Identifying sources of groundwater recharge in the Merguellil basin (Tunisia) using isotopic methods: implication of dam reservoir water accounting

Thirty-two groundwater samples collected from the Merguellil Wadi basin (central Tunisia) complemented by the Haouareb dam reservoir water samples have been isotopically analysed in order to investigate the implication of the reservoir water to recharging the aquifer, and also to infer the sources, relative ages and mixing processes in the aquifer system. Plots of the stable isotopes data against the local meteoric lines of Tunis-Carthage and Sfax indicate a strong implication of the dam water noticeable up to a distance of 6–7 km. A contribution as much as 80% of the pumped water has been evidenced using isotopic mass balance. In addition, poorly distinguished water clusters in the stable isotope plots, but clearly identified in the diagrams δ¹⁸O versus ³H and ³H versus ¹⁴C, indicate various water types related to sources and timing of recharge. The isotopic signatures of the dam accounting water, the “old” and “native” recharged waters, have been evidenced in relation to their geographical distribution and also to their radiogenic isotopes (³H and ¹⁴C) contents. In the south-western part of the aquifer, mixing process occurs between the dam reservoir water and both the “old” and “native” water components.     

Deterministic approach to the seismic hazard of dam sites in Kızılırmak basin,Turkey

Dams constructed on the seismically active regions have a high-risk potential for downstream life and property. Strong ground motion can result in instability of the dam and strength loss of foundation. Active faults within the foundation of dam have the potential to cause damaging displacement of the structures. Appropriate design measures should be considered to obtain rational solution to the problem of catastrophic release of water from the reservoir, and especially to resist earthquake loads. Safety concerns for dams under the earthquake loads involve the seismic hazard evaluation of dam site for the overall stability of structure. Various types of analyses can be used, ranging from a simplified analysis to more complex procedures based on ground motion parameters and response spectra. This paper briefly evaluates seismic hazard analyses for dam structures, and introduces the analyses for thirty-six dams with height ranging from 15 to 195 m in Kızılırmak basin, Turkey. The seismic hazard analyses have indicated that peak ground acceleration varies within a wide range (0.09–0.45 g) for the dam sites of the basin.     

Siltation analysis in the Neyyar reservoir and forest degradation in its catchment: a study from Kerala state, India

 Impact of catchment erosion and the resultant reservoir siltation from a tropical environment is reported here to discuss the effect of a reservoir in the natural degradation of an evergreen-forested segment. While an area of 8.01 km² has been affected by direct inundation at the full reservoir level, another 2.6 km² area once under thick forest cover, had also lost its identity over the last 38 years by indirect degradation. This zone mainly falls in the confluence of tributaries, namely Neyyar and Mullayar, with the reservoir. The capacity of the reservoir was found to be reduced by 28.8 Mm³ during this period and the annual average loss is calculated as 0.75 Mm³ (0.71%), indicating the intensity of erosion from the catchment zone. In case the proposed upper dam in the reservoir comes into existence, an additional area of 2.4 km² from the virgin forest would be submerged and more area would face degradation around the inundated zone. Received: 29 July 1998 · Accepted: 16 November 1998     

泥石流拦挡坝优化设计

拦挡坝设防高度决定着库容,因此确定合理的设防高度在拦挡坝的设计中极为重要。在坝址确定的情况下提高拦挡坝的设防高度可以加大库容,增强防治工程的抗灾能力,但其泄洪能力会受到影响,因此拦挡坝的库容与其泄洪能力是矛盾的。既有设计理论中泥石流峰值流量按照全流域面积汇水输沙总量计算,该理论认为每个拦挡坝的设计洪峰流量是相同的,而实质上对于流域面积大的泥石流沟,设置在上游、中游及下游的拦挡坝由于汇水面积的差异而导致泥石流峰值流量相差较大,本文作者提出了按有效汇流面积计算泥石流峰值流量的优化设计方法,用该方法设计的拦挡坝的溢流断面面积较小,从而达到提高设防高度,增大库容,提高拦挡坝的容灾能力。     

西南地区某岩溶水库渗漏分析

西南地区某水库位于云贵高原中北部,库区可溶盐岩分布较广且岩溶较发育,中部有一条近南北走向的区域性断裂（F1）穿过两岸,为论证此水库成库的可能性,通过地表调查及物探,结果表明:此水库向低邻谷渗漏的可能性小,沿F1断裂带向南部或向下游渗漏的可能性问题不大,存在沿灰岩溶蚀通道向下游和向库外渗漏的可能性,沿左岸大理岩与灰绿岩接触带或大理岩向坝下游绕坝渗漏的可能性不大;水库正常蓄水位在Kc1底板高程以下有成库的可能。      

自强水库库区工程地质评价与坝线选址研究

自强水库位于陕南秦巴山地中低山地貌区,水库为镇巴县备用水源地及旅游观光风景区,属小(1型水库。通过对库坝区地质构造、地层岩性、岩溶发育等工程地质条件分析可知,对工程建设及坝线选址有影响的工程地质问题主要为库区内发育逆冲叠瓦小断裂以及岩溶发育可能导致水库渗漏等。库区内无大型活动性断裂构造,构造较为稳定,且库区蓄水范围小,蓄水量不大,不易诱发地震。而拟选坝址位于自强河段,沟谷对称顺直,综合水库坝址区地形地貌、工程地质等条件进行坝线比选,推荐下游坝线为较为理想的坝线位置,可满足工程建设要求。     

Monitoring of Bashkara Glacier lakes (Central Caucasus, Russia) and modelling of their potential outburst

Glacier lakes pose threat to downstream settlements and infrastructure. In recent decades the number and area of lakes have been growing at an accelerating rate due to worldwide glacier shrinkage. In the Russian Caucasus this process is understudied. We present results obtained during a 12-year (1999–2010) continuous field monitoring of the Bashkara proglacial lakes group, which we identified as the place with the highest GLOF risk in the region. Recession of the parent Bashkara Glacier was the main driver of the rapid expansion of the lower Lake Lapa. The upper Lake Bashkara has not been enlarging, but its water level has shown significant inter- and intra-annual fluctuations. The lake outburst probability has increased in recent years, and in 2008 we observed surface overflow over the moraine dam. Taking into account that in the late 1950s lake outbursts at this site led to large-scale glacial debris flows, we have simulated a potential outburst using River and FLO-2D software and carried out hazard zonation. An early warning system has been designed and established at Lake Bashkara, and measures to mitigate risk have been proposed. Rapid change of proglacial lakes requires regular monitoring in ‘hot spot’ areas where the GLOF hazard is high and is dynamically changing.     

大连地区水资源人工调控研究

通过分析大连地区水资源特点及人工控制现状,得出区内水资源仍具有人工调控潜力的认识.结合流域径流资源、区域人工控制特点分析,及有坝地下水库技术研究,筛选设计出5项地表水利工程、7项地下水库工程及13处地下水库潜力区.水量分析表明,通过加大水资源的人工调控,可净增水资源利用量4.38亿m3/a,完全可以解决近期供水问题,增强了大连地区应急水源的保障能力.     

库水位骤降后面板缺陷坝体渗漏量和坝坡稳定性分析

为研究库水位变动情况下面板不同缺陷的面板堆石坝渗透稳定特性,利用著名岩土分析软件Geo-studio的Seep/w与Slope/w模块,以浙江省临海市西部括苍镇境内某面板堆石坝为例,对不同土工膜缺陷及库水位变动工况的组合进行了渗流特性及稳定性的数值模拟分析,得到了浸润线,渗漏量及稳定性系数的变化曲线,计算结果表明:(1)面板一旦发生缺陷,静库水位下坝体的浸润线有一个明显的抬升,缺陷尺寸越大,浸润线高程越高,但是差异不大。库水位高程越高,静库水位下坝体内部的浸润线高程也就越高;(2)库水位水平越高,缺陷尺寸越大,坝体渗漏量也就越大;(3)库水位骤降下面板坝内部浸润线呈现先疏后密的规律,库水位下降速率越大,上游坝体浸润线疏的部分则越疏。在库水位骤降经过面板坝缺陷高程时,有一个浸润线突降的过程;(4)从整体上看,上游坝坡的稳定性系数要大于下游坝坡的稳定性系数;静库水位下,库水位水平越高,上游坝坡稳定性系数越大,而下游坝坡稳定性系数则越小,缺陷位置越高,稳定性系数越低;库水位骤降情况下上游坝坡稳定性系数随库水位下降呈现先下降后上升的趋势,下游坝坡则呈现一直上升的规律,一旦面板发生缺陷,稳定性系数较完整面板来说有一个较大幅度的下降,面板缺陷尺寸越大,稳定性系数整体上越小。     

不同洪水重现期下橡胶坝调控对洪水风险的影响

现有针对河湖水系连通伴生风险分析的方法或不具备物理过程模拟,或缺乏对风险随机性的探讨。以沂沭河水系连通工程为例,在水力学模型的基础上,考虑连通河网不同河流洪峰相关性,创建随机水情条件下河湖水系连通伴生风险分析模型。通过1 200组水情条件,对沂沭河水系上游进行洪水过程模拟,针对橡胶坝可能造成的洪峰叠加问题,提出不同洪水重现期下橡胶坝运行调度风险管控建议。结果表明:① 50年一遇与100年一遇洪水重现期条件下,均呈现出橡胶坝坝址处水位风险极高（概率P>0.8）,流速风险较低（P < 0.3）的规律,且每当橡胶坝高度升高25%的设计坝高时,沂河与沭河坝前水位风险皆提高约70%,沭河坝址处流速风险降低约50%。②若在汛前塌坝下泄蓄水,人为洪峰的叠加会使沭河中下游河段产生极高风险。③通过划分水位、流速综合洪水风险安全域,洪水重现期50年一遇时,建议沂沭河橡胶坝在汛前调节至低于50%设计坝高,且控制沭河水深和流速分别在12 m和2.23 m/s以内,可以降低水位和流速风险至低风险（P < 0.4）;洪水重现期100年一遇时,需将橡胶坝调至25%设计坝高以下,或者汛前尽早缓慢塌坝下泄蓄水,才能有效降低沂沭河水系防洪压力。     

Risk variation of reservoir regulation during flood season based on bivariate statistical approach under climate change: a case study in the Chengbihe reservoir,China

The risk analysis of reservoir regulation in the flood season is crucial and provides the valuable information for reservoir flood control, safety operation, and decision making, especially under climate change. The purpose of this study is to propose a framework for reasonably estimating the variation of reservoir regulation risk including the dam extreme risk and the overtopping risk during the flood season under climate change. The framework consists of an integrated diagnostic system for detecting the climate abrupt change time, a copula function-based bivariate statistical approach for modeling the dependence between the flood peak and flood volume, a Monte Carlo simulation for generating numerous random flood peak–volume pairs, and a risk calculation model for routing the design flood hydrographs to obtain the frequency curve of the maximum water level reached in front of dam and evaluating the reservoir regulation risk. The methodology was implemented in the Chengbihe reservoir in south China by using the 55-year (1963–2017) hydrometeorological data, including temperature, evaporation, precipitation, and streamflow, in the flood season. Results show that the hydrometeorological series during the flood season changed abruptly in 1992 and the entire data can be divided into two periods (1963–1992 and 1993–2017). The dam extreme risk and overtopping risk during the two periods are assessed, respectively, and a comparison analysis is made based on different flood limit water-level schemes (185.00–188.50 m). It demonstrates that both the dam extreme risk and the dam overtopping risk increase under the influence of climate change. The dam extreme risk increases by 22.91–95.03%, while the climate change-induced increase in the dam overtopping risk is between 38.62 and 123.59%, which indicates that the dam overtopping risk is more sensitive to climate change than the dam extreme risk. The risk evaluations in the study are of great significance in the safety operation and risk management of reservoirs under future climate change.

     

The 12 May Wenchuan earthquake-induced landslide lakes: distribution and preliminary risk evaluation

The Wenchuan earthquake, measured at M _s 8.0 according to the China Earthquake Administration, occurred at 14:28 on 12 May 2008 in the Sichuan Province of China. It brought overwhelming destruction to eight provinces and cities. Landslides and rock avalanches triggered by the earthquake produced 257 landslide lakes which were distributed along the fault rupture zone and river channels. The authors traveled to the disaster zone immediately after the earthquake to examine some of the features of the debris dams and performed a quick evaluation of the potential for outburst of earthquake-induced landslide lakes for the purpose of disaster relief. The preliminary analysis indicated that the landslide lakes could be classified as those exhibiting extremely high risk, medium risk, and low risk according to field observations and remote sensing, to determine material composition, dam structure, dam height, maximum water storage capacity, and size of the population potentially affected area. The failure risk of 21 debris dams were evaluated as follows: one dam with an extremely high danger risk, seven dams with a high danger, five dams with a medium danger, and eight dams of low danger. More concern was given to the Tangjiashan Lake and different scenarios for the potential sudden failure of its dam were assessed. The risk evaluation result was accepted in full, by the earthquake disaster relief office. A successful emergency dam treatment for risk reduction was planned, based on our assessments, and these measures were quickly carried out. According to this research, the earthquake destabilized the surrounding mountains, resulting in a prolonged geohazard for the area. Landslides and debris flows will continue to develop for at least 5 to 10 years after the Wenchuan earthquake and will produce additional dammed lakes. Recommendations and plans for earthquake–landslide lake mitigation were proposed, based on past successful practices.     

Dynamic characteristics of tailings reservoir under seismic load

Earthquake is one of the most important factors that leads to the liquefaction of tailings and to the instability of the tailings reservoir. Therefore, it is of great practical significance to study the instability mechanism of the tailings reservoir under seismic load. In this study, the dynamic characteristics of the tailings reservoir under seismic load were investigated by carrying out a model test on the dynamic characteristics of the tailings dam. A model test of tailings dam failure and the dynamic characteristics model of the tailings reservoir under seismic load were established. Additionally, the dynamic characteristics under a seismic load were investigated. Additionally, the correctness of the dynamic characteristics model of the tailings reservoir was verified by numerical calculation. Researches show that with the increase in input peak acceleration, pore water pressure, earth pressure, and the horizontal and vertical displacements of the dam monitoring points are gradually increased. However, the acceleration amplification factor shows a declining trend. In the process of increasing the input peak acceleration, the saturation line and the lifting speed increases gradually. There is no obvious slip surface in the failure of the tailings dam, and the overall sliding is shown by the failure mode. The tailings reach each of the downstream sections. The mud height increases to the peak value, and then decreases gradually until stagnation. The results of this study can provide the theoretical basis and reference values for the stability analysis of a tailings reservoir under a seismic load, and the results are of great significance for controlling the risk factors in the operation of tailings reservoir, reducing the risk of tailings production safety, preventing the occurrence of tailing pond accidents, protecting the property safety of the downstream residents and enterprises, maintaining social stability around the reservoir area and creating a good ecological environment.     

Gypsum-karst problems in constructing dams in the USA

Gypsum is a highly soluble rock and is dissolved readily to form caves, sinkholes, disappearing streams, and other karst features that typically are also present in limestones and dolomites. Gypsum karst is widespread in the USA and has caused problems at several sites where dams were built, or where dam construction was considered. Gypsum karst is present (at least locally) in most areas where gypsum crops out, or is less than 30–60 m below the land surface. These karst features can compromise on the ability of a dam to hold water in a reservoir, and can even cause collapse of a dam. Gypsum karst in the abutments or foundation of a dam can allow water to pass through, around, or under a dam, and solution channels can enlarge quickly, once water starts flowing through such a karst system. The common procedure for controlling gypsum karst beneath the dam is a deep cut-off trench, backfilled with impermeable material, or a close-spaced grout curtain that hopefully will fill all cavities. In Oklahoma, the proposed Upper Mangum Dam was abandoned before construction, because of extensive gypsum karst in the abutments and impoundment area. Catastrophic failure of the Quail Creek Dike in southwest Utah in 1989 was due to flow of water through an undetected karstified gypsum unit beneath the earth-fill embankment. The dike was rebuilt, at a cost of US $12 million, with construction of a cut-off trench 600 m long and 25 m deep. Other dams in the USA with severe gypsum-karst leakage problems in recent years are Horsetooth and Carter Lake Dams, in Colorado, and Anchor Dam, in Wyoming.     

The effect of reservoir length on seismic performance of gravity dams to near- and far-fault ground motions

In this article, the effect of reservoir length on seismic performance of gravity dams to near- and far-fault ground motions is investigated. For this purpose, four finite element models of dam–reservoir–foundation interaction system are prepared by using the Lagrangian approach. In these models, the reservoir length varies from H to 4H (H: the height of dam). The Folsom gravity dam is selected as a numerical application. Two different ground motion records of 1989 Loma Prieta earthquake are used in the analyses. One of ground motions is recorded in near fault; the other is recorded in far fault. Also, the two records have the same peak ground acceleration. The study mainly consists of three parts to assess the effects of reservoir length on the seismic performance of the concrete gravity dam. In the first part, the linear time-history analyses of the four finite element models prepared for the Folsom gravity dam are performed. In the second part, the seismic performance of the dam is evaluated according to demand–capacity ratio and cumulative inelastic duration. Finally, the nonlinear time-history analyses of the finite element models of the dam are carried out by using Drucker–Prager yield criteria for dam concrete. It is seen from the analyses results that the seismic behavior of the concrete gravity dams is considerably affected from the length of the reservoir. The reservoir length of 3H is adequate for concrete gravity dams. The selection of ground motion is on of the important parts of seismic evaluation of gravity dams. Also, the frequency characteristics of the ground motion having the same peak ground acceleration affect the seismic performance of the dam. The near-fault ground motions are generally creates more stress on the dam body than far-fault ground motions. The used performance approach provides a systematic methodology for assessment of the seismic performance and necessity of nonlinear analyses for dam systems.     

燕山水库坝基防渗墙优化设计

因现场资料不足或分析手段落后等原因,当前进行水库坝基防渗墙设计,往往存在过于保守的倾向。以河南省燕山水库为例,基于优化设计的思路,采用目前较为成熟的二维有限单元法,对不同防渗条件下的坝基渗流场分别进行了模拟,并将计算所得比降、流量与允许比降、允许流量做了对比,从定量的角度提出了既安全、又经济的防渗方案:防渗墙厚度取0.8m,深度取打入破碎带5m。     

Hydrogeochemical study of the thermal and mineralized waters of the Banaz (Hamamboğazi) area,western Anatolia,Turkey

The Hamamboğazi spa in western Turkey was built around natural hot springs with discharge temperatures in the range of 30–54°C; the waters have near neutral pH values of 6.50–7.10 and a TDS content between 2,694 and 2,982 mg/l. Thermal water with a temperature of 47.5–73°C has been produced at 325 l/s from five wells since 1994, causing some springs to go dry. A management plan is required in the study area to maximize the benefits of this resource, for which currently proposed direct uses include heating in the district and greenhouses, as well as balneology in new spas in the area. The best use for the water from each spring or well will depend on its temperature, chemistry and location. The thermal waters are mixed Na–Mg–HCO₃–SO₄ fluids that contain a significant amount of CO₂ gas. The chemical geothermometers applied to the Hamamboğazi thermal waters yield a maximum reservoir temperature of 130°C. Isotope results (¹⁸O, ²H, ³H) indicate that the thermal waters have a meteoric origin: rainwater percolates downward along fractures and faults, is heated at depth, and then rises to the surface along fractures and faults that act as a hydrothermal conduit. The basement around the Banaz Hamamboğazi resort is comprised of Paleozoic metamorphic schist and marbles exposed 8 km south and 15 km north of Banaz. Mesozoic marble, limestone and ophiolitic complex are observed a few km west and in the northern part of Banaz. These units were cut at a depth of 350–480 m in boreholes drilled in the area. Overlying lacustrine deposits are composed of fine clastic units that alternate with gypsum, tuff and tuffites of 200–350 m thickness. The marble and limestones form the thermal water aquifer, while lacustrine deposits form the impermeable cap.     

Assessment of water seepage through a geologic barrier surrounding a large reservoir using groundwater levels, soil condition, and a numerical model

Though the geologic barrier surrounding a dam reservoir plays an important role in preventing water seepage to the outside of a reservoir, a detailed survey to assess bedrock conditions of the whole reservoir boundary is seldom performed when designing a dam. In this study, a variety of investigations and analyses have been conducted to reveal a seepage phenomenon through a reservoir boundary composed of highly fractured metamorphic rocks at the Daechung multipurpose dam. At the study site, groundwater levels at monitoring wells located close to a reservoir tend to change proportionally to reservoir water levels, usually with a rapid response time of 1 day or less. Soil moisture content also changes with respect to the reservoir water level, and the area where seepage from the reservoir is a possibility has a relatively high soil moisture content. The similarity of measured seepage rates at the outflow site and the seepage rate estimated by Darcy’s law suggests strong connectivity and high density of the fractures. The estimated seepage rate using a numerical model for the northernmost valley (Zone 1) is approximately 127.2 m³/day in the case of high reservoir water level and 24.3 m³/day in the case of low water level. Continuous monitoring to obtain time series data for water levels, quality, and bedrock displacement is recommended to assess the sustainable stability of this geologic barrier.     

Study of the Engineering Geological Problems of the Havasan Dam,with Emphasis on Clay-Filled Joints in the Right Abutment

Havasan dam site is located in northwest of Iran. The planned concrete dam is to be built on Cretaceous limestone. Faulted and fractured limestone is exposed at the dam abutments and in the reservoir area. Rock mass properties including the deformation modulus and uniaxial compressive strength were calculated using different rock mass classification systems (RMR, Q, GSI and DMR). Laboratory tests indicate that joint filling materials contain clay with low to high plasticity (CL to CH) and low to medium potential swelling pressures. X-ray diffraction analysis confirms that the reason for potential swelling of joint fillings is the existence of clay minerals (such as illite and montmorillonite). The study results about the shear strength of clay-filled joints show that under JRC–JCS condition (laboratory scale), JRC _n –JCS _n (large scale) and normal stress equal to 0.25–4 MPa, the range of shear strength of clay-filled joints will be equal to 0.2–2.17 and 0.14–1.72 MPa. In some areas dissolution along the joints results in high permeability, especially in the right abutment. Three dominant joint sets occur in the exploration galleries which have been excavated in the right abutment. The maximum aperture of these joints varies from 7 to 9 cm, and the joints are typically filled with clay. Preliminary analysis shows that the presence of open joints which will cause seepage of water, combined with the impact of the clay-filled joints and forces acting on the slopes, could lead to slope failures and rock falls. In addition, the assessment of slope stability results in abutments using limited equilibrium method and Swedge software under dynamic and static conditions shows that two wedges formed on the slopes of the abutment by the natural joints are potentially unstable. The rock wedge on the left abutment is smaller but presents higher sliding potential. In addition, there is no probability of planar failure due to the geological condition of the dam abutments. This paper summarizes the site investigation and subsequent analysis, which resulted in a recommendation not to construct this site. We offer some potential mitigation plans to consider if a dam were to be built at this site.     

Analysis on the disaster mechanism of rock collapse of M4.4 reservoir-induced earthquake on January 17, 2010, at Dongjing reservoir in Guizhou Province,China

Dongjing reservoir with storage capacity of 955 million m³ and 150 m dam height had been set up in Guizhou province, southeastern China on May in 2005. After filling with water in August 20, 2009, the reservoir-induced earthquake in 20 km took place first in September 2009 at the 440 m water level. When the water level changes, the number of earthquakes is increased rapidly. On January 17, 2010, the largest M 4.4 earthquake with depth of 7 km has happen and month frequency achieved 21 events at the highest water level. M 4.4 earthquake caused rock collapse with the disaster of killed six people and nine injure. After our investigation and study, the reason of higher epicentral intensity of earthquake was the surface effect of near-field elastic wave transmission. The disaster of rock falls certainly depended on the very very shallow earthquake, the height of valley and fault. Comparing as same magnitude of natural earthquake, very shallow earthquake increased 1–2° of epicentral intensity I₀, more than twice amplitude of S-wave at 200 m height of valley and the largest displacement on fault. The superposition of three factors has increased the epicentral intensity of earthquake and directly caused rock collapse with the disaster of killed six people and nine injure.