Dam Construction Research Articles

Changes in wetland landscape and inundation patterns in the middle and lower reaches of the Yangtze River Basin from 1990 to 2020

Wetlands are crucial to diverse societies and ecosystems but are threatened globally. Natural wetlands in the middle and lower reaches of the Yangtze River Basin (MLRYRB) have long been exploited to meet the increasing food and energy demands, especially in recent decades. However, how their landscapes and hydrological patterns changed over time was poorly qualified, which was crucial to conserving biodiversity and ecosystems. In this study, we proposed a new wetland classification procedure taking advantage of the shape, topography, landscape patterns, and phenology to map the distribution of six wetland types in the MLRYRB in 1990 and 2020 with Landsat images. The transitions among different wetland types and associated driving factors were examined. Artificial wetlands expanded by 3907.6 km2 while natural wetlands decreased by 423.2 km2, resulting in a net area increase of 3484.4 km2. Farmland reclamations, aquacultural activities, urban expansion, and dam constructions induced 70 % of the area's loss of natural wetlands. Meanwhile, spatiotemporal patterns in wetland inundation dynamics were determined with agglomerative hierarchical cluster analysis. Widespread transitions from perennial water to seasonal wetlands were detected. Notably, 47.8 % of the natural wetlands experienced significant drying trends, and as a result, the mean yearly inundated periods for natural wetlands decreased from 303 days in 1990 to 272 days in 2020. Given the substantial structural alterations, wetland destruction was more severe than the area reflected. Our results suggested that category-based changes in wetland areas, inundation patterns, associated driving forces, and underlying ecological consequences should be comprehensively assessed to conduct scientific conservation and prevent “paper offsets.”

Climate control on the channel morphodynamics of the Sittaung River, Myanmar

The spatio–temporal development of a meandering river is controlled by its channel morphodynamics. In regions of rapid channel evolution, understanding the driving factors of meander migration is crucial in forecasting the rate and extent of morphological change. Sediment supply and fluvial discharge are the primary influences on migration rate, however climate oscillations are also integral in indirectly regulating migration rate through their control of regional precipitation, as well as the monsoon season of sub-tropical Asia. Despite this, an in-depth investigation into the impact of climate oscillations on meander bend migration remains undocumented. This study presents a satellite-based analysis of multi-decadal climatic forcing on the migration rate of the Sittaung River in Myanmar, through interpretation of the El Niño Southern Oscillation (ENSO). The mode of ENSO exerts significant climatic control on the migration rate of the meandering channels of the Sittaung River, with low-to-average migration rates recorded during dry El Niño events and peak migration rates observed during wet La Niña events. However, this climatic signal may have been obscured by certain local environmental conditions. In cases where meanders faced geological basement, the basement rock inhibited their migration through extension, forcing more rapid migration by way of seaward translation. Consequently, these translating meanders developed to be more elongate, with lower curvatures. Meanders downstream of the approximate tidal limit were less downstream skewed, indicative of tidal modulation, potentially obscuring the impact of fluvially driven climate forcing. Additionally, downstream of a major confluence, the input of sediment and fluvial discharge may have been regulated by upstream anthropogenic activities such as mining and dam construction, leading to greater variability in migration rate downstream of this confluence and further obfuscation of the climate signal.

Identification of fish specimens of the Tocantins River, Brazil, using DNA barcoding.

The fish fauna of the Tocantins River possesses many endemic species; however, it is little studied in molecular terms and is quite threatened by the construction of several hydroelectric dams. Therefore, the objective of this study was to identify the ichthyofauna of the Tocantins River using DNA barcoding. For this, collections were carried out in five points of this river, which resulted in the capture of 725 individuals from which partial sequences of the cytochrome oxidase subunit I (COI) gene were obtained for genetic analysis. A total of 443 haplotypes were recovered with the mean intraspecific K2P genetic distance of 1.82%. Altogether, 138 species were identified based on morphological criteria, which was a quantity that was much lower than that indicated by the four molecular methods (assemble species by automatic partitioning [ASAP], barcode index number [BIN], generalized mixed Yule coalescent (GMYC), and Bayesian Poisson tree processes [bPTP]) through which 152-157 molecular entities were identified. In all, 41 unique BINs were obtained based on the data generated in the BOLDSystems platform. According to the result indicated by ASAP (species delimitation approach considered the most appropriate in the present study), there was an increase of 17 molecular entities (12.32%), when compared to the number of species identified through their morphological criteria, as it can show cryptic diversity, candidates for new species, and misidentifications. There were 21 incongruities indicated between the different identification approaches for species. Therefore, it is suggested that these taxonomic problems be cautiously evaluated by experts to solve such taxonomic issues.

Effects of irrigation dams on riverine biota in mountain streams

Mountain streams harbor unique biodiversity and provide essential ecosystem services to human societies. Yet, these ecosystems face numerous threats, such as the construction of dams and land use changes, leading to rapid habitat degradation, water pollution, and biodiversity loss. In this study, we assess the effect of irrigation dams on mountain riverine biota using traditional biotic indices and trait-based approaches. We selected diatom and macroinvertebrate communities surveyed between 2015 and 2017 in mountain streams located in different regions in northern Spain (Cantabrian Cordillera, Iberian System, and Pyrenees) under natural and altered flow conditions (i.e., downstream of irrigation dams). Hydrological and biological changes related to the presence of dams, the mountain range, and the interaction between these two factors were identified. Summer flows, frequency of high flow events, and minimum annual flows timing were significantly affected by irrigation dams, independently of the region. Winter flows, the magnitude of high flow extremes, and the number of flow rises and falls varied significantly with the dam-mountain range interaction. The frequency and duration of flow pulses depended on the mountain range only. In the Cantabrian Cordillera, a region with larger reservoirs (>150 hm3), impacted sites showed a marked inversion of the seasonal flow patterns (i.e., increased summer flows but reduced winter flows). In the other mountain ranges, reservoirs had smaller storage volumes and multiple purposes, causing significant flow change frequency variations. Diatom traits, taxonomic richness, diversity, and IPS score varied with dam presence and mountain ranges, while macroinvertebrate traits and biotic indices responded weakly. These findings suggest that diatom communities might be more sensitive to hydrological alteration, while macroinvertebrates might be more influenced by space-related factors, such as biogeography and dispersal, overriding dam-related impacts. Furthermore, dam-related changes in ecosystems may depend not only on the presence of dams and their characteristics (e.g., reservoir size and operation), but also on local conditions and biogeography. Our findings emphasize that, when using pre-existing biomonitoring datasets, although some dam-related patterns emerge (e.g., with diatoms), other patterns may be constrained by the datasets’ low spatio-temporal coverage and taxonomic resolution, highlighting the need of well-structured study designs.

Tailings dams’ classification based on risk using data from SIGBM

The Brumadinho and Mariana tailings dam failures in Brazil tragically highlighted the critical need for robust risk management in the mining sector. Tailings dams, by their very nature, pose significant risks to downstream communities and the environment in the event of failure. To mitigate these risks, a comprehensive risk classification system is essential. This abstract emphasizes the real-world impact of dam failures and strengthens the importance of risk classification. Risk analysis plays a central role in identifying, quantifying, and ultimately mitigating the potential consequences of tailings dam failure. The classification process considers various factors that influence dam stability and safety, including dam geometry and construction methods — the design and construction techniques employed significantly impact a dam's stability; tailings characteristics — the physical and chemical properties of the stored tailings can influence factors like liquefaction potential; operating conditions — factors like the rate of tailings deposition and the presence of seismic activity need evaluation; drainage system effectiveness — a well-functioning drainage system is crucial for managing pore pressures within the dam. By analyzing these elements, risk classification aims to categorize tailings dams into distinct risk levels, typically ranging from low to very high. This categorization allows for targeted risk mitigation strategies to be implemented based on the specific vulnerabilities of each dam. This paper proposes a methodology for risk classification of tailings dams utilizing data from the Brazilian National Mining Agency's (ANM) Integrated Mining Dam Management System (SIGBM). The study focuses on 203 dams situated in Minas Gerais, a Brazilian state with a history of dam failures. Data was extracted from SIGBM in February 2023. This research not only presents a general risk classification for the assessed dams but also delves deeper, offering a quantitative measure of vulnerability, risk potential, and potential consequences of a failure event for each individual dam.

Decreased river runoff on the Mongolian Plateau since around 2000

ContextMongolian Plateau is one of the largest contingent arid and semi-arid regions of the world. Rivers on the plateau provide vital water for millions of indigenous Mongolian people and numerous endangered wildlife, but are increasingly disturbed by climate change and human activities. Yet, long-term changes in river runoff across the plateau remain poorly studied due to data unavailability.ObjectivesThis study aimed to analyze the temporal trends in gauged river runoff on the Mongolian Plateau, identify drivers of the observed changes, and evaluate CMIP6 models' performance in simulating historical runoff changes across the plateau.MethodsWe compiled possibly the largest database of long-term (20 - 71 years) river runoff for the plateau comprising measurements over 30 major rivers. Statistical analyses were conducted to assess trends in river runoff and correlations between runoff and climatic variables. Additionally, we applied the Budyko curve framework to identify the influence of human activities on river runoff in specific basins. Furthermore, we compared ground-measured runoff data with simulations from CMIP6 models to evaluate the ability of CMIP6 models to replicate runoff dynamics in typical arid and semi-arid regions.ResultsWe observed pervasive and abrupt reduction in runoff in 21 out of the 30 rivers within 5 years before or after the year of 2000. Variations in river runoff were most significantly caused by changes in total precipitation (TP). In particular, 27 rivers experienced abrupt TP changes around 2000, and there was a significant positive correlation between annual fluctuations in TP and river runoff for 18 rivers. In addition to climate factors, the influence of human activities was identified in certain basins. The CMIP6 simulations failed to capture the abrupt changes in runoff occurred pervasively across the plateau around 2000.ConclusionsAround 2000, major rivers on the Mongolian Plateau, especially in Inner Mongolia, experienced runoff declines, primarily due to TP changes. Human activities like dam construction and water diversion further influenced local runoff. CMIP6 historical runoff simulations were inaccurate across the plateau, highlighting the difficulty of simulating river runoff in this critical region. Our study could contribute to a more comprehensive understanding of the water resource changes on the Mongolian Plateau, with direct implications for enhancing ecological conservation and management practice.

Decadal evolution of fluvial islands and its controlling factors along the lower Yangtze River

Fluvial islands are vital from both morphological and ecological perspectives and consequently have been hotspots of morphodynamic research in large rivers around the world. This study selected 14 representative fluvial islands in the lower reaches of the Yangtze River and explored their spatial-temporal evolution, including their shape and area dynamics during 1945–2016, by interpreting remote sensing images and analyzing the hydrological data. Results indicated that the total area of the 14 fluvial islands showed a growing trend at an average rate of 0.30 km2 yr−1 during the 72 years. The island Fenghuangzhou experienced the largest change in area, while Xiaohuangzhou (XHZ) had the smallest change in area. Sediment discharge and flooding were assumed to be the primary natural factors controlling the island dynamics. Furthermore, dam construction and bank reinforcement also played a critical role in preventing shoreline collapse, improving channel conditions, and promoting the stability of fluvial islands. From 1976 to 2016, the maximum erosion occurred on the left XHZ, while the maximum accretion was found on the Qingjiezhou island. Almost the entire river section experienced an accretion process on the right bank, which was assumed to be caused by the construction of erosion control structures. Besides, the dynamics of the fluvial islands along the lower Yangtze River appears to follow the erosion processes of the river bank. Our findings can provide an important reference for sustainable utilization and management of fluvial islands.

Statistical and machine learning analysis for the application of microbially induced carbonate precipitation as a physical barrier to control seawater intrusion

Seawater intrusion in coastal aquifers is a significant problem that can be addressed through the construction of subsurface dams or physical cut-off barriers. An alternative method is the use of microbially induced carbonate precipitation (MICP) to reduce the hydraulic conductivity of the porous medium and create a physical barrier. However, the effectiveness of this method depends on various factors, and the scientific literature presents conflicting results, making it challenging to generalise the findings. To overcome this challenge, a statistical and machine learning (ML) approach is employed to infer the causes for the reduction in hydraulic conductivity and identify the optimum MICP parameters for preventing seawater intrusion. The study involves data curation, exploratory analysis, and the development of various models to fit the input data (k-Nearest Neighbours – kNN, Support Vector Regression – SVR, Random Forests – RF, Gradient Boosting – XgBoost, Linear model with interaction terms, Ensemble learning algorithms with weighted averages – EnL-WA and stacking – EnL-Stack). The models performed reasonably well in the region where permeability reduction is sensitive to carbonate increase capturing the permeability reduction profile with respect to cementation level while demonstrating that they can be used in initial assessments of the specific conditions (e.g., soil properties). The best performing algorithms were the EnL-Stack and RF followed by XgBoost and SVR. The MICP method is effective in reducing hydraulic conductivity provided that the various biochemical parameters are optimised. Critical biochemical parameters for successful MICP formulations are the bacterial optical density, the urease activity, calcium chloride concentration and flow rate as well as the interaction terms across the properties of the porous media and the biochemical parameters. The models were used to identify the optimum MICP formulation for various porous media properties and the maximum permeability reduction profiles across cementation levels have been derived.

Increasing cascade dams in the upstream area reduce nutrient inputs to the Three Gorges Reservoir in China

The upstream cascade dams play an essential role in the nutrient cycle in the Yangtze. However, there is little quantitative information on the effects of upstream damming on nutrient retention in the Three Gorges Reservoir (TGR) in China. Here, we aim to assess the impact of increasing cascade dams in the upstream area of the Yangtze on Dissolved Inorganic Nitrogen and Phosphorus (DIN and DIP) inputs to the TGR and their retention in the TGR and to draw lessons for other large reservoirs. We implemented the Model to Assess River Inputs of Nutrients to seAs (MARINA-Nutrients China-2.0 model). We ran the model with the baseline scenario in which river damming was at the level of 2009 (low) and alternative scenarios with increased damming. Our scenarios differed in nutrient management. Our results indicated that total water storage capacity increased by 98 % in the Yangtze upstream from 2009 to 2022, with 17 new large river dams (>0.5 km3) constructed upstream of the Yangtze. As a result of these new dams, the total DIN inputs to the TGR decreased by 15 % (from 768 Gg year−1 to 651 Gg year−1) and DIP inputs decreased by 25 % (from 70 Gg year−1 to 53 Gg year−1). Meanwhile, the molar DIN:DIP ratio in inputs to the TGR increased by 13 % between 2009 and 2022. In the future, DIN and DIP inputs to the TGR are projected to decrease further, while the molar DIN:DIP ratio will increase. The Upper Stem contributed 39 %–50 % of DIN inputs and 63 %–84 % of DIP inputs to the TGR in the past and future. Our results deepen our knowledge of nutrient loadings in mainstream dams caused by increasing cascade dams. More research is needed to understand better the impact of increased nutrient ratios due to dam construction.

Impact of Türkiye’s Dam Construction on the Water Resources of the Transboundary Aras River Basin in Iran

Abstract The Aras River Basin, a significant transboundary river basin in the Caucasus region, is shared among four riparian countries, including Türkiye, Armenia, Iran, and Azerbaijan. Although positive measures have been taken to enhance water cooperation in this river basin, the Eastern Anatolia Project (DAP) and the hydraulic mission of Türkiye remain the primary factors that could potentially reverse the cooperative atmosphere of the basin and lead to conflict. In recent decades, Türkiye has utilised transboundary water resources to bolster its economic power, advance political strategies, and establish hydro-hegemony. Despite the significant Mega-Project and hydraulic mission of the upstream in the Aras River Basin, they have not received adequate attention in hydro politics studies. This study employs secondary sources to investigate Türkiye’s actions in the region. It discusses the implications of Türkiye’s projects on downstream riparian states in general and Iran’s water resources, including dam construction.

From Chingford to Carsington: impact of soil mechanics on dam construction, 1937–1987

In 1937 the investigation of the failure during construction of Chingford number 2 embankment dam brought the concepts of modern soil mechanics to bear on the construction of British embankment dams. Effective stress theory highlighted the crucial significance of pore-water pressure in understanding embankment stability and it became standard practice to monitor pore pressures during embankment construction using twin-tube hydraulic piezometers. By the 1980s, embankment stability might have seemed assured, with embankment design utilising limit equilibrium stability analyses that incorporated strength parameters of fill and foundation materials determined by laboratory testing. However, in 1984 the upstream slope of Carsington dam suffered a major slip in the final stage of construction. Recently developed advanced finite-element analyses were able to demonstrate that progressive failure was a major factor in the slope instability, but the failure was also a reminder of the continuing need for experience-based judgement in design.

Prediction of fracture failure and fracture parameters for dam gallery concrete specimens of arbitrary size and age via boundary effect model and fracture extreme theory

Cracking-associated problems may occur in the construction and operation periods of dam galleries, necessitating attention to the fracture characteristics of gallery concrete. The fracture parameters of concrete exhibit size effects and also change with age. A correct evaluation of the cracking risk or crack stability of gallery structures at any given time requires a comprehensive understanding of both the size effect and time-variant characteristics of the gallery concrete fracture parameters. In the present study, 75 wedge-splitting specimens, with effective heights ranging from 200 mm to 600 mm, were cast using gallery concrete produced by the concrete mixing system at the Baihetan Dam construction site. Subsequently, fracture tests were conducted on these specimens at curing ages spanning from 7 days to 90 days. According to the test results, the fracture parameters of concrete with a specific size exhibited an increasing trend with age within 90 days, while the fracture parameters of concrete at specific ages show a significant size effect, tending to stabilize as the effective depth of specimens gradually increases. The boundary effect model was utilized for analyzing the fracture test results of concrete specimens at different ages, yielding the size-independent double-K fracture parameters and scale parameters for concrete at each age, along with their time-varying patterns. Subsequently, equations for predicting the failure loads of concrete specimens of any age and size were established. Based on the prediction results of failure loads, the double-K fracture parameters of concrete specimens of any age and size were solved by the fracture extreme theory. The predicted failure loads and fracture parameters were in good agreement with the experimental results. The findings of this study can be applied to the full lifecycle crack risk analysis or crack stability assessment of Baihetan Dam gallery structures.

The effect of the gravity on the earthquake performance of roller compacted concrete dams

Roller compacted concrete (RCC) is a dry concrete mixture often utilized in the construction of large dams. The interlayer of the RCC dam, which is the weakest plane of the structure, can easily fail under hydraulic shear load, geological impact, earthquake force and environmental impact. In this study linear and performance analyzes were carried out for eight different scenarios for foundation effect, gravity effect and empty and full reservoir situations. In analyses, the earthquake response and performance of the Akçakoca RCC Dam, taking into account the interaction between the dam and the water. The reservoir water behavior is simulated using the Eulerian-Lagrangian coupled (CEL) approach with finite elements modeling. Linear analyses reveal that hydrodynamic pressure leads to increased displacements and principal stresses. The earthquake performance evaluation of the Akçakoca RCC dam indicates that critical concrete damages are expected based on linear time-history analyses conducted for both empty and full reservoir scenarios. Besides, according to this study, gravity effect clearly increases the earthquake performance of the dam.

Seismic performance evaluation of concrete buttress dram (Dynamic linear analysis)

Abstract Due to a variety of reasons, including the water retained inside and the intrinsic weight of the dam itself, dam constructions have the ability to move both horizontally and vertically. If these displacements exceed a crucial limit, a dam’s structural integrity is jeopardized. Concrete buttress dams in particular may be susceptible to high-frequency vibrations because of their slender structure, especially when the flow of water is involved. The Khassa Chi Dam, which is located northeast of Kirkuk City, is the subject of this study’s attempt to offer an alternative since the constructed dam is an embankment dam. In this research, a concrete buttress dam design was studied as an alternative dam to the constructed one. Such designs exemplify one form of gravity dams widely implemented on diverse soil types. Finite element model (FEM) was employed to simulate the behavior of the dam. The simulation utilized DIANA FEA, which relies on governing equations. There are several steps involved in developing an accurate FEM that faithfully simulates the actual behavior of a dam and predicts its future responses. The model is evaluated in later analyses in terms of stress and displacement. In this context, RSA was conducted on the modeled buttress dam. The outcome of the displacement analysis of the buttress dam exhibited its safety across all load combinations after undergoing linear dynamic analysis. This analysis included Eigenvalue Analysis and RSA. The response remained low at seismic frequencies below 3 Hz, and the extent of displacement correlated with the frequency values.

The fog of war: development, conflict narratives, and civilian victimisation in Colombia

Conflict generates uncertainty and a supply of violent actors willing to contract their services to third parties that makes identifying motivation for civilian victimisation difficult. In this paper, I examine how elites not only have opportunities to capitalise on violence during war for developmental interests, but also take advantage of the fog of war to lump all cases of victimisation under a clear overarching narrative of political contestation rather than repression for economic interests. I build on the literature of developmental violence in conflict to assess two cases of dam construction by the Public Enterprises of Medellin (EPM) in Antioquia, Colombia between 1995 and 2018: Hidroituango and Porce II. I argue that civilians opposing the dams were associated with one of the armed groups in the territory and elites dismissed their victimisation as a product of competition between insurgents and counterinsurgents. This conflict narrative obscures other potential realities and precludes deeper investigation into the ambiguous motivations behind attacks, even as the victims themselves may challenge and present counternarratives of developmental violence.

Dams in the Mekong: a comprehensive database, spatiotemporal distribution, and hydropower potentials

Abstract. Dams have proliferated along the Mekong, spurred by energy demands from economic development and capital from private companies. Swift dam evolution has rendered many databases outdated, in which mismatches arise from differing compilation methods. Without a comprehensive database, up-to-date spatial assessment of dam growth is unavailable. Looking at future development, hydropower potential specifically within the Mekong remains to be systematically evaluated. In this paper, we offer (1) an open-access and unified database of 1055 dams, (2) a spatiotemporal analysis of dams on a sub-basin and country level from the 1980s to the post-2020s, and (3) a grid-based assessment of the theoretical basin-wide hydropower potential using present-day discharge from the CaMa-Flood model (2011–2015, 0.05°) and future discharge from the WaterGAP2 model used for ISIMIP2b (2021–2040, 0.5°). The dam count of 1055 is more than twice the largest existing database, with 608 hydropower dams generating a boom in hydropower capacity from 1242 MW in the 1980s to 69 199 MW post-2020s. While China had the largest capacity increase from the 2000s to the 2010s (+16 854 MW), Laos has the most planned dams and the highest projected growth post-2020s (+18 223 MW). Based on present-day discharge, we estimate a basin-wide hydropower potential of 1 334 683 MW, where Laos is the highest at 514 887 MW. Based on future discharge modeled with climate change, hydropower potential could grow to over 2 000 000 MW. Laos and China are the highest at around 900 000 MW each, together forming over 80 % of the total potential. Our database facilitates research on dam-induced hydrological and ecological alterations, while spatiotemporal analysis of hydropower capacity could illuminate the complex transboundary electricity trade. Through both spatiotemporal and hydropower potential evaluation, we address the current and future vulnerability of countries to dam construction, highlighting the need for better planning and management in the future hydropower hotspot Laos. The Mekong dam database is publicly available at https://doi.org/10.21979/N9/ACZIJN (Ang et al., 2023).

Empirical design for the excavation method and support system at Budong-Budong Dam Diversion Tunnel, Central Mamuju, West Sulawesi Province

Budong-Budong Dam, located in the West Sulawesi Province of Indonesia, was designed to use a tunnel to divert river flow during the dam construction. The Rock Mass Rating was used to examine the tunnel design with a less detailed drill core investigation. The rock strength parameter is only based on the field estimation. The entire diversion tunnel will pass through Breccia with weak strength. Evaluation is required using integrated and precise data to guarantee safety during and post-construction. The RMR classification was used to determine the excavation and preliminary tunnel support, while the Q-System was used to compare the support of the tunnel. Those classifications were used to anticipate the geological conditions uncertainty. Geological data were collected by geological mapping, evaluation of subsurface drilling, and laboratory analysis. The tunnel will pass through a Tuffaceous Breccia and Tuffaceous Sandstone insert of Tuffaceous Siltstone. In addition, a poor-quality rock was found around the inlet and outlet, and a fair-quality rock in the middle of the tunnel. Hence, drilling and blasting were recommended for the excavation. The tunnel’s proposed support system included shotcrete, wire mesh, and rock bolts in the middle of the tunnel. Steel sets are added around the inlet and outlet.

Transverse variability of residual currents, sediment fluxes, and bed level changes in estuaries with an estuarine dam: Role of estuarine type, dam location, and discharge interval

Estuarine dams are constructed in estuaries for reasons such as freshwater, flood control, and navigation. By changing tidal and river properties, estuarine dams can change the circulation and sediment transport in estuaries. Previous studies have investigated the along-channel changes in flow and sediment transport, however across-channel changes due to an estuarine dam are not well understood. To increase our understanding, this study analyzed an idealized estuary using the COAWST numerical modeling system. Models of strongly stratified, partially mixed, periodically stratified, and well-mixed estuaries were run for one year. Then, the models were subject to the construction of an estuarine dam and run for another year. For each estuarine type, scenarios with an estuarine dam at x = 20, 55, and 90 km from the mouth and freshwater discharge intervals of Δt = 0.5, 3, and 7 days were investigated, and the scenarios were compared. The results indicated that the river-dominated and tide-dominated estuaries behaved differently. In river-dominated estuaries, the residual circulation tended to be inflow in the channel and outflow over the shoals due to the estuarine exchange flow, and the secondary circulation was bottom divergent due to differential advection. The exchange flow and secondary circulation were found to weaken with longer discharge interval. The sediment fluxes in the channel were dominant, and, despite the weaker exchange flow, were found to be greater and directed seaward due to strong dam discharge for long discharge intervals. In tide-dominated estuaries, the residual circulation tended to be inflow over the shoals and outflow in the channel due to the tide-induced circulation, and the secondary flow was bottom convergent due to differential advection resulting from Stokes return flow. As the estuarine dam was located nearer to the mouth, the tide-induced circulation was replaced with exchange flow, and the secondary flow became bottom divergent. The sediment fluxes in the channel were dominant in this case as well, and were determined by tidal asymmetry from the interaction of the tides with the residual current, becoming directed landward as the seaward tide-induced circulation decreased with the estuarine dam near the mouth. With respect to bed level change, gradients in along-channel sediment fluxes were found to contribute most to bed level change near the mouth and estuarine dam, whereas gradients in across-channel sediment fluxes contributed most to deposition on the estuarine shoals. This study demonstrates that estuarine dam location and discharge interval can alter estuarine transverse variability and improves our understanding compared to previous analyses based solely on along-channel processes.

Understanding Morphological Dynamics of the Mahanadi River Reach

Abstract This work examines specific river morphometry parameters like bank erosion, active channel bank shift, and the sinuous behavior at identified stretches of the Mahanadi River. The specific stretches of the Mahanadi River from Baipur to Gopinathpur, Cuttack of around 270 km have been subdivided into five different reaches to simplify the study from a large scale to an average range. The Digital Shoreline Analysis System was used to investigate the river bank shifting and for the bank shifting prediction using Kalman Filter Model. The outcomes of the work show that, for the most part, the Mahanadi River is sinuous; however, at Kantilo, which is designated as reach four is meandering. In terms of Sinuosity, most reaches are unstable, whereas reaches 2 and 3 are stable. The flow area ratio to channel area has fallen by 25-30% due to the construction of barrages and dams in the upper portion of the Mahanadi River, affecting aquatic life, people and industries. At the same time, due to climate change, irregular rainfall causes floods in the lower reach of the river. The river flow erodes the bank along which it flows, even when the discharge is minimal. According to the bank shift analysis, the right bank is more unstable, ranging from 222 to -2900 m, while the left bank fluctuates from 996 to -1600 m. This study will help to understand the pattern of river bank shifting and change in the planform dynamics at the respective locations of the Mahanadi River.

Variable analysis for supporting reservoir impounding modeling

The impounding stage of the reservoir is a stage after the implementation of dam construction is finished. The process of reservoir impounding is started by closing the tunnel diversion gate and the elevation of the water level will be moving up slowly. The speed of the increasing reservoir water level elevation is affected by the dry season or rainy season, so it is arranged in such a way for obtaining the daily increase is not more than 1.0 m/day, due to dam safety. This research intends to build this modeling, at first by studying which variables are affecting in order to get the safe period of impounding. The methodology consists of a correlation analysis of inflow, outflow, and the ratio between storage volume and inflow volume to the optimal impounding equation. The statistical hydrology approach is used in this modeling that will assess the 7 observed reservoir impounding which is started from base elevation until Full Supply Level (FSL). This modeling will help in decision-making about the selection of the safe and optimal period of reservoir impounding. At the end of impounding, the reservoir will be full and it starts to be allocated regarding the utilization that has been designed.