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1.
Large dam construction for irrigation, hydropower, water supply, and flood control in tropical to sub-tropical areas increased markedly after 1950. Many of the dams built during this period have filled with sediment and no longer perform to their original design specifications; in many cases, forecast dam life was greatly overestimated. This study investigates the useful life of Burdekin Falls Dam (BFD), northeastern Australia and compares the findings with other tropical reservoirs. Using two independent methods it is estimated that between 61 and 65 million m3 of sediment has been deposited in the reservoir over the 24 years of operation through 2011. This sediment volume equates to an average of 0.15% of capacity lost per year since construction was completed. If current sediment loads/climate regimes persist, reservoir capacity will be reduced by 50% after 345 years. However, the useful life of the BFD reduces to just 276 years when drawdown data are considered; these data show reservoir use would be affected once 40% of storage was filled with sediment, with a 60% drawdown return period of 1 in 15 years. When compared to similar large tropical to sub-tropical reservoirs, the BFD has a slightly longer reservoir useful life than dams in India and a much longer half-life than for both similar-sized and larger dams in China, Brazil, and Iran. Properties of the BFD that promote a longer useful life include a lower trap efficiency, relatively low annual sediment load delivered to the reservoir, limited sediment deposition behind the dam wall (and uniform distribution of deposited sediment), and the export of highly turbid annual floodwaters before settling and deposition of any remaining sediment within the reservoir.  相似文献   

2.
Introduction During and before the construction of the Three Gorges Project, the annual observation was continuously undertaken by the Three Gorges gravity observation network established around the head area of the reservoir (the section between Sandouping and Badong). This network has pro-vided substantial high precise data related to seismic activity. However, the annual gravity survey together monitoring of the existed observation stations can hardly effective monitor some potential sei…  相似文献   

3.
通过对水口水电站重力坝强震反应台站在古田地震中获取的强震反应观测资料进行信噪比、反应谱和功率谱分析,得到如下结论:①大坝在0.7～15 Hz频率段的振动特性较为可信;②坝基和自由场输入地震动富于高频,峰值加速度反应谱存在较大差异;③坝基输入地震动存在差异性,建议今后此类大坝抗震设计时考虑多点地震动输入;④单个卓越频率携带的能量对反应谱影响不大,反应谱是和输入地震动总能量相关的;⑤坝体刚度较大,此次地震中还处于线弹性状态。初步了解了强震记录的地震动特性和大坝结构的抗震性能,对认识水库地震近场地震动特性和重力坝地震反应有一定的参考意义。  相似文献   

4.
This paper presents a new hazard-consistent ground motion characterization of the Itoiz dam site, located in Northern Spain. Firstly, we propose a methodology with different approximation levels to the expected ground motion at the dam site. Secondly, we apply this methodology taking into account the particular characteristics of the site and of the dam. Hazard calculations were performed following the Probabilistic Seismic Hazard Assessment method using a logic tree, which accounts for different seismic source zonings and different ground-motion attenuation relationships. The study was done in terms of peak ground acceleration and several spectral accelerations of periods coinciding with the fundamental vibration periods of the dam. In order to estimate these ground motions we consider two different dam conditions: when the dam is empty (T?=?0.1?s) and when it is filled with water to its maximum capacity (T?=?0.22?s). Additionally, seismic hazard analysis is done for two return periods: 975?years, related to the project earthquake, and 4,975?years, identified with an extreme event. Soil conditions were also taken into account at the site of the dam. Through the proposed methodology we deal with different forms of characterizing ground motion at the study site. In a first step, we obtain the uniform hazard response spectra for the two return periods. In a second step, a disaggregation analysis is done in order to obtain the controlling earthquakes that can affect the dam. Subsequently, we characterize the ground motion at the dam site in terms of specific response spectra for target motions defined by the expected values SA (T) of T?=?0.1 and 0.22?s for the return periods of 975 and 4,975?years, respectively. Finally, synthetic acceleration time histories for earthquake events matching the controlling parameters are generated using the discrete wave-number method and subsequently analyzed. Because of the short relative distances between the controlling earthquakes and the dam site we considered finite sources in these computations. We conclude that directivity effects should be taken into account as an important variable in this kind of studies for ground motion characteristics.  相似文献   

5.
The dynamics of a coupled concrete gravity dam-intake tower–reservoir water–foundation rock system is numerically studied considering two hollow slender towers submerged in reservoir of gravity dam. The system is investigated in the frequency-domain using frequency response functions of the dam and the towers, and in the time-domain using time-history seismic analysis under a real earthquake ground motion. The analyzes are separately conducted under horizontal and vertical ground motions. The coupled system is three-dimensionally modeled using finite elements by Eulerian–Lagrangian approach. It is shown that presence of the dam significantly influences the dynamic response of the towers under both horizontal and vertical excitations; however the dam is not affected by the towers. When the dam is present in the model, the water contained inside the towers has different effects if the foundation is rigid, but it alleviates the towers motion if the foundation is flexible. It is concluded that the effects of foundation interaction are of much importance in the response of tall slender towers when they are located near concrete gravity dams.  相似文献   

6.
Lewis and Clark Lake is located on the main stream of the Missouri River. The reservoir is formed behind Gavins Point dam near Yankton, South Dakota, U.S.A. The Lewis and Clark Lake reach extends about 40 km from the Gavins Point dam. The reservoir delta has been growing since the closure of Gavins Point dam in 1955 and has resulted in a 21% reduction of storage within the maximum pool of the reservoir. Among several sediment management methods, drawdown flushing has been recommended as a possible management technique. The engineering viability of removing sediments deposited in the lake should be examined by numerical modeling before implementing a drawdown flushing. GSTARS4 was used for this study and calibrated by using measured data from 1975 to 1995. Channel cross-section changes and amount of flushed sediment were predicted with four hypothetical flow scenarios. The flushing efficiencies of all scenarios were estimated by comparing the ratios between water consumption and flushed sediment during flushing.  相似文献   

7.
A finite element method for the dynamic analysis of concrete gravity dams is presented. Displacement based formulation is used for both fluid and structural domains. During severe ground motion, the impounding fluid in the reservoir may separate from the dam and cause forming of micro bubbles. As a result, the compressibility of water is reduced. This nonlinear phenomenon of the reservoir is termed cavitation. When the direction of the ground motion is changed, the micro bubble's region of fluid collapses, and an impact will occur. By using different damping ratios in the fluid and solid domains the spurious oscillations which were caused by the impact are removed. The cavitation is confined to the upper part of the reservoir, where it has an effect of paramount importance on the tensile stresses. To illustrate the cavitation effect, the response of the non-overflow monolith of the Pine Flat dam subjected to the first 6.5 s of the May 1940 El-Centro, California earthquake, is considered. In order that the cavitation phenomenon take place more widely, maximum acceleration was scaled to give an amplitude of 1 g.  相似文献   

8.
We analyze the ground motion time histories due to the local seismicity near the Itoiz reservoir to estimate the near-source, surface 3D displacement gradients and dynamic deformations. The seismic data were obtained by a semipermanent broadband and accelerometric network located on surface and at underground sites. The dynamic deformation field was calculated by two different methodologies: first, by the seismo-geodetic method using the data from a three-station microarray located close to the dam, and second, by single station estimates of the displacement gradients. The dynamic deformations obtained from both methods were compared and analyzed in the context of the local free-field effects. The shallow 1D velocity structure was estimated from the seismic data by modeling the body wave travel times. Time histories obtained from both methods result quite similar in the time window of body wave arrivals. The strain misfits between methods vary from 1.4 to 35.0 % and rotational misfits vary from 2.5 to 36.0 %. Amplitudes of displacement gradients vary in the range of 10?8 to 10?7 strains. From these results, a new scaling analysis by numerical modeling is proposed in order to estimate the peak dynamic deformations for different magnitudes, up to the expected maximum M w in the region (M5.5). Peak dynamic deformations due to local M w5.5 earthquakes would reach amplitudes of 10?5 strain and 10?3 radians at the Itoiz dam. The single station method shows to be an adequate option for the analysis of local seismicity, where few three-component stations are available. The results obtained here could help to extend the applicability of these methodologies to other sites of engineering interest.  相似文献   

9.
基于正交展开的非平稳随机地震动模型,并考虑混凝土材料的非线性和坝体与库水之间的流固耦合,对印度Koyna重力坝进行有限元分析,得到坝顶水平位移和坝颈拉应力,结合概率密度演化方法和等价极值事件的思想,获得丰富的概率信息。这为坝体结构的随机地震反应分析和可靠度研究提供新的途径。  相似文献   

10.
A procedure is presented to analyse the response of concrete gravity dams due to horizontal and vertical earthquake ground motion components considering dam-water interaction and partial absorption of hydrodynamic pressure waves at the reservoir bottom into the foundation medium. The effects of reservoir bottom absorption on the hydrodynamic force on a rigid dam are examined first. The harmonic response of an idealized dam cross-section is presented for a wide range of parameters characterizing the properties of the dam, the impounded water and the foundation medium. Based on these frequency response functions the effects of dam-water interaction and of reservoir bottom absorption in the response of dams due to horizontal and vertical components of ground motion are investigated.  相似文献   

11.
新疆克孜尔水库诱发地震的形成条件和诱发机制问题初探   总被引：1，自引：0，他引：1  
翟世龙 《内陆地震》2002,16(1):89-96
克孜尔水库自 1991年 8月下闸蓄水后 ,穿过水库大坝的 F2 活断层 (克孜尔活断层 )出现了水平和垂直形变的特大异常变化。分析后认为是前期水库施工开挖土石方、填筑土石方及水库蓄水引起地面负荷变化的综合效应所致 ,同时地震活动规律也产生了与形变同步的异常变化。综合测震、水文、地质分析认为 :1水库蓄水可以诱发地震 ,震级主要在 MS3.0级以下 ;2蓄水诱发 F1活断层 (却勒塔格活断层 )上中等地震的可能性比较大 ,而诱发 F2 活断层上中等地震的可能性则很小  相似文献   

12.
On December 4, 1983 an eruption started at vents located 1.5 km southwest of the summit of Piton de la Fournaise at the base of the central cone. After 31 months of quiescence this was one of the longest repose period in the last fifty years. The eruption had two phases: December 4 to January 18 and January 18 to February 18. Phase 1 produced about 8 × 106 m3 of lava and Phase II about 9 × 106 m3. The erupted lava is an aphyric basalt whose mineralogical and geochemical composition is close to that of other lavas emitted since 1977.The precursors of the December 4 outbreak were limited to two-week shallow (1.5–3 km) seismic crisis of fewer than 50 events. No long-term increase was noted in the local seismicity which is very quiet during repose periods and no long-term ground inflation preceded the eruption. Outbreaks of Phases I and II were preceded by short (2.5 hours and 1.5 hours) seismic swarms corresponding to the rise of magma toward the surface from a shallow reservoir. Large ground deformation explained by the emplacement of the shallow intrusions, was recorded during the seismic swarms. A summit inflation was observed in early January, before the phase II outbreak, while the phase I eruption was still continuing.Piton de la Fournaise volcanological observatory was installed in 1980. Seismic and ground deformation data now available for a period of 4 years including the 1981 and the 1983–1984 eruptions, allow us to describe the physical behavior of the volcano during this period. These observations lead us to propose that the magma transfer from deep levels to the shallow magma reservoir is not a continuous process but a periodic one and that the shallow magma reservoir was not resupplied before the 1981 and 1983–1984 eruptions. Considerations on the eruptive history and the composition of recent lavas indicate that the reservoir was refilled in 1977.  相似文献   

13.
新疆克孜尔水库地震危险性预测研究   总被引：1，自引：0，他引：1  
应用库区多项形变观测资料，对克孜尔水库蓄水后出现的形变异常及诱发水库地震的危险性进行了研究。结果认为：①穿过水库大坝的F2活断层在水后出现水平和垂直形变的特大异常变化主要是前期水库施工开挖土石方、填筑土石方及水库蓄水引起地面负荷变化的综合效应所致；②克孜尔水库虽然存在诱发水库地震的潜在因素，但从库容、坝高、F2活断层产状、地质构造背景、水地质条件、岩性以及世界各国发生水库 诱发地震的充分条件；③由库区各项形变观测资料分析表明，库区地壳形变已由施工－蓄水初期时的反向异常变化恢复到了施工蓄水前的正常变化状态，各种受力因素经过调整达到了新的平衡，已进入相对稳定的继承性运动期，因此今后因蓄水诱发水库地震的可能性不大。  相似文献   

14.
三峡大坝上下游水质时空变化特征   总被引：6，自引：2，他引：4  
为探索三峡大坝上下游（坝上99.9 km、坝下63.0 km、全长162.9 km）水质时空变化特征,运用主成分分析和方差分析对2016年近坝段水质时空变化特征进行了分析.主成分分析表明,水文因子流量（Q）、气温（T）、水位（Z）和水质因子（水温（WT）、pH、电导率（EC）、溶解氧（DO）、悬浮物（SS）、高锰酸盐指数（CODMn）、硫酸盐（SO42-）、氟化物（F-）、总硬度（T-Hard）、硝态氮（NO3--N）、总氮（TN）和硒（Se））的变化主导着研究区域水质变化;各采样点主成分得分和双因素方差分析结果显示研究区域水质因子时间变化主要呈现出季节和不同水库运行时期的差异.消落期（2-5月）,T-Hard、F-、SO42-和EC是影响河流水质变化的主导因子;汛期（7-8月）,Q、SS、CODMn、NO3--N、TN和Se是影响河流水质变化的主导因子;T和WT主导着汛末（9月）河流水质变化,并引起了DO等理化特性的变化;高水位运行期（12月）,Cl-是影响河流水质变化的主导因子.现阶段,DO、有机污染物（CODMn）、无机盐（SO42-和F-）、营养盐类（NO3--N和TN）、类金属元素（Se）和水体的矿化程度（T-Hard）的变化主导着区域水质的变化,是三峡大坝近坝段水域水质的控制因子.方差分析表明,河流的理化特性（DO、pH和SS）、营养盐组分构成（NH3-N和NO3--N）、无机盐类（EC和Cl-）、石油类有机污染物及粪大肠菌群（FC）等指标在坝上与坝下断面存在显著性差异.气温、水温、降雨、含沙量的季节性影响因素和水库调度运行模式是影响近坝段水质时间差异的主要因子;空间差异主要受城区污染排放和三峡水库调度引起的坝上和坝下水文和水动力学条件差异影响.因此控制研究区域因人类活动等造成的外源性污染,并针对不同类污染物质的季节变化特征实施合理的水库运行方式是近坝段水质提升的关键.  相似文献   

15.
The linear response of an idealized concrete gravity dam monolith to harmonic horizontal or vertical ground motion is presented for a range of the important system parameters that characterize the properties of the dam, foundation rock, impounded water and reservoir bottom materials. Based on these frequency response functions, the effects of alluvium and sediments at the reservoir bottom on the response of the dam, including its interaction with the impounded water and foundation rock, are investigated. It is shown that the partial absorption of hydrodynamic pressure waves by the reservoir bottom materials has an important effect on the dynamic response of concrete gravity dams.  相似文献   

16.
李祖忠  张旭东  江聪  杜涛  曾凌 《湖泊科学》2023,35(5):1822-1831
三峡水库蓄水引起库区水位抬升,水面面积显著增加,对区域水文循环过程产生了一定影响。为揭示三峡水库蓄水前后水面面积及蒸发损失变化规律,选取三峡库区坝前至寸滩区间作为研究区,利用Landsat影像数据提取1982—2021年水面面积,分区建立水位与面积关系曲线,进而推求库区逐日水面面积。在估计三峡库区水面面积的基础上,结合站点潜在蒸发资料推求水面蒸发损失量。研究结果表明:2010年三峡水库全面运行后,坝前至寸滩库区平均水面面积由蓄水前的372.96km2,增加到761.31km2,较蓄水前增加了1.04倍。同时,三峡水库的蓄泄调节改变了库区河段原有的水文节律,使得库区水面面积的季节性变化特征较蓄水前发生了显著变化。蓄水后,冬季水面面积最大,平均为843.81km2,较蓄水前增加了1.89倍;秋季、春季次之,水面面积分别为818.73和735.28km2,较蓄水前分别增加了97.17%和1.28倍;夏季水面面积最小,为653.03km2,较蓄水前仅增加了39.06%。水库全面运行后,...  相似文献   

17.
三峡水库澎溪河消落区土-气界面CO2和CH4通量初探   总被引：1，自引：0，他引：1  
李哲  张利萍  王琳  郭劲松  高旭  方芳  蒋滔 《湖泊科学》2013,25(5):674-680
水库近岸湿地(消落区)温室气体(CO2、CH4)产汇是水库温室气体效应问题的重要组成部分.本文以三峡水库支流澎溪河的白家溪、养鹿两处大面积消落区为研究对象,于2010年6 9月水库低水位运行期间,对近岸消落区土-气界面CO2、CH4通量进行监测.白家溪消落区土-气界面CO2通量均值为12.38±2.42 mmol/(m2·h);CH4通量均值为0.0112±0.0064 mmol/(m2·h).养鹿消落区CO2、CH4通量均值分别为10.54±5.17、0.14±0.16 mmol/(m2·h).总体上,6 9月土-气界面CO2通量呈增加趋势,而CH4通量水平呈现显著的递减趋势.消落区土地出露后植被恢复,在一定程度上促进了土壤有机质含量的增加,使得6 9月CO2释放通量的总体趋势有所增加.消落区退耕后,其甲烷氧化菌的活性得到恢复,加之在土地出露曝晒过程中土壤透气性增强,使得消落区土壤对大气中CH4吸收氧化潜势增强.尽管如此,仍需进一步的研究以明晰消落区土-气界面CO2、CH4产汇的主要影响因素.  相似文献   

18.
The reservoir of Fierza on the Drini River, Northern Albania, is Albania's largest reservoir and it is one of the world's largest reservoirs of high dams (reservoir volume at maximum water level, 2.8 * 109 m3; dam height, 167 m and dam capacity 8 * 106 m3). We compare pre-and postimpounding seismicity of the area surrounding the Fierza reservoir. An increase of seismic microactivity was observed after the impounding of the reservoir. More than 300 microearthquakes, occurred in the immediate vicinity of the main body of the reservoir, with local magnitude ranging between 1.3 and 3.6. A significant change of theb value in the magnitude-frequency relationship was observed. One swarm of microtremors occurred in the northern part of the reservoir on April 4–5, 1981, where an alteration of the tensor of natural tectonic stresses is revealed. The theoretical additional stress and displacement induced by water-load in the bank of the reservoir were estimated for four cross-profiles of the reservoir area and the maximum values resulted near the location of the above swarm.  相似文献   

19.
The linear response of a selected arch dam to harmonic upstream, vertical or cross-stream ground motion is presented for a wide range of the important system parameters characterizing the properties of the dam, foundation rock, impounded water and reservoir boundary materials. Based on these frequency-response functions, the dam-foundation rock interaction effects in the dynamic response of arch dams are investigated.  相似文献   

20.
张永岗 《内陆地震》2003,17(4):332-336
利用动态平差原理，处理了克孜尔水库水准监测网的14期跨断层流动水准资料，对穿过库区主坝、副坝之间F2断层的形变机制进行了初步研究。结果表明F2断层的活动属继承性活动，其活动方式为小幅度蠕变。这种活动方式对库区应力集中起到了解除的作用。  相似文献   

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