Dam Operation Research Articles

A Study on the Development and Evolution of Fractures in the Coal Pillar Dams of Underground Reservoirs in Coal Mines and Their Optimum Size

The western mining areas of China, which are rich in coal resources, lack water resources. Large-scale and high-intensity coal mining in China’s western mining areas has led to the loss of groundwater resources. Underground reservoirs in coal mines are an effective means of achieving the protection and utilization of water resources in these western mining areas. One of the important standards for the safety of an underground reservoir in a coal mine involves checking whether the development of cracks in the coal pillar dam body, under the dual stress conditions of overlying strata and lateral water pressure, passes through the coal pillar dam body or its top and bottom plates, forming a seepage channel for mine water. This article focuses on the safety issues associated with coal pillar dams in the underground reservoirs of coal mines. From the perspectives of overlying rock pressure and lateral water pressure on coal pillar dams, mechanical models, numerical calculations, and similar simulation methods were used to analyze macroscopic deformation, displacement, and crack development in coal pillar dams of different sizes under vertical and horizontal stress and to study the optimum width of coal pillar dams. Our research results indicated that the optimal width of the coal pillar dam body can be determined via numerical simulation based on the deformation and stress state in a given dam. When the horizontal stress increases, the smaller the coal pillar width is, the greater the increment of syy and sxx becomes, and the more likely the coal pillar is to be damaged. Similar simulations showed that the smaller the size of the coal pillar is, the easier it is to generate stress concentration, and the more likely this stress is to “eat away” the coal pillar dam body. There is a certain relationship between the size of the coal pillar dam and the range of crack development. The larger the coal pillar size is, the less obvious the stress concentration effect becomes, and the less likely the crack is to penetrate the internal and external parts of the reservoir. Taking the Shangwan mine as an example, it was determined that the maximum water head height that could be carried by the 15-m coal pillar dam body was 50 m. A comprehensive study of the development and evolution of cracks in the coal pillar dam of an underground reservoir in a coal mine, and the characteristics of sliding instability, was conducted to determine the optimal size and maximum water storage height of a coal pillar that does not penetrate the inner and outer parts of the reservoir. The development and evolution of cracks are important factors affecting the stability of coal pillar dams. This study can expand and improve the basic theory of underground reservoirs in coal mines, provide a scientific basis for determining the optimum size of a coal pillar dam, guarantee the long-term safe and stable operation of the coal pillar dams of underground reservoirs in coal mines, and continuously save mine water resources and increase the economic benefits of coal mines. These implications are of great significance for the long-term stable operation of underground reservoirs in coal mines under similar geological conditions.

Dujiangyan irrigation system optimization (DISO): A novel metaheuristic algorithm for dam safety monitoring

This work utilizes a novel metaheuristic algorithm named Dujiangyan Irrigation System Optimization (DISO) to resolve the dam deformation prediction problem. The Dujiangyan irrigation system (DIS) served as the model for the DISO algorithm, which has good metaheuristic algorithmic properties to handle various issues. This study utilizes the Fish Mouth project, the Baopingkou project, and the DIS's water separation and sand discharge principle. With the help of a mathematical model and implementation, DISO can perform the optimization process in various search spaces. Two comparative experiments with various characteristics are performed to evaluate the effectiveness of the DISO algorithm. 29 CEC 2017 benchmark test functions, 4 high-constrained test functions, and 2 typical engineering design challenges are chosen in the first step. 14 advanced heuristic techniques are chosen from the literature, and the statistical outputs of these techniques are examined and compared. Three nonparametric statistical tests are performed to confirm the proposed algorithm's effectiveness. The results demonstrate that the DISO algorithm outperforms all the evaluated algorithms. In the following stage, the proposed algorithm is applied to the dam deformation prediction problem, and a KICA-DISO-SVM spatial–temporal monitoring model is established for dams. The findings of the studies indicate that the proposed method can effectively monitor the influence of dam displacement on dam operation. The proposed model overcomes the inability of the standard single measurement point mode to capture the intrinsic relationship of the spatial deformation field accurately. The suggested DISO technique offers encouraging outcomes in resolving complex optimization problems.

Numerical Modelling of a Dam-Regulated River Network for Balancing Water Supply and Ecological Flow Downstream

Dam operation is regarded as an effective way to increase water, food, and energy security for society. However, with the increasing water demand and frequent extreme droughts, numerous rivers worldwide go through periods of water scarcity and water ecosystem deterioration to varying degrees. Balancing the water supply and ecological flow of the dam-regulated river network is essential in the context of river restoration. In this study, we proposed a hydrodynamic and water quality model of a dam-regulated river network balancing water supply and ecological flow using the Environmental Fluid Dynamics Code (EFDC). A section of Jinjiang watershed located in the southwestern of China was chosen as the study area. Firstly, the model was calibrated and validated. By comparing the simulated values with the measured values, the statistical analysis results showed that the relative root mean-squared error (RRMSE) values of water level, COD and NH3-N were 5.5–8.1%, 23.6% and 28.4%, respectively, indicating an adequate degree of agreement between simulation and observation. Based on the established model, dam operation schemes under a dry hydrologic scenario and emergency contamination scenario were formulated to ensure the requirement of ecological water flow and water quality simultaneously. For the dry hydrologic scenario, the ecological water requirement could be satisfied through the dam operation. However, in an emergency contamination scenario, regional water quality requirements cannot be met through dam operation. The dam operation only plays a role in controlling the scope of pollution. This study is expected to provide scientific support for dam-regulated river network management and downstream river ecosystem protection.

The NADI Mathematical Model on the Danger Level of the Bili-Bili Dam

The research discusses the NADI mathematical model due to the overflow of the Bili-Bili dam, using secondary data obtained through online literature review by collecting various information related to the Bili-Bili Dam, starting from the Jeberang River Scheme, the chronology of floods, normal or dry conditions, and dam operation patterns. The aim of this study is to predict the level of danger of Bili-bili dam overflow over time, considering extreme weather factors and standard operating procedures performed by humans. The research uses analytical and computational methods. The study obtained the NADI mathematical model due to the overflow of the Bili-Bili dam, with two equilibrium points: (1) the equilibrium point free of disaster, (2) the disaster equilibrium point, and a basic disaster reproduction number of R0 = 1.219. This indicates that the water discharge from the dam is high and has an impact on the overflowing water for communities around the Jeneberang river. Therefore, it can be concluded that the NADI model can be used to simulate the Bili-bili dam process based on extreme weather and dam SOP, and predict the level of danger of Bili-bili dam overflow, which is also a novelty that has not been done in previous studies.

Archaeological sites in Grand Canyon National Park along the Colorado River are eroding owing to six decades of Glen Canyon Dam operations

The archaeological record documenting human history in deserts is commonly concentrated along rivers in terraces or other landforms built by river sediment deposits. Today that record is at risk in many river valleys owing to human resource and infrastructure development activities, including the construction and operation of dams. We assessed the effects of the operations of Glen Canyon Dam – which, since its closure in 1963, has imposed drastic changes to flow, sediment supply and distribution, and riparian vegetation – on a population of 362 archaeological sites in the Colorado River corridor through Grand Canyon National Park, Arizona, USA. We leverage 50 years of evidence from aerial photographs and more than 30 years of field observations and measurements of archaeological-site topography and wind patterns to evaluate changes in the physical integrity of archaeological sites using two geomorphology-based site classification systems. We find that most archaeological sites are eroding; moreover, most are at increased risk of continuing to erode, due to six decades of operations of Glen Canyon Dam. Results show that the wind-driven (aeolian) supply of river-sourced sand, essential for covering archaeological sites and protecting them from erosion, has decreased for most sites since 1973 owing to effects of long-term dam operations on river sediment supply and riparian vegetation expansion on sandbars. Results show that the proportion of sites affected by erosion from gullies controlled by the local base-level of the Colorado River has increased since 2000. These changes to landscape processes affecting archaeological site integrity limit the ability of the National Park Service and Grand Canyon-affiliated Native American Tribes to achieve environmental management goals to maintain or improve site integrity in situ. We identify three environmental management opportunities that could be used to a greater extent to decrease the risk of erosion and increase the potential for in-situ preservation of archaeological sites. Environmental management opportunities are: 1) sediment-rich controlled river floods to increase the aeolian supply of river-sourced sand, 2) extended periods of low river flow to increase the aeolian supply of river-sourced sand, 3) the removal of riparian vegetation barriers to the aeolian transport of river-sourced sand.

Flow and thermal regimes altered by a dam caused failure of fish recruitment in the upper Mekong River

Abstract Riverine fishes have been increasingly threatened by the global proliferation of both small dams and large hydropower projects to meet the soaring water, energy and food demands from growing human populations and urbanisation. However, empirical evidence of the direct effects on a specific species before and after dam construction and operation is rare. Causes of population decline vary among species and, although little known, they are of great importance for successful environmental flow regulation. We monitored the hydroenvironment and population dynamics of a Schizothoracinae fish (Schizothorax lissolabiatus) for 9 years before and after dam (i.e., Dahuaqiao) construction in the upper Mekong River to understand fish response processes and the underlying mechanisms. Optimal hydroenvironmental conditions for key reproduction stages (e.g., pre‐spawning, hatching and post‐hatching) were reconstructed using daily increment analysis of larval otoliths and hydroenvironmental data. The flow regime was substantially disrupted by the dam, and water temperature was only slightly changed. The disappearance of young of the year from downstream after dam operation indicates that the changed hydroenvironment caused recruitment failure in S. lissolabiatus. By matching optimal hydroenvironmental conditions for S. lissolabiatus reproduction with the monitored hydroenvironmental data series before and after dam operation, we found that changes in thermal regime alone caused narrowing of the reproduction window by an average of 41%, whereas flow‐regime change alone narrowed it by 96% and it was narrowed by 98% for thermal and flow changes combined. This study shows that the altered flow regime, but not the thermal regime, was the primary driver of the recruitment failure of S. lissolabiatus. The findings highlight the importance of prioritising flow‐regime management to improve recruitment success for S. lissolabiatus and to favour the persistence of other imperilled Schizothoracinae fishes and native species in dammed rivers.

Dam Safety Evaluation Method after Extreme Load Condition Based on Health Monitoring and Deep Learning.

The safety operation of dams after extreme load is an important frontier research topic in the field of dam engineering. The dam health monitoring provides a reliable data basis for a safety evaluation after extreme loads. This study proposes a novel data-driven fusion model for a dam safety evaluation after extreme load based on monitoring data derived by sensors. First, the relationship between dam environmental quantity and effect quantity is deeply excavated based on bidirectional long short-term memory (BiLSTM) network, which is a deeply improved LSTM model. Aiming at the parameter optimization problem of BiLSTM model, sparrow search algorithm (SSA), which is an advanced optimization algorithm, is integrated. Second, conducting the constructed SSA-BiLSTM model to estimate the change law of dam effect quantity after the extreme load. Finally, the Mann-Whitney U-test theory is introduced to establish the evaluation criterion of the dam safety state. Project case shows that the multiple quantitative prediction accuracy evaluation indicators of the proposed method are significantly superior to the comparison method, with mean absolute percentage error (MAPE) and mean absolute error (MAE) values decreasing by 30.5% and 27.8%, respectively, on average. The proposed model can accurately diagnose the dam safety state after the extreme load compared with on-site inspection results of the engineering department, which provides a new method for dam safety evaluation.

Rainfall and Discharge Variability in the Senegal River Basin Based on the IHA/RVA

The hydrological regime of a river is a driving force of its ecosystem. The operation of dams and locks has significant impacts on the hydrological situation of rivers. The objective of this study was to study the change and variability of precipitation and hydrological data in the Senegal River basin and to assess the change in the discharge regime of the Senegal River caused by the operation of the Manantali hydroelectric dam. Based on the IHA (Indicators of Hydrologic Alteration), a range of variability of thirty-three hydrological parameters was calculated and the hydrological alteration associated with the functioning of the dam was quantified. Using the RVA (Range of Variability Approach) method, the hydrological alteration at the Bakel site was evaluated and showed the influence of the dam on the hydrological state. The results showed a strong influence of the dam on the hydrological regime. The fluvial eco-hydrological objectives calculated in this study can constitute certain support for the management of water resources and ecosystems of the Senegal River basin.

Dynamic transport of particulate organic carbon in the Yellow River during dam-orientated Water-Sediment Regulation

The Yellow River has experienced prolific environmental changes from dam regulations that have significantly altered the downstream hydrologic regime, and transport of sediment and POC within the river-coast continuum. Here, we investigated the contrasting changes in sources and transport of POC from the lower Yellow River to the river mouth, at two different stages (e.g., Water vs. Sediment regulation) of dam operation - during the period of Water-Sediment Regulation Scheme (WSRS). Riverbed erosion downstream the Xiaolangdi Dam contributed the POC with more enriched δ13C stable isotopic values, along with those more isotopically depleted POC from riparian floodplains and the reservoir at the Water-regulation stage, when clear water was released from the reservoir. At the Sediment-regulation stage, muddy floodwaters were released, while soil-derived POC and fine-grained sediment released from the reservoir became dominant with evidently increasing POC content. The dispersal and distribution of river-laden POC at the river mouth were primarily modulated by the plume dynamics, as remotely impacted by dam regulation, in combination with the dynamic shear front. As a result, the POC distribution was confined within 10 km off the river mouth due to the rapid deposition of coarse-grained sediments. In contrast, the fine-grained sediment and more isotopically depleted POC, from modern sources (e.g., C3 vascular plant), were delivered to the far-field plume region. POC transport along the Yellow River-Estuary continuum exhibited complex behaviors, coupled with natural and dam-regulated drivers, on a variety of spatial-temporal scales. These findings provide important insights into dynamic linkages on how coastal carbon cycling can be significantly altered, remotely from the upstream dam regulations, in a large global river system.

Dynamic and delayed channel geomorphic responses to changing hydrological processes following the Three Gorges Dam operation

AbstractThe characteristics of dynamic and delayed channel geomorphic responses to changing hydrological processes are still insufficiently understood, especially in large dammed rivers and segments farther downstream from the dam. Geomorphic effects farther downstream from the dam could be easily underestimated. This study investigated the hydrological changes and channel adjustments in the Chenglingji–Jiujiang Reach (CJR), ~450 km downstream from the Three Gorges Dam. The post‐dam evolution developed from early low‐intensity alternating erosion/deposition to later intense erosion. This is because the increasing sediment starvation caused by the dam and attenuated upstream sediment replenishment produced streams with excess transport capacity for the farther downstream channel, where the early mild evolution and fine‐sandy riverbed guaranteed adequate sediment availability. Additionally, the increasing geomorphic contribution of low‐to‐medium flows, coupled with revetment resistance to lateral adjustments, promoted migration of the major adjustment area from above the bankfull channel to below the medium‐flow channel and characterized erosion by one‐way incision with no evident channel narrowing/widening. The net increase in reach‐averaged thalweg incision depth during a later period (2.85 m) was 35 times larger than that during an earlier period (0.08 m). Channel morphogenetic intra‐annual hydrological processes were identified to contain all discharges smaller than 39 000 m3/s, and discharges of 30 000–39 000 m3/s exerted maximum geomorphic effects. On this basis, a method for estimating the cumulative erosion volume at equilibrium was proposed and integrated into the Delayed Response Model. The encouraging simulation and prediction results indicate that geomorphological adjustments within the CJR were greatly influenced by the hydrological conditions of current year and previous 4 years, while the impacts of extreme and rare events depended more on the consistency of their hydrological behaviours with channel evolutionary trends than on their temporal distances. This work facilitates the understanding and prediction of channel self‐adjustments farther downstream from the dam.

Structural identification of super high arch dams using Gaussian process regression with improved salp swarm algorithm

Structural identification is critical for evaluating the operation of high arch dams, and has become an important topic. This paper proposes a novel inverse analysis framework combining an improved salp swarm algorithm and Gaussian process regression to identify the material parameters of concrete dams. First, the hydrostatic component is separated from the prototype measured data using the multiple linear regression method. Subsequently, the Gaussian process regression is adopted to build the mapping relationship between elastic modulus and the calculated relative hydrostatic component of the dam. Finally, the improved salp swarm algorithm is used to estimate the real elastic modulus of the dam by minimizing the discrepancy between the measured and calculated relative hydrostatic components. The performance of the proposed method is verified on a real concrete arch dam with sufficient monitoring data. Results show that the proposed inverse analysis method can identify the material parameters accurately and efficiently.

Impact of Paddy Field Reservoirs on Flood Management in a Large River Basin of Japan

The flood retention capacity of paddy fields is well-recognized in Japan, and all the existing flood control practices via paddy field management achieve reductions in peak flood discharge. However, the previous studies have not assessed the flood management potential of paddy fields in a large river basin with average paddy coverage, and the existing hydrological models are not quite suitable for simulating river discharge from closed-drainage paddy reservoir storage. We herein attempt to improve the watershed-scale version of global hydrological model H08 to simulate a reduction in the peak discharge from paddy reservoirs in the Abukuma River basin of Japan. The NSE and R2 index showed fair reliability of the H08 model during the calibration and validation stages. The simulated results from the improved model show 11% and 6% peak reductions in high paddy coverage areas for a normal year (2018) and a major typhoon year (2019), respectively. The peak-reduction percentage increased with decreasing rainfall, depending on the overflow from the paddy reservoirs. The results indicate that the paddy reservoir is not highly effective in a large river with less than 20% paddy coverage, but the peak discharge reduction capacity shows that paddy reservoirs can make some contribution when used in combination with dam operation.

Development of Multi-Inflow Prediction Ensemble Model Based on Auto-Sklearn Using Combined Approach: Case Study of Soyang River Dam

Accurate prediction of dam inflows is essential for effective water resource management and dam operation. In this study, we developed a multi-inflow prediction ensemble (MPE) model for dam inflow prediction using auto-sklearn (AS). The MPE model is designed to combine ensemble models for high and low inflow prediction and improve dam inflow prediction accuracy. We investigated the impact of datasets assigned to flow regimes on the ensemble composition and compared the performance of the MPE model to an AS-based ensemble model developed using a conventional approach. Our findings showed that the MPE model outperformed the conventional model in predicting dam inflows during flood and nonflood periods, reducing the root mean square error (RMSE) and mean absolute error (MAE) by 22.1% and 24.9% for low inflows, and increasing the coefficient of determination (R2) and Nash–Sutcliffe efficiency (NSE) by 21.9% and 35.8%, respectively. These results suggest that the MPE model has the potential to improve water resource management and dam operation, benefiting both the environment and society. Overall, the methodology of this study is expected to contribute to the development of a robust ensemble model for dam inflow prediction in regions with high climate variability.

High-temporal-resolution monitoring of reservoir water storage of the Lancang-Mekong River

The Lancang-Mekong River (LMR) is an important transboundary river in Southeast Asia shared by China, Myanmar, Laos, Thailand, Cambodia, and Vietnam from upstream to downstream. Construction and operation of dams in the LMR basin has profoundly affected its natural streamflow regime. It is therefore important to monitor changes in reservoir water storage and to quantify the impact of reservoir operation on the redistribution of surface water resources over this basin. Given the difficulty in obtaining in-situ measurements of reservoirs on the LMR, we integrated multisource remote sensing, including satellite altimetry and optical and synthetic aperture radar (SAR) images, to generate weekly water levels and water storages of nine largest reservoirs on the main stem of the LMR from 2017 to 2021. Specifically, partial surface water extent (SWE) of reservoirs was extracted from Sentinel-1 SAR images and digital elevation models (DEMs), using Random Forest algorithms trained by partial SWE derived from Sentinel-2 optical images, showing an overall accuracy higher than 95%. Based on the partial SWE and water level estimates from ICESat-2 and Global Ecosystem Dynamics Investigation (GEDI, International Space Station-based) data, the relationships between water levels and partial SWE were derived to convert partial SWE into water level time series. Furthermore, water storage time series of the nine reservoirs were obtained from water level time series and hypsometric functions derived from SRTM DEMs that were corrected by ICESat-2 data to remove systematic errors. For the Xiaowan Reservoir on the Lancang River, there is close agreement between remote sensing-derived water levels and in-situ water levels in terms of a normalized RMSE lower than 5%. Results indicate that multisource remote sensing has large potential for high-temporal-resolution monitoring of reservoir water levels and water storage. This could more precisely evaluate impacts of cascade reservoirs on the streamflow of the LMR and facilitate drought and flood mitigation for riverine countries.

Riparian cottonwood mortality following compound impacts from river water withdrawal and hydroclimatic variation

AbstractOriginating in Glacier Park, Montana, the transboundary St. Mary River has provided a focus for international water sharing for a century. It was dammed and diverted in the USA, and more extensively in Alberta, where it supports Canada's centre for agricultural irrigation. Following water withdrawals, the riparian cottonwoods (Populus angustifolia) collapsed, and we assessed the woodland decline downstream from the St. Mary Dam, through eight sets of aerial photographs over seven decades. These revealed 88% woodland loss from 1951 to 1999 (R2 = 0.984), including a steeper decline with the 1980s drought. Following the implementation of an environmental flow regime that increased minimum flows after 1993, the remnant woodlands were stabilized, with a slight recovery by 2022. Analyses of the historical hydrology revealed compound contributions to the woodland mortality. (1) Annual river flows declined with increasing water diversion, and (2) late summer flows were particularly depleted. (3) Dam operations resulted in abrupt stage recessions and irregular spikes. (4) Accompanying climate warming, the spring snowmelt advanced and late summer flows declined. (5) The greatest climatic influence involved multiple‐year clusters with high versus low flows, corresponding with the Pacific decadal oscillation (PDO) from 1920 to 1990 (R2 = 0.365), but less coupled thereafter. This long‐term study demonstrates the coordination between hydroclimatic variation, water management and the fate of riparian woodlands, which reveal ecosystem health. An environmental flow regime provided benefit, and for other regulated rivers in dry ecoregions, we recommend functional flow regimes that provide sufficient minimum flows and avoid abrupt flow recession or irregular spikes.

Effects of small hydropower dams on macroinvertebrate and fish assemblages in southern Brazil

Abstract Hydropower dams affect freshwater biodiversity by virtue of modifying flow regimes and degrading habitat conditions both above and below the water impoundment and diversion structure. In recent decades, there has been a global proliferation of Small Hydropower Plants (SHPs) propelled by incentive policies and a general perception that small dams are less harmful to the environment. However, limited science is available on the effects of SHPs on freshwater biodiversity, which is concerning considering their sheer numbers and the high variability in the size and operation of dams classified as SHPs. We investigated the ecological effects of 12 SHPs on macroinvertebrate and fish assemblages of the Chapecó River Basin, Brazil. Our study included sites located upstream of the SHPs and sites directly affected by their operations (i.e., reservoir, dewatering section and downstream of the powerhouse). This design allowed us to quantify shifts in taxonomic composition and examine the relative role of different SHP attributes (e.g., dam height, reservoir area, age) in explaining these changes. Our results reveal that SHPs modify the composition of both macroinvertebrate and fish assemblages, but the magnitude of such changes vary widely among dams. Both assemblages exhibited directionality in taxonomic shifts, resulting in a gradual replacement of taxa associated with fast‐flowing habitats by other groups more commonly associated with standing waters. We also found that changes in assemblage structureare related to structural (dam height, reservoir area) and spatial attributes (distance from headwaters) of SHPs, although the predictive power of these attributes varied taxonomically and among reservoir, dewatering and downstream sites. Overall, our results demonstrate that SHPs have important and heterogeneous effects on freshwater assemblages, which may manifest individually or cumulatively across the riverscape. This suggests that it is unlikely that a priori classifications of dams based on their structural attributes can replace site‐specific and cumulative impact assessments. The results also shed light on the need for better understanding of how SHP attributes shape their ecological effects, so that a full assessment of the potential environmental impacts of the wide range of "small" dams is possible.

Study on Analysis Method and Control Index for Deformation of Super-High Arch Dam Suffering Alkali-Aggregate Reaction

Alkali-aggregate reaction can not only cause uneven expansion of concrete but also lead to cracking and even destruction and consequently affect the working behavior and long-term safety of hydraulic concrete structures. Present researches on alkali-aggregate reaction focus on improving the composition ratio of concrete materials through experimental study to inhibit the reaction, whereas there is a lack of quantitative calculation and analysis. In the present study, the problem of alkali-aggregate reaction in the super-high arch dam of Jinping I Hydropower Station was taken as an example. The expansion of concrete suffering the alkali-aggregate reaction was simulated by means of the overall temperature rise in the dam. Similarly, the yield zone, the expansion process, and the deformation change law with the development of concrete expansive deformation under various load combinations were analyzed by using the elastic–plastic finite element method. Finally, a control index of allowable alkali-aggregate expansion of dam concrete under various load combinations was put forward. The research results demonstrated that the control index was 400~800 με. Since the arch dam has a low safety reserve when operating at a low water level, the lowest reservoir level should be raised as much as possible in dam operation to reduce its drawdown rate, thus restraining the adverse impact of alkali-aggregate reaction in concrete on the dam.

Changes in hydrological processes in the headwater area of Yellow River, China during 1956–2019 under the influences of climate change, permafrost thaw and dam

Discharge characteristics are crucial for detecting changes in hydrological processes. Recently, the river hydrology) in the Headwater Area of the Yellow River (HAYR) has exhibited erratic regimes (e.g., monotonously declining/low/high hydrograph, even with normal precipitation) under the effects of climate change, permafrost thaw and changes in dam operation. This study integrates hydroclimatic variables (air temperature, precipitation, and potential evapotranspiration) with anthropogenic dam operation and permafrost degradation impact data to systematically examine the mechanisms of these hydrological process changes during 1956–2019. The results show the following: 1) compared with the pre-dammed gauged flow, dam construction (January 1998–January 2000) and removal of dam (September 2018–August 2019) induced monotonously low (−17.2 m3 s−1; −61%) and high (+54.6 m3 s−1; +138%) hydrographs, respectively; 2) hydroclimatic variables mainly controlled the summer–autumn hydrological processes in the HAYR; 3) the monotonous decline of the hydrograph of Yellow River in the HAYR in some hydrological years (e.g., 1977, 1979, 1990 and 1995) was closely related with unusually high atmospheric demands of evaporation and low-intense rainfall during summer–autumn seasons; and 4) the lengthening of subsurface hydrological pathways and residence time, permafrost degradation reduced the recession coefficient (−0.002 per year) of winter flow and altered the hydrological regimes of seasonal rivers, which resulted in flattened hydrographs that reduced and delayed the peak flow (of 0.05 mm per year and 1.65 d per year, respectively) as well as boosted the winter baseflow (0.01 mm per year). This study can provide updated and systematic understanding of changing hydrological processes in typical alpine catchments on northeastern Qinghai–Tibet Plateau, China under a warming climate.

Safety assessment of massive buttress dams in the presence of thermal cracks in them

In the 1950s, the construction of hydropower facilities began in the regions of Siberia and the Far East, characterized by harsh climatic conditions, which should be taking into account to predict the stress state of dams. The aim of the study is an assessment of the conditions for the formation of temperature cracks in concrete dams and their influence on the further operation of the structure, as well as measures and technologies to combat cracking in massive concrete. Thermal stresses often exceed the stresses caused by the action of external loads and lead to the appearance of cracks in the concrete. Almost all modern concrete dams are subject to thermal cracking today. Appropriate design and technological measures must be provided for. When studying the thermally stressed state of lightweight concrete dams, the method of direct reproduction of thermal deformations on models made of brittle materials and computational methods oriented towards computer methods of solving problems are used. The results of modeling and computational studies of massive buttress dams are presented and the influence of the main influencing factors is considered, taking into account the effect of cracking on the operation of such dams.

Distribution of diversity of fishes in an Andean fluvial network

Introduction: The distribution of freshwater fishes in the Colombian Andes results from the interaction between historical and recent factors. Currently, the Andean landscape is facing rapid transformation processes. However, the knowledge regarding species distribution and environmental requirements is advancing slower than the transformations underway in the fluvial networks. Objective: To understand the conformation of the fish assemblage in the middle and lower Cauca River basin, considering the local environmental context before the construction of the Ituango Dam, and quantifying β diversity and its two components (turnover and nestedness) amongst local fish communities. Methods: 58 localities were monitored during nine years (between February 2010 and November 2018), the period before the dam's operation. The species richness (α-diversity), species turnover (β-diversity), and assemblage composition were estimated for the given localities. Results: 114 species were recorded, representing ~ 49 % of the total richness of known species for the Magdalena basin. The richness distribution showed that the number of species varies among the aquatic environments. Swamps presented the most significant number of species, followed by the Cauca River, while streams had the lowest values of richness. The spatial analyses of β-diversity revealed a high variation component in the study area due to species replacement between the aquatic environments. Conclusions: The implementation of long-term monitoring allowed us to recognize that the Cauca River basin conserves a great variety of species-rich environments. The species turnover indicates a high proportion of endemism or multiple sites with unique species. Finally, our study will serve as a baseline to verify, over time, whether the dam's construction is associated with essential changes in the structure of fish communities.