Failure mechanism of a large-scale composite deposits caused by the water level increases

The failure of slope caused by variations in water levels on both banks of reservoirs is common.Reservoir landslides greatly threaten the safety of reservoir area.Taking large-scale composite deposits located on the Lancang River in Southwest China as a study case,the origin of the deposits was analyzed based on the field investigation and a multi-material model was established in the physical model test.Combined with numerical simulation,the failure mechanism of the composite deposits during reservoir water level variations was studied.The results indicate that the deformation of the large-scale composite deposits is a staged sliding mode during the impoundment process.The first slip deformation is greatly affected by the buoyancy weight-reducing effect,and the permeability of soil and variation in the water level are the factors controlling slope deformation initiation.The high water sensitivity and low permeability of fine grained soil play an important role in the re-deformation of deposits slope.During the impoundment process,the deformation trend of the deposit slope is decreasing,and vertical consolidation of soil and increasing hydrostatic pressure on the slope surface are the main reasons for deformation attenuation.It is considered that the probability of large-scale sliding of the deposits during the impoundment period is low.But the damage caused by local bank collapse of the deposit slope still needs attention.The results of this paper will further improve our understanding of the failure mechanism of composite deposits caused by water level increases and provide guidance for the construction of hydropower stations.

Numerical Simulation of Water-Air Two-Phase Flow in Soil Slope under Water Level Rise Condition

In order to simulate the unsteady seepage in soil slopes under water level rise condition, including water seepage and air seepage, and to investigate the influence of the capillary pressure on the slope safety coefficient, the water-air two-phase flow model was used and its solving method and definition condition were given. By the two-phase flow model, the pore air and pore water seepage of a soil slope under steady seepage and water level rise conditions were shown, and the slope stability in different cases was analyzed from the simulation results. We find that under water level rise condition, the pore air pressure in the unsaturated zone increased evidently and the capillary pressure should be considered while the pore air pressure can be neglected in slope stability analysis.

IMPACTS OF FUTURE SEA LEVEL RISE ON SALT WATER INTRUSION IN THE CHANGJIANG RIVER ESTUARY

Sea level rise could increase the salinity of an estuary by altering the balance between fresh water and salt water. The implications of sea level rise for increasing salinity have been examined in the Changjiang (Yangtze) River estuary. By correlative analysis of chlorinity, discharge and tidal level and calculation of two-dimensional chlorinity, distribution of the Changjiang River estuary, the changes of the intensity and lasting hours of salt water intrusion at Wusong Station and the changes of chlorinity distribution in the South Branch of the Changjiang River estuary have been estimated when future sea level rises 50-100 cm. The intensity of salt water intrusion in the future will be far more serious than current trend.

Saline Intrusion Response to Sea Level Rise and Its Implications on Water and Coastal Management: A Case Study in Brazil

Global temperature is predicted to increase in the end of the century and one of the primary consequences of this warming is the sea level rise. Considering the vulnerabilities on coastal systems and water resources, it is important to evaluate the potential effects of this rising in coastal areas, since the saline intrusion on rivers would be intensified, leading to problems related to water quality. In this context, the present work aimed to verify saline intrusion changes along an important river, S&#227o Francisco Canal, located in Rio de Janeiro State, Brazil. For this purpose, a hydrodynamic modeling was performed using SisBaHiA, considering different sea levels and tide conditions. According to the results, it was verified the intensification on saline intrusion and higher salinity values due to a sea level rise of 0.5 m. These results show that new licenses for water withdrawals must be carefully analyzed as the fluvial flow plays an important role to contain the saltwater intrusion on the studied river. Accordingly, it is recommended the evaluation of climate change effects in order to choose best strategies to reduce coastal vulnerability, and the use of this theme on environmental licensing and territorial planning, integrating water planning with coastal management.

Estimation of Peak Water Level in Pearl River Estuary under the Background of Sea Level Rise

[Objective] The study aimed to predict the peak water level in Pearl River Estuary under the background of sea level rise. [Method] The changing trends of peak water level at Denglongshan station and Hengmen station were analyzed firstly on the basis of regression models, and then sea level rise in Pearl River Estuary in 2050 was predicted to estimate the 1-in-50-year peak water level in the same year. [Result] Regression analyses showed that the increasing rate of peak water level over past years was 6.3 mm/a at Denglongshan station and 5.8 mm/a at Hengmen station. In addition, if sea level will rise by 20, 30 and 60 cm respectively in 2050, it was predicted that the 1-in-50-year peak water level will reach 3.04, 3.14 and 3.44 m at Denglongshan station, and 3.19, 3.29 and 3.59 m at Hengmen station separately. [Conclusion] The estimation of peak water level in Pearl River Estuary could provide theoretical references for water resources planning.

INFLUENCE OF SEA LEVEL RISE ON SHANGHAI ASTRONOMICAL TIDE AND STORM SURGE AND ESTIMATION OF PROBABLE WATER LEVEL

A nonlinear two-dimension dynamic model of storm surge (SS) and astronomical tide(AT) was used to investigate the effects of SS and AT on expected sea level rise (SLR) at principalcoastal stations in the Shanghai region and to estimate numerically the probable maximum water lerel for2010 - 2050. Evidence suggests tha SLR causes reduction of SS; that its influence on SS depends on theintensity and path of a tropical cyclone and the station locality; tha the SLR’s effects on AT vary periodi-cally, with the peried being the same as tha of the AT’s: and that as the SLR increment grows, its impactincreases; below mean sea level (MSL) the effect is positive at rising tide and negative at ebb tide, andvice versa for the effect above MSL. Study of the probable maximum water level (by assuming SLR, SSalong favorable tropical cyclone’s path, its possible maximum intensity and effectivee spring AT at a rangeof set paths of Cyclones 5612, 8114, 9417) showed that the probable maximum water level is 740, 745,and 751 cm in the years 2010, 2030, and 2050, respetively, over the target region.

Water Intrusion in the Chesapeake Bay Region: Is It Caused by Climate-Induced Sea Level Rise?

Sea level rise due to climate change is a contentious issue with profound geographic and economic implications. One region in the USA identified as being particularly susceptible to seal level rise is the Chesapeake Bay region, and it has been estimated that by the end of the century Norfolk, Virginia could experience sea level rise of 0.75 meters to more than 2.1 meters. Water intrusion is a serious problem in much of the Chesapeake Bay region. The question addressed here is whether this water intrusion is the result of climate-induced seal level rise or is being caused by other factors. Our findings indicate that the water intrusion problems in the region are due not to “sea level rise”, but primarily to land subsidence due to groundwater depletion and, to a lesser extent, subsidence from glacial isostatic adjustment. We conclude that water intrusion will thus continue even if sea levels decline. These findings are critical because the water intrusion problems in the Chesapeake Bay—and elsewhere—cannot be successfully solved unless their causes are correctly identified and appropriate remedies are devised. For the Chesapeake Bay region, the required remedy is the reversal of groundwater withdrawal rates, which has been used successfully elsewhere in the USA and other nations to solve water intrusion problems.

FORECAST OF IMPACTS OF SEA-LEVEL RISE ON THELOW COLONIZED ISLANDS AND THEIR SURROUNDING WATERS IN THE CHANGJIANG RIVER MOUTH

As a worldwide authoritative, IPCC forecasted in 1990 that the world- s sea level would most probably rise by 0. 66 m by the end of the 21 st century. Combined with the local depression caused by the sink of the earth’s crust and the human activity, the relative sea level in the Chanaiiang River mouth will rise by about 1. 0 m during the same peried. Based on this figure, the article forecasted the impacts of sea-level rise on the safety coefficient of coastal structures and civil facilities, loss of wetlands, flood hazard as well as water intrusion. The results show that: 1 ) 40% as large as the present engil1eering mass should be added to the coastal structures in order to maintain the safety coefficient; 2 ) a dynamic loss of 60 km2 of wetlands, as much as 15% of the present total area, would be caused; 3) to hinder the increase inflood hazard dy11amic capacity to drain water must increase by at least 34 times as large as the present; 4) to maintain the present navigation conditions, about 100 million yuan (RMB) is needed to reconstruct over 30(X) bridges and 30 sluices;and 5 ) the disastrous salt water intrusion caused by the sea-level rise could be encountered by the increase in water discharge from the Three Gorge Reservoir in the dry season.

Prediction of China's Submerged Coastal Areas by Sea Level Rise due to Climate Change

Based on the simulation with the Ocean-Atmosphere Coupled Model CCSM and Ocean Model POP under the greenhouse gas emission scenario of the IPCC SRES A2(IPCC,2001),and on the earth crust subsidence and glacier melting data,the relative sea level change is obtained along the coast of China in the 21st century.Using the SRTM elevation data the submergence of coastal low land is calculated under the extreme water level with a 100-year return period.The total flooding areas are 98.3×103and 104.9×103km2for 2050 and 2080,respectively.For the three regions most vulnerable to extreme sea level rise,i.e.,the coast of Bohai Bay,the Yangtze River Delta together with neighboring Jiangsu Province and northern Zhejiang Province,and the Pearl River Delta,the flooded areas are 5.0×103,64.1×103and 15.3×103km2in 2050 and 5.2×103,67.8×103and 17.2×103km2in 2080,respectively.

Impact of Grouting and Loading of Building Construction on the Water Level of Tangshan Mine Well

The water level rising rate of Tangshan mine well significantly accelerated in 2010,and the ascensional range was obviously higher than that of the same period in previous years.From the view of groundwater dynamics and loading effects,and based on the water pumping( pouring) water test model and semi-infinite elastic space theory model under uniform load,the effects of grouting and loading of nearby building construction on the well water level were analyzed. Results show that grouting at a distance of 200 ~ 700 m to the well,with amount of 2500m3 per day and duration of 270 d,can cause an 8 ~ 11 m rise of well water level; and loading of large-area building construction can cause about a 4m rise of well water level. Through the analysis of these factors,we find that the water level anomalous rising of Tangshan mine well was relevant to grouting and loading of the nearby building construction. This study provides a scientific basis for anomalous rising analysis of water level of Tangshan mine well.

海面上升导致泄洪延时-子牙新河案例分析

【研究目的】尽管人们普遍认为全球变化背景下的海面上升是海岸带环境变化的重要驱动因素,但对一个具体地区而言,仍缺少定量化的影响评估,以至于气候变化基础研究与海岸带实际经济社会活动之间存在日渐明显的脱节。本文是试图弥合这种脱节的一次探索。【研究方法】2023年夏秋京冀津地区大暴雨,达到了1963年之后60年一遇的量级,造成生命财产和区域经济的重大损失。本文根据子牙新河洪水闸口泄洪的具体案例,探寻海面上升潮位升高泄洪延时之间可能存在的因果关系。【研究结果】研究发现在21世纪海面上升背景下,渤海湾西岸存在潮位升高1 cm、泄洪时间减少0.02小时的潮位上升与泄洪延时之间的定量时空关系。【结论】提出潮位高于洪水位时不能泄洪的“临界点”概念,并根据联合国政府间气候变化专门委员会(IPCC)关于海面上升的最新预案,尝试做出了今后三个时间节点(2030、2040和2050年)的泄洪延时预测。

不同水位升降速率对库岸桥基边坡稳定性影响分析

为了研究库水位升降下桥基岸坡的稳定性,以西南地区某桥基岸坡为例,开展室内物理试验,并基于非饱和渗流理论,应用geostudio软件计算不同水位升降速率下桥基岸坡的渗流场、位移场与稳定性系数变化规律。结果表明:水位升降,坡内浸润线既有同步性,又有滞后性,滞后性随水位升降速率增大而增强。岸坡横向位移在水位升降时,先快速增加后缓慢减少,最大横向位移发生于桥基左侧岸坡上;水位升降速率增加,前期横向位移变化速率加快、变化幅度增大。桥基岸坡稳定性系数在水位上升时先快速增加后逐渐减小,在水位下降时先快速减小后缓慢增加。

水位升降和潮汐水位作用下围堰的安全稳定性

为了分析水位升降和潮汐水位作用下滨海区域围堰的安全稳定性,基于厦门市集美岛车站工程实例,应用Plaxis有限元程序的非饱和土渗流理论,采用有限元强度折减法,进行不同水位升降速度及潮汐水位循环作用下围堰的稳定性分析,通过围堰的安全系数变化曲线分析水位变化对围堰稳定性影响的机理。结果表明:围堰安全系数在水位升高时减小,水位上升速度越快,围堰安全系数减小速率越大;水位下降时存在临界水位降速,临界水位降速为1.0 m·d^(-1),当水位下降速度超过临界水位降速时,围堰安全系数先减小后增大,当水位下降速度小于临界水位降速时,围堰安全系数逐渐增大;围堰安全系数在落潮时增大,在涨潮时减小,潮汐振幅越大,围堰安全系数增值越大,随着循环次数的增加,相邻两次循环间围堰安全系数增量逐渐减小并趋于稳定。

Study of Water Flow in a Single Clay Crack

A model has been constructed to study water flow in a single clay crack, and a new concept of the critical rise rate of water level in the crack has been put forward. When the water level rises faster than this critical rate, the flow in a crack will increase, and vice versa. The flow in a crack is not in proportion to the water level. The maximium water flow in clay is 30-40 times smaller than that in a rock fissure under the same condition. In the process of water discharge, the flow in a crack will lessen gradually, and the crack will grow narrower by 3.0-4.0cm, with its depth reducing by over 50%.

Case analysis of water exchange between the Bohai and Yellow Seas in response to high winds in winter

Based on the data from a special project titled China's Offshore Marine Integrated Investigation and Evaluation as well as Regional Ocean Modeling Systems(ROMS)diagnostic numerical model,we studied the influence of high wind processes on the circulation and water exchange between the Bohai and Yellow Seas(BYS)in winter.The results show that the vertical structure of the Yellow Sea Warm Current(YSWC)is relatively uniform under condition of high winds,showing obvious barotropic features.However,this flow is not a stable mean flow,showing strong paroxysmal and reciprocating characteristics.A comparison of the changes in sea level suggests that the intensity of the northwards upwind flow is consistent with the abnormal fluctuations in the sea level.It indicates that the upwind flow is closely related to the water exchange between the BYS.The impact of high wind processes on the water exchange between the BYS is enormous.It can make the flux through the Bohai Strait,as well as that through the mouth of each constituent bay(i.e.,Liaodong Bay,Bohai Bay,and Laizhou Bay)far greater than usual,resulting in a significant increase in the water exchange rate.The exchange capacity,which is about 8%of the total volume of the Bohai Sea,can be completed in a few days.Therefore,the water exchange of the Bohai Sea may be completed by only a few occasional high wind processes in winter.

Impact of Tidal River Management (TRM) for Water Logging: A Geospatial Case Study on Coastal Zone of Bangladesh

Bangladesh is a floodplain dominated country. Coastal delta areas of Bangladesh convey multiple impacts of climate change worth-hit. Most of the rivers carry a huge amount of sediment from upstream piedmont area. The river bed rises due to insufficient upstream water supply. Similarly, the deposited sedimentation creates a large number of sandbars inside the river. That’s why, water logging and siltation turn into a serious problem in the south-western region of Bangladesh, especially in Satkhira, Khulna and Jessore district. In the middle of September, 2011 the Tidal River Management (TRM) project approved at the study site for four years to develop the water logging problem with basic consideration of silt management. In this circumstance, this study focused on the consequences of the TRM on water logging in the coastal area of Bangladesh. Primary and secondary data have been used. Geospatial analyses have been used following the NDWI in Arc GIS for water logging area detestation using Landsat Enhance Thematic Mapper (ETM) and Landsat Operational land Image (OLI) satellite images. The geo-spatial analysis denoted, about 5090 acres of agricultural land and about 729 acres of homestead land have been water logged during TRM implementation period.

库水位初次升降对卧沙溪滑坡粉质黏土蠕变特性的影响及其变形规律研究

以卧沙溪滑坡为研究对象,通过对该滑坡滑带土的原状土样及干湿循环处理试件进行三轴蠕变试验,分析其蠕变特性,分别建立了Merchant模型、Burgers模型和西原模型并对比分析三种蠕变模型的拟合精度;此外,基于FLAC 3D内置代码简化Burgers模型对卧沙溪滑坡变形及长期稳定性作出预测。结果表明:干湿循环会造成土体承载能力降低,蠕变变形增大,达到稳定的时间变长,且土体衰减蠕变初始阶段的应变速率增大;偏应力水平对蠕变特性的影响体现在低应力下土体经历瞬时变形,衰减蠕变和稳定蠕变阶段,中应力下和高应力下经历瞬时变形,衰减蠕变和等速蠕变阶段;Burgers模型较适用于卧沙溪粉质黏土,且自重影响下的滑坡滑体的蠕变变形主要集中在中上部凸起区域,应加强对该区域的防护。

降雨和河流水位上升作用下沿河路基边坡稳定性研究

由于山区气候多雨,强降雨和河流水位快速上升等现象时常发生,在复杂多变的降雨及河流水位作用下路基边坡极易发生失稳破坏。为了掌握降雨和河流水位上升对边坡稳定性的作用机理,确保沿河公路的安全运营,采用Midas-GTS/NX有限元分析软件建模,针对3种不同降雨工况和2种坡前水位上升速率进行边坡稳定性分析,并根据稳定性研究结果,提出坡面防渗措施。结果表明:1)降雨强度、坡前河流水位上升速率与边坡的稳定性呈负相关;2)在坡面铺设防水层可有效减少雨水渗入,提高边坡的安全系数及稳定性。

基于Visual Modflow的刘东煤矿闭坑水位回升预测

随着我国能源产业结构调整,越来越多不符合国家要求的矿井被关闭,导致我国闭坑矿井数量迅速增加,矿井闭坑后产生的老空水,会对周围矿井生产造成威胁。以淮北刘东煤矿为研究对象,使用Visual Modflow软件对矿井闭坑后的水位回升进行了预测,以此为周边矿井安全生产提供依据和保障。结果表明:随着时间的推移,闭坑矿井内的水位会不断上升,深部较快,浅部较慢,并且得出了闭坑矿井水位变化趋势,矿井回灌时间约为240 d。研究结果也为相似地质条件的矿井防治老空水提供参考。