Predicting cumulative sediment depostition in large reservoirs

Sediment deposition and its accumulation in a large resorvoir depends on the inflow and reservoir storage content, respectively. Because of this fact it is possible to model the cumulative deposition of sediment as an additive process defined on a bivariate Markov chain. Using the bivariate Markov chain model the mean and variance of the cumulative deposition of John Martin Reservoir, Colorado, U.S.A. are estimated and compared with observed sedimentation data.     

Predicting cumulative sediment depostition in large reservoirs

Sediment deposition and its accumulation in a large resorvoir depends on the inflow and reservoir storage content, respectively. Because of this fact it is possible to model the cumulative deposition of sediment as an additive process defined on a bivariate Markov chain. Using the bivariate Markov chain model the mean and variance of the cumulative deposition of John Martin Reservoir, Colorado, U.S.A. are estimated and compared with observed sedimentation data.     

Evidence of karst from behaviour of the Asmari limestone aquifer at the Khersan 3 Dam site,southern Iran

Abstract

The Asmari limestone formation is the major aquifer system at the Khersan 3 Dam site, Zagros, Iran. Characterization of the aquifer system and study of karst development are essential for forecasting leakage potential and to plan remediation works. The aquifer functioning and karst structure were evaluated by geology, well hydrodynamics and natural tracing studies, showing one unconfined and three artesian sub-aquifers, the last being characterized by rapid flow, with contributing old recharge water, and a recharge at higher elevation than the unconfined sub-aquifer. The anticline structure outcrops the artesian sub-aquifers downstream of the site. The confining layers disappear and the aquifer system discharges as a mix of all groundwater. Artesian groundwater is estimated to contribute about 80% (dry season) and 50% (wet season) of flow in the mixing zone. Very few karst features are observed in cores and galleries at the site, despite some karst landforms in the reservoir area. However the aquifer exhibits fast flow of karst type in the artesian sub-aquifers.     

Sediment yield and delivery in the blanket peat moorlands of the southern Pennines

In contrast to much previous research on blanket peat moorland, which has concentrated upon studies of the form and causes of gully erosion, this paper attempts to investigate sediment transport and to estimate both short-term and long-term sediment yields in such terrain. The research was conducted on Wessenden Head Moor to the west of Huddersfield, Yorkshire, where automatic stream sampling continued over a period of two years. Use of corrected rating curves (Ferguson, 1988) provided a mean estimate of sediment yield over this period of 55 t km^?2 yr^?1. In addition an estimate of longer-term sediment yield was derived from four reservoir sediment surveys in the Wessenden Valley. Total yield was 203.69 t km^?2 yr^?1, including an organic fraction of 38.82 t km ^?2 yr^?1. Stream sampling at three sites on Shiny Brook, including headwaters and the outflow to the reservoir, suggested that there is great temporal and spatial variability in mineral and organic inputs to the reservoirs. Although not excessive in gravimetric terms, the low density of peat means that there is a serious erosion problem. Estimates of erosion rates for the peat gully network at Shiny Brook appear to confirm earlier evidence concerning the relatively recent occurrence of this erosion, within the last two centuries.     

Background Concentrations of Nickel in the Sediments of the Carpathian Dam Reservoirs (Southern Poland)

The background nickel (Ni) concentrations in the sediments of two sub‐mountain reservoirs (Dobczyce and Czorsztyn) situated in the Carpathian Flysh (southern Poland) were evaluated. Ni concentrations (15.6–83.1 µg g^?1 dry wt.) in both reservoir sediments were affected mainly by the high background content of Ni in the surrounding watershed. Distribution of elevated Ni concentrations mostly revealed an impact of long‐range transport influenced by the flow of the main tributary. Ni spatial pattern was mainly influenced by mineral compounds of Fe, Mn, and Al, and to a lesser degree by organic matter content and silt and clay fractions of the sediments of both investigated reservoirs. Spatial distribution was additionally modified by hydrological conditions (flood events and course of the old river‐bed). In both reservoirs, substantial portions of Ni were bound to potentially immobile phases, i.e., moderately reducible and residual phases (64–82% in total). Laboratory experiments showed that changes in pH affected Ni leaching from the sediment to a small degree (at pH ～3 up to 19.9%). Our results indicated that Ni in these reservoirs has low mobility and, therefore, poses a low toxicological risk to aquatic organisms.     

瀑布沟水库区域地震的重新定位

利用双差定位方法对瀑布沟水库区域内2006-10-13~2013-07-31之间发生的3 784个地震进行了重新定位,获得了3 601个地震的重新定位结果,到时残差平均为0.12 s,E-W、N-S和U-D三个方向上平均定位误差分别为0.15 km、0.17 km和1.10 km。重新定位结果显示,在研究区域内的西南方向和水库流域,地震分布密集,这个区域处于鲜水河断裂中南段、安宁河断裂北段和大凉山断裂北段的位置,此区域内地震震源深度主要分布在5~30km间,表明该区域的地震主要是构造活动引起的,而水库库区内地震震源深度主要分布在0~5 km区间,分布比较集中,该地区的地震为水库诱发和人工爆破引起的地震。     

近断层水库大坝的震后变形问题分析

本文以拟建水库大坝为例计算了位于断层附近的坝址区在发生6~7级地震时的位移、应变和应力。结果表明这种位移、应变和应力都达到很大的值,对于近断层的重大工程设施必须考虑断层发震产生的震后变形引起的“抗断问题”。     

Safety of Italian dams in the face of flood hazard

Most rivers in Italy are segmented by dams that need rehabilitation because of (1) safety requirements by increasingly risk-averse societies, (2) changes in the downstream river and riparian system after dams building, (3) poor initial design at the time of completion and (4) modified priorities of watershed management. Safe design of flood spillways is a major concern, and requires to cope with low frequency flood hazard. One must estimate flood figures with high return periods (R ⩾ 1000–10,000 years) but statistical methods involve large uncertainties because of the short length of the available records. This paper investigates the return period of the design flood of existing spillways R_S of large dams in Italy. We used re-normalized flood frequency approach and regionalization using the Generalized Extreme Value distribution. The estimation of the site specific index flood is carried out by simple scaling with basin area at the regional level. The result show that 55% (245) of the 448 examined dams are equipped by spillway with R_S > 10,000; and 71% (315) of the dams have R_S > 1000. Conversely, 29% (130) of the dams display R_S < 1000 years, lower than acceptable hazard. The spillway of 14% (62) of the dams has R_S < 100 years, indicating potential exceedance of spillways capacity. Reservoir routing may dampen the outflow hydrograph, but one should carefully account for the need of achieving accurate dam safety assessment of these dams based on site specific investigations, also accounting for global change forcing.     

龙潭水库诱发地震震源参数分析

利用广西龙滩水库地震台网记录的数字地震波资料,用波谱分析方法计算了龙滩水库库区ML2．5—4．5级共计95个地震的震源参数。并对震源参数进行分析,结果表明：库区视应力的范围在0-3．5巴之间,2007年7月17日库区最大4．5级地震的视应力最大,为3．07巴。视应力随震级的增大呈幂函数增大趋势,两者的拟合关系为：σap...     

高密度电阻率法在水库堤坝隐患探测中的应用效果分析

介绍了高密度电阻率法的原理、野外采集数据的方法以及资料解释等基本理论。通过对某水库大坝探测成果的分析，说明了高密度电阻率法在堤坝隐患探测中的可行性和有效性；提出用高密度电阻率法探测构造地裂缝的设想。     

面板堆石坝的地质雷达检测

面板堆石坝以其建设周期短,投资少的优点而在为当今国际上一种较广泛的坝型。但其渗漏较严重是一个亟待解决的问题,我们采用地质雷达的方法,利用不同天线组合,以渗漏通道介电性质差异为目的进行探测,并追踪确定渗漏通道。实践证明,该方法能有效地确定渗漏部位和渗漏通道,该资料为堵漏和工程施工提供重要依据。     

Reservoir-induced seismicity in Karun III dam (Southwestern Iran)

Statistical analyses of the Karun III reservoir seismicity reveal a remarkable correlation between seismicity rate and water-level harmonic changes. It seems that seismicity in this dam depends on rapid water-level changes. The three biggest earthquakes of Karun III, measuring 4, 4.1, and 4.3 on the Richter scale (ML), occurred after two stages of rapid filling of the dam on March 22, 2005 and May 12, 2006. These earthquakes happened when the water reached the maximum operational level. Since the beginning of filling the reservoir on November 8, 2004 until March, 2006, most reservoir-induced seismicity has been localized in three main clusters. The majority of the earthquakes occurred in the frontal anticline of Keyf Malek; the second and third clusters happened near Karun Blind Fault (KBF) and Mountain Front Fault (MFF), respectively. Filling Karun III reservoir immediately led to an increase in the occurrence of earthquakes. Further, following abrupt water-level changes, a considerable increase in the number of earthquakes is observed. Finally, in terms of seismicity rate, vertical and horizontal migration, magnitude, and distance, the earthquakes of Karun III behave differently.     

水下爆破对大坝影响的离心模拟试验研究

由于离心机能够在原型应力条件下模拟爆破对大坝的影响。本文使用中国水利水电科学研究院研制的离心模拟爆破系统,在不同重力加速度之下研究了在不同水深,距坝面不同距离的情况下雷管爆破对于大坝的影响。     

The impact of the Three Gorges Dam on summer streamflow in the Yangtze River Basin

The Three Gorges Dam is the world's largest capacity hydropower station located in the Hubei province along the Yangtze River in China, which began operations in 2003. The dam also functions to store and regulate the downstream releases of water in order to provide flood control and navigational support in addition to hydropower generation. Flow regulation is particularly important for alleviating the impacts of low- and high-flow events during the summer rainy season (June, July, and August). The impact of dam operations on summer flows is the focus of this work. Naturalized flows are modelled using a canonical correlation analysis and covariates of subbasin-scale precipitation resulting in good model skill with an average correlation of 0.92. The model is then used to estimate natural flows in the period after dam operation. A comparison between modelled and gauged streamflow post 2003 is made and the impact of the dam on downstream flow is assessed. Streamflow variability is found to be strongly related to rainfall variability. An analysis of regional streamflow variability across the Yangtze River Basin showed a mode of spatially negatively correlated variability between the upper and lower basin areas. The Three Gorges Dam likely mitigated the occurrence of high-flow events at Yichang station located near the dam. However, the high flow at the remaining stations in the lower reach is not noticeably alleviated due to the diminishing influence of the dam on distant downstream flows and the impact of the lakes downstream of the dam that act to attenuate flows. Three types of flow regime changes between naturalized and observed flows were defined and used to assess the changes in the occurrence of high- and low-flow events resulting from dam operations.     

Numerical simulation of sedimentation processes in reservoirs as a function of outlet location

This paper builds on a recently published one-dimensional moving-boundary model of the coevolution of topset, foreset and bottomset in a reservoir that captures the dynamics of the internal muddy pond typical to reservoirs. This model was modified to account for different outlet locations at the reservoir＇s downstream end. This model considers a river carrying two sustained phases of sediments： coarse （sand） and fine （mud）. The coarse phase deposits in the topset and delta foreset, while the fine phase forms a dilute suspension of wash load in the river. As the river enters the reservoir, the muddy water plunges on the foreset to form a Froude-supercritical （purely depositional） turbidity current. This turbidity current emplaces the bottomset. The modified numerical model was tested against five laboratory experiments previously reported by the author. The model successfully locates the muddy-water/clear-water interface. In addition, modeled and measured bed deposits are in good agreement. Results clearly indicate that the location of the internal hydraulic jump plays a key role in the final bed deposit.     

基于遗传算法优化神经网络权值的大坝结构损伤识别

针对传统 BP 神经网络存在着容易陷入局部极小点、训练时间太长等缺点,本文采用基于浮点编码的遗传算法,对 BP 神经网络的初值空间进行了遗传优化。用基于浮点编码的遗传算法来优化 BP 神经网络的权值,可得到最佳初始权值矩阵,并按误差前向反馈算法,沿负梯度搜索进行网络学习。文中以混凝土重力坝结构作为算例,用结构的模态频率变化作为网络的输入向量,结构的损伤位置作为输出向量,对网络进行了训练。仿真结果表明：遗传 BP 神经网络的收敛和诊断能力优于传统 BP 神经网络,可有效地运用到大坝结构的健康诊断与损伤识别中。     

长江三峡工程库首区胡家坪 M_S4.1水库诱发地震研究

本文在系统收集有关资料并对地震现场进行考察的基础上,分析了2008年11月22日发生在秭归县归州镇香溪村胡家坪 M_S4.1级地震及其发生的地质-水文地质与地震活动背景条件,介绍了地震灾害. 并进一步讨论了相关的地震前兆异常、地震成因等科学问题,认为该地震是在水库水体荷载与库水下渗的共同作用下沿仙女山断裂发生的构造型水库诱发地震, 并认为震前有一定的前兆异常,这个地震的发生除了水库蓄水作用之外,可能还与汶川地震对该区应力场的影响有关.     

Distribution of erosion intensity in the Jingjiang reach influenced by the Three Gorges Dam

Elucidation of the fluvial processes influenced by dams provides better understanding of river protection and basin management. However, less attention has been given to the erosion intensity distribution of riverbeds and its association with channel morphology and hydrological conditions. Based on hydrological and topographic data, the spatial and temporal distributions of erosion intensity (2002–2014) influenced by the Three Gorges Dam (TGD) were analyzed for the Jingjiang reach of the Yangtze River. The mechanisms underlying the distribution of erosion intensity in response to hydrological conditions were investigated. The results are as follows: (1) The erosion intensities of different discharges were not uniform, and moderate flow (10 000–27 000 m³/s) produced the largest erosion magnitude among all flow ranges. Owing to the hydrological changes caused by flood reduction and prolongation of moderate flow duration after the TGD began operating, up to 70% of the erosion amount was caused by moderate flows. (2) The lateral distribution of erosion intensity was extremely uneven, as the proportion of cumulative erosion of the low‐flow channel within the bankfull channel reached 88% in 2013. This caused the channel to become narrower and deeper. (3) The longitudinal distribution of erosion intensity was inhomogeneous. The erosion intensity in the wide reaches was greater than that in the narrow reaches, leading to smaller differences in channel morphology along the river. (4) Changes in hydrological conditions influenced by the TGD, significant reduction of sediment concentration along with flood abatement, and increased duration of moderate flow discharges were the main factors affecting erosion distribution in the post‐dam period. Our conclusions can be applied to the Yangtze River as a basis for riverbed change estimations, and river management strategies. Copyright © 2018 John Wiley & Sons, Ltd.     

紫坪铺水库地震监测预测

紫坪铺水库微震台网已经运行逾6年,强震台网已经运行逾3年,水库蓄水逾4年。2006年10月水磨突发ML1.4级微小地震群,库区及附近和库坝区地震活跃,依据监测研究较准确预测了2006年11月至2007年2月的水磨ML2.5级地震群。研究认为ML2.5级地震群是蓄水初期诱发的一些浅表卸荷型或岩溶塌陷型小地震。2008年5月12日汶川8级特大天然地震发生在微震台网监测范围内,水库微震台网和强震台阵的运行正常,为政府抗震救灾有效决策提供了科学依据,为稳定社会发挥了作用。