Dam Operation Research Articles

The cause and inspiration of the nonlinear impact of the Three Gorges Dam operation on stage-discharge relation in downstream channels

Evaluating the effects of dam operations on downstream hydrological regimes is crucial to cope with the threat of flood. Some channels in dammed rivers have experienced erosion and counterintuitive higher flood water levels. However, the impacts of dam-induced channel changes and dam-altered streamflow on downstream hydrological regimes have been less thoroughly evaluated. Herein, we integrated the Distributed Time Variant Gain Model and a proposed grey model to thoroughly decouple the effects of TGD-altered Yangtze River streamflow and TGD-induced river channel changes on the stage-discharge relation in Jingjiang reach of the middle Yangtze River basin, from 2003 to 2014. The stage-discharge relation in Jingjiang reach is presented by the relation between water level at Chenglingji station (Zcl) and discharge at Luoshan station (Qls). The results indicate that the TGD operation increases Zcl by 0.01 ∼ 0.06 m and 0.02 ∼ 0.48 m on average when Qls is below 12,000 and exceeds 24000 m3/s, respectively. However, the TGD operation decreases Zcl by 0.01 m on average when Qls is around 18000 m3/s. Hence, the TGD operation has a nonlinear impact on downstream stage-discharge curves, which results from the TGD interception of the release, water–sediment regulation of the TGD, and the erosion of the fine-grained channel. Given that the causes of the nonlinear impact are widespread, we speculated that the resulting changes in downstream stage-discharge curves influenced by the water–sediment regulation of dams in fine-grained rivers will be nonlinear and exhibit the hook curve. Meanwhile, the purposed grey model helps to evaluate the impacts of dam-induced river channel changes on downstream hydrological regimes in data-scarce rivers. Our work helps to thoroughly evaluate the impacts of dam operations on downstream hydrological regimes and the resulting flood threat.

Persistence of native riverine fishes downstream from two hydropower dams with contrasting operations

Identifying hydropower dam operations that lessen detrimental effects on downstream fauna could inform conservation strategies for native fishes. We compared occurrence of native fishes in 20 shoal habitats downstream from two differently operated hydropower dams in the Coosa River system, Georgia, USA. Species richness averaged 7 and 11, respectively, in surveys downstream from (1) a hydropeaking dam and (2) a dam with a re-regulation structure that stabilized downstream flows. In contrast, surveys in two nearby reference communities averaged 19 and 24 species. Species persisting downstream from the dams tended toward water-column orientation, larger body size, longer life span, and greater prevalence in tributary stream collections, compared with missing or rarely captured species. We observed no evidence of recovery toward reference conditions when operations were paused for 28 months at the hydropeaking dam. Our observations suggest that (1) strongly contrasting dam operations can result in similar alterations to native fish assemblages, potentially reflecting effects of thermal alteration by hypolimnetic water release, and (2) periodic dispersal from tributary streams may enhance fish persistence in flow-altered rivers.

Strategic siting and design of dams minimizes impacts on seasonal floodplain inundation

Dams and reservoirs aid economic development but also create significant negative impacts. Dams fragment rivers and reduce longitudinal connectivity on a network scale. However, dams may also alter discharge regimes and flood peaks, consequently reducing floodplain inundation and lateral channel floodplain connectivity, which impacts floodplain associated ecosystems. Strategic planning has emerged as a promising approach to find a balance between dam impacts and benefits. Yet, strategic planning has predominantly focused on longitudinal connectivity due to the difficulty of including the complex interactions between dam design and operations, hydrologic regime alteration, and the hydrodynamic processes controlling downstream flood extent. Here, we present how to reduce conflicts between hydropower development and loss of floodplain inundation extent by jointly optimizing siting and design of many dams in a data scarce basin. We deploy a coupled hydrological—hydraulic simulation model linked to a multiobjective optimization framework to find development options with the least trade-offs between power generation and downstream impacts on floodplains. Our results for the Pungwe Basin in Mozambique indicate that whilst portfolios of many small storage and run-of-river diversion hydropower plants might create less impacts on the downstream floodplains, installation of some large storage dams would be necessary to attain higher levels of hydropower generation.

Human activities reshape the drought regime in the Yangtze River Basin: a land surface-hydrological modelling analysis with representations of dam operation and human water use

Human activities reshape the drought regime in the Yangtze River Basin: a land surface-hydrological modelling analysis with representations of dam operation and human water use

Deformation critical threshold estimation of Xiaowan ultrahigh arch dam with time-varying grey model

The structural behavior of the Xiaowan ultrahigh arch dam is primarily influenced by external loads and time-varying characteristics of dam concrete and foundation rock mass during long-term operation. According to overload testing with a geological model and the measured time series of installed perpendicular lines, the space and time evolution characteristics of the arch dam structure were analyzed, and its mechanical performance was evaluated. Subsequently, the deformation centroid of the deflective curve was suggested to indicate the magnitude and unique distribution rules for a typical dam section using the measured deformation values at multi-monitoring points. The ellipse equations of the critical ellipsoid for the centroid were derived from the historical measured time series. Hydrostatic and seasonal components were extracted from the measured deformation values with a traditional statistical model, and residuals were adopted as a grey component. A time-varying grey model was developed to accurately predict the evolution of the deformation behavior of the ultrahigh arch dam during future operation. In the developed model, constant coefficients were modified so as to be time-dependent functions, and the prediction accuracy was significantly improved through introduction of a forgetting factor. Finally, the critical threshold was estimated, and predicted ellipsoids were derived for the Xiaowan arch dam. The findings of this study can provide technical support for safety evaluation of the actual operation of ultrahigh arch dams and help to provide early warning of abnormal changes.

Modified Andersen and Modified ICOLD (DOISP-2) Methods of Risk Score for Dams in West Region of Indonesia

Risk assessment for the dams in West Java Province with a method of Modified Andersen and Modified ICOLD (DOISP-2) have been done; the assessment is part of the activities of Dam Operation Improvement Safety Project-2 (DOISP-2) at Central Project Implementation Unit (CPIU), Ministry of Public Works and Housing. Dams were studied to analyse the risks of the deficiency of the structure due to the load under normal operating conditions, flood conditions, and earthquake conditions. This article summarizes the risk assessment process, assessment results, conclusions and recommendations for both risk index methods. The document also includes an assessment of the risk assessment process and policy recommendations for the operation and maintenance of dams. The results are risk rankings between the two methods give different sequences; this is due to differences in the risk assessment approach of both methods. Modified Andersen focused on structural deficiencies, especially visually, and modification ICOLD Method (DOISP-2) focused on design flaws and risks downstream of the dam. Although both methods have different approaches, both methods can be used in risk analysis of the dam’s adjusted purposes of risk index assessment.

Synthesis and characterization of cement clinker based on Tunisian dam sediments

Siltation is a permanent threat to the operation of dams since it reduces its storage capacity. In Tunisia, the annual siltation of dams is estimated at 22 Mm3 / year. Sediments currently cover 20% of the total capacity of the reservoirs, which could be a national water security issue in the years to come. Considering that sediments contain the oxides, SiO2. Al2O3. Fe2O3 and CaO, as main chemical constituents, a partial replacement of the raw materials in the cement production is suggested. This work concerns dam sediments from different regions in Tunisia. Characterisation results show that studied sediments are suitable for a beneficial reuse in the clinker production. However, according to the chemical composition, the incorporation rate of sediments in the raw mix varies from one sediment to another but still relatively important, ranging between 9 and 27 wt%. The characterization of produced clinkers show that mineralogy depends on minor oxides contents, especially SO3. MgO and equivalent Na2O. It has been proven that it is possible to substitute natural materials with 27.4 %SS sediment. The obtained clinker is characterized by the presence of M1 C3S and orthorhombic C3A. The high free lime content associated to incomplete alite formation can be surmounted by increasing slightly the clinkerization temperature.

Global Sensitivity Analysis Method for Embankment Dam Slope Stability Considering Seepage–Stress Coupling under Changing Reservoir Water Levels

Ensuring the long-term, efficient, and safe operation of reservoir dams relies on the slope stability of embankment dams. Periodic fluctuations of the reservoir water level due to reservoir scheduling operations make the slope of the reservoir bank vulnerable to instability. To investigate the influence of various factors and their interactions with embankment dam slope stability under changing reservoir water levels, a global sensitivity analysis method is proposed that accounts for seepage–stress coupling. An embankment dam in Shaanxi Province, China, is studied as an example, with COMSOL Multiphysics software simulating the seepage and slope stability of the dam under fluctuating reservoir water level conditions and seepage–stress coupling. The global sensitivity analysis of factors affecting dam slope stability is accomplished by combining Plackett–Burman and Box–Behnken experimental designs, with ANOVA determining the sensitivity of each factor and interaction term. The results demonstrate that during the impoundment period of the reservoir, the saturation line is concave, and the overall stability safety of the dam slope increases first and then tends to be stable, according to the coefficient. The internal friction angle φ, cohesion c, and soil density ρs represent the three most sensitive factors affecting the stability and safety of the dam slope, while c × ρs is a second-order interaction term with significant sensitivity to the stability and safety coefficient of the dam slope. The reservoir drainage period infiltration line is convex, and dam slope stability first reduced and then increased. The magnitude of water level change H, internal friction angle φ, cohesion c, and soil density ρs are the four most sensitive factors for the coefficient of safety of dam slope stability, while c × ρs, H × ρs, and φ × ρs are the second-order interaction terms with significant sensitivity to the coefficient of safety of dam slope stability. These research findings and methods can offer valuable technical support and reference for the investigation and evaluation of the stability of embankment dam slopes.

Hydrological and sediment-transport characteristics of the middle and lower Yangtze River: Analysis from a magnitude-frequency perspective

In natural quasi-equilibrium rivers or anthropogenically-influenced nonequilibrium rivers, the occurrence frequency and sediment transport capacity of different flow levels are greatly important to understanding the linkage between forms and processes. However, our knowledge of the controlling factors on flow frequency and sediment-transport magnitude in large river systems remains limited. In this paper, the hydrological and sediment-transport characteristics of the middle and lower Yangtze River (MLYR) were systematically examined before and after impoundment of the Three Georges Reservoir (TGR). More than 30 years of daily discharge and suspended sediment concentration data were collected from six hydrological stations. The results showed that in the pre-TGR period, the flow frequency distributions (FFDs) and sediment-transport rating curves had segmentation characteristics. Generally, the FFDs of medium-high flow agreed well with the broken power law, and the sediment-transport rating curves deviated from the power law at high flow. This was because the floodplains, especially the Dongting Lake, had significant effects on flood attenuation and sediment storage. Compared the inflection points of the FFD and the sediment-transport rating curve, as well as the effective discharge and bankfull discharge, these four values were of the same order of magnitude. This suggested that the local river system had a dominant effect on the hydrological and sediment-transport characteristics. In the post-TGR period, the overall characteristics of the FFDs were preserved, but the segmental characteristics of the sediment-transport rating curves at higher discharges disappeared. Through analysis, the effective discharge was largely determined by the inflection value (a1) of the FFD. The reduced a1 induced a 10%–20% decrease in effective discharge, which indicated flood channel shrinkage in the long run. These findings not only further the understanding of water-sediment regimes in a large alluvial river with an extensive floodplain system but also offer guidance for improving dam operation schemes for river restoration.

Cause Investigation of Fractures in the Anti-Arc Portion of the Gravity Dam’s Overflow and the Top of the Substation Tunnel

Clarifying the origins of fractures and adopting acceptable repair plans are crucial for the design, maintenance, and safe operation of concrete gravity dams. In this research, numerical simulation is largely utilized to investigate the reasons for fractures in the anti-arc portion of the concrete gravity dam and the top of a substation tunnel in Guangdong Province, China. The calculation parameters are chosen based on the design information and engineering expertise to model the temperature field and stress field distribution of the dam during both normal operation and severe weather. The study demonstrates that under the effect of severe structural restraints and high temperatures, the tensile stress at the top of the substation tunnel would be 2.64 MPa in the summer, which is more than the tensile strength by 1.5 MPa and causes deep cracks. The tensile stress reaches 3.0 MPa in the summer under the effect of severe weather near the top of the substation tunnel. When a cold wave strikes in the winter, the concrete’s tensile stress on the overflow dam surface rises from 1.6 MPa to 4.0 MPa, exceeding the tensile strength by 1.9 MPa, resulting in the formation of a connection fracture in the reverse arc section. Both the actual observed crack location and the monitoring findings of the crack opening, as determined by the crack gauge, agree with the modeling results. The technique to lessen the structural restrictions of a comparable powerhouse hydropower station is pointed out based on engineering expertise, and various and practical repair strategies are proposed to guarantee the structure’s safe operation.

Three Gorges Dam Operations Affect the Carbon Dioxide Budget of a Large Downstream Connected Lake

AbstractThe effects of dams on carbon dioxide (CO2) fluxes in downstream lakes remain elusive. Here we combined eddy covariance observations and random forest models to examine multi‐decadal variations in CO2 fluxes in the Poyang Lake, the largest freshwater lake in China, and quantified the contribution of the Three Gorges Dam (TGD), the world's largest hydraulic project. We found the lake fluctuated between CO2 source and sink in 1961–2016, and tended to be CO2 sink in the post‐TGD period (2003–2016) when vegetation expanded early and spatially due to declining water level. TGD can explain approximately 6% of the total differences in annual CO2 fluxes, with major contributions in the impoundment period (up to 22% in middle September to October). The results show a positive side of operational major hydraulic projects on lake carbon sink, and probably caution the negative side of carbon release after dam removal.

Combining hydro-acoustics and hydraulic modeling for evaluating fish entrainment risk

Individual fish may be involuntarily removed from hydropower reservoir populations due to dam operations, a phenomenon known as fish entrainment. Entrainment for two life stages (age-0 and age-1) of Kokanee salmon (Oncorhynchus nerka) was evaluated within the forebay of the Revelstoke Dam in the upper Columbia River, British Columbia, Canada. Intensive fish surveys using hydro-acoustics were conducted to estimate fish density in the forebay at two different times (day & night) and across three seasons (spring, summer and winter). The number of fish entrained into intakes was monitored using hydro-acoustics continuously over one year. Surveyed fish densities and entrainment numbers were combined with Computational Fluid Dynamic modeling of the velocity field around the penstock intakes to estimate the threshold velocity for entrainment where 50% of the fish within this volume of water would be entrained. Fish density decreased with increasing distance from the dam face and it also decreased with increasing water depths. Entrainment of age-0 kokanee was consistently higher compared to age-1 in all times and seasons evaluated. The threshold velocities resulting in entrainment of age-0 kokanee were consistently lower (range 0.24 to 0.59 m/s) compared to those estimated for age-1 kokanee (range 0.30 to 1.08 m/s). Additional modeled scenarios showed that fish entrainment risk increased both with increasing intake discharge and the number of intakes in operation. Results demonstrate combing computational fluid dynamics models with ecological information collected using hydro-acoustics allows age-specific entrainment risk to be evaluated for vulnerable species and warrants application to other species and hydropower facilities.

An overview on the potential dam hazard and pre-qualitative analysis on the selected critical dam in Malaysia

Apart from flood control and water storage for irrigation, dams were used for hydropower generation, navigation, drinking water supply, recreation and in mining operations as tailing dams. Human errors and mistakes have undermined safety in many dam operations, resulting in serious safety issues and numerous failures. Safety concerns were also largely caused by increased population and land use in dam downstream areas and by failing to perform necessary inspection, maintenance, or upgrade work. Dam safety cannot be concerned only with the structure itself, but it should be considered in relation to the population at risk in the downstream flood plain. Several potential dam hazards were listed in MyDAMS guidelines but for this research, the hazards chosen are overtopping and seepage failure considering the condition of Malaysian dam. Only one (1) selected dam will be chosen as the most critical dam. The selection criteria of the dam will be based on their type of dam, hazard classification, dam purpose and downstream population. A qualitative analysis was done by using the secondary data prepared by DID and hazard classification was done using dam hazard rating. Batu Dam was chosen as the most critical dam with high hazard rating as it has the highest crest elevation, water level and has the shortest distance between dam and populated area downstream.

Dynamic Resilience Quantification of Hydropower Infrastructure in Multihazard Environments

Ensuring the continued functionality of hydropower infrastructure is of the greatest importance, considering the devastating socioeconomic and environmental impacts of dam operation failures. Among the different approaches currently adopted in hydropower dam operational safety, those that are resilience-based are at the leading edge because they focus on assessing the dynamic system performance pre-, during-, and post-hazard exposures. However, the main challenge for such assessment pertains to the complexity associated with the dynamic operation simulation of hydropower dam systems that consist of several components with nonlinear interdependencies. Moreover, the infrastructure’s exposure to a multihazard environment, which may impact one or more hydropower critical system components, poses further challenges to understanding possible subsequent dam operation failure scenarios. This study develops a resilience-centric system dynamics simulation model that provides a holistic representation of hydropower dam system components to estimate the system’s dynamic resilience in multihazard environments. The study also discusses a combinatorial procedure to generate multihazard scenarios, where a primary hazard can trigger one or more subsequent hazards. Finally, an actual hydropower dam is employed to demonstrate the developed model utility in assessing the resilience of complex infrastructure under a wide range of multihazard scenarios. The proposed model provides valuable decision support tools for infrastructure systemic risk mitigation in multihazard environments—facilitating the development of effective resilience planning strategies.

The Egyptian-Ethiopian Dispute over the Nile: Lessons from the Past for Future African Peace and Prosperity

Abstract: Many African water-related conflicts have their roots in so-called colonial treaties. This article examines the dispute between Egypt and Ethiopia regarding the construction and operation of an Ethiopian dam at the headwaters of the River Nile. We start by reviewing these countries' current political and economic circumstances as a prerequisite to assessing the severity of the conflict. We then trace the dispute back to the treaties used by each country to prove its rights to the Nile's water. We identify political circumstances that provide hidden motives behind the stalled negotiations. We conclude that current bilateral economic and political circumstances push decision makers away from reaching a concrete settlement of the dispute and argue that the treaties are only worsening the situation. Cooperation in the field of development in general is required to break the current deadlock, strengthen Egyptian-Ethiopian relations, and promote regional prosperity.

Multigeneration Pedigrees to Monitor Hatchery Broodstock Composition and Genetic Variation of Spring/Summer Chinook Salmon in the Columbia River Basin

AbstractHatchery production of Chinook Salmon Oncorhynchus tshawytscha in the Columbia River basin comprises most of the anadromous salmonid production in this region. Hatchery facilities and programs serve to mitigate for impacts to salmonids due to the construction and operation of hydropower dams and habitat impacts from development in addition to the conservation and restoration of natural populations. A genetic method referred to as parentage‐based tagging (PBT) enables highly reliable detection of hatchery‐origin fish and inference of multigeneration pedigrees. This study compiles 11 years of PBT data from nearly 125,000 interior stream‐type Chinook Salmon from 24 spawning hatcheries located on tributaries of the mid‐ and upper Columbia River and in the Salmon, Clearwater, and Grande Ronde River subbasins. Multigenerational pedigrees allowed for investigation of the proportions of natural‐ and hatchery‐origin broodstock (pNOB and pHOB, respectively) for each hatchery and enumeration of the scale of production between segregated and integrated programs. We then compared how pHOB and the scale of production influenced the number of stray fish observed, genetic diversity, relatedness, and age‐class compositions within broodstocks. Over 91.0% of hatchery broodstock could be assigned back to their parents, and overall less than 1.0% of broodstock consisted of fish that were unintentionally incorporated into nonnatal hatchery programs. We evaluated 11 segregated programs with 0.0–10.0% pNOB, 9 intermediate programs (10.1–50.0% pNOB), and 3 integrated programs (>50.0% pNOB). There was no correlation between the scale of production or pNOB with the level of genetic diversity, but as production size increased, so did the effective number of breeders. This study demonstrates the utility of PBT as a monitoring tool for hatchery broodstocks, and results suggest that segregated and integrated programs have tradeoffs that generally align with their intended broodstock management purpose of providing fish for harvest and/or fish for supplementation or reintroduction.

Geotechnical behavior of gravity dams built on sedimentary rocks: pore pressures and deformations analysis of Dona Francisca HPP foundation

In Brazil, some dams have been built on sedimentary rock masses, which usually present greater deformability and permeability in comparison to metamorphic or igneous rock masses. This article describes a case study whose goal is to present and analyze the main data related to the monitoring of foundation behavior of the Dona Francisca dam, whose foundation is essentially constituted by sedimentary rocks. Dona Francisca gravity dam is a hydroelectric power plant (HPP) and was built in 2000, on the Jacuí River, in the central region of the Rio Grande do Sul State, Brazil. The analysis of the foundation behavior was done in terms of pore pressures and deformations recorded during seventeen years of dam operation. The geological and geotechnical conditions of the foundation are related to the Formação Caturrita rocks, made up mainly of sandstones and intercalated levels of siltstone and argillite. In the first five years of operation there was an intense stabilization process of the foundation rocky mass. After this period, it was verified the occurrence of stabilization at a lower rate. The deformation of the Dona Francisca HPP foundation is higher when compared with other larger dams, such as the Itaipu HPP dam. It was carried out an analysis of the 18 vibrating wire piezometers data, allowing a global assessment about the uplift water pressures behavior. Most piezometers indicated a reduction in the pore pressure values over time with a current trend of stabilization, and readings below the control values recommended in design.

A Digital Twin Dam and Watershed Management Platform

This paper presents an innovative digital twin dam and watershed management platform, K-Twin SJ, that utilizes real-time data and simulation models to support decision-making for flood response and water resource management. The platform includes a GIS-based geospatial digital twin of the entire Sumjin dam and river water system in Korea, with high-precision geospatial topography and facility information for dams and rivers (watershed area 4913 km2, river length 173 km, and 91 water infrastructures). The platform synchronizes real-time data such as rainfall, dam and river water levels, flow rate, and closed-circuit television (CCTV), and incorporates three hydraulic and hydrological simulation models for efficient dam operation considering the river conditions. AI technology is also used to predict the river water level and suggest optimal dam discharge scenarios. Additionally, the platform includes a geotechnical safety evaluation module for river levees, advanced drone monitoring for dams and rivers, and an AI CCTV video surveillance function. The digital-twin-based platform supports efficient decision-making for smart flood responses and contributes to reducing flooding damage and optimal operation through better smart water management.

Balancing Sediment Connectivity and Energy Production via Optimized Reservoir Sediment Management Strategies

AbstractSediment connectivity plays a fundamental role in sustaining ecosystem goods and services in fluvial systems, including hydropower production. Dams alter the natural processes of sediment transport by trapping sediment and reshaping downstream hydrology and geomorphology. Due to these processes' interconnected nature, dams' impacts extend in time and space beyond the dam site to the entire river system. System‐scale approaches to reduce dam impacts commonly only consider dam siting, overlooking the potential of sediment management strategies integrated into the dam operations to offer more flexible solutions for mitigation. Herein, we contribute a sediment routing model (D‐CASCADE) to assess the impacts of reservoirs and their management strategies on river sediment connectivity. D‐CASCADE is applied to the 3S river system, a tributary of the Mekong River, a hotspot of potential dams in the Lower Mekong. We analyze three dam development portfolios. The effect of reservoir management is examined by assessing daily sediment delivery with specific dam release strategies. Model results predict sediment yield to the Mekong to reduce by 31%–60%. Finally, we explore trade‐offs between hydropower generation and sediment connectivity across cascades of multiple reservoirs. Results show that repeated flushing operations during the early wet season could significantly increase sediment delivery with minimal (max 6%) hydropower losses. While poor trade‐offs between sediment and hydropower have been locked‐in in the Mekong, our results highlight the potential of including sediment connectivity models in multi‐objective decision‐making frameworks to devise integrated water and sediment management strategies that mitigate connectivity disruptions while minimizing losses in other sectors.

A Control Program for Hydropower Operation Based on Minimizing the Principal Stress Values on the Dam Body: Mosul Dam Case Study

This study examines the vibrations produced by hydropower operations to improve embankment dam safety. This study consists of two parts: In the first part, ANSYS-CFX was used to generate a three-dimensional (3-D) finite volume (FV) model to simulate a vertical Francis turbine unit in the Mosul hydropower plant. The pressure pattern result of the turbine model was transformed into the dam body to show how the turbine unit's operation affects the dam's stability. The upstream reservoir conditions, various flow rates, and fully open inlet gates were considered. In the second part of this study, a 3-D FE Mosul dam model was simulated using an ANSYS program. The operational turbine model's water pressure pattern is conveyed to the dam's turbine-shared zone. The maximal and minimal upstream reservoir water levels were investigated. A control program was created depending on the principle stress model results collected from the operation of the hydropower plant with the minimum principal stress on the dam body. This research suggests an enhanced turbine operating system, reducing stress on the dam body and increasing dam operation life.