TEM study of the geoelectrical structure and groundwater salinity of the Nahal Hever sinkhole site, Dead Sea shore, Israel

Since the 1990s a large number of sinkholes have appeared in the Dead Sea (DS) coastal area. Sinkhole development was triggered by the lowering of the DS level. In the literature the relationship between the sinkholes and the DS level is explained by intrusion of relatively fresh water into the aquifer thereby dramatically accelerating the salt dissolution with creation of subsurface caverns, which in turn cause sinkholes. The main goal of our project was detection and localization of relatively fresh groundwater. During our study we used the transient electromagnetic method (TEM) to measure the electrical resistivity of the subsurface. As a test site we selected Nahal Hever South which is typical for the DS coast. Our results show that resistivity of the shallow subsurface reflects its vertical and lateral structure, e.g., its main hydrogeological elements explain the inter-relations between geology, hydrogeology, and sinkholes. The TEM method has allowed detailed differentiation of layers (clay, salt, etc.) in the subsurface based on their bulk resistivity. The 10 m-thick salt layer composed of idiomorphic crystals of halite deposited during the earlier Holocene period was extrapolated from borehole HS-2 through the study area. It was found that in Nahal Hever the typical value of the bulk resistivity of clay saturated with the DS brine varies between 0.2 and 0.3 Ωm, whereas saturated gravel and sandy sediments are characterized by resistivity between 0.4 and 0.6 Ωm. The high water salinity of the aquifer (enveloping the salt layer) expressed in terms of resistivity is also an important characterization of the sinkhole development mechanism. The electrical resistivity of the aquifer in the vicinity of the salt unit and its western border did not exceed 1 Ωm (in most cases aquifer resistivity was 0.2-0.6 Ωm) proving that, in accordance with existing criteria, the pores of the alluvial sediments are filled with highly mineralized DS brine. However, we suggest that the criterion of the aquifer resistivity responsible for the salt dissolution should be decreased from 1 Ωm to 0.6 Ωm corresponding to the chloride concentration of approximately 100 g/l (the chloride saturation condition reaches 224 g/l in the northern DS basin and 280 g/l in the southern one).Based on TEM results we can reliably conclude that in 2005, when most of sinkholes had appeared at the surface, salt was located within a very low resistivity environment inside sediments saturated with DS brine. Intrusion of relatively fresh groundwater into the aquifer through the 600 × 600 m²area affected by sinkholes has not been observed.     

大跨连续钢桁拱桥动力系数影响因素研究

以南京大胜关长江大桥为研究对象,建立其车桥耦合动力分析模型,采用逐步积分法求解动力方程,以动力系数作评判标准,讨论行车速度、阻尼比、行车方向、车辆数、吊杆布置方式等参数对动力性能的影响.结果表明:动力系数随行车速度的提高而增大;吊杆索力的动力系数与无应力索长成反比;随着阻尼比的增大,各构件动力系数均有所降低;同向行驶时...     

我国大气降水中稳定同位素研究进展

大气降水中稳定同位素的比率与降水产生过程中的气象条件密切相关,可以利用其时空分布特征来反演大气过程,示踪水汽来源,反映天气气候的区域性特征.对影响我国大气降水中稳定同位素组成与分布进行了总结,探讨了影响降水中氢氧同位素的因素及空间变化特征,并分别介绍了我国青藏高原区、西北干旱区和东部季风区等地区近年来降水中稳定同位素的...     

Geochemistry of groundwater,Markandeya River Basin,Belgaum district,Karnataka State,India

The Markandeya River Basin stretches geographically from 15o56′ to 16o08′ N latitude and 74o37′ to 74o58′ E longitude, positioned in the midst of Belgaum district, in the northern part of Karnataka. The groundwater quality of 54 pre-monsoon samples in the Markandeya River Basin was evaluated for its suitability for drinking and irrigation purposes by estimating pH, EC, TDS, hardness and alkalinity besides major cations (Na+, K+, Ca2+, Mg2+) and anions (HCO3–, Cl–, SO42–, PO43-, F-, NO3–), boron, SAR, % Na, RSC, RSBC, chlorinity index, SSP, non-carbonate hardness, Potential Salinity, Permeability Index, Kelley’s ratio, Magnesium hazard and Index of Base Exchange. Negative Index of Base Exchange indicates the chloro-alkaline disequilibrium in the study area and the majority of water samples fall in the rock dominance field based on Gibbs’ ratio. Permeability indices of classes I and II suggest suitability of groundwater for irrigation. Based on Cl, SO4, HCO3 concentrations, water samples can be classified as normal chloride (96.3%) and normal sulfate (94.4%) and normal bicarbonate (44.4%) water types.     

咸淡水共存区物探资料处理技术

针对AMT法数据的特点,介绍了提高其纵向分辨率、去除噪声干扰、压制静态效应的常用处理方法及其特点;就咸淡水共存区AMT资料处理技术以及矿化度评价工作中数学模型建立问题进行了探讨,介绍了两种建立孔隙地层地下水矿化度数学模型的方法,并给出了相应的应用实例;同时说明,不同物探手段和不同反演方法都会造成获得地层电阻率值的差异性,在同一工区利用同一矿化度评价数学模型要注意工作方法和反演方法的一致性。     

井点降水实验在渭河大桥承台施工中的应用

井点降水是一种方便易行的降水方式,在黄河湿地承台施工中较好地解决了基坑开挖基坑涌水、流沙现象的发生。     

甘肃武都马槽沟滑坡特征及治理对策

甘肃武都地区新构造和地震活跃,降雨集中且多为暴雨,加之地形复杂,人地矛盾紧张,因而生态环境恶劣,这为滑坡地质灾害的发育提供了条件。为了有效地防灾减灾,本文以马槽沟滑坡为典型实例,从滑坡形态特征、形成条件、触发因素等角度入手,阐述了该区滑坡发生的机理,在此基础上对当前滑坡所处的稳定程度进行了分析。并提出了滑坡工程治理的具体方案,以期对该地区滑坡防治有参考价值。     

城市垃圾及排污沟渠对拟建水源地地下水水质的影响研究

在对地下水水源地附近的垃圾场及排污沟渠进行预测分析的基础上,通过建立地下水水质模拟模型分析污染源对地下水水质的影响,得出影响结论。     

悬浮泥沙含量与电导率关系及其影响因素的实验研究

为了寻求一种简单、快速、连续测定悬浮泥沙含量的方法,以高含沙量海区黄河口泥沙为研究对象,利用电导率仪测定了不同悬浮泥沙含量水体的电导率.前期实验结果已经证明悬浮泥沙含量与电导率之间有很好的线性关系.在此基础上扩大研究范围,并对影响悬浮泥沙含量与电导率关系的因素进行定量分析,结果表明,盐度、温度、颗粒粒径对电导率具有一定...     

Dynamics of hypersaline coastal waters in the Great Barrier Reef

The coastal waters of the Great Barrier Reef (GBR) are hypersaline (salinity ∼37) during the dry season as a result of evaporation greatly exceeding rainfall, of shallow waters, and of the presence of numerous bays along the coast preventing rapid flushing. These hypersaline waters are not flushed out by salinity-driven baroclinic currents because these waters are vertically well-mixed. Instead these waters are transported by a longshore residual current and thus form a coastal boundary layer of hypersaline waters. As a result the hypersalinity distribution is 2-D with both cross-shelf and longshore gradients of salinity. The cross-shelf gradients are largely controlled by turbulent diffusion, while the longshore gradients are controlled by the residual currents that transport hypersaline waters longshore south ward in the central and southern regions of the GBR. Because every bay supplies hypersaline waters, the width of the coastal hypersaline layer increases southwards. Steady state is reached in about 100 days, which is the typical duration of the dry season. The dynamics of the GBR hypersaline coastal boundary layer thus differ from the classical inverse hypersaline systems, e.g. in Saloum River Estuary, Laguna San Ignacio, Mission Bay, Tomales Bay, San Diego Bay, Hervey Bay, Shark Bay, Coorong Coast Lagoon, Spencer Gulf, Gulf of California and many others where the salinity gradient is mainly 1-D with a dominant along-channel salinity gradient.