Effects of mixed physical barrier on residual saltwater removal and groundwater discharge in coastal aquifers

Physical barriers are widely used to control seawater intrusion (SWI). Amongst different kinds of physical barriers, mixed physical barriers (MPBs) are shown to be an effective approach to prevent SWI. However, the system may hinder the discharge of fresh groundwater and the removal of residual saltwater trapped in the inland aquifers of MPBs. Herein, using the validated numerical model, for the first time, we investigated the dynamics of residual saltwater and groundwater discharge after the installation of MPBs. For examining the applicability of MPB and its response to structural variations and hydraulic gradient, the comparison with traditional physical barriers and sensitivity analysis was also carried out. The MPB increased the mixing area of freshwater and saltwater at the beginning of the removal process, resulting in the reduction of the saltwater wedge length (R_L) by 74.6% and the removal of total salt mass (R_M) by 62.6% within the 4% of the total removal time. Meanwhile, the groundwater discharge (Q') rose rapidly after a sharp decline from 100% to 40% in the first stage. As the residual saltwater wedge was retreated, the mixing intensity and removal efficiency decreased substantially in the second stage. Similarly, Q' raised with a declining rate at this stage. The removal efficiency was positively correlated with wall depth and hydraulic gradient and there were optimal distance of the middle spacing and height of lower dam to reach the highest efficiency. The groundwater discharge reduced monotonously with the increase of dam height and wall depth as well as the decrease of barrier spacing and hydraulic gradient. Under certain conditions, the efficiency of MPB in removing residual saltwater could be 40%–100% and 0%–56% higher than that of traditional subsurface dam and cutoff wall, respectively. The laboratory scale conclusions provide valuable physical insight for the real field applications regarding dynamic mechanism and regularity. These findings will always help decision makers choose proper engineering measures and protect groundwater resources in coastal areas.     

金川超基性岩体可分解为“南岩带”与“北岩带”

金川超基性岩体可分解为"南岩带"与"北岩带"."南岩带"由Ⅱ、Ⅳ号小岩体组成,"北岩带"由Ⅰ、Ⅲ号小岩体组成,南、北岩带分别位于大理岩构造透镜体的南、北两侧.在超基性岩体侵位前,古元古代地层产生了高角闪岩相峰值变质变形,顺大理岩层发育逆冲推覆型韧性剪切滑动系统,形成了变质带倒置的层状变质岩片、构造混合岩、剪切流变褶皱及...     

细基江蓠(Gracilaria tenuistipitata)对海水池塘养殖区Cu~(2+)生物修复的初步研究

随着海水养殖业迅速发展,食用海产品重金属(如Cu、Cd等)超标问题日益突出。作为提取藻胶原材料及海洋养殖动物饲料的细基江蓠,可以大规模生长在海水池塘养殖区,有望用于该水域重金属污染的生物修复。本实验通过研究细基江蓠(Gracilaria tenuistipitata)在5个不同Cu2+浓度梯度(0、0.05、0.2、0.8、2.0mg/L)环境下的自身生长状况,及其对Cu2+的吸收富集情况,初步探究了细基江蓠对海水池塘养殖区Cu2+的生物修复能力。实验结果显示细基江蓠对Cu2+有较强的耐受性和吸收富集能力,在0.8mg/L Cu2+浓度下细基江蓠既能保证正常生长,又能吸附水体中最大量的Cu2+。     

Saltwater intrusion modelling in Jorf coastal aquifer,South‐eastern Tunisia: geochemical,geoelectrical and geostatistical application

Marine intrusion is the most serious problem facing the coastal Jorf shallow aquifer, located in south‐eastern Tunisia on the Mediterranean Sea. Jorf Aquifer is intensively exploited to supply the growing needs of agriculture and domestic sectors. This work proposes a multidisciplinary investigation, involving hydro‐geochemical, geoelectrical survey and geostatistical techniques for modelling the saltwater intrusion. For this purpose, 36 water samples were conducted and analysed. Electric conductivity, pH, total dissolved solids and major ions were measured and analysed. Pie and Durov Diagrams, Q‐mode hierarchical cluster and geostatistical analysis were considered to identify the main groundwater mineralization processes. Results revealed that the Na‐Cl‐Ca‐SO₄ is the dominant water type suggesting that dissolution of halite and gypsum was the main mineralization source of groundwater in the central and southern part of study area. However, saltwater intrusion was shown to control groundwater quality essentially in coastal areas. Variographic analyses were used to select the variographic model that best fits the spatial development of apparent resistivity. Kriged apparent resistivity profiles showed an abnormal decrease of resistivity values in the coastal zone, implying highly saline water because of seawater intrusion. Apparent resistivity values also decrease considerably in the faulted areas, suggesting a contribution of faults to seawater intrusion. Finally, saltwater mixing ratio was computed for each sample, and a refined seawater intrusion map was developed. Copyright © 2012 John Wiley & Sons, Ltd.     

Modelling study on the impact of deep building foundations on the groundwater system

Coastal areas are usually the preferred place of habitation for human beings. Anthropogenic activities such as the construction of high‐rise buildings and underground transport systems usually require extensive deep foundations and ground engineering works, which may unintentionally modify the coastal groundwater system because the construction materials of foundations are usually of low hydraulic conductivity. In this paper, the impact of these building foundations on the groundwater regime is studied using hypothetical flow and transport models. Various possible realizations of foundation distributions are generated using stochastic parameters derived from a topographical map of an actual coastal area in Hong Kong. The effective hydraulic conductivity is first calculated for different realizations and the results show that the effective hydraulic conductivity can be reduced significantly. Then a hypothetical numerical model based on FEFLOW is set up to study the change of hydraulic head, groundwater discharge, and saltwater‐fresh water interface. The groundwater level and flow are modified to various degrees, depending on the foundations percentage and the distribution pattern of the buildings. When the foundations percentage is high and the building foundations are aggregated, the hydraulic head is raised significantly and the originally one‐dimensional groundwater flow field becomes complicated. Seaward groundwater discharge will be reduced and some groundwater may become seepage through the ground surface. The transport model shows that, after foundations are added, overall the seawater and fresh groundwater interface moves landward, so extensive foundations may induce seawater intrusion. It is believed that the modification of the coastal groundwater system by building foundations may have engineering and environmental implications, such as submarine groundwater discharge, foundation corrosion, and slope stability. Copyright © 2007 John Wiley & Sons, Ltd.     

盐水钻井液配制方法对其性能的影响

随着钻井技术的发展,深井、超深井钻遇复杂地层的情况越来越多,对钻井液性能提出了越来越高的要求。通过对盐水钻井液的配制方法进行理论分析和对比,并结合现场应用,利用已有抗盐材料,基于预水化对钻井液性能影响机理及预水化时间的长短对钻井液性能的影响进行了研究。试验得出,预水化对钻井液的性能起着至关重要的作用,且随预水化时问的变化,钻井液性能产生不同的变化趋势,根据钻井液要求的侧重点不同,为配制不同性能指标的钻井液提供实践指导和理论依据。     

磨刀门水道咸潮入侵及其变异分析

随着区域经济及人口的进一步增长,珠江三角洲磨刀门水道已成为江门、中山、珠海、澳门等城市重要的水源地,相应咸潮入侵对供水安全造成的危害也越来越严重。本文依据实测资料和现场调研,对磨刀门水道咸潮入侵的潮相变化、径流—咸潮的响应模式、风对咸潮入侵的影响及咸潮入侵的历史演变趋势及其变异、最小压咸流量及最佳压咸时机等进行了研究。研究结果表明,影响咸潮入侵的主要因素是径流,有利于咸潮入侵的风向为北风～东北风。以思贤滘流量(即马口水文站与三水水文站流量之和)为参照,为保障珠海、澳门供水安全,磨刀门水道最小压咸流量范围为2200-2700m3/s,平均流量为2450m3/s,最佳压咸补淡的时机为大潮转小潮期,也就是朔望(半月)周期的落潮期。     

基于随机森林模型的咸潮预报

在候选预报因子的基础上,通过Pearson相关系数和重要度指数分别确定了主要预报因子及其滞后期,进而利用确定滞后期的预报因子建立基于随机森林的咸潮预报模型,并应用于磨刀门水道大涌口站的枯水期咸潮预报。结果发现：通过相关系数确定的主要预报因子与含氯度之间存在1~3 d不等的滞后期;考虑预报因子滞后作用的随机森林模型,其预报结果不仅能很好地满足咸潮预报的精度要求,而且明显优于未考虑预报因子滞后作用的随机森林模型,即考虑预报因子的滞后作用能显著提高模型的拟合效果。此外,与传统的马尔科夫链相比,随机森林模型的预报结果不仅精度更高,而且在中长期预报上更有优势。     

钱塘江河口水流-河床相互作用及对盐水入侵的影响

通过长系列实测水文、地形资料分析,钱塘江河口上段河床具有大冲大淤和洪冲潮淤的演变特性,影响河口上段的潮汐强弱,进而影响盐水入侵。若年内丰水期径流量大,则河床出现“大冲”,河床容积增大,潮汐增强,导致秋季强潮期盐水入侵加剧;反之,若年内丰水期径流量小,河床容积较小,导致秋季强潮期盐水入侵减弱。结果表明,钱塘江径流对盐水入侵存在直接和间接影响:直接影响是盐水入侵与径流量成反比;间接影响是通过径流冲刷河床,引起潮汐增大,间接导致盐水入侵加剧,这是钱塘江河口大冲大淤以及对潮汐巨大反作用的特性造成的。     

东特提斯域思茅盆地钾盐成矿研究进展

思茅盆地位于东特提斯域,其内的勐野井钾盐矿是我国唯一的前第四纪固体钾盐矿,长期以来对此钾盐矿与呵叻巨型钾盐盆地的资源量差异和成因存在着有较大争议。特别是如下几个问题:其钾盐成矿时代是晚白垩世和古新世,还是侏罗纪的争议;其物质来源还存在陆源,海源和多源的不同认识;矿床成因机理模式也悬而未决。本文在前人研究基础上,结合项目组的最新进展,对上述这些问题的进行梳理与评述认为:勐野井组地层为晚白垩世Albian-Cenomanian期,同沉积的原生钾盐也是在此时期富集成矿;钾盐成矿后期特别是约14Ma以来,受到多期次的热液流体作用,形成次生脉状钾盐:钾盐成矿物质可能以中特提斯洋侵入的海水为主,辅以陆源水体和深部流体。总结认为,思茅与呵叻等盆地在晚白垩世都是干旱沙漠环境中彼此隔绝的小湖盆,随着中特提斯洋海水自西向东的入侵,海水由思茅流向了呵叻,形成了统一的思茅-呵叻海,这个模型可以解释有关成钾物源及思茅与呵叻盆地的成钾关系。思茅盆地钾盐矿的形成和后期变化始终受到了构造活动的控制,经历了最初断陷阶段,到沉积后期受印度-欧亚大陆碰撞导致的挤压和走滑运动影响。