error margin, while equations computed resultant centerline velocities and flow profiles with ±15% accuracy, representing satisfactory agreement. These findings can also be helpful in designing efficient suction systems in various sediment-laden water environments. Practical Applications: The current study on hydrosuction sediment removal presents practical solutions for addressing the persistent challenge of reservoir sedimentation. Hydrosuction is an efficient and cost-effective method of sediment removal with minimum disturbance to the connecting structures and surrounding ecosystem and aquatic life, ensuring sustainable reservoir management. The study focuses on providing detailed insight into the behavior of the flow below the suction pipe under varying conditions, which is responsible for sediment movement during hydrosuction. The study also investigates the minimum suction velocity required to lift the sediment off the bed surface. Applicability of hydrosuction is not limited to the desilting of a reservoir; it also holds potential for various applications in multiple fields, such as river and canal restoration, dredging of navigational channels, irrigation canal cleaning, dewatering and slurry removal, contaminant cleanup, trench excavation, flood control, and wastewater management. [ABSTRACT FROM AUTHOR]

The reservoir properties of super-heavy oil reservoirs in fluvial sedimentation are relatively poor, with high heterogeneity directly affecting the steam injection rate and expansion velocity of the steam chamber in the SAGD process. In order to significantly improve SAGD production performance, a combination of laboratory testing and physical simulation experiments was used to analyze the changes in reservoir-rock structure, rock geomechanical characteristics, and porosity and permeability during high-pressure injection, through rock geomechanics testing, core-flood experiment, and SEM scanning analysis. Large-scale two-dimensional physical simulation experiments were designed to analyze the effect of different injection agents in assisting the expansion of steam chambers. The experimental results showed that, with the increase in injection pore pressure, the reservoir permeability increased from 2.74 D to 4.56 D, and the contact between rock particles became looser after expansion, indicating a significant improvement in reservoir properties through high-pressure-injection-induced dilation. The results of the two-dimensional physical simulation experiments demonstrated that the solvent-assisted steam-chamber dilation speed was further increased compared with the conventional huff-n-puff dilation. Cyclic gas-injection volume can be increased from 0.16 PV in pure-steam injection cases to 0.32 PV. The hybrid-agent system of solvent-plus-gas can produce the dual positive effect of solvent dissolution and gas diffusion, more effectively improve the steam-chamber expansion speed, enhance the phased oil-recovery degree by 23.41%, and increase the oil/steam ratio from 0.27 to 0.33, indicating encouraging potentials in improving heavy oil and bitumen production performance by the dilation strategy. [ABSTRACT FROM AUTHOR]

Reservoir sedimentation has always been a problem that troubles the reservoir management department. Scientifically and reasonably utilizing reservoir operation methods to achieve efficient sediment reduction in reservoirs is an effective means to solve reservoir sedimentation. This paper analyzed the reservoir sediment regulation of the Haibowan Reservoir on the Yellow River from 2019 to 2022, and combined the inflow and outflow water and sediment data during the flood season since the construction of the reservoir to carry out research on efficient sediment reduction of the Haibowan Reservoir. The research results indicate that: a) the goal of reservoir sediment reduction is achieved in 2019, 2020 and 2022, and the balance of erosion and sedimentation is basically achieved in 2019, while the sediment reduction effect is better in 2020 and 2022. b) The water level in front of the dam is a key factor affecting the sediment reduction of the Haibowan Reservoir, while the inflow water and inflow sediment are secondary factors affecting the outflow sediment volume. By fitting the influencing factors, an empirical formula for sediment reduction from the Haibowan Reservoir is obtained. c) Different combinations of inflow water and sediment require different scheduling measures to achieve efficient sediment reduction in the reservoir. Efficient sediment reduction in the reservoir can only be achieved by reasonably matching the inflow water and sediment conditions and the water level in front of the dam. [ABSTRACT FROM AUTHOR]

Simple Summary: Methanogens are a group of microorganisms with the capability to convert inorganic or organic compounds into methane, impacting the global carbon cycle and greenhouse gas emissions. In anaerobic environments such as wetlands, paddy fields, and reservoirs, methanogens are the primary contributors to methane production. In this study, high-throughput sequencing of the mcrA functional gene was utilized to conduct a comprehensive analysis of the community structure, metabolic pathways, and influencing factors of methanogens in the sediment of 18 reservoirs on the northeastern Qinghai Plateau. The results indicated that the construction of reservoirs has altered the physicochemical properties of river water and sediments, significantly impacting the distribution and succession of methanogenic communities in the sediment. In general, this study can improve our understanding of the biological mechanisms of methane emissions from the reservoirs on the Qinghai Plateau. Reservoirs are a hotspot for methane emissions, a potent greenhouse gas. However, the microbial basis for methane production in the Qinghai Plateau reservoirs remains unclear. To explore the characteristics of methanogenic communities in reservoir sediments on the northeastern Qinghai Plateau, sediment samples were collected from 18 reservoirs in the Yellow River basin during May 2023 (dry season) and August 2023 (wet season). High-throughput sequencing technology was employed to analyze the community composition, diversity, and co-occurrence network of methanogens. Furthermore, FAPROTAX and Mantel analysis were used to assess the metabolic functions of methanogens and their influencing factors. The results showed that (1) the predominant genera of methanogens were Methanobacterium (28.87%) and Methanosarcina (21.67%). Hydrogenotrophic methanogenesis was the main pathway in the sediments. (2) Significant spatiotemporal differences were observed in the diversity of methanogenic communities (p < 0.05). The composition and diversity of these communities were found to be significantly influenced by temperature, pH, altitude, organic carbon, and total nitrogen (p < 0.05). (3) Methanosarcina, Methanobacterium, and Methanospirillum play crucial roles in maintaining the stability of methanogenic community networks. The co-occurrence network nodes are predominantly positively correlated (99.82%). These results provide data for further studies on carbon cycling in the Qinghai Plateau reservoirs. [ABSTRACT FROM AUTHOR]

Many dammed reservoirs in dry climate conditions witness high sediment inflow rates due to higher soil erodibility, yet there are limited actual sediment influx measurements. Therefore, this study first applies the Soil and Water Assessment Tool (SWAT) hydrologic model to simulate reservoir sedimentation inflow to the Haditha Reservoir. Next, utilizing sediment inflows estimated by the SWAT model, the Trap Efficiency Function (TEF) is employed to estimate its remaining storage capacity and its useful life at multiple reservoir water levels. Calibration (1986–1997) and validation (1998–2007) of the SWAT model were conducted at three streamflow gaging stations and one sediment station located upstream of the reservoir. Results show that the SWAT model performed better during calibration than during the validation period for all streamflow and sediment gaging stations. In addition, modeled streamflow and sediment predictions were relatively more accurate on a monthly scale than on a daily scale. Simulated daily sediment inflow to the reservoir demonstrates slightly lower accuracy than daily streamflow, where the Coefficient of Determination (R2) and Nash-Sutcliffe Efficiency values are 0.34 and 0.32 in the case of sediment load, compared to 0.39 and 0.33 for streamflow, respectively. Reservoir storage capacity for the period (1986–2005) shows a continuous decrease with time at all reservoir water levels, which indicates an increase in sediment accumulation. According to measurements taken between 1986 and 2005, sediment accumulation has reduced the reservoir's capacity by approximately 15% at a water level of 112 m (the lowest water level in the reservoir). During the same period, the storage capacity loss at 147 m (the design working water level in the reservoir) was calculated to be 35%. Over 19 years of operation (1986–2005) at the 147-m water level, the total sediment buildup in the reservoir is estimated at 3.2 million tons. Notably, about one-third of this sediment was deposited in the five-year span from 2000 to 2005. [ABSTRACT FROM AUTHOR]

Zengwen Reservoir, the largest water resource in Taiwan, has been seriously impacted by sedimentation, contributed mainly by typhoon floods. Therefore, it is chosen as a case study to investigate the effectiveness of an integrated reservoir management strategy of sediment routing and removal by constructing a dredged guiding channel to route turbidity currents generated during typhoon floods. The strategy is evaluated by simulating flood events of four return periods using a 3D numerical model, the effectiveness of which, with and without the dredged guiding channel, is compared in terms of the venting efficiency of reservoir outlets and the arrival time of turbidity currents. The numerical model is calibrated using the laboratory data and validated using the physical model and field data. The simulated results show a significant increase in the venting efficiency and a decrease in the arrival time of turbidity current for all the flood events in the presence of a dredged guiding channel. In addition, results also aid in predicting trapping efficiency based on the Brune curve trend for different capacity inflow ratios for single flood events. The findings demonstrate the feasibility and effectiveness of the integrated reservoir management strategy in the field before high-intensity flood events. [ABSTRACT FROM AUTHOR]

Dams are one of the most critical hydraulic structures worldwide. Sediment, entering the reservoirs of the dams with the water flow due to human interference in the dam catchment area, gradually destroys the functional storage through a deposition. Sedimentation threatens the sustainability of all reservoirs in the absence of adequate prevention and mitigation measures. Deposition of sediments in reservoirs can also affect the safe and proper operation of water intakes and bottom outlets belonging to the vital outlet structures. Turbidity currents are among the main impacts on dam reservoir sedimentation. One technique to decrease the impact of more sedimentation is to use bottom outlet gates that preserve the reservoir's useable volume. This procedure may affect the quality of water exiting the dam. The present study experimentally investigated the venting of turbidity current of lock exchange with varying concentrations on the rigid bed, while there were two outlet gates with various levels and diameters at the same time. According to the available information, in the case of , the average value of the concentrated input current was equal to the output concentration, which is the best level for the outlet gate installation based on the primary experimental conditios. The discharge efficiency is also higher when the inlet concentration is lower. [ABSTRACT FROM AUTHOR]

Several reservoirs across the United States are filling with sediment, which jeopardizes their functionality and increases maintenance costs. USACE developed the Reservoir Sedimentation Information (RSI) system to assess reservoir aggradation and track dam operation suitability for water resource management and dam safety. The RSI data set contains historical elevation-capacity data for approximately 400 dams (excluding navigation structures), which correspond to less than 1% of dams across the United States. Thus, there is a critical need to develop methods for estimating reservoir sedimentation for unmonitored sites. The goal of this project was to create a generalized method for estimating reservoir sedimentation rates using reservoir design information and watershed data. To meet this objective, geospatial tools were used to build a refined composite data set to complement the RSI system's data with precipitation and watershed characteristics. Nine deep learning models were then used on the benchmark data set to determine its accuracy at predicting capacity loss for the RSI reservoirs: four supervised machine learning models, four deep neural network (DNN) models, and a multilinear power regression model. A DNN model, containing a progressively increasing node and layer construction, was deemed the most accurate, with R2 values from its calibration and validation data sets being 0.83 and 0.70, respectively. The best model was recalibrated over the entire data set, which showed greater accuracy on the prediction of the RSI reservoir's capacity loss, with an R2 of 0.81. This predictive model could be used to evaluate the capacity loss of unmonitored reservoirs, forecast sedimentation rates under future climate conditions, and identify reservoirs with the highest risk of losing functionality. Practical Applications: Many communities depend on reservoirs for a variety of socioeconomic benefits, such as providing reliable water sources and flood mitigation. Rivers entering reservoirs are a constant source of silt, sand, and gravel particles (i.e., sediments) that deposit slowly, filling the reservoirs over time, thus reducing their volume capacity and effectiveness. Surveys to measure reservoir capacities are labor intensive and expensive and many sites go unmonitored. This study provides prediction tools to estimate capacity loss over time using data derived from publicly available data sources (e.g., digital elevation models, monthly precipitation data, and the National Inventory of Dams). A key role of this tool is to forecast reservoir capacity loss over time under varying climate change conditions and relate the associated sedimentation processes to local and regional conditions. The tool can also be applied broadly to hindcast capacity loss for reservoirs with or without prior surveys for identifying high-risk sites that should be investigated further. USACE plans to use these prediction tools with the RSI database to conduct a national assessment of reservoir impacts, which will inform distributions of federal resources to address water security concerns related to reservoir sedimentation. [ABSTRACT FROM AUTHOR]

This study illustrates the comprehensive investigation to assess the sedimentation, deposition pattern, and futuristic active capacity of the reservoir in a minimal period. A multi-collaborative methodology was developed using Geographic information system (GIS) & Artificial Neural Networks (ANN). The sedimentation analysis was carried out on a GIS environment using satellite rasters. The satellite data captures the live water region with a combination of visible and Near-Infrared (NIR) bands. The ANN model was developed using feed-forward backpropagation algorithm to forecast the revised water spread. A Multi-Layer Perceptron [2-1(10)-1(1)-1] ANN structure best captures the trend of water-spread reduction with the coefficient of determination (R2)1,1,1 & 0.977 for training, testing, validation, and overall performance respectively. The designed approach provides a performance comparison of GIS and ANN methods for the prediction of reservoir capacity. Also, the observations of sedimentation analysis were superimposed on the Borland & Miller graph to portray the pattern of deposition. The research framework was applied to the Kerwan reservoir located in the capital of central India. This analysis reveals that the useful capacity of the reservoir had reduced from 22.67 to 15.13 Mm3 in 46 years (1976–2022) and the depositing pattern was shifting towards Type-II (Flood Plain-Foot Hill) which was designed as Type-III like Hilly reservoir. From the Neural Network fittings, it was concluded that Kerwan would be suppressed to 59.95% in 2030 and reduced up to 49.49% & 40.84% for 2050 & 2070 respectively, if siltation carried on. [ABSTRACT FROM AUTHOR]

This article presents an approach to the assessment of the environmental impact of a dam construction for agricultural use in the Boutheldja region. This region's environment is rich in natural resources and forms a part of the El Kala National Park (P.N.E.K). It was designated a wetland of international importance under the Ramsar convention by UNESCO in 1983 and later declared a biosphere reserve in 1990. It is among the most significant aquatic areas in this region (contains about 40% of surface water resources). The physical characteristics of the watershed support the construction of the dam, although there could be a number of unfavorable effects: upstream -- including soil erosion and reservoir sedimentation, reduced storage capacity, lower water quality and loss of productivity of flooded area; downstream -- removal of silt from downstream flows, loss of fertilising functions, changes in water quality, changes in productivity, reduction in natural floods, loss of access to resources and ecological disturbance. Such processes will have an impact on an ecosystem so fragile. Although Boukhroufa dam provides significant benefits to the city, such as controlling stream regime, preventing floods, and supplying agricultural water from stored water, it also has significant negative effects on the surrounding watershed ecosystem. [ABSTRACT FROM AUTHOR]

Sediment Bypass Tunnels (SBTs) are proven to be an effective measure to reduce or even stop reservoir sedimentation by bypassing sediment laden flows around reservoir dams to the downstream river reach. They are mostly used in Switzerland, Japan, and Taiwan. However, hydraulic and sedimentological operating conditions and the resistance of the invert materials against hydroabrasive erosion affect their cost-effectiveness. Hydroabrasion is a pressing issue at SBTs, other hydraulic structures and steep bedrock rivers exposed to high sediment transport rates under supercritical flow conditions. The present study was therefore conducted to address this issue by aiming at improving knowledge on abrasion mechanics and calibrating a mechanistic saltation abrasion model enhanced by Demiral-Yüzügüllü (2021). To this end, the abrasion resistance of fourteen different invert materials installed at Solis, Pfaffensprung and Runcahez SBTs in Switzerland was quantified by annual 3D laser scanning and the hydraulic conditions and sediment transport rates were regularly monitored between 2017 and 2021. The analysis of invert scans and hydraulic conditions revealed that Prandtl's first and second kinds of secondary currents occurring in the bends and straight sections of the SBTs, respectively, and the observed abrasion patterns were strongly interrelated. The tested potassium aluminate cement and steel fibre concretes, granite, cast basalt and steel plates had better abrasion resistance against impact of sediment-laden flows compared to other materials. Sediment mineralogical composition i.e., bulk hardness relative to the invert material properties significantly affected hydroabrasion. The enhanced abrasion prediction model was calibrated with the present data and a quasi-constant abrasion coefficient of k v = (4.8 ± 2.2) × 104 was obtained. The enhanced model is well-suited for both laboratory and field scales. The present findings will contribute to the sustainable utilization and operational safety of hydraulic structures, optimization of SBT and reservoir operations regarding bypassing efficiency and reservoir lifetime and modelling of bedrock river erosion. [ABSTRACT FROM AUTHOR]

Dissimilatory nitrate reduction to ammonium (DNRA) is an important nitrate reduction pathway in freshwater sediments. Many studies have focused on the DNRA process in various natural habitats. However, the joint operation of cascade reservoirs will affect the physical and chemical properties of sediments, which may change the DNRA process and bacterial community pattern in the surface sediments of cascade reservoirs. Our study was the first to investigate the spatiotemporal distribution patterns of potential DNRA rate, nrfA gene abundances, and DNRA bacterial community diversity in surface sediments of the Lancang River cascade reservoirs. The results of slurry incubation experiments combined with the 15N isotope tracer experiment ascertained that the potential rates of DNRA were 0.01-0.15 nmol-N cm-3 h-1, and qPCR results indicated that the abundance range of nrfA was 1.08 × 105-2.51 × 106 copies g-1 dry weight. High throughput sequencing of the nrfA gene revealed that the relative abundance of Anaeromyxobacter (4.52% on average), Polyangium (4.09%), Archangium (1.86%), Geobacter (1.34%), and Lacunisphaera (1.32%) were high. Pearson and RDA correlation analysis exhibited that nrfA gene abundance was positively correlated with altitude, pH, OC, and sand concentration. Anaeromyxobacter was positively correlated with reservoir age and DNRA potential rate. The deterministic environmental selection process plays a crucial role in the formation of the DNRA bacterial community. Network analysis displayed that the dominant DNRA genus was the key population of the DNRA microbial community in the sediments of Lancang River cascade reservoirs. This study reveals that the variation of DNRA bacterial activity and community structure is largely driven by the construction of cascade reservoirs, and provides a new idea for further understanding the characteristics of the DNRA community in the cascade reservoir ecosystem. [ABSTRACT FROM AUTHOR]

Reservoir sedimentation in mountainous watersheds, such as the Zagros mountains, is high. Reservoir sedimentation reduces water storage and threatens water resource management. This study aims to simulate reservoir sedimentation in Dokan Lake, Iraq for 55 years, beginning in 1959. Multiple combinations of the revised universal soil loss equation—sediment delivery ratio (RUSLE-SDR) method have been tested using geographic information system (GIS) and remote sensing techniques. Two types of satellite precipitation data, six Digital Elevation Model (DEM), Harmonized World Soil Database (HWSD), and AQUA eMODIS NDVI V6 data have been used to prepare forty-eight RUSLE-SDR models. These models have been evaluated using three sets of in situ measurements (one topographic map and two bathymetric data sets) to select the suitable models. The rate of error test shows that the best model by far is model #38, which has an error of less than 8.31% for the three in situ measurements. The annual reservoir sedimentation rate (between 1959 and 2014) at Dokan Lake is 0.0034 km3·y−1 (6,347,800 ton·y−1). This rate has been decreased to 0.0027 km3·y−1 (2018 to present) due to short-term fluctuations in precipitation and temperature and construction of the Sardasht Dam, which contributed to the decrease in the amount of the water mass reached to Dokan lake. The sediment delivery ratio which is based on the basin model shows better results than the sediment delivery ratio which depends on the IC model although the SDR IC model is working well, too. As a result of neglecting this aspect, one-third of Dokan Lake volume has been lost already due to reservoir sedimentation. The results show that the GPM data is better than the TRMM data in estimating the R factor. Moreover, the best RUSLE-SDR model shows that the MODIS land cover (MCD12Q1) performs better than the AQUA eMODISNDVI V6 to estimate the cover-management (C) factor, which comprises the preventing effects of the crop or vegetation cover. We propose constructing check dams in the Dokan Lake basin to reduce reservoir sedimentation is among the most important measures to increase the dam's lifespan. [ABSTRACT FROM AUTHOR]

The identification of areas prone to soil erosion in ungauged river basins is crucial for timely preventive measures, as erosion causes significant damage by lowering soil productivity and filling reservoirs with sedimentation. This study proposes a novel approach to prioritize sub-watersheds (SWs) in Ponnaniyar river basin. It utilizes different combinations of five objective-based weighting methods and seven Multi-criteria Decision Making (MCDM) techniques under outranking and synthesis methods with soil loss, morphometry, land use/land cover (LULC), and topography parameters. The results obtained from different hybrid models are validated using metrics like percentage and intensity of change. The findings reveal that MW-PROMETHEE (53.85%) and CRITIC-WASPAS (8.31) perform best in prioritizing areas based on morphometry, while CRITIC-TOPSIS (48.35% and 7.58) is more effective in prioritizing areas based on land use/land cover (LULC) and topography. The grade average method is used to integrate the rankings from 71 models: 35 based on morphometry, 35 based on LULC, and 1 based on the RUSLE model. The analysis identifies SW2 with a grade value of 4.34 as severely affected by soil erosion, followed by SW11 (5.45), SW5 (5.56), and SW9 (5.68), all falling within the very high priority level. This study recommends implementing appropriate water harvesting structures, which might be helpful in mitigating soil degradation, promoting soil conservation, and ensuring sustainable agricultural productivity. [ABSTRACT FROM AUTHOR]

Dead storage of reservoir usually designed by soil erosion rate of catchment area result in certain year without considering land use and precipitation dynamic in the catchment and sedimentation distribution analysis at the bottom of the reservoir as well. Development of protocol is needed for more accurate prediction of reservoir sediment transport to describe the real condition and accommodate data limitations. It will give good perspective in design, operation and maintenance strategy for reservoir. The proposed protocol is consisted of long-term soil erosion prediction, modelling long-term sediment discharge, modelling spatial-temporal reservoir sediment transport and predicting reservoir sediment volume and distribution in the future. The case study is in Wonogiri reservoir, Indonesia. Simulation of the proposed protocol at the case study began by obtaining long-term soil erosion prediction from 1993 - 2019. Sediment discharge was modelled from soil erosion and synthetic long-term hydrographs using the FJ Mock method and validated with sediment rate measured directly in the field. Reservoir sediment transport model was using MIKE software. The simulation gives volume and distribution of sedimentation validated by bathymetry result of the reservoir. Prediction of future sedimentation was using the modular regression method. This protocol promotes spatial reservoir sediment transport model and sedimentation prediction by modular regression. The prediction result of reservoir sediment volume in 2069 is 146.7 million m³. [ABSTRACT FROM AUTHOR]

We investigated the magnitude of reservoir sedimentation upstream and its sediment-shadow effect on a large downstream-linked lake, Lake Tana (Ethiopia). To better understand the reservoir-induced reductions of fluvial sediment downstream, sediment budgets for two scenarios were developed. The results indicated that reservoir sedimentation is extremely high, with annual storage capacity losses (1–4.2%) exceeding the global average. Consequently, unless mitigation measures are implemented, the reservoirs' dead storage volume will be filled with sediment in less than 42% of their designed life expectancy. The sediment-trapping conditions created by the reservoirs will also reduce sediment inflow from tributaries into the lake by 15–52%, overbank sedimentation on floodplains by 33–48%, and sediment deposition in Lake Tana by 16–54% annually. Overall, under the current environmental set-up, the ongoing and planned reservoir constructions could extend the expected useful lifetime of Lake Tana from 918 to 2022 years. [ABSTRACT FROM AUTHOR]

The sustainable use of water reservoirs is threatened by sediment accumulation, but loss of storage volume can be prevented or limited by appropriate sediment management strategies that work in a variety of expected conditions. The development of a reservoir flushing strategy, tested against water and sediment inflow that might occur over centuries, is presented. A typical length of water and sediment records of 50 years was used to represent the range of variability within a year, and extended by deducing longer term inter-annual variability from suitable indicators (sediment cores in natural lakes, tree-ring chronologies etc.). It was concluded that, over past centuries, water inflows over a period of 50 years could typically vary by about 10%, while sediment inflows could vary by about 20%. The resilience of flushing rules derived solely on the recorded dataset over centuries-long periods was tested using a long-term computer simulation of reservoir sedimentation. The simulations showed that some modifications to the flushing rules would increase performance over centuries-long periods. Although the approach was derived for a specific project, it is based on some generally applicable parameters, such as the discharge at which operation stops and the moving average of the annual peak flow. [ABSTRACT FROM AUTHOR]

Reservoir sediment flushing, one of the most effective strategies for alleviating reservoir sedimentation, involves discharging sediment-laden flows downstream through bottom tunnels. However, whether flushing can be accomplished if the intake of a bottom tunnel is initially covered by cohesive sediment remains poorly understood. Here, flume experiments were done to investigate cohesive sediment flushing in a reservoir. It is demonstrated that cohesive sediment in a reservoir is harder to flush than non-cohesive sediment. A higher water level in the reservoir, initially smaller cover layer thickness, and lower dry density of the sediment favor the occurrence of sediment flushing. The flushing process of cohesive sediment is significantly affected by seepage. Under the combined action of gravity erosion and water erosion, the scour hole upstream of the dam is characterized by angular and broken edges. The threshold conditions for flushing of non-cohesive and cohesive sediments are evaluated. Empirical formulas applicable to both non-cohesive and cohesive sediment are proposed to estimate the equilibrium scour depth immediately upstream of the bottom tunnel intake. Also, empirical models are proposed for the time variation of sediment position in the bottom tunnel. The current findings are significant for informing the design and operation of reservoirs on rivers carrying fine-grained cohesive sediment in support of reservoir benefits and capacity preservation. [ABSTRACT FROM AUTHOR]

In Algeria, the loss of water capacity in reservoirs is a major challenge in the face of a significant increase in water demand. This loss of resources is due to the sedimentation of reservoirs, one of the most serious consequences of erosion. The use of hydrological indices is widely recognized as a highly effective method of providing input data for the cartographic representation of prone-to-erosion areas within geographic information systems. In the present study, the hydrological indices essential for erosion modeling were obtained through meticulous processing and analysis of a digital elevation model. The various indices, including the sediment transport index, composite topographic index, and stream power index, were combined with other relevant variables such as slope, curvature, channel spacing, and channel density. The results of the survey showed that a significant part of the Oued Rhumel watershed, located in the eastern region of Algeria, specifically 24.35% or 1,292.72 km2, is located in an extremely high or high erosion zone, which requires the immediate implementation of conservation measures. In addition, a total of 190.81 km2 or 2,024.47 km2 is located in areas with a moderate or low risk of erosion, respectively. It is therefore evident that the use of primary and secondary derivatives of the digital elevation model, as well as morphometric parameters, through the application of a spatial analysis tool, is an effective and comprehensive method for identifying erosion-sensitive zones. This approach can be used on a regional or continental scale to facilitate watershed management and monitoring. [ABSTRACT FROM AUTHOR]

An increase in soil erosion affects the storage capacity of reservoirs, navigation, floodplain inundation, water quality, and quantity in different parts of the world. Therefore, identifying vulnerable soil erosion zones within the watersheds and developing a catchment treatment plan can minimize soil erosion losses and improve reservoir sedimentation management. In this study, we calculated the average annual soil loss using the revised universal soil loss equation (RUSLE) method for the Hirakud catchment of the Mahanadi River Basin, India. The Hirakud dam, located on the river Mahanadi is considered the longest dam in Asia, witnessing major sedimentation problems over the past years. Our results suggest that the average annual soil loss is approximately 29 tons per hectare per year. At the same time, 0.7% of the land area contributes to very high erosion. The average annual soil loss is 0.8 t/ha. Using remote sensing and GIS tools, suitable soil conservation methods are recommended based on the watershed's Prioritization. Utilizing Saaty's AHP (Analytic Hierarchy Process) techniques, each erosion hazard parameter (EHP) is designated by weight, and the vulnerable regions are prioritized by overlaying the weights over the study area. Overall, nearly 17% of the area falls under the high priority, and 1% falls under the category of extremely high priority. In the extremely high-priority watershed, it is recommended to construct 38 farm ponds, 14 check dams, nine gully plugs, 27 percolation ponds, and two surface dikes, depending on the ground and stream characteristics. [ABSTRACT FROM AUTHOR]

Soil erosion and sediment buildup are the factors that speed up the decline in capacity and function of reservoirs, agricultural products, and water resources. In order to simulate sediment and runoff and map high sediment-yielding sub-basins in the Gibe Gojeb catchment in southwest Ethiopia, this study used the Soil and Water Assessment Tool (SWAT) model. Using data on sediment and river flow, calibration and validation were carried out. Between 2003 and 2016, the catchment produced an average annual sediment loading of 62.5 tons ha−1 yr−1, with loading fluctuations ranging from 0.2 to 108.4 tons ha−1 yr−1. The acceptable sediment yield threshold value ranges from 12.3 to 108.4 tons ha−1 yr−1 for 56 sub-basins, and from 0.2 to 10 tons ha−1 yr−1 for 5 sub-basins. The most significant sub-basins with very high to extremely severe sediment yields were sub-basins 1 to 30, 32 to 44, 47, 48, 50, 51, and 53 to 61. After thirteen years of operation, the yearly amount of 58,802 tons of sediment transferred from the catchment and deposited into Gibe One reservoir has decreased the capacity by 5.7 %. The accumulation of sediment in a reservoir has an impact on its functionality, power production, and capacity, affecting the safety of dams and the environment. The study's findings enhanced our comprehension of sediment accumulation in reservoirs and furnished us with the necessary information regarding reservoir safety, integrated soil, and water management.

Sediment flushing through bottom tunnels has been widely applied in engineering practice to alleviate reservoir sedimentation. However, there is limited understanding of whether flushing can be accomplished once the tunnel intake is covered by deposited sediment. Here, a three-dimensional model is used to resolve the hydro-sediment-morphodynamic processes and reveal the physical mechanism for the occurrence of reservoir sediment flushing through an initially covered bottom tunnel. The results demonstrate that the reservoir water level and initial cover layer thickness have a significant impact on the pressure difference between tunnel inlet and outlet and the resistance of tunnel walls, determining the momentum of the water-sediment mixture. If water level is low or cover layer is thick, the pressure is not sufficient to overcome the resistance. The momentum tends to zero, and tunnel blockage occurs. If water level is high or cover layer thickness is small, the scour hole depth will exceed the cover layer thickness and the sediment concentration in tunnel decreases. The resistance is reduced significantly, and sediment flushing is accomplished. The present work facilitates enhanced understanding of sediment flushing, thereby informing reservoir engineers and managers of potential approaches to benefit maximization and sustainable sediment management.

River impoundment is usually accompanied with consequences of alteration in the hydrological system and change in the biodiversity composition of the ecosystem. This study investigated the impact of the dams built on Challawa (that is, Challawa George-Dam) and Kano (that is, Tiga Dam) on the fish biodiversity of the reservoir and below-dam sections of the two rivers. Fish sampling was done using long lines, Malian traps, cast and gill nets from stations on the reservoir and below-dam sections of the rivers. Ten fish species were identified from the reservoir and the below-dam sections of Challawa River belonging to nine families and four orders. Fish communities of the reservoir and below-dam sections of Kano River consisted of 28 species belonging to 12 families and 7 orders. Results of the Shannon diversity index (H' ) indicated that the two reservoirs have relatively higher fish species diversity measures (that is, Challawa=1.948 & Kano=2.294) than the below-dam parts (that is, Challawa=1.833 & Kano=2.247) of their respective rivers. Non-metric Multidimensional Scaling (NMDS) analysis produced two-dimensional maps with stress values of 0.0554 and 0.0537, an indication that the model provided good representation of the original data in reduced-dimensional space. The ordination map indicated wide dissimilarities between fish communities of the impounded and below-dam sections. Furthermore, a one-way analysis of similarity indicated significant difference (P=0.0001) and high dissimilarities (R=0.643) between fish communities in the two sections of Challawa River and also in Kano River (P=0.001, R=0.929). Analysis of Similarity Percentage indicated 74.45% of the dissmilarities between fish communities in the two sections were cummulatively contributed by four species in Challawa River and 72.18% by five species in Kano River. The distinct differences in fish abundance and richness between the two sections is ascribed to increased ecosytem productivity often associated with the inundated portion of dammed river. It is recommended that more water flow across the dams should be encouraged as a mitigating measure to boost basin sizes of the rivers at the below-dam sections. [ABSTRACT FROM AUTHOR]

The complex contacts between gas hydrate and free gas have been confirmed by gas hydrate pilot production in the Pearl River Mouth Basin, South China Sea. The laminated clay silt reservoirs have high amplitude reflections which may be filled with different saturations of gas hydrates, free gas and the coexistence between gas hydrate and free gas. To distinguish the variations of amplitude reflections caused by different reservoirs properties below the bottom simulating reflection, we combine the forward modelling, pre‐stack gathers with different incident angles and well log analysis to conduct the seismic responses. A number of geological models are established with variable saturations and different interfaces between gas hydrate and free gas. First, we analyse the seismic and well log responses at Sites W11, W01 and W17 near the production test area. Then, we perform the forward modelling to quantify the differences among seismic reflections with different saturations, thickness, incident angles and strata dips in free gas‐ or gas hydrate‐bearing geological models. We extract the seismic amplitudes along the bottom simulating reflection and other layers to compare with the amplitudes generated from forward modelling. The results indicate that the inclined intervals below the bottom simulating reflection have high amplitude, continuous reflection and polarity reversal which may be caused by thin gas reservoir and the interlayered gas hydrate and free gas with different saturations. The top interfaces of the gas hydrate‐ and free gas‐bearing layers show typical Class III amplitude versus offset and exhibit high amplitude reflections at seismic data with near, mid and far‐incident angles, which are easy to distinguish. Seismic response of far‐incident angle can be used to identify the coexistence of gas hydrate and free gas. [ABSTRACT FROM AUTHOR]

The Dongsha area, a key region in the northern South China Sea (SCS), features both diffusive deep and seepage shallow gas hydrate reservoirs. Utilizing sediment samples from gas hydrate reservoirs and adjacent layers at sites W08 and W16 in the Dongsha area, this study aims to uncover the sediment property differences between deep and shallow gas hydrate reservoirs and their impact on gas hydrate accumulation through grain size, X-ray diffraction, and specific surface area (SSA) analyses. The findings classify the study intervals into four distinct layers: shallow non-gas hydrate layer (shallow-NGHL), shallow gas hydrate reservoir (shallow-GHR), deep non-gas hydrate layer (deep-NGHL), and deep gas hydrate reservoir (deep-GHR). In the clayey silt sediment reservoirs, grain size has a minor influence on gas hydrate reservoirs. Both shallow and deep NGHLs, characterized by high smectite content and SSA, possess a complex structure that impedes gas and fluid migration and offers limited potential reservoir space. Consequently, both shallow and deep NGHLs function as sealing beds. The deep GHR, having low smectite content and SSA, exhibits a strong capacity for gas and fluid migration and greater potential reservoir space. As a result, sediment properties significantly influence the deep GHR. Seepage primarily controls the shallow GHR. [ABSTRACT FROM AUTHOR]

Fragmentation of watercourses poses a significant threat to biodiversity, particularly for migratory fish species. Mitigation measures such as fishways, have been increasingly implemented to restore river connectivity and support fish migration. The effects of such restoration efforts are typically tested using telemetry and fisheries methods, which do not fully capture the broader population movements that may have important consequences for population viability. We performed a before‐and‐after control‐impact (BACI) study using genetic tools (SNPs) to investigate the effect of a newly implemented fishway, aiming to enhance upstream spawning migration of brown trout (Salmo trutta Linnaeus) in a reservoir with two headwater tributaries fragmented by man‐made weirs. Another reservoir with two barrier‐free tributaries was also analysed as a control. Our results showed that the isolated brown trout population was spawning in the reservoir before the installation of the fishway, and we found genetic structuring and differentiation between fragmented headwater tributaries before the fishway construction, but not in the control reservoir. Unexpectedly, after the fishway construction we observed signals consistent with increased genetic differentiation between populations of newly recruited juvenile fish in the reservoir tributary and fish in the reservoir. We propose this was caused by newly enabled philopatric behaviour of brown trout to their natal spawning tributary. In contrast, we did not find any genetic changes in the tributary without a fishway or in the barrier‐free reservoir system. Given the scarcity of similar studies, we advocate for an increased use of genetic analyses in BACI studies to monitor and evaluate the effect of efforts to restore habitat connectivity and inform future management strategies. [ABSTRACT FROM AUTHOR]

The demand for macadamia nut production worldwide has led to increased use of pesticides and chemicals for pest and disease control. Reservoirs in these macadamia farming sectors are at risk, since these chemicals can enter and contaminate the water through direct application, runoff, and atmospheric deposition, subsequently negatively affecting aquatic organisms. The current study investigated macroinvertebrate colonisation and succession associated with two macadamia orchards and two communal area reservoirs. The potential effects of stressors from these land uses was tested for and compared using stone substrates over a 6-week period. Stone substrates from both reservoir types were abundantly colonised over time and the total macroinvertebrate taxa and abundance showed an increasing trend across the sampled weeks, with macadamia orchards having the highest number of macroinvertebrate taxa. Strong ecological succession was observed across reservoirs, with the initial succession of early colonisers - i.e., Chironominae (collectorgatherers), Ostracoda (collector-filterers) and Anax sp. (predator) within communal area reservoirs, and Chironominae, Ostracoda and Radix natalensis (scrapers) in macadamia orchard reservoirs - followed by predatory colonisers such as Gyrinidae larvae, Trithemis sp. (macadamia orchard reservoirs), and Ranatra sp. (communal area reservoirs). Macroinvertebrate community structure differed significantly across sites and weeks, with no similarity being observed for communities across the different reservoirs. Redundancy analyses further highlighted 11 sediment chemistry variables (i.e., pH, resistivity, P, K, Na, Ca, Mg, Cu, B, Fe and S) which were significantly related to macroinvertebrate community structure. Thus, sediment variables were found to be better predictors of macroinvertebrate community structure in macadamia orchard reservoirs than communal area reservoirs. Consequently, we concluded that differences in colonisation ability among taxa and environmental stressors were important factors driving succession. These results add to the understanding of the macroinvertebrate colonisation processes and environmental stressors within agricultural landscapes, which can aid in the development of conservation management of freshwater ecosystems. [ABSTRACT FROM AUTHOR]

The study compares the structure of invertebrate communities inhabiting two types of bottom sediments in Krzynia Reservoir, known also as Lake Krzynia (on the Słupia River, northern Poland). The lake is prone to intensive sedimentation because it is limnic. This limnicity is due to the impact of the river, rather than to surface runoff from the catchment area, where the heavy predominance of natural habitats over transformed ones slows the transport of mineral suspensions from adjacent terrain. In the organic-poor sediments dominated by sand and gravel, the mean density of benthic invertebrates was ten-fold higher than in silty, organic-rich sediments, while invertebrate biomass was only slightly and non-significantly higher in organic-poor sediments than in organic-rich sediments. Simultaneously, the mean invertebrate body weight was markedly lower in organic-poor sediments (0.03 g) than in organic-rich sediments (0.18 g). No significant differences in taxonomic diversity (number and Shannon index of taxa) were found between the studied sediment types in the analysed communities. Among the major invertebrate groups, the Oligochaeta and Mollusca significantly differed in density between sediment types, while the Oligochaeta and Chironomidae differed in biomass. An increased percentage of silt fraction in bottom sediments resulted in a drastic decrease in abundance of benthic fauna, but their biomass declined only slightly. Thus, plans to construct new reservoirs should aim to reduce the rate of silt accumulation in them, in order to preserve their primary function and support biodiversity in transformed river valleys. [ABSTRACT FROM AUTHOR]

Sediment deposition at the bottom of artificial reservoirs has become a worldwide problem. This comprises a dual issue that is, in the first place, associated with the reduction in storage capacity and lifetime of large reservoirs. The second aspect comprises the threat that the sediment represents for the dam structure. This research is mainly aimed at identifying and inferring the main sediments' triggering processes through a rigorous analysis of deposition shapes in a large reservoir. For identifying the main deposition shapes, a sequential methodology was designed and developed comprising the following stages. First, an analysis of XYZ cartography from bathymetric development was conducted. Then, a shapes categorization was developed that comprises the identification of six types of shapes based on four parameters: slope continuity, slope break, absolute and relative slope, and arc configuration. The third stage comprised a visualization and spatial calculation of shapes through GIS-based cartography. The fourth stage comprised an interpretation of deposition shapes processes: for that, a dual analysis was developed. First, an analysis based on fluvial sediments transport processes was realized. The second stage implied an analysis of the dam influence on fluvial hydrodynamics and sediments transport. Results comprised a quantitative assessment of each shape as well as physical processes identification and interpretation, generating a robust equivalence between shapes and triggering processes. This research proved successful for the identification and characterization of the main deposition and transport processes that may help to prevent, palliate, and/or correct phenomenon of silting in large reservoirs. This detailed knowledge of deposition forms opens new strategies to release sediments from storage water more effectively. [ABSTRACT FROM AUTHOR]

Reservoir sedimentation affects lifespan, hydropower generation, water resource use, and ecosystem sustainability. In this study, using measured data from the worldrenowned Three Gorges Reservoir (TGR), sediment transport capacity was analysed from 2002 to 2020 at four TGR gauging stations (Cuntan, Qingxichang, Wanxian, and Miaohe). The result indicated that: (1) a significant decrease in sediment transport capacity occurred in the TGR before and after dam construction, with an overall reduction of 82% in the perennial backwater zone. Notably, Qingxichang, Wanxian, and Miaohe experienced reductions of 40%, 91%, and 59%, respectively. Since the initial operation phase, their maximum monthly sediment transport capacity has consistently occurred in July. (2) Changes in the water level in front of the dam, the incoming flow, and sediment influxes were the primary factors driving the annual variations in sediment transport capacity. Among the factors affecting the variation of sediment transport capacity along the TGR, the influence of the cross-sectional morphology was more pronounced than that of the distance from the dam. Sediment transport capacities in the wide and shallow sections were considerably lower than those in the narrow and deep sections. (3) A sediment transport amplitude index (Fd) was proposed to assess the sediment dynamics within the TGR, which effectively characterized the sedimentation conditions based on the relative importance of these influencing factors. These findings provide a theoretical basis for operational strategies in the TGR and offer insights into the patterns of sediment transport capacity changes in reservoir areas before and after dam construction in other river-type reservoirs. [ABSTRACT FROM AUTHOR]

Among the most characteristic offsite effects of soil erosion, reservoir sedimentation is one of the longlasting problems pertaining to storage capacity and dam operations. In this work, sedimentation rates of the Fortezza reservoir in South Tyrol (Italian Alps) are analysed for nine erosive events over 14 months. Sediment rates are calculated through a modified Universal Soil Loss Equation (USLE) combined with a Sediment Delivery Ratio (SDR) module at 2.5 m resolution. The topographic factor is adjusted to the Alpine terrain, and an additional factor is included to consider the nonerodible parts of the basin. The results are validated against a 14-month sediment yield obtained by high-resolution (0.2 m) reservoir bathymetric analyses. The calculated sediment yield has an absolute deviation of 4.8% from the measured one. The results indicate that these methods can be successfully applied for the estimation of reservoir sedimentation rates in the Alps. [ABSTRACT FROM AUTHOR]

The ecosystem structure of a Mediterranean high-altitude artificial lake (Aoos Springs, Northwest Greece) was assessed and quantified using the Ecopath with Ecosim model. The artificial lake was created in 1990 for hydroelectric production and the fish fauna has been enriched across years due to deliberate or accidental fish stockings, as well as the introduction of the invasive pumpkinseed (Lepomis gibbosus), which may cause adverse effects on aquatic ecosystems and their biota. The model considered 20 species/taxa groups with biological data gathered during 2021–2022 from field surveys, interviews with recreational anglers and literature. The results revealed that the artificial lake of Aoos is a resilient ecosystem to unexpected events with low intensity of fisheries exploitation. The biomass of the introduced invasive species Lepomis gibbosus is low, due to the low biomass level of its diet, Chironomidae and zoobenthic organisms as well as other fish species. [ABSTRACT FROM AUTHOR]

Reservoir sedimentation management has become an important topic for large dams in the United States due to their historical design, current age, and increased environmental regulation. Less attention has been paid to small dams (hydraulic size < 0.01) in remote mountains with urgent sedimentation problems. In drier climates, such reservoirs may be frequently drained and trans-catchment flows routed over their sediment deposits heading from one mountain tunnel to another. This study asked an unexplored scientific question focusing on this special setting: how do different amounts of water transfers interact with different reservoir stages to affect sediment erosion and its redistribution in the backwater zone? Mindful timing and magnitude adjustment of water transfer, involving water diverted across watersheds by tunnels, through a reservoir were hypothesized to strategically redistribute sediment erosion for sites with water transfer/diversion facilities in the main channel. For a study site in the north-central Sierra Mountains of California, 2D hydrodynamic modeling revealed that sediment erosion within the backwater zone increased by > 100% when water transfer was maximized, involving a flow 12 times higher than mean annual discharge. With reservoir stage drawdown, the increment of sediment erosion was further increased by > 50% compared with water-transfer-only scenarios. The natural upstream inflow with daily flow occurrence of 5–25% was the optimal water transfer to avoid disturbing sediment. These results indicated that water transfer and stage drawdown optimization is a promising strategy to promote or abate redistribution of deposited sediment through a smaller reservoir.

Reservoir sedimentation increases economic cost and overflow of dam water. An optimal control problem (OCP) with singularly perturbed equations of motion is perused in the fields of sediment management during a finite lifespan. Subsequently the OCP is transformed to a nonlinear programming problem by utilizing a collocation approach, and then we employed the imperialist competitive algorithm to improve the execution time and decision. So, the solutions of the optimal control and fast state as well as the maximization of net present value of dam operations are obtained. An illustrative practical study demonstrated that sedimentation management is economically favourable for volume of confined water and total amount in remaining storage and effectiveness of the propounded approach.

Large dam removal can trigger changes to physical and biological processes that influence vegetation dynamics in former reservoirs, along river corridors downstream of former dams, and at a river's terminus in deltas and estuaries. We present the first comprehensive review of vegetation response to major fluvial disturbance caused by the world's largest dam removal. After being in place for nearly a century, two large dams were removed along the Elwha River, Washington, USA, between 2011 and 2014. The exposure, erosion, transport, and deposition of large volumes of sediment and large wood that were impounded behind the dams created new fluvial surfaces where plant colonization and growth have occurred. In the former reservoirs, dam removal exposed ~290 ha of unvegetated sediment distributed on three main landforms: valley walls, high terraces, and dynamic floodplains. In addition to natural revegetation in the former reservoirs, weed control and seeding and planting of desirable plants influenced vegetation trajectories. In early years following dam removal, ~20.5 Mt of trapped sediment were eroded from the former reservoirs and transported downstream. This sediment pulse, in combination with transport of large wood, led to channel widening, an increase in gravel bars, and floodplain deposition. The primary vegetation responses along the river corridor were a reduction in vegetated area associated with channel widening, plant establishment on new gravel bars, increased hydrochory, and altered plant community composition on gravel bars and floodplains. Plant species diversity increased in some river segments. In the delta, sediment deposition led to the creation of ~26.8 ha of new land surfaces and altered the distribution and dynamics of intertidal water bodies. Vegetation colonized ~16.4 ha of new surfaces: mixed pioneer vegetation colonized supratidal beach, river bars, and river mouth bars, and emergent marsh vegetation colonized intertidal aquatic habitats. In addition to the sediment-dominated processes that have created opportunities for plant colonization and growth, biological processes such as restored hydrochory and anadromous fish passage with associated delivery of marine-derived nutrients may influence vegetation dynamics over time. Rapid changes to landforms and vegetation growth were related to the large sediment pulse in the early years following dam removal, and the rate of change is expected to attenuate as the system adjusts to natural flow and sediment regimes. [ABSTRACT FROM AUTHOR]

In this study, a new empirical equation was established to predict the sedimentation volume resulting from the construction of a multi-purpose weir or low-head dam using experimental approaches. Applying the 1-D numerical model (STAFF), which is based on Exner's equation, 2545 cases were simulated and laboratory experiments were conducted with various sediment particle sizes, channel slopes, inlet discharge, and outlet water elevation. Short-term predictions were conducted through laboratory experiments with movable bed, and the results indicated that dimensionless unit stream power and the Shields parameter exhibited the most significant correlation with dimensionless deposition volume. In particular, we analyzed the phenomenon in which the backwater effect and reservoir delta. Using a multiple regression approach, the developed empirical equation was validated for predicting sedimentation in the upstream reservoir of the weir. [ABSTRACT FROM AUTHOR]

Ayu Plecoglossus altivelis altivelis is a valuable osmeroid species for inland fishery in Japan. It is classified into two ecological forms of amphidromous migrating between rivers and sea and landlocked migrating between rivers and lakes or dam reservoirs. The number of dams and their reservoirs has remarkably increased in the twenty-first century under climate change, because of their respective roles in hydropower generation with negligible carbon emissions and in flood control. Dam reservoirs therefore become increasingly important as inland nursery grounds of ayu. In this study, we investigated the reproduction status of landlocked ayu migrating in the Haidzuka Dam reservoir and the Tabusa River in western Japan by molecular phylogenetic analysis based on population structure and demographic history for year cohort dynamics. A total of 849 individuals were collected monthly from October 2018 to September 2021 according to an annual life cycle of ayu. Nucleotide sequences of the partial mitochondrial DNA control region yielded 31 haplotypes, consisting of 4 shared haplotypes among the 2019, 2020 and 2021 cohorts and 27 unique haplotypes. The overall haplotype diversity and nucleotide diversity were calculated to be relatively low at 0.3503 ± 0.0206 and 0.0077 ± 0.0045, respectively, suggesting a founder event by dominant haplotypes. Star-shaped radiational haplotypes from dominant shared haplotypes on the median-joining network likely support a founder event. Although pairwise ФST values were determined to be very low among the year cohorts, only the 2019 cohort was found to have a significant difference from the 2020 and 2021 cohorts, for both of which Tajima's D values were also statistically significant. For the overall population, multimodal mismatch distribution and negative Tajima's D and Fu's Fs values in the neutrality test suggested population expansion or population subdivision. The native riverine population in the Tabusa River suffered habitat fragmentation and population bottleneck from dam construction, and therefore severe founder effect remained behind the artificially landlocked population with a low level of genetic diversity in the Haidzuka Dam reservoir. [ABSTRACT FROM AUTHOR]

One of the most conspicuous impacts of dam construction on fish is the blocking of their migratory routes. However, the formation of the reservoir, a lentic environment with distinct hydrological and ecological characteristics, can also constitute an obstacle to migration. This impact, however, is poorly explored in the scientific literature. Therefore, this study aimed to assess the movements of Prochilodus argenteus tagged with radio telemetry transmitters and manually translocated across the Três Marias Dam in the São Francisco River. The Três Marias reservoir covers an area of 1090 km2 and ranks among the largest artificial reservoirs in Brazil. Individuals translocated to the Três Marias reservoir showed reduced movement rates and home ranges. They appeared disoriented in the new environment, with many of them settling near fish farms and remaining there throughout the study period. A comparative analysis with existing literature on Neotropical species' reproductive migration through artificial reservoirs revealed a trend: the ability of migratory fish to navigate reservoirs diminishes with their area, especially those exceeding 50 km2 or with a residence time surpassing 30 days. These results indicate that caution is needed when designing fish passage facilities for dams that form larger artificial reservoirs in the Neotropics. Even if these facilities are efficient in attracting and translocating migratory species, behavioral and physiological thresholds may prevent them from reaching suitable areas to complete their reproductive cycle in the new environment formed. [ABSTRACT FROM AUTHOR]

This article provides a comprehensive review and best practices for numerically simulating hydraulic flushing for reservoir sediment management. Three sediment flushing types are discussed: drawdown flushing, pressure flushing, and turbidity current venting. The need for reservoir sediment management and the current practices are reviewed. Different hydraulic drawdown types are described in terms of the basic physical processes involved as well as the empirical/analytical assessment tools that may be used. The primary focus has been on the numerical modeling of various hydraulic flushing options. Three model categories are reviewed: one-dimensional (1D), two-dimensional (2D) depth-averaged or layer-averaged, and three-dimensional (3D) computational fluid dynamics (CFD) models. General guidelines are provided on how to select a proper model given the characteristics of the reservoir and the flushing method, as well as specific guidelines for modeling. Case studies are also presented to illustrate the guidelines. [ABSTRACT FROM AUTHOR]

Microplastic contamination poses a major threat in freshwaters, and rivers are considered sinks and pathways of plastic pollution to different ecosystems. Plastic abundance and concentration can be influenced by spatial factors, and artificial water bodies such as reservoirs can alter how plastics are distributed and interact with the biota. Additionally, biological traits like the trophic guilds and habitat use of animals can be important variables affecting plastic uptake. In this study, we investigated microplastic contamination in a fish community from a Neotropical reservoir. We assessed whether the distinct reservoir zones (fluvial, transitional, and lacustrine) had an influence on plastic ingestion by fish and also examined the effect of biological characteristics such as trophic guild and habitat use. Fibers and fragments of plastics were found in nine fish species and were identified as polyamide, polystyrene, and polyethylene. In general, plastic ingestion had a low incidence when compared to other reservoirs; however, we found that fish from the lacustrine zone, insectivores, and benthopelagic species showed a significant correlation with plastic ingestion. The findings presented here provide insights into the causes and the current state of microplastic pollution in Neotropical reservoirs. [ABSTRACT FROM AUTHOR]

In recent years, interest in natural therapeutic mud has been growing all over the world. This natural product has a positive therapeutic effect on the skin and has fewer side effects on the human body. There are more than 40 thousand salt lakes in Kazakhstan. Most of them have natural mud sources, the potential of which has not yet been fully explored. The review presents an analysis of the available information on the physical and chemical properties of the main sources of natural mud from salt lakes in Kazakhstan and Kazakh sanatoriums that use natural mud in the treatment. All available publications, presenting the systematic studies, were used for data analysis. A comparative analysis of the mineralization of water, brine, and silt in one reservoir shows that the mineralization of water is not always the least. The available data indicate a point and partial nature of peloid studies, e.g., inorganic composition of natural muds from Western and Southern Kazakhstan is well described in the literature. In turn, there is a lack of these data from Northern and Eastern Kazakhstan. Studies of peloids in these regions seem to be a promising direction of the future research for both local and world scientists. What is more, there is also a big gap in the analysis of organic matter of muds from the Kazakh lakes. Comparing the state of the art, i.e., the studies from other parts of Asia and Europe, the identification of the organic part of muds is another desirable direction as a potential source of biologically active compounds of natural origin. [ABSTRACT FROM AUTHOR]

• A coupled model is proposed integrating a 2D double layer-averaged model for reservoir and a 1D model for bottom tunnel. • High water level, small cover layer thickness, short tunnel length and steep tunnel slope favour the occurrence of sediment flushing. • Low water level, large cover layer thickness, long tunnel length and gentle tunnel slope are more likely to cause tunnel blockage. Sediment flushing through a bottom tunnel is one of the most effective methods to alleviate reservoir sedimentation. However, the multi-physical hydro-sediment-morphological processes of reservoir sediment flushing through an initially covered bottom tunnel intake have remained poorly understood, and a physically enhanced and practically viable mathematical model is required. The present study uses an integrated model to resolve sediment flushing through an initially covered bottom tunnel intake. The proposed model couples a two-dimensional double layer-averaged model for the reservoir with a one-dimensional model for the bottom tunnel by means of numerical fluxes calculations at the inner boundary. The governing equations are solved synchronously using a well-balanced finite volume method. Several parameters related to boundary resistances and sediment exchange flux need to be determined for model closure. The model is tested against data from a series of physical experiments on reservoir sediment flushing, with sound agreement achieved between computed and measured scour hole geometries. Moreover, the present model successfully predicts the occurrence of tunnel blockage. The results prove that reservoir sediment flushing is best accomplished for high reservoir water level, small cover layer thickness, short tunnel length and steep tunnel slope. The present model facilitates reservoir design and operation to help preserve reservoir capacity. [ABSTRACT FROM AUTHOR]