Tidal effects of groundwater levels in the coastal aquifers near Beihai, China

Four times of observation of the ocean tide and groundwater levels in the coastal aquifers near Beihai, China show that fluctuation in the tide-induced groundwater levels follows the tide, with the highest and lowest water levels corresponding to the high water level syzygy tide and the low water level neap tide. The tidal coefficient is less than 0.5, decreasing approximately exponentially with the distance from the coast. The tide can affect the groundwater levels at observation wells as far as about 4,200 and 3,300 m in the southern and northern coasts in Beihai. Observations and spectrum analyses of the time series of the tide and water levels suggest that the tide and water levels have similar changes with complex fluctuations of a long period of 14.37 days and two short periods of 24.7 and 12.5 h. Time lags of water levels to the tide at observation wells last several hours and increases roughly linearly with the distance from the coast. Mathematic models consisting of a periodic term plus a linear term are established to describe the changes in the tide and the groundwater levels. The periodic terms for the tide and water levels are constructed using finite Fourier’s series consisting of 7 to 11 terms other than a single term of a sine function in earlier work. Computed water levels with the models can fit the observed water levels with reasonable accuracy and satisfactory prediction of the changes in the water levels is also obtained.     

Characteristics of natural low pH groundwater in the coastal aquifers near Beihai, China

Groundwater with low total dissolved solids （less than 200 mg/L） occurs in the unconfined and confined aquifers near Beihai in southern Guangxi, China. Under natural conditions the groundwater ranges in pH from 3,33 to 7,0 with an average value of 5.12. The pH in the unconfined aquifer varies from 3.67 to 7.0 with an average value of 5.17 and the pH in the confined aquifer is in the range 3.33-6.97 with an average value of 5.07. The pH in the groundwater does not show significantly increasing or decreasing trends with time. Fluctuations in pH exist at some of the monitoring wells and the pH in groundwater is a bit higher in the rainy season than in the dry season, Monitoring data show that the pH in rainwater is higher than in groundwater in the unconfined aquifer, whereas the pH in the latter is a bit higher than in the confined aquifer. A slightly decreasing trend in the pH was also found from the inland area to the coastal zone. The occurrence of weakly acidic groundwater in this area is attributed to the recharge from low pH precipitation and the multi-aquifer and leaky groundwater system.     

Environmental impact of an urban landfill on a coastal aquifer (El Jadida, Morocco)

The El Jadida landfill is one among many uncontrolled dumping sites in Morocco with no bottom liner. About 150 tons/day of solid wastes from mixed urban and industrial origins are placed directly on the ground. At the site of this landfill, the groundwaters circulate deeply (10–15 m) in the Cenomanian rock (calcareous–marl), which is characterised by an important permeability from cracks. The soil is sand–clay characterized by a weak coefficient of retention.The phreatic water ascends to the bottom of three quarries, which are located within the landfill. These circumstances, along with the lack of a leachate collection system, worsen the risks for a potential deterioration of the aquifer.To evaluate groundwater pollution due to this urban landfill, piezometric level and geochemical analyses have been monitored since 1999 on 60 wells. The landfill leachate has been collected from the three quarries that are located within the landfill. The average results of geochemical analyses show an important polluant charge vehiculed by landfill leachate (chloride = 5680 mg l⁻¹, chemical oxygen demand = 1000 mg l⁻¹, iron = 23 000 μg l⁻¹). They show also an important qualitative degradation of the groundwater, especially in the parts situated in the down gradient area and in direct proximity to the landfill. In these polluted zones, we have observed the following values: higher than 4.5 mS cm⁻¹ in electric conductivity, 1620 and 1000 mg l⁻¹ respectively in chlorides and sulfate (), 15–25 μg l⁻¹ in cadmium, and 60–100 μg l⁻¹ in chromium. These concentrations widely exceed the standard values for potable water.Several determining factors in the evolution of groundwater contamination have been highlighted, such as (1) depth of the water table, (2) permeability of soil and unsaturated zone, (3) effective infiltration, (4) humidity and (5) absence of a system for leachate drainage. So, to reduce the pollution risks of the groundwater, it is necessary to set a system of collection, drainage and treatment of landfill leachates and to emplace an impermeable surface at the site of landfill, in order to limit the infiltration of leachate.     

The impact of tourism on coastal areas

The manifold influences of tourism on coastal areas are analysed from three different angles: (1) The development of seaside tourism including the changes of socio-economic and settlement patterns; (2) its cultural impact on the local population; (3) its environmental aspects. Point 1 is described with the help of a model showing four peripheries in space and time: (I) the North Sea and Baltic coasts since the 18th century; (II) Southern Europe during the 19th century; (III) the North African shores around 1950; (IV) the tropical oceans after 1965. Within every periphery, several phases (pioneer, domestic, international) can be distinguished according to the origin of tourists, the investment, the know-how etc. While the beginning of every phase is dominated from abroad, later-on national actors play an increasing role. This applies also to point 2, which refers mainly to developing countries. As for point 3, mass tourism may result detrimentally on water supply, sensitive coastal landscapes, socio-cultural identity etc. Among the questions to be raised are: How far are industrial societies responsible for any negative impacts of tourism, and what are the chances for, and a general consciousness on, a sustainable tourism development?     

Impact of desalination plants brine injection wells on coastal aquifers

A new methodology is developed in assessing environmental impacts of desalination plants discharging brine into the ground. The main environmental problem of the desalination of seawater is the brine disposal. The brine is commonly discharged into the sea or injected into a saline aquifer. In the case of injection into the ground, it is necessary to design a disposal system in a way that respects the environment and is sustainable. Laboratory and computational methods have been utilized to simulate the unsteady three-dimensional (3D) phenomena of subsurface brine disposal. The computational software used is SEAWAT, which is a 3D unsteady variable-density flow simulation model. The model is first used to simulate the laboratory results, and good agreement is achieved. Then, hypothetical problems are designed and simulated of groundwater extraction and brine disposal by desalination stations. The major purpose of these hypothetical problems is to delineate a methodology and to create design charts for design and management of production and injection well fields for coastal desalination plants. Several design charts have been developed with 36 scenarios for two well configurations created by four design parameters: relative salt concentration (RSC), production and injection rates (Q _d , Q _r ), well spacing (S), and simulation period (T).     

Seasonal variation in natural recharge of coastal aquifers

Many coastal zones around the world have irregular precipitation throughout the year. This results in discontinuous natural recharge of coastal aquifers, which affects the size of freshwater lenses present in sandy deposits. Temperature data for the period 1960–1990 from LocClim (local climate estimator) and those obtained from the Intergovernmental Panel on Climate Change (IPCC) SRES A1b scenario for 2070–2100, have been used to calculate the potential evapotranspiration with the Thornthwaite method. Potential recharge (difference between precipitation and potential evapotranspiration) was defined at 12 locations: Ameland (The Netherlands), Auckland and Wellington (New Zealand); Hong Kong (China); Ravenna (Italy), Mekong (Vietnam), Mumbai (India), New Jersey (USA), Nile Delta (Egypt), Kobe and Tokyo (Japan), and Singapore. The influence of variable/discontinuous recharge on the size of freshwater lenses was simulated with the SEAWAT model. The discrepancy between models with continuous and with discontinuous recharge is relatively small in areas where the total annual recharge is low (258–616 mm/year); but in places with Monsoon-dominated climate (e.g. Mumbai, with recharge up to 1,686 mm/year), the difference in freshwater-lens thickness between the discontinuous and the continuous model is larger (up to 5 m) and thus important to consider in numerical models that estimate freshwater availability.     

海潮引起滨海含水层地下水位变化的初步研究

依据短序列和长序列的潮汐效应观测数据,分析了北海地区海潮引起滨海含水层地下水位变化的动态特征.结果表明,受海潮影响的滨海含水层地下水位与海潮有相似的波动特征,但变幅减小,受海潮的影响程度与观测点离海岸的距离有关,随着离海岸距离的增加地下水位的变幅和潮汐系数大致呈负指数减小.在南、北海岸距离海岸分别达3756m和2276m以远时地下水位不受海潮变化的影响.长序列的观测资料显示,海潮和岸边地下水位有15天的长周期和1天的短周期的波动.     

Assessing the impact of natural and anthropogenic activities on groundwater quality in coastal alluvial aquifers of the lower Liaohe River Plain,NE China

The lower Liaohe River Plain (LRP) is an economically and ecologically important area situated on an alluvial plain, where anthropogenic activities are very intensive. Field investigations were conducted in the LRP and 15 water quality parameters surveyed at 216 wells during September and October of 2009 and 2010. These showed significant variation in the hydrochemistry of groundwater throughout the plain. A Piper plot was used to identify the major geochemical processes occurring in the entire plain. Principal components analysis (PCA) was used to identify various underlying natural and anthropogenic processes that created these distinct water types. The Stuyfzand classification was used to subdivide and interpret the complex groundwater hydrochemistry of the Liaohe River delta. Five principal components (PCs) were extracted in terms of PCA, which can be invoked to explain 82% of the total variance in water quality parameters. The PCA results can be categorized by five major factors: (1) Holocene transgression and mixing; (2) surface water infiltration; (3) multi-factor processes; (4) rainfall and agricultural fertilizer contamination; and (5) Geogenic F enrichment. This study demonstrates that the great variation of groundwater hydrochemistry in the LRP should be attributed to both natural and anthropogenic processes.     

Assessing the impacts of climate change on sustainable management of coastal aquifers

Water is a vital resource for the survival of not only human population, but also almost all ecosystems. Constituting 30 % of all freshwater, groundwater is the main source of available freshwater. Coastal aquifers, which serve as the major freshwater source for densely populated zones, are of vital importance and quite vulnerable to climate change. This paper examines the significant consequences of climate change, decreasing recharge rates, sea-level rise and increasing freshwater demand on the sustainable management of coastal aquifers, via a hypothetical case study. A 3-D numerical model is developed using SEAWAT, to simulate a circular island aquifer in the form of a freshwater lens surrounded by saltwater. Issues such as sloping land surface resulting in landward migration of the coastal boundary and transient response of the system due to pumping are considered through a set of predictive simulations. To assess the sensitivity of the model results to important parameters, a sensitivity analysis is performed. Results of this research, revealing the effects of mentioned pressures on the long-term sustainability of the freshwater resource, are evaluated on the basis of groundwater reserves and intrusion of the freshwater–saltwater interface in lateral and vertical directions. These outcomes are further used to determine the sustainable pumping rate of the system, considering both quantity and quality of the groundwater resources.     

Hydrogeochemical characteristics of groundwater in coastal phreatic aquifers of Alleppey district,Kerala

Hydrogeochemical characteristics of groundwater in phreatic aquifers of Alleppey district were studied. Factor analysis has been applied to the chemical analysis data of 32 water samples collected from dug wells to extract the principal factors corresponding to the sources of variation in the hydrochemistry. 12 hydrochemical parameters were correlated and statistically examined. Varimax rotation was used to define the factor scores and percentage of variance in the hydrogeochemistry. A four-factor model is extracted and explains over 80.394% of the total groundwater quality variation. Factor-1 has high loading values of Electrical Conductivity (EC), Ca⁺⁺, and Cl⁻, and reflects the signature of saline water. Similarly strong correlation exists between F3 score and pH. The correlation coefficient matrix between EC and Na⁺, Cl⁻, SO₄⁻⁻ is significant. The mineralogy of coastal aquifers and the marine aerosol are playing significant role in the hydrogeochemistry of groundwater in the phreatic aquifer system.     

电法探查海岸带含水层咸淡水界面的调查研究

本文在理论上对电法探查多层土层组成的海岸带含水层的咸淡水界面的可能性进行探讨的基础上,对太平洋沿岸某地区进行了实地调查研究.在测量设置在海岸附近及分布于海岸纵深方向的调查井垂直方向电导率的同时,在调查井附近进行了电法探查.结果表明,电法探查的咸淡水界面的深度与依据井水电导率区分的混合区域上端几乎一致,即对于不同类别土质构成的岩土层,电法不但能探查确定咸淡水界面的深度,而且与以往的手法比较也是一种简单、快速、可靠、成本低廉的确定咸淡水界面深度的方法.     

Seawater intrusion in Syrian coastal aquifers, past, present and future, case study

Overexploitation of shallow aquifers on the Syrian coast, north of Latakia (Damsarkho) for irrigation and tourism has caused an intrusion of seawater. The seawater intrusion into this aquifer has been presented by a three-dimensional finite element model using the FEFLOW numerical code. This conceptual model is based on field and laboratory data collected during the period 1966–2003. Meteoric infiltration and flows from the adjoining carbonate aquifer recharge the aquifer; natural outflow occurs through a diffuse flow into the sea; and artificial outflow occurs through intensive extraction of groundwater from wells. Water exchanges in the aquifer occur naturally (leakage) and artificially (multi-screened wells). The model was calibrated for transient conditions. The model helped establish that seawater intrusion is essentially due to withdrawals near the coast during the irrigation season and that it mainly occurs in the Damsarkho plain. The effects of hypothetical aquifer exploitation were assessed in terms of salt budget.     

Impact of sandy beach recovery on solute transport in coastal unconfined aquifers

Hydrogeology Journal - Beach recovery describes the processes by which there is a natural restoration of beach material and coastal morphology following storm events, and these processes are common...     

Comparative study of urban development and groundwater condition in coastal areas of Buenos Aires,Argentina

The geomorphological evolution of a sand-dune barrier in Buenos Aires, Argentina, is analyzed as a factor regulating the fresh groundwater reserves available. The impact of geomorphological evolution and the consequences for the social and economic development of two coastal areas are assessed. This is one of the most important tourist destinations in the country; for study purposes, it was divided into a northern sector and a southern sector. In the southern sector, the exploitable groundwater is associated with the Holocene and upper Pleistocene geomorphological evolution, which generated three interrelated aquifer units, constituting a system whose useful thickness reaches at least 45 m. In contrast, the northern sector is restricted to two Holocene aquifer units, whose total thickness is on the order of 12 m. The morphological characteristics and the occurrence of the largest fresh groundwater reserves in the southern sector are indicators of better conditions for economic growth, which is mainly reflected on the expansion of real estate ventures. The relationships of transmissivity vs area of real estate ventures (Arev), and total water consumption vs Arev, are indicators for the sustainable management of the water resources. The approach chosen may be used by decision makers in other regions to assess the feasibility of future tourism projects on the basis of the availability of water resources associated with geomorphological features.     

The integrated impacts of natural processes and human activities on groundwater salinization in the coastal aquifers of Beihai,southern China

Salinization in coastal aquifers is usually related to both seawater intrusion and water–rock interaction. The results of chemical and isotopic methods were combined to identify the origin and processes of groundwater salinization in Daguansha area of Beihai, southern China. The concentrations of the major ions that dominate in seawater (Cl^?, Na⁺, Ca²⁺, Mg²⁺ and SO ₄ ^2– ), as well as the isotopic content and ratios (²H, ¹⁸O, ⁸⁷Sr/⁸⁶Sr and ¹³C), suggest that the salinization occurring in the aquifer of the coastal plain is related to seawater and that the prevailing hydrochemical processes are evaporation, mixing, dissolution and ion exchange. For the unconfined aquifer, groundwater salinization has occurred in an area that is significantly influenced by land-based sea farming. The integrated impacts of seawater intrusion from the Beibuwan Gulf and infiltration of seawater from the culture ponds are identified in the shallowest confined aquifer (I) in the middle of the area (site BBW2). Leakage from this polluted confined aquifer causes the salinization of groundwater in the underlying confined aquifer (II). At the coastal monitoring site (BBW3), confined aquifer I and lower confined aquifer II are heavily contaminated by seawater intrusion. The weak connectivity between the upper aquifers, and the seaward movement of freshwater, prevents saltwater from encroaching the deepest confined aquifer (III). A conceptual model is presented. Above all, understanding of the origin and processes of groundwater salinization will provide essential information for the planning and sustainable management of groundwater resources in this region.     

Vulnerability of groundwater systems with sea level rise in coastal aquifers, South Korea

Groundwater systems in coastal aquifers may be affected by sea level change as increased seawater intrusion occurs with sea level rise. Artificial pumping taking place at the same time will increase this impact. In order to estimate the vulnerability of groundwater systems with sea level rise within coastal aquifers in South Korea, long-term groundwater data were analyzed using basic statistics, trend analysis, and correlation analysis. Conductivity depth profiling was also periodically conducted. Groundwater levels increased in wells with relatively low groundwater elevations but decreased in wells with higher groundwater elevations. At the same time, conductivity variations were greater in wells located in reclaimed land areas, which vertical conductivity profiles indicated were more affected by sea level variations, but decreased on the mainland. Results of auto-correlation analysis showed a decreasing trend with cyclic variations and significant periodic patterns during dry seasons, indicating that groundwater levels were not affected by artificial factors and that those in reclaimed land areas were less affected by rainfall than on the mainland. These results coincided with those from cross-correlation analysis showing that groundwater level was affected by sea level variation during the dry season. Sea level changes, which may be related to climate change, as well as rainfall in South Korea can influence groundwater levels, and the groundwater system in reclaimed land areas may be more affected than on the mainland, especially under dry conditions.     

The impact of cattle pasturing on groundwater quality in bedrock aquifers having minimal overburden

Widespread agricultural activity may threaten water quality in fractured bedrock aquifers having little overburden protection. A study in Canada improves the understanding of the potential impact of agriculture on water quality in bedrock aquifers, focusing on spatial and temporal variability of nitrate and bacteria. A research site was developed in and adjacent to a hay field where a gneissic aquifer is overlain by a thin veneer of unconsolidated glacial material. Ten wells were installed, hydraulically tested and completed as multilevel piezometers. Results of monthly sampling for nitrate, dissolved organic carbon, and E. coli show significant temporal and spatial variation in concentrations. Intensive 5-day sampling rounds conducted during baseflow and recharge conditions indicate that bacterial concentrations vary daily, with higher concentrations during recharge periods. The location of the impacted monitoring wells is correlated to an upgradient cattle pasture that is used periodically each summer. It is evident that periodic upgradient sources, dilution from recharge, and heterogeneous flow systems lead to varied and unpredictable contaminant concentrations. The temporal and spatial variability of contaminants in bedrock aquifers with minimal overburden must be considered for the protection of human health, as annual or even monthly groundwater monitoring may not capture unsafe concentrations.     

近松散含水层下采煤安全性熵值模糊综合评判

基于模糊数学理论,通过统计经验数据,采用熵值法对影响近松散含水层安全开采的关键因素赋权,利用GIS定量确定各个因素的隶属度,构造了基于熵值的模糊综合评判模型。以山东某矿六采区01工作面开采为例,选择覆岩厚度、断层构造、第四系底部粘土层厚度、底部含水层的单位涌水量、煤层开采厚度、导水裂隙带高度6个影响因素为评判指标,确定了可行性程度的评判集:{较低,低,中等,高,很高},依据水体下开采的有关安全规程,采用GIS方法确定了各个因素的隶属度,并利用历史开采经验数据确定各个影响因素的权重。对该工作面近松散含水层下开采的评判结果表明,该工作面控制采高为2 m时开采是安全可行的,开采过程中针对薄弱环节采取了相应措施,没有发生突水溃砂事件,初步验证了该模糊综合评判模型的实用性。