Dam Operation Research Articles

Losing flow in free‐flowing Mediterranean‐climate streams

Stream drying is happening globally, with important ecological and social consequences. Most examples of stream drying come from systems influenced by dam operations or those with highly exploited aquifers. Stream drying is also thought to be driven by anthropogenic climate change; however, examples are surprisingly limited. We explored flow trends from the five recognized Mediterranean‐climate regions of the world with a focus on unregulated (non‐dammed or non‐diverted) streams with long‐term gauge records. We found consistent evidence of decreasing discharge trends, increasing zero‐flow days, and steeper downward discharge trends in smaller basins. Beyond directional trends, many systems have recently undergone shifts in flow state, including some streams that have transitioned from perennial to intermittent flow states. Our analyses provide evidence of stream drying consistent with climate change but also highlight knowledge gaps and challenges in empirically and statistically documenting flow regime shifts. We discuss the myriad consequences of losing flow and propose strategies for improving detection of and adapting to flow change.

Damage characteristics and dynamic responses of high arch dams under rockfall impact loads

Rockfall is a typical natural disaster that is sudden, high in speed, unpredictable, and can easily adversely affect the structures. High arch dams are usually constructed in deep valleys, where rockfall is a typical destructive load. However, there is currently a lack of research on the effects of rockfall on the safe operation of high arch dams. Therefore, the Wudongde arch dam in China is selected in this paper for exploring damage characteristics and dynamic responses of high arch dams under rockfall impact loads. To improve the authenticity of numerical simulation, a coupled model is established based on the actual dam shape and terrain characteristics of the dam. The concrete damaged plasticity model is used for dam concrete and the rockfall is described by the JH-2 model to simulate mechanical properties of materials and reflect strain rate effects. The trajectories of falling rocks at the dam site are first investigated to analyze the locations where they may impact the dam. Based on the obtained results, two impact positions are considered possible in the analysis, namely, the dam crest and the gate slot, and then the nonlinear dynamic responses of the dam impacted by rockfall at different positions are compared. Finally, a sensitivity analysis is carried out to evaluate the influence of the rockfall properties on the damage characteristics of the dam. The results indicate that the trajectory and impact velocity of falling rocks are related to the falling height, rock size, and initial velocity. The rockfall impact on the dam crest has little influence on the safety of the dam for the robust mass dam concrete, while the track beam near the gate slot is vulnerable to rockfall impact. The damage degree to the structure is related to rockfall properties. Compared to larger-sized rockfalls, rockfalls with a diameter of 1 m cause minimal damage to the structure and have little impact on its safety. Higher impact velocity and stiffness of the rock lead to more severe damage, while the effect is relatively smaller compared to the rockfall size. The high stiffness also reduces the damage to the rock itself.

Monitoring model group of seepage behavior of earth-rock dam based on the mutual information and support vector machine algorithms

The establishment of a high-precision piezometric water level monitoring model ensures the safe operation of earth-rock dams. The hysteresis effect of the upstream water level and rainfall should be considered during modeling. In the traditional method, the average factors are used to express this effect, and linear regression modeling is adopted. These factors reduce the accuracy of the model. In this paper, the mutual information (MI) and support vector machine (SVM) algorithms are proposed. MI has a powerful correlation analysis capability, and it is innovatively used to address hysteresis effects. SVM has a strong nonlinear modeling ability, and it is used as a modeling algorithm. During this study, it was found that the lag time of rainfall varied. In view of this characteristic, the concept of an innovative model group, which is an important extension of the traditional single model, is proposed. In the example, the mean square error (MSE) is used as the precision index. Compared with the traditional single model established by linear regression, the MSE of the MI–SVM model group can be reduced by approximately 60.98%–68.75%. Compared with the model group established by linear regression, the MSE of the MI–SVM model group can be reduced by approximately 41.28%–45.45%. The new method effectively improves the accuracy of the model and can precisely monitor the seepage state of the dam. Moreover, it is beneficial for improving the level of dam safety management and can be extended to other fields involving hysteresis effects and nonlinear modeling.

Priority Strategy For Improving Dam Operation and Maintenance Performance (Cacaban Dam Case Study)

Dam operation and maintenance activities are critical, so the dam usually works and provides benefits according to plan. Over time, the performance of the Cacaban Dam has decreased significantly. The physical condition of the main building, supporting buildings, and instruments have experienced damage, which could pose a risk to the dam's safety. The main objective of this research is to determine priority strategies for improving operations and maintenance of the Cacaban Dam. Determining priority strategies for improving operations and maintenance in this research uses the DSS (Decision Support System) method with SWOT (Strength, Weakness, Opportunity, and Threat) and QSPM (Quantitative techniques Strategic Planning Matrix). Based on the SWOT analysis results, the resulting strategy is the Diversity Strategy, meaning that the Cacaban Dam is in good internal condition. In contrast, the external condition is not good. The proposed strategy is to minimize external threats/threats with strategic priorities referring to the scoring results using the QSPM method. Meanwhile, from the results of the dam performance assessment, Cacaban Dam obtained an average performance score of 3.45, considered adequate performance. However, if you look at several items of poor performance, there are two items, namely reservoir condition and border and greenbelt conditions, which have poor performance. There are seven components, namely intake buildings, spillway buildings, support hills, dam services, emergency action plans, instrumentation, and surrounding communities, whose performance is quite close to the deficient limit and has the potential for performance to decline. Extra handling is needed to restore the performance of dams and reservoirs.

ResORR: A globally scalable and satellite data-driven algorithm for river flow regulation due to reservoir operations

We propose a globally scalable algorithm, ResORR (Reservoir Operations driven River Regulation), to predict regulated river flow and tested it over the heavily regulated basin of the Cumberland River in the US. ResORR was found able to model regulated river flow due to upstream reservoir operations of the Cumberland River. Over a mountainous basin dominated by high rainfall, ResORR was effective in capturing extreme flooding modified by upstream hydropower dam operations. On average, ResORR improved regulated river flow simulation by more than 50% across all performance metrics when compared to a hydrologic model without a regulation module. ResORR is a timely software algorithm for understanding human regulation of surface water as satellite-estimated reservoir state is expected to improve globally with the recently launched Surface Water and Ocean Topography (SWOT) mission.

Seepage prediction model of the earth-rock dam based on TCN considering rainfall lag effect

Renewable energy has the highest conversion efficiency, is the most flexible in regulating peak power in the grid, and has the potential to significantly reduce emissions. Hydropower is one of the main ways to optimize power energy structure by building earth-rock dams that block water and generate electricity. Seepage is a physical quantity that characterizes the safety of earth-rock dams. Studying the intelligent prediction model of earth-rock dams is an effective means of understanding the evolution of seepage behavior, and it is also crucial for the safe operation and energy efficiency of earth-rock dams. To create a rainfall factor expression reflecting the hysteresis effect of rain, actual monitoring data of different piezoelectric tubes on the upstream and downstream sides of the soil core wall of an earth-rock dam is considered. Based on the key influencing factors of the seepage behavior of earth-rock dams, the novel temporal convolutional network (TCN) algorithm in deep learning is introduced into the seepage behavior prediction of earth-rock dams, constructing the intelligent prediction model of seepage of earth-rock dams based on TCN. The engineering example shows that the seepage prediction model of the earth-rock dam based on TCN has better prediction performance than the seepage prediction model of the earth-rock dam based on support vector regression (SVR), extreme learning machine, and long-short term memory. The determination coefficient is more significant than 0.9, and the relative error of prediction is less than 1‰. The model’s prediction accuracy is high, and the stability of the prediction performance is good. The model’s prediction performance also improves after considering the rainfall lag effect.

Evaluating the context dependency of large river nursery habitats for fishes in the lower Red River catchment

AbstractBoth fine‐ and coarse‐scale physicochemical conditions affect the quantity and quality of nursery habitats within riverine ecosystems. Nursery habitats in large, braided, and sandbed streams such as the lower Red River of Oklahoma, Texas, and Arkansas are not well described and likely vary among species. Identification of nursery habitats is important for developing proper conservation and management actions. We used an occupancy model framework to determine how hierarchical habitat factors related to the occupancy of 38 juvenile fish species. Our findings indicate that large river nursery habitats can generally be defined by reaches with off‐channel slackwater habitat, having deep pools but shallow thalweg depths, typically located further away from dams, and with low percentages of limestone lithology. Species within the same genera often exhibited variable relationships with river slope, amount of large woody debris, channel shape, discharge, and position of reaches within the stream network. Our results indicate important species‐specific relationships that define nursery habitats, indicating an important context dependency of nursery habitats even within fishes that are taxonomically similar. If the goal is to improve recruitment by native fishes, then consideration of the important species‐specific differences would be beneficial if improvements are made to nursery habitats. Moreover, careful consideration of the effects of dam operations will help maintain proper connectivity to off‐channel habitats important in downriver portions of the river network.

Effects of hydropeaking by an upstream dam on thermal mixing in a riverine lake

The hydropeaking operations of a hydropower dam can significantly affect the flow and thermal regimes in riverine reservoirs, and this effect is very complex, both in space and time. In this study, we used a 3D hydrodynamic model, calibrated with field datasets, to investigate the thermal mixing resulting from hydropeaking within Paldang Lake (PL) in South Korea. The spatiotemporal temperature patterns revealed that density currents critically affected thermal mixing in the reservoir and developed differently based on upstream dam operations and flooding events. Notably, the confluence of the North Han River (NHR) and South Han River (SHR) played a key role in shaping the thermal regime. During the hydropeaking release from the upstream dam in the NHR, the colder water of the NHR from the deep-water discharge of the upstream dam plunged beneath the warmer water of the SHR, leading to three-dimensional mixing. Consequently, the thermal mixing patterns varied depending on the discharge patterns from the upstream dam. Additionally, diurnal variations in the dam discharge frequently affected areas of the reservoir exhibiting high Schmidt stability. During the non-operation period of the upstream dam, the SHR flow backflowed into the downstream section of the NHR, resulting in the confluent area exhibiting the poorest vertical mixing. Secondary currents also played a crucial role in influencing the flow and thermal regimes, with the intensity of the secondary flow varying along the longitudinal mainstream of the reservoir. The thermal mixing state was predominantly weakened to partial mixing within a curved reach owing to the secondary current. Overall, this study demonstrates that the complexity of flow and thermal processes in the PL is significantly influenced by hydropeaking events. These findings emphasize the importance of understanding density currents and secondary flows according to dam operation in managing riverine reservoirs for enhanced ecological health and sustainable water resource management.

Cross-border impacts of cascade reservoirs on the temperature of the Lancang-Mekong river

The Lancang-Mekong River Basin (LMRB) is an important transboundary river basin containing large-scale cascade hydropower dams. There has been increasing interest in the cross-border impacts of cascade reservoirs and climate change on the water temperature of the LMRB. However, there remain limited related basin-scale quantitative studies. This study applied a deep learning method (Long short-term memory neural network, LSTM) to reconstruct the natural water temperature of the Lower Mekong River (LMR), which was compared with observation data influenced by dam operation. The aim of this study was to assess the impacts of the dams and climate change on the dynamics of water temperature in the basin. The results showed that: (1) Climate change had a relatively minor effect on the water temperature of the LMRB, with the warming effect of climate change gradually increasing from upstream to downstream. (2) The operation of the cascade reservoirs has resulted in seasonal warming and cooling of water temperature, although the average annual water temperature of the LMRB has increased by 0.27–0.59 °C. (3) The slight increase in annual average water temperature due to reservoir operation gradually weakened from upstream to downstream. (4) The increase in annual river temperature became more pronounced from 2008 to 2016 with the completion of Xiaowan, Nuozadu, and other power stations. This study characterized the responses of streamflow temperature to climate change and cascade reservoirs and can act as a reference for water resources management and hydropower development in the LMRB.

Swimming behaviour of Atlantic salmon kelts migrating past a hydropower plant dam: Effects of hydraulics and dam operations

Hydropower plants commonly impede the downstream migration of Atlantic salmon (Salmo salar) kelts. Thus, understanding the effects of hydraulic conditions on kelt behaviour and passage performance at dams is crucial for developing effective mitigation measures. In this study, we investigated the influence of hydraulic conditions on kelt passage performance and swimming behaviour at a Norwegian hydropower plant. We combined biological data from 48 kelts collected via acoustic telemetry with hydraulic data modelled using computational fluid dynamics. We assessed kelt passage performance using metrics such as time-to-pass, total number of detections, and total number of detections per day. Additionally, we analysed swimming depths and speeds in relation to the hydraulic conditions created by different dam operating conditions. We found that the dam operation schedule impacted the kelts' ability to find a route past the dam. Though kelts could have passed the dam throughout the study period via a submerged pipe at the dam (which had seemingly sufficient discharge for the kelts to find), 98 % of the kelts instead waited for a spill gate to open partway through the study period. The swimming depth analysis indicated diel variation, with kelts swimming nearer to the water surface during the night. We found that swimming speed increased with increasing kelt body length, particularly under high turbulence kinetic energy and during the day. Furthermore, kelts swam faster as water velocity increased, but slowed down again as turbulence intensity increased. Our findings reveal the effects of hydraulic conditions and dam operations on the migration behaviour of Atlantic salmon kelts. This provides valuable insights for developing strategies to optimise dam operations and improve fish passage performance, including the need to spill enough water to increase passage success and will contribute to sustainable management of Atlantic salmon populations in regulated rivers.

How to mitigate flood events similar to the 1979 catastrophic floods in the lower Tagus

Abstract. The floods that struck the lower Tagus valley in February 1979 correspond to the most intense floods in this river and affected the largest number of people in a river flow event in Portugal during the last 150 years. In fact, the vast area affected significantly impacted circa 10 000 people in the lower Tagus sector (and an additional 7000 in other regions of Portugal), including thousands of people evacuated or made homeless. In this context, the present study focuses on an in-depth analysis of this event from a hydrodynamic perspective by means of the Iber+ numerical model and on developing strategies to mitigate the flood episodes that occur in the lower section of the Tagus River using the exceptional floods of February 1979 as a benchmark. In this sense, dam operating strategies were developed and analyzed for the most important dam along the Tagus River basin in order to propose effective procedures to take advantage of these infrastructures to minimize the effect of floods. Overall, the numerical results indicate a good agreement with watermarks and some descriptions of the 1979 flood event, which demonstrates the model capability to evaluate floods in the area under study. Regarding flood mitigation, results obtained indicate that the frequency of floods can be reduced with the proposed strategies, which were focused on providing optimal dam operating rules to mitigate flooding in the lower Tagus valley. In addition, hydraulic simulations corroborated an important decrease in water depth and velocity for the most extreme flood events, and also a certain reduction in the flood extension was detected. This confirms the effectiveness of the proposed strategies to help in reducing the flood impact in the lower Tagus valley through the efficient functioning of dams.

Multidimensional valorization of sediments trapped by dams for sustainable and integrated water resources management

This article introduces an innovative demarche to sustainable and integrated water resource management by proposing a new strategy for valorizing sediments retained by dams, explicitly focusing on the Moroccan context. The novel demarche presented encompasses five critical dimensions related to sediment valorization: quality, quantity, space, time, and regulation. To achieve this, we have designed an optimal valorization approach complemented by a specific valorization guide tailored to the nuances of Moroccan laws and standards. Our methodology includes a detailed quantitative analysis of retained sediments, a qualitative assessment of their physical and chemical properties, and a spatiotemporal analysis of dam siltation. The optimal valorization approach aims to maximize the use of retained sediments by identifying suitable applications. Simultaneously, the specific guide provides a methodological and regulatory framework aligned with the region's legal requirements. The quantitative analysis evaluates measures taken to quantify sediments retained by dams, while the qualitative analysis assesses their physical and chemical characteristics and suitability for various applications. The spatiotemporal analysis offers a dynamic perspective on dam siltation, emphasizing the most affected areas and the evolution of trends over time. Anchored in the Moroccan context, this research provides crucial insights into the sustainable management of water resources through the integrated valorization of sediments trapped by dams. The presented results have significant implications for watershed management and the optimization of dam operations and reservoirs. Furthermore, they pave the way for similar approaches in regions grappling with reservoir sedimentation issues.

Analysis of Effects of Spatial Distributed Soil Properties and Soil Moisture Behavior on Hourly Streamflow Estimate through the Integration of SWAT and LSM

This study addresses the challenge of accurately estimating hourly flow and soil moisture by integrating the Soil and Water Assessment Tool (SWAT) with a Land Surface Model (LSM). Our approach enhances SWAT by incorporating spatially distributed soil properties and a physically-based soil moisture process, using the Noah LSM for hourly soil moisture estimation. This integration captures spatial variations in soil moisture and hydraulic properties from remote sensing across the watershed. The parameter sensitivity analysis and the calibration of hourly flow were significantly impacted by the physically-based hourly soil moisture routing and the incorporation of spatially distributed soil properties. Consequently, the modified SWAT model showed improved accuracy in hourly flow simulations for long-term and multiple rainfall events. Validation results showed significant improvements, with Coefficient of Determination (R2) and Nash and Sutcliffe Efficiency (NSE) increasing by 25.95% and 33.3%, respectively, and Percent Bias (PBIAS) decreasing by 85.8%. Notably, the average error for peak flows across eight events decreased by 49%. These findings highlight the importance of initializing soil parameters based on spatial soil moisture distribution and incorporating physical process-based moisture routing to enhance hourly flow simulation accuracy. Future research should focus on validating the physical feasibility of the soil parameter set in the study area with detailed hourly flow and soil moisture data and exploring its applicability in various regions. This study provides valuable insights for the scientific community, water resources, and agricultural decision-makers regarding integrated modeling of soil moisture and hourly flow, which can inform dam operation management, disaster planning, and crop yield improvement.

Event-based soil erosion and sediment yield modelling for calculating long-term reservoir sedimentation in the Alps

ABSTRACT 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.

Dam operation affects the evolution and propagation of hydrological extremes

ABSTRACT Dams are an integral component of water resources systems and management in the Upper Ganga basin. However, the impact of dam operations on the characteristics of hydrological extremes and their regional spatial pattern is less explored. Based on observational datasets, we studied the changes in the flood and drought characteristics at local and regional scales by comparing them during pre- and post-dam periods. It was observed that the annual frequency of streamflow is missing from the spectral representation of daily streamflow at the Tehri catchment during the post-dam period. The dam operation has reduced the flood peaks but increased their duration and volume, and the dam has influenced the variability in drought duration, intensity, and deficit. The operation of dams has changed the timing and strength of seasonality of these extremes. Ultimately, the dam has increased the risk of regional occurrences of droughts and minimized the risk of floods.

Estimating the Peak Outflow and Maximum Erosion Rate during the Breach of Embankment Dam

Understanding and modeling a dam breaching process is an essential investigation, because it aims to minimize the flood’s hazards, and its impact on people and structures, using suitable mitigation plans. In the current study, three-dimensional numerical modeling is carried out using the FLOW-3D HYDRO program to investigate the impact of various factors, including the dam grain size materials, crest width, inflow discharge, and tail water depth on the dam breach process, particularly the peak outflow, and the erosion rate. The results show that changing the grain size of the dam material from fine sand to medium and coarse sand leads to an increase in the peak outflow discharge by 16.0% and the maximum erosion rate by 20.0%. Furthermore, increasing the dam crest width by 40% leads to a decrease in the peak outflow by 3.0% and the maximum erosion rates by 4.50%. Moreover, increasing the inflow discharge by 25.0% increases the peak outflow by 23.0% and the maximum erosion rates by 21.0%. Finally, increasing the tail water depth by 50.0% leads to decreasing the peak outflow by 4.50% and the maximum erosion rate by 43.0%. The study findings are considered of high importance for dam design and operation control. Moreover, the results can be applied for the optimum determination of the crest width and tail water depth that leads to improving the dam stability.

AIoT Monitoring Technology for Optimal Fill Dam Installation and Operation

Fill dam structures are generally considered safe, but frequent heavy rainfall in recent years due to climate change has increased their risk of collapse. Technologies for the monitoring and safety management of these structures have attracted considerable attention, and methods to utilize technologies such as artificial intelligence (AI) and Internet of Things (IoT) for maintenance have been investigated. However, the measurement and communication processes of sensors used in the IoT technology are prone to measurement errors. Moreover, the communication environment and frequency range used by unlicensed operators vary within a country. Technologies for accurate interpretation of measurement results and optimal communication are required to address these issues. In this study, a technology for dam safety management and communication environment optimization was developed using AIoT (AI+IoT), and its field applicability was verified.

Challenges in the operation of dams

Challenges in the operation of dams

Assessment of the reliability of protective structures made of composite materials

This article discusses the protective structures of dams made of composite materials. The authors propose a method for determining the reliability of structures and illustrate its application using the example of a membrane-cabling structure dam as a system consisting of three main objects: a water-retaining shell, an anchor assembly and an apron. According to this method, the reliability of a structural element is determined by its service life, counted from the start of operation until the moment of failure. It is assumed that the service life of the element is a random variable, and on the basis of this, the distribution law of the service life is chosen, which characterizes the reliability of the element. Based on the analysis of the operating period of membrane-cabling structure dams, new technological solutions of experimental and theoretical studies, the authors have developed scientifically grounded measures to improve the safety and reliability of the operation of the membrane-cabling structure dam. Dependencies are established that characterize the reliability of each element of the dam with a membrane-cabling structure.

Tolerance threshold of a pelagic species in China to total dissolved gas supersaturation: from the perspective of survival characteristics and swimming ability.

Total dissolved gas (TDG) supersaturation downstream of dams can occur in the Yangtze River basin and is known to cause stress and even death in fish. Consequently, it is important to establish tolerance thresholds of endemic fish to protect local aquatic resources. We conducted experiments to assess survival characteristics and swimming ability of bighead carp, an important commercial fish dwelling in the Yangtze River, to evaluate its tolerance threshold to TDG supersaturation. The typical external symptoms of gas bubble trauma (GBT) were observed and the time when the fish lost equilibrium and died were recorded. The results showed that the mortality occurred when TDG level exceeded 125%, with obvious symptoms such as exophthalmos and bubbles on the head. The interval between loss of equilibrium and mortality decreased with an increase in TDG level. Neither exposure time nor TDG level significantly affected the critical swimming speed (Ucrit) of fish exposed to non-lethal exposure (110%, 120% and 125% TDG) over a 7day period. Significant reductions in Ucrit were found under 130% and 135% TDG conditions when the exposure lasted 52.0h and 42.9h, respectively. The Ucrit also significantly decreased after exposure of 1.6h under 140% TDG condition. Moreover, after exposure to 140% TDG for 39.2h, 135% TDG for 56.5h and 130% TDG for 95.9h, bighead carp were transferred into air saturated water to recover for 24h or 48h; however, swimming performance remained impaired. The results of this study indicate that 125% TDG was the highest TDG level where limited mortality was observed and the swimming ability was not impaired, showing that 125% TDG can be set as the tolerance threshold of this species to guide the operation of dams in the Yangtze River Basin.