Formation process of cover collapse sinkholes related to groundwater level decline in karst areas

The decline in groundwater level is a key factor contributing to cover collapse in karst areas.In this study,the model tests and numerical simulations are conducted to reveal the breeding process and formation mechanism of cover collapse sinkholes caused by the decline of groundwater level in karst area.Firstly,the model tests confirm that the decline of groundwater level generates negative pressure at the lower edge of overlying soil.The negative pressure experiences four distinct phases during the groundwater drawdown process:rapid rise,slow decline,rapid decline,and gradual dissipation.The maximum negative pressure is influenced by the particle size distribution of the overlying soil.Then,the numerical simulations are carried out to investigate the change process of negative pressure caused by the loss of fillers in karst pipe.The simulated results indicate that the rate of groundwater decline and the thickness and initial void ratio of the overlying soil can affect the maximum negative pressure.As groundwater level drops,a negative pressure zone forms underground,causing tensile failure in the surrounding soil and creating an arched soil hole,which weakens the support for the overlying soil.This phenomenon can also lead to the collapse of the overlying soil under its self-weight.Groundwater table decline in karst areas can result in both internal and surface collapses.When the overlying soil is thin,internal and surface collapses occur simultaneously.In contrast,for thick overlying soil,internal collapse happens first,followed by a layer-by-layer collapse,ultimately forming sinkholes.Finally,the breeding process and formation mechanism of the Yujiawan Reservoir sinkholes are discussed.Geological conditions and groundwater level decline significantly affect internal collapse in karst areas,requiring careful consideration from on-site engineers.

Effect of Sea Level Rise and Groundwater Withdrawal on Seawater Intrusion in the Gulf Coast Aquifer: Implications for Agriculture

The two main factors contributing to depletion of freshwater resources are climate change and anthropological variables. This study presents statistical analyses that are local in its specifics yet global in its relevance. The decline in Gulf Coast aquifer water quality and quantity has been alarming especially with the increased demand on fresh water in neighboring non-coastal communities. This study used seawater levels, groundwater use, and well data to investigate the association of these factors on the salinity of water indicated by chloride levels. Statistical analyses were conducted pointing to the high significance of both sea water level and groundwater withdrawals to chloride concentrations. However, groundwater withdrawal had higher significance which points to the need of water management systems in order to limit groundwater use. The findings also point to the great impact of increased groundwater salinity in the Gulf Coast aquifer on agriculture and socioeconomic status of coastal communities. The high costs of desalinization point to the increased signification of water rerouting and groundwater management systems. Further investigation and actions are in dire need to manage these vulnerabilities of the coastal communities.

Study on Establishing a Monitoring System for Groundwater in the Condition of Climate Change and Sea Level Rise： Case Study of Ma River Basin in Vietnam

The results presented in this paper are a part of the research results of the thesis ＂research on scientific basis and practice of develop a system of monitoring the impacts of climate change on surface water and groundwater＂. Case study： Ma river basin in Vietnam. The results were implemented： （i） data collection, fieldwork survey, synthesis and analysis of information and data; （ii） partitioning the influence degree of climate change and sea level rise to groundwater; （iii） determining criteria to select monitoring routes, location of monitoring groundwater in the condition of climate change and sea level rise and （iv） developing the monitoring system. The research＇s results have practical implications for the water resources management in the context of climate change and sea level rise in Ma river basin.

Economic Valuation of Sea Level Rise Impacts on Agricultural Sector: Damietta Governorate, Egypt

The Nile Delta is considered to be one of the most vulnerable river deltas to Sea Level Rise (SLR) in the world. SLR is expected to affect large agricultural areas of the Nile Delta, either through inundation or higher levels and salinity of groundwater. It could be argued that such impacts would augment the problems experienced already in the area in terms of high groundwater table and salinity levels. In order to guide policy and decision making, especially in terms of assessing the economics of various adaptation options, there is a need to provide estimates of potential economic damage that could result from such changes. The paper in hand aims to estimate the economic value of potential primary impacts of higher levels of groundwater table due to expected SLR on agriculture productivity in Damietta Governorate as one of the Nile Delta coastal governorates. To conduct such an assessment, relationship between groundwater table level and agricultural productivity was first investigated in relevant literature. This was followed by reviewing prevailing conditions in the agricultural sector in the study area. Thereafter, a regression analysis for the main crops in the study area, between crop yield and groundwater table levels, was conducted. Based on the developed regression, a GIS (Geographic Information System)-based hydrological model, and a production economic model, were employed to assess economic value of higher levels of groundwater table impacts on agriculture productivity. It was found that future accumulative crop yield loss was estimated, using segmented linear regression, up to the year 2100 to be as much as L.E. 6.43 billion. It is worth mentioning that these estimates do not include indirect impacts of higher levels of groundwater table, which may include loss of jobs and/or earnings, impacts on food supply and food security in the area. A potential adaptation option, namely redesigning and upgrading existing drainage infrastructure, was found to cost a total of L.E. 190.8 million, representing about 4.5% of the estimated accumulative potential damage to agricultural productivity up to the year 2100.

Characteristics of groundwater in Northeast Qinghai-Tibet Plateau and its response to climate change and human activities:A case study of Delingha,Qaidam Basin

Delingha is located in the northeast margin of Qaidam Basin.Bayin River alluvial proluvial fan is the main aquifer of Delingha,in which groundwater generally flows from north to south.The hydrochemistry results showed that two different hydrochemical evolution paths formed along southeast and southwest directions,respectively.Cl-Na type groundwater was formed in front of Gahai Lake,and SO_(4)·HCO_(3)-Na·Ca type groundwater was formed in front of Keluke Lake.The results of deuterium(D)and 18O revealed that the groundwater mainly originated from the continuous accumulation of precipitation during geological history under cold and humid climate conditions.In addition,results of ^(14)C indicated that the groundwater age was more than 1140 years,implying relatively poor renewal capability of regional groundwater.Moreover,our numerical modeling results showed that the regional groundwater level will continue to rise under the warm and humid climate conditions.

Assessing the Impacts of Sea Level Rise Using Existing Data

Local communities want to know the cost of improvements needed to their drainage system based on projected sea level rise. Prior research demonstrates that in coastal areas, groundwater will rise with sea level. As a result the combination of groundwater levels and tidal data must be used to predict local impacts of sea level rise on the drainage system. However, it would appear to complicate the situation if the amount of data available for making sea level rise projections with groundwater is limited. The objectives of this task were to identify available data in a data limited community, compare the available data, assess the impact of sea level rise on the community, and its impact on the stormwater system, identify vulnerable areas in the City, provide an estimate of long-term costs for improvements, and provide a toolbox of strategies to employ at the appropriate time. The project was conducted using ArcGIS tools to import tidal, groundwater, topographic LiDAR and infrastructure improvements into GIS software and performing analysis based on current data. The cost of improvements was based on applying actual 2015 construction costs in the subject comments across a larger vulnerable area. It was found that the data sources provided similar results, despite different timelines and dates so did not interfere with the subsequent analysis. The data revealed that over $400 million in current dollars might be needed to address stormwater issues arising from sea level rise before 2100.

Perceptions of Climate Change, Sea Level Rise, and Possible Consequences Relate Mainly to Self-Valuation of Science Knowledge

This study examines perceptions of climate change and sea level rise in New Jersey residents in 2012 and 2014. Different surveys have shown declines in interest and concern about climate change and sea level rise. Climate change and increasing temperatures have an anthropogenic cause, which relates to energy use, making it important to examine whether people believe that it is occurring. In late 2012 New Jersey experienced Super storm Sandy, one of the worst hurricanes in its history, followed by public discussion and media coverage of stronger more frequent storms due to climate change. Using structured interviews, we tested the null hypotheses that there were no differences in perceptions of 1260 interviewees as a function of year of the survey, age, gender, years of education, and self-evaluation of science knowledge (on a scale of 1 to 5). In 2012 460 of 639 (72%) rated “global warming occurring” as “certain” (#4) or “very certain” (#5) compared with 453 of 621 (73%) in 2014. For “due to human activities” the numbers of “certain” or “very certain” were 71% in 2012, and 67% in 2014 and for sea level rise the numbers were 64% and 70%. There were some inconsistent between-year differences with higher ratings in 2012 for 3 outcomes and higher ratings in 2014 for 5 outcomes. However, for 25 questions relative to climate change, sea level rise, and the personal and ecological effects of sea level rise, self-evaluation of science knowledge, independent of years of education, was the factor that entered 23 of the models, accounting for the most variability in ratings. People who believed they had a “high knowledge” (#4) or “very high knowledge” (#5) of science rated all issues as more important than did those people who rated their own scientific knowledge as average or below average.

Investigation of groundwater quantitative change, Tehran Province, Iran

Changes in groundwater level in Homand-Absard plain, located in north-west of Kavir-e-Markazi watershed and east of Tehran province, were studied. The used research method was descriptive approach, and the research study was conducted based on field and desk surveys. The data needed was provided from field surveys, contours maps, and data of observation wells. There were 17 observation wells in the study area where the changes in groundwater levels were measured during 1996-2013, and an index hydrograph was prepared for the aquifer of plain. The sharpest decline in the groundwater level was in the central of Homan-Absard plain. There was 1.43 m decline in the groundwater level of aquifer annually, compared with similar studies in other parts of Iran, it has a high rate, and to the average, the groundwater level of plain has dropped equal to 25.76 m, 1996-2013. According to the study findings, the groundwater level changes with those in rainfall weren't match and the drop in groundwater level during wet years and then has continued which represents the high water extraction factor on the groundwater level drop.

济南龙洞片区某工程区地下水位升高原因及控制措施

地下水位升高会对周边环境、工程建设等产生不同程度的影响。以济南市龙洞片区某工程为例,通过水文地质钻探、地球物理勘探、示踪试验、地表水测流以及水化学分析等方法探究工程区地下水位升高的原因,并提出了合理、有效的水位控制措施。南部山体浅层岩溶水侧向径流和大辛河河水是工程区地下水重要的补给源,且大辛河是主要补给源;在地下水补给量增大的同时,工程建设破坏了原本地下水径流通道,工程地下结构阻挡了地下水流动,最终导致地下水位升高。实施地下水位控制的雨水沟改造方案后,工程区地下水水位升高速率从2.4 m/h降至0.1 m/h,有效控制了地下水位的升高。

Groundwater Rising as Environmental Problem, Causes and Solutions: Case Study from Aswan City, Upper Egypt

This paper examines the rise in the level of the groundwater in the Quaternary aquifer at Aswan city, Upper Egypt. Since the 1960’s, the areal extent of Aswan City and the urban populations are growing at a high pace which introduces new sources of water that increase groundwater recharge. As a result of leakages or infiltrations from different sources, the natural groundwater balance is overturned into an unbalance where the input to water table is comparatively much more than the natural groundwater flow towards the Nile River. The present study shows a variation in the groundwater level, from 1971 up to 2014, where the water table rising ranges between 12.55 and 13.69 m. Also, it shows an abrupt increase in the water levels in 2010 continuing up till now. The groundwater rising phenomena that happened in 2010 can be directly refereed to the cessation of groundwater pumping from El-Shallal wells, and to the reduction of pumping from KIMA factory wells. Generally, the rate of water rising is much higher in the western side of the city and in Kima factory area, where they are characterized by low relief and dense population. The most troublesome groundwater mounds under urban areas are likely to develop in low-lying areas of relatively high permeability aquifer, which is not exploited for water supply. These damages will become more widespread if the rising groundwater table remains uncontrolled.?The environmental impact of the water rising includes: forming ponds in low lying areas (Kima and El Shallal ponds), flooding building’s basements, and inundating underground infrastructure.?A general deterioration in groundwater quality was identified.

利用ArcGIS研究密怀顺回补区地下水位时空变化

密怀顺地区是北京市重要的水源涵养区,直接影响着主城区的供水安全。2014年南水北调盈余水量通过潮白河河道回补地下水,地下水位持续抬升,地下水升幅带不断变厚,包气带厚度变薄。基于ArcGIS软件,通过对区域地下水位2014—2022年进行研究,结果表明:研究区地下水位持续快速升高,升幅为26.38 m,其中密云区升幅19.01 m,怀柔区升幅28.26 m,顺义区升幅31.67 m;地下水位低升幅带面积为144.47 km^(2),占研究区面积的29.67%,地下水位中升幅带面积约为128.85 km^(2),占研究区面积的26.47%,地下水位高升幅带面积约为213.52 km^(2),占研究区面积的43.86%;研究区包气带厚度由43.07 m减小至16.69 m,减少了26.38 m,其中密云区由43.42 m减小至24.41 m,减少了19.01 m,怀柔区由39.38 m减小至11.13 m,减少了28.26 m,顺义区由45.83 m减小至14.11 m,减少了31.72 m。结果基本反映了该地区地下水时空变化特征,分区结果可进一步支撑地下水管理、地下水政策制定及地下水型水源地的精细化管理。

基于模型试验的阻-透型岩溶塌陷演化过程与机理研究

地下水位下降是诱发地面塌陷的关键因素之一。为研究地下水位下降触发岩溶地面塌陷的过程和机理,以塌陷区上阻下透结构盖层(上层为黏性土、下层为砂性土)的典型塌陷坑为研究对象,通过室内土工试验获取了盖层土体的物理力学性质和水理性质参数,并在室内构建地质物理模型,设计符合现场实际的5组试验工况,探讨不同排水速率条件下的溶洞内真空负压变化与盖层表面变形的本质关系。基于极限平衡理论分析盖层的受力特征,提出盖层稳定性的判别模型。并利用判别模型对物理模拟试验结果进行验证,显示两者总体吻合。研究结果表明:1)盖层表面变形、塌陷与溶洞内地下水位下降速率关系密切。当盖层处于塌陷临界状态时,溶洞内真空压强到达峰值,地下水位下降速率到达谷值,孔隙水压力出现“倒V形”曲线段。2)地下水位下降产生的渗透压力、真空吸蚀力是触发此类岩溶地面塌陷的关键因素,控制着盖层的变形和演化行为。3)致塌力、抗塌力均随地下水位的下降而增大,当地下水位的初始下降速超过临界值8.9×10^(-3)m/s时,产生的致塌力超过抗塌力,塌陷发生。塌陷演化过程总体可划分为盖层逐渐向下变形和突然失稳塌陷2个阶段。研究成果具有一定合理性和参考意义,可为塌陷区防灾减灾工作提供重要技术支撑。

浅析开采条件下地下热水资源的演变

地下热水的分布可以分为埋藏型(或盆地型)和出露型(或温泉型)。埋藏型分布于沉积盆地深处,热储层规模大,有较大的储存资源,但补给资源极为有限或缺乏,开采地下热水主要是消耗储存资源,可导致热水系统水位持续下降。出露型多见于山区,地下热水以温泉的方式出露地表,其储存资源和补给资源均有限,在温泉附近开采热水可导致温泉流量减小直至干涸。热水系统水位、水温也会持续下降。在某些特定条件下在温泉附近打成的自流孔可使地下热水资源量有所增加。温泉的自封闭作用可使其流量减少。

海河流域平原浅层地下水位持续下降动因与效应

本文从近几十年来海河流域降水量变化、山前拦蓄地表水和超采地下水三个方面 ,阐述了山前平原浅层地下水位持续下降的动因 ,揭示了拦蓄和超采对地下水位持续下降的主导作用和气候变化的催化作用 ,探讨了地下水位持续下降所带来的四个方面危害。在此基础上 ,提出了立足大陆尺度科学规划和利用水资源 。

华北滹滏平原地下水位下降与灌溉农业关系

针对华北粮蔬主产区滹滏平原浅层地下水位不断下降成因问题,基于大量实测资料和相关分析方法与MapGIS技术,通过对近50年来区内地下水位、粮蔬播种强度、有效灌溉面积变化特征和降水量、气温变化下地下水位下降对粮蔬播种强度响应机制研究,结果表明:1980年前粮蔬播种强度每增加0.01或夏粮和蔬菜播种面积每增加1万hm2,研究区地下水位下降幅度为0.36 m或0.43 m;1980年以来随粮蔬播种强度增大,地下水位下降幅度明显增大,粮蔬播种强度每增加0.01或夏粮和蔬菜播种面积每增加1万hm2,地下水位降幅分别达0.69 m和1.15 m。不仅与因播种强度增大导致农业开采量增加有关,而且还与1980年以来降水量不断减少密切相关。降水量减少100 mm,区内农业开采量增加35.7 mm。

牵引式滑坡演化模式研究

该研究以甘肃黑方台为区域背景,通过离心模型试验与应力路径试验相结合的手段,研究地下水位抬升引发牵引式黄土滑坡的演化模式和力学机理。离心模型试验中,模型边坡的尺寸为0.8 m×0.4 m×0.45 m(长×宽×高),离心加速度为100g。在试验中,通过水位控制系统实现地下水位的不断抬升,利用数码摄像、孔隙水压力及激光位移传感器、侧面示踪点等仪器设备详细记录地下水位抬升过程中边坡内的孔隙水压力、边坡变形、滑动面形态及坡面裂缝的形成和发展过程。应力路径试验中,通过恒载增孔压试验和偏压固结不排水试验,模拟了滑坡酝酿启动过程和局部破坏向整体滑移的发展过程。基于以上成果,提出饱水黄土在上覆荷载下因孔隙水压力增大而失稳,在卸荷条件下使应力重分布,导致局部剪切带发展并逐渐形成贯通的破坏面,边坡表现为牵引式的破坏模式。该研究结果有助于深入认识水位抬升引发牵引式滑坡的演化模式和力学机理,为治理此类滑坡提供科学依据。

地下水傍河水源地数值模拟

为了研究沈阳市浑南高新技术开发区水源的地下水中途停采对地下水位的影响,针对目前开采量不变和中途停采这两种情况,对该区地下水位进行了数值模拟,预测了地下水停采后地下水水位的变化趋势.笔者应用VisualMODFLOW软件,进行了研究区剖分、时间离散、参数分区、边界条件及源汇项处理、模型识别、验证,直至预测分析.预测结果表明了中途停采后,原开采漏斗附近地下水位会迅速回升,将对该区地下建筑产生不利影响.

冀中山前农业区地下水位强降弱升特征与机制

针对冀中山前平原农业区浅层地下水位不断下降问题,采用时间序列异变特征和趋势分析方法,基于小时级、自记监测的地下水位动态资料,通过农业区灌溉期、非灌溉期地下水位变化程度的差异特征及机制研究,结果表明:该平原农业区浅层地下水位变化在主灌溉期呈"cm/d"级(大于1.0 cm/d)下降、非灌溉期呈"mm/d"级(小于1.0 cm/d)上升的特征,这些特征与降水量、年内降水分配状况及其影响的农业开采强度密切相关。前期降水偏枯,灌溉期地下水位下降过程线和年内水位上升过程线的大部分位于当地多年地下水位变化趋势线之下;前期降水偏丰,位于趋势线之上。农业集中开采是地下水位"cm/d"级下降特征的动因,厚大包气带是地下水位"mm/d"级上升特征形成的重要条件。

地下水水位上升对地铁隧道结构的影响分析

在分析北京地区地下水水位上升情况的基础上,采用FLAC数值模拟方法,以拱顶埋深6 m、直径10 m的地铁隧道为例,研究地下水水位逐步回升情况下,隧道结构在位移、变形、内力(弯矩和轴力)、塑性区等方面的变化趋势和分布规律。分析结果表明,在地下水水位明显回升的情况下,隧道发生整体上浮、结构整体破坏的可能性不大,但会使隧道结构的内力(弯矩和轴力)发生变化,并且产生变形,会对地铁结构产生一定的影响。这些变化甚至有可能引起结构的开裂、渗水以及由此带来的一系列问题。因此在进行地铁、地下结构的规划、设计和施工过程中应对地下水的变化给予重视。

太行山山前平原浅层地下水位动态分析——以河北省栾城县为例

通过对太行山山前平原地区地下水位变动过程的分析发现,该区地下水位多年平均年下降速率为0.7m;20世纪80年代该区地下水位季节变动量和季节恢复量变化平稳,90年代以来变动量和恢复量显著增大;年降水量与年地下水位下降速率呈高度线性相关,相关系数r=0.7798,年降水量每增加100mm则地下水位可回升0.66m。只有建立切实可行的农业节水系统,加强山区的林业生态综合治理,才能缓解该区地下水位持续下降。