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The earthquake hazard of the wide plateau comprising significant dams around the East Anatolian Fault Zone (EAFZ) in eastern Türkiye is studied by means of the seismicity assessment and probabilistic seismic hazard analysis (PSHA). The fault segments of the EAFZ in the east of Kahramanmaraş city, which were previously assigned as a seismic gap, are shown to produce an earthquake in the order of at least Mw = 7.4. b values of the frequency–magnitude distribution calculated from the declustered Mw ≥ 3.2 seismicity after 1995 indicate significant temporal (a gradual decrease from 1.6 to 0.8 between 2010 and 2019) and spatial variations (between 0.75 and 2.1), leading to a short recurrence time estimation of as low as 90 years for an earthquake size comparable to the 2020 Sivrice earthquake (Mw = 6.7). No matter which attenuation relationship is used, the PSHA assuming a 475-year recurrence period results in considerably higher PGA values (average 0.25–0.64 g) as compared to the previous local and regional scale studies, suggesting higher seismic hazard than known so far. The presence of the seismic gap, the decreasing b value as an indication of rising ambient crustal stresses, the estimated shortest recurrence time of 90 years and the computed PGA values imply a significant earthquake hazard for the study area. Considering that the study area contains large cities with historic heritages, important industrial capacities and the existence of big crucial dams, requiring to be on alert in terms of seismic safety and preparedness of the population. [ABSTRACT FROM AUTHOR]

The awareness of the transmission of the sticky sediments for the development and maintenance of reservoirs and water transfer network is very important. This research was carried out to recognize and understand the dynamic behavior of fine-sticky sediments to obtain the necessary information for the Karkheh dam reservoir management. Sediment samples were taken from the four different points located in the dam reservoir. Liquidity and plasticity behaviors and their indices of the samples that were combined together were determined by doing the Atterberg limits experiment. To investigate the initial erosion threshold shear stress, the impact of consolidation and sediment depth were examined by cylindrical settling columns. Using a circular flume in, Shahrekord University Lab, the concentration process, changes of eroded sediments, shear stress threshold of erosion, erosion rates, etc. in different consolidation periods (3, 14 and 30 days) were studied. The results showed that the concentration of eroded sediments is a function of time for the consolidation of reservoir sediment and bed shear stress and also observed that the duration of consolidation time is an effective factor on critical erosion shear stress. So, the threshold shear stress values for consolidation time of 3, 14 and 30 days were, 0.16, 0.22, 0.31 N/m2, respectively. The results of the erosion rate suggest an inverse relationship between this parameter and the life of the settled sediments based on the results the best flow shear stress for sediment removal by flashing from the Karkheh dam reservoir should be greater than 0.31 N/m2. [ABSTRACT FROM AUTHOR]

This paper presents a study of karst conduit genesis as well as establishing a groundwater circulation model: an isotopic approach for revealing binary mixing of cold and the thermal water underlying hydropower plant (HPP) at Visegrad, Bosnia, and Herzegovina. The study was conducted with the aim of water-leakage mechanism in the porous karst. Before the first filling of the HPP Visegrad reservoir, water from springs downstream of the dam had a temperature of 19 °C with a discharge capacity of around 0.5 m3/s. After the reservoir had been filled, the elevated hydrostatic pressure started increasing the discharge rate from 1.4 m3/s in the first year of HPP Visegrad operation, up to 15 m3/s after 20–22 years with a temperature decreasing of 7–9 °C in average. After large and expensive remediation works, the leakage effect was decreased to a discharge rate of 3.5 m3/s with an increase of the temperature to 14–15 °C. The main purpose of this paper has been to define a binary-mixing mechanism for disjunction cold (reservoir water) and thermal groundwater (deep aquifer) discharge capacity. Besides temperature modeling, environmental tracers (2H, 18O, 3H, 3H/3He apparent age, noble gases, and carbon isotopes [13C, 14C]) have been used to identify different components in the leakage water and deep thermal water. According to these analyses, water discharge from the same springs can be divided into three different types (regarding age) as: young water component (age of 0 year), an older part of young water component (age of about 30 years), and old water component (age above 1000 years). Based on all data percentage share, the total discharge amount of two older components of thermal water is around 15%, while that of water leaking directly from the reservoir was 85%. [ABSTRACT FROM AUTHOR]

In this study, two ephemeral streams are compared in assessing bio-geomorphic change to channels intersected by the Central Arizona Project (CAP) canal. Water and sediment are fully or partially restricted to move downstream due to the CAP canal, which acts as a dam to these streams. Upstream of traversed channels, vegetation cover has increased over time causing the development of a green-up area. Along the canal, several channels remain longitudinally connected via culvert or overchute to the downstream sections of the stream channels. The two streams examined both had longitudinal connectivity, but only one of the streams had a green-up area upstream. Field work and channel surveys reveal that this is due to the culvert’s peak discharge outflow. The stream with a developed green-up area had a culvert size that is approximately three times less than the discharge of this ephemeral stream causing the partial damming upstream during flow events. Green-up zones slowly enlarge over time as bed levels and adjacent desert surface heights increase from continual sediment deposition upstream causing the floodplain to laterally increase due to overbank flooding. It is estimated that the green-up area for the partially dammed stream will increase by approximately 1570 m2 over the next 36 years. Suggestions for urban and agricultural development are presented in this paper in relation to these dynamic green-up areas. Understanding biogeomorphic processes along dammed ephemeral streams lends valuable insight to riparian conservation efforts and future urban development plans in desert regions. [ABSTRACT FROM AUTHOR]

Leakage detection and the prediction of the behavior of fractured rocks subjected to variations in hydrostatic pressure are important issues in hydropower engineering. Some large water reservoirs are constructed in karstic carbonate areas. In order to understand underground circulation in the limestone/dolomite foundation of the Vouglans dam (Jura, France), groundwater chemistry analysis, according to geological conditions, is used. Statistical analyses (PCA and DFA) are carried out: (1) to accurately characterize the contrast in chemical composition resulting from the interaction between surface and groundwater in a poorly contrasted environment, due to the shared carbonated context, and (2) to reassign individuals into homogeneous groups with respect to the variables studied. PHREEQC is used to determine the potential for the precipitation of secondary minerals from the water chemistry mainly in order to determine the geochemical control of clogging. Three types of hydrodynamic behavior were identified in the sector. The origin and transfer time of inflows vary with respect to seasons. The area of influence of the rapid transit of the lake water varies predominantly in response to changes in the lake water level. The hydrostatic pressure of the water column influences the opening and closing of cracks at the bottom of the dam. Drains intercepting an upstream fissure are highlighted by hydrochemical measurements. Inflows are oversaturated with respect to calcite and are thus likely to precipitate this mineral. Zones with a strong clogging capacity correspond to the zones with slow transit groundwater. [ABSTRACT FROM AUTHOR]

Water quality can be used to reflect the hydro-geological features and seepage restrictions around grout curtains. Xiangjiaba Dam, a large hydropower station constructed in southwest of China, was investigated as a case study. Groundwater samples were collected and analysed qualitatively using hydrochemistry diagrams, after which the presence of four major water groups was determined by hierarchical cluster analysis and saturation indices of each group were calculated. Finally, inverse geochemical models of the groups were developed using PHREEQC to elucidate the dissolution/precipitation quality of different minerals and the relative contributions of different seepage sources. The hydro-geochemical methods used were found to be useful for revealing seepage behaviour within the domain during construction of a hydropower station. [ABSTRACT FROM AUTHOR]

The foundations of dams containing soluble material, typically gypsum and limestone, undergo a dissolving process as a consequence of reservoir seepage. In due course, such dissolution of soluble material increases the volume of holes through which water may flow, in turn involving an increase in flow rate through the dam foundation. To adapt dam design to the particular conditions of these foundations, especially in foundations containing gypsum, with the main aims of delaying the dissolution process and avoiding damage or loss of functionality during dam lifespan, a procedure that models the dissolution process coupled with seepage phenomena is necessary. The objective of this paper is to provide this procedure and test it under experimental conditions. This entails coupling a conventional code for calculation of seepage networks, by means of the finite-element method, with a code developed by the authors to calculate the solution front advance (the zone where the dissolution is taking place). The procedure is verified by performing permeameter testing using sand and soluble material mixtures, with the tests being numerically modelled. [ABSTRACT FROM AUTHOR]

Employing the histogram matching approach, the sediment regime alteration of the upper Yangtze River was assessed and its possible causes and environmental influences were discussed. Daily sediment load and flow data from 1950 to 2008 were collected from Yichang hydrometric station. The annual sediment load series was segmented by heuristic segmentation algorithm in 1986 and 2003, and the multi-year mean values of the three phases were 5.28 × 10, 3.89 × 10 and 0.57 × 10 t, respectively. One change point was found by cross wavelet transform in 2003 when the cross wavelet power became insignificant, which indicates the interruption of the common annual cycle of the sediment load and flow series. The sediment regime from 1986 to 2002 was altered by a total of 41 % compared with the regime from 1950 to 1985. It may be mainly attributed to numerous dams constructed in the tributaries, the Gezhouba Dam constructed in the mainstream, and land use and land cover change, e.g., the increased grassland with a coverage density larger than 50 %. The sediment regime alteration after 2003, assessed to be a total of 83 %, may be mainly attributed to the Three Gorges Reservoir. It breaks the natural process of sediment transport, reduces sediment concentration and releases clear water to the downstream which may result in some environmental problems, e.g., limited nutrients availability, river bed erosion, benthic habitat destruction, etc. The assessment of sediment regime alteration may provide some references for the environmental management and conservation of the Yangtze River. [ABSTRACT FROM AUTHOR]

The Doosti Dam, with a reservoir capacity of 1,250 million cubic meters, was constructed on the Harirood River at the border of Turkmenistan and Iran. The reservoir is in direct contact with permeable formations on the right abutment of the dam including the Neyzar Sandstone, the Kalat Limestone and the Pesteleigh alternative layers of marlstone and sandstone. After the reservoir impoundment, several new springs and seepages emerged from these formations and the alluvium. The amount of leakage increased with the rise in reservoir water level. Fifteen kilograms of sodium fluorescein were injected into a 113-m deep borehole intersecting three permeable sandstone layers of the Pesteleigh formation. Dye was detected downstream of the grout curtain in boreholes and springs that were in direct contact with parts of the Pesteleigh formation having the same sandstone layers as the injection borehole. The dye velocity was in the range of diffuse flow, confirming the good performance of the grout curtain in the Pesteleigh formation. No dye was detected in the other formations because the injection borehole was not in direct contact with these formations. The hydraulic relation of the other formations with the reservoir was determined by considering direct contact of the formations with the reservoir, emergence of new springs and seepages after reservoir impoundment, correlation of time variations of the springs discharge and the borehole's water level with the reservoir water level, and in some cases the hydrochemistry of the water. The results show that the Kalat and Neyzar formations are hydraulically connected to the reservoir, but the small amounts of leakage from these formations at a hydraulic gradient of 24% indicates good performance of the built grout curtain. The total reservoir leakage at maximum reservoir water level was 100 l/s which is insignificant compared with the 15 m/s average annual release of the reservoir. [ABSTRACT FROM AUTHOR]

The multipurpose dam and reservoir “Bogovina” in the Crni Timok valley is one of several projects that have been initiated to improve water availability in Serbia. The site and height of the dam were initially proposed without consideration of risk factors such as water leakage or stability of the banks. Later, complex hydrogeological and speleological surveys and tests identified the potential of significant water losses from the reservoir area connected mainly to the karstic aquifer, and the nearby Bogovina cave system. The analyses show that once the reservoir is filled up, groundwater flow currently oriented towards the future reservoir would saturate the upper part of the karstified rocks, reactivate currently unsaturated pathways and form a reverse discharge outside of the reservoir area. In response to these findings, the dam design and technical details have been adapted accordingly: the dam height has been reduced by 9 m, and it is proposed that grouting and consolidation work be conducted both at the foundation of the dam and extensively on the embankments. It was concluded that although the proposed remedial measures cannot guarantee reservoir tightness, they can reduce the risk of large-scale leaking. [ABSTRACT FROM AUTHOR]

Turbid-water problem of reservoirs due to soil erosion causes a major issue in dam operation. This study presents a methodology to quantitatively analyze the occurrence possibility of turbid-water in four hydrologic basins (Sayeon, Degok, Gwangdong, and Imha Dam basins in S. Korea), quantifying the weighting value of turbid-water occurrence in reservoirs. To do this, the study conducted indoor tests, including laser-assisted particle size analysis, X-ray powder diffraction method analysis, and scanning electron microscope, to give the geologic characteristics such as the distribution of soil particle size, settlement time, landslide, and existing sediment yield. The study used RUSLE models to calculate sediment yield on the basis of soil maps, DEMs, and landcover maps as auxiliary data. This study classified factors for evaluating the possibility of turbid-water occurrence into geology, sediment yield, landslide and soil components, and these evaluation items’ weighting and score are presented using the analytic hierarchy process technique. The suggested method is promising in that it can analyze the risk factor of turbid-water occurrence in basins and that can provide a guideline to estimate the turbid-water occurrence of reservoir in dam construction. [ABSTRACT FROM AUTHOR]