Fresh Groundwater Resources Research Articles

Management of Seawater Intrusion in Coastal Aquifers: A Review

Seawater intrusion (SWI) is one of the most challenging and widespread environmental problems that threaten the quality and sustainability of fresh groundwater resources in coastal aquifers. The excessive pumping of groundwater, associated with the lack of natural recharge, has exacerbated the SWI problem in arid and semi-arid regions. Therefore, appropriate management strategies should be implemented in coastal aquifers to control the impacts of SWI problems, considering acceptable limits of economic and environmental costs. The management of coastal aquifers involves the identification of an acceptable ultimate landward extent of the saline water body and the calculation of the amount of seaward discharge of freshwater that is necessary to keep the saline–freshwater interface in a seacoast position. This paper presents a comprehensive review of available hydraulic and physical management strategies that can be used to reduce and control SWI in coastal aquifers. Advantages and disadvantages of the different approaches are presented and discussed.

Investigation into the microbial communities and associated crude oil-contamination along a Gulf War impacted groundwater system in Kuwait

During the First Gulf War (1991) a large number of oil wells were destroyed and oil fires subsequently extinguished with seawater. As a result Kuwait’s sparse fresh groundwater resources were severely contaminated with crude oil. Since then limited research has focused on the microbial community ecology of the groundwater and their impact on the associated contamination. Here, the microbial community ecology (bacterial, archaeal and eukaryotic) and how it relates to the characteristics of the hydrocarbon contaminants were examined for the first time since the 1991 event. This study was conducted using 15 wells along the main groundwater flow direction and detected several potential hydrocarbon degrading microorganisms such as Hyphomicrobiaceae, Porphyromonadaceae and Eurotiomycetes. The beta diversity of the microbial communities correlated significantly with total petroleum hydrocarbon (TPH) concentrations and salinity. The TPH consisted mainly of polar compounds present as an unresolved complex mixture (UCM) of a highly recalcitrant nature. Based on the proportions of TPH to dissolved organic carbon (DOC), the results indicate that some minor biodegradation has occurred within highly contaminated aquifer zones. However, overall the results from this study suggest that the observed variations in TPH concentrations among the sampled wells are mainly induced by mixing/dilution with pristine groundwater rather than by biodegradation of the contaminants. The findings make an important contribution to better understand the fate of the groundwater pollution in Kuwait, with important implications for the design of future remediation efforts.

Global potential for the growth of fresh groundwater resources with large beach nourishments

Whether a coastal area is suitable for beach nourishments and can induce a growth in fresh groundwater resources depends on the appropriateness of the intended site for beach nourishments, and the attainable growth in fresh groundwater resources. In this study we presume that all eroding sandy beaches are suitable for large beach nourishments, and focus on the impact of these nourishments on fresh groundwater in various coastal settings. The growth in fresh groundwater resources – as a consequence of the construction of a beach nourishment – was quantified with 2-D variable-density groundwater models, for a global range in geological parameters and hydrological processes. Our simulation results suggest that large beach nourishments will likely lead to a (temporary) increase of fresh groundwater resources in most settings. However, for a substantial growth in fresh groundwater, the coastal site should receive sufficient groundwater recharge, consist of sediment with a low to medium hydraulic conductivity, and be subject to a limited number of land-surface inundations. Our global analysis shows that 17% of shorelines may consist of erosive sandy beaches, and of these sites 50% have a high potential suitability. This shows a considerable potential worldwide to combine coastal protection with an increase in fresh groundwater resources.

Integrating hydrogeological, geophysical, and remote-sensing data to identify fresh groundwater resources in arid regions: a case study from Western Iraq

There is a limited availability of fresh groundwater in the western part of Iraq due to the aridity of the region, and new water supplies are required to meet the demands of potential industrial, mining, and agricultural projects. Consequently, the factors that influence the quality, availability, and distribution of fresh groundwater in the region were assessed by combining hydrogeological, geophysical, and remote-sensing data within a GIS environment. For this purpose, the Shuttle Radar Topography Mission elevation data, geophysical data (gravity and magnetic), and hydrogeological database were used in an integrated approach. It was concluded that both a regionally extensive, deep intergranular aquifer and shallow-fractured and karstified carbonate aquifers have the potential to contain fresh groundwater in the region. It was inferred from the hydrochemical statistics that the main factors controlling groundwater chemistry are the dissolution of evaporite minerals and the weathering of carbonate rocks. Gravity (measured and satellite) data and magnetic data were processed and interpreted to identify the locations and characteristics of subsurface structures. Source Parameter Imaging was applied to calculate depth to the magnetic basement map from gridded magnetic data. The decompensative anomaly maps showed that zones with fresh groundwater are distributed on gravity lows which coincide with areas with a large depth to basement. Most of the fresh groundwater zones in the region are distributed between the pre-Tertiary and Tertiary axes of the Ha’il Arch due to increased recharge along this structure caused by intense fracturing. The extension of the gravity high outside the Iraq territory may suggest similar freshwater zones of groundwater occur in Syria, Jordan, and Saudi Arabia.

Potential of mixed hydraulic barriers to remediate seawater intrusion.

Remediation measures are crucial to prevent or reverse seawater intrusion deteriorating coastal fresh groundwater resources. The mixed hydraulic barrier approach, as a combination of positive and negative hydraulic barriers, holds promising advantages especially for arid areas because extracted water provides a resource for injection after treatment. However, transient remediation mechanisms and impact of parameters are still unsatisfyingly understood. Therefore, the feasibility and optimal management of mixed hydraulic barriers as well as a comparison to single positive and negative barriers are explored with a synthetic 2D variable-density model of an already salinated, unconfined coastal aquifer using SEAWAT and FloPy. The hydraulic conductivity, porosity, injection and extraction rate, barrier locations, injection salt concentration, and reduction of pumping stress are varied jointly to determine the parameters' impact and interdependencies. The hydraulic conductivity controls the overall remediation potential as a hydrogeological component. Reduced inland abstractions of supply wells and the injection rates of the positive barrier show the largest remediation effects. However, locating the positive barrier within the salt wedge poses the risk of trapping salt landside. A sole negative barrier did not improve remediation substantially. This study thus shows that remediation with mixed hydraulic barriers can be feasible if implemented according to local conditions.

Combined influence of weir construction and sea-level rise on freshwater resources of a coastal aquifer in northern Germany

A significant volume of an aquifer along the coastline in the German Bight is salinized by seawater intrusion. The mean sea-level rise (MSLR) is expected to continue in the future due to global climatic change, subsequently degrading the fresh groundwater resources. To impede further salinization in the future, a solution is proposed based on weir construction in an existing canal hydraulically connected to the aquifer. The effect is twofold: (1) the elevated groundwater level can upgrade present fresh groundwater resources by shifting the saltwater–freshwater interface position further seaward, or by inhibiting its landward movement, and (2) the inland water level can be elevated, expanding surface water ponds. A fully coupled three-dimensional numerical surface-subsurface model (a modified HydroGeoSphere code) was used to simulate the effects of variable weir construction heights under different MSLR rates, and to quantify the gain of aquifer freshwater volume and loss of usable land due to surface ponding. Construction of a higher weir increases the desalinized aquifer volume and decreases the newly salinized aquifer volume under future MSLR. A minimum height of a weir was determined under a certain MSLR rate to maintain the present freshwater resource. Both weir construction and MSLR can cause the loss of land usage. Computed loss-gain ratio curves can be utilized to determine the optimal weir height, meeting the economic requirements of coastal land management under future MSLR.

Application of VES and ERT for delineation of fresh-saline interface in alluvial aquifers of Lower Bari Doab, Pakistan

Geophysical methods are effectively used to delineate intrusion boundary between the fresh and saline aquifers because of their intrinsic capability to assess the lateral variations in the pore-water salinity. In this study, an integrated geophysical approach of vertical electrical sounding (VES) and electrical resistivity tomography (ERT) has been conducted to delineate the contaminated aquifers in the Lower Bari Doab, Pakistan. Electrical resistivity tomography (ERT) using Schlumberger array with 5 m electrode spacing was conducted along eleven profiles at three selected sites (LBD1, LBD2 and LBD3) in the investigated area. The surface geoelectrical method was performed by sixty electrical resistivity soundings using the same array with maximum current electrode spacing (AB = 150 m). The integration of formation resistivity with ten boreholes reveals four discrete subsurface layers i.e., clay having saline aquifer, clay-sand containing brackish aquifer, sand with fresh aquifer and gravel-sand containing fresh aquifer. Estimation of Dar-Zarrouk Parameters (i.e., longitudinal resistivity, transverse resistance and longitudinal conductance) from different combinations of aquifer thickness and resistivity delineated the fresh, brackish and saline water zones with specific values range through mapping and graphical analysis. Geochemical method was performed on forty wells for main cations (K+, Na+, Ca2+ and Mg2+), anions (SO42−, Cl−, HCO3– and NO3−) and other parameters (As, EC, TDS and pH) to validate the results obtained from the geophysical methods. The fresh/saline aquifers delineated by the inclusion of ERT and geoelectrical method are in good agreement with those revealed by the physicochemical analysis and the local hydrogeological data. The results suggest that the use of non-invasive geophysical methods can reduce the number of expensive boreholes to obtain an interface between the fresh and saline water for the exploitation of fresh groundwater resources in any large area of homogeneous or heterogeneous aquifers.

Automatic identification of fresh–saline groundwater interfaces from airborne electromagnetic data in Zeeland, the Netherlands

ABSTRACTIn a setting of predominantly saline surface waters in Zeeland, the Netherlands, the only available shallow fresh groundwater resource is present in the form of freshwater lenses floating on top of saline groundwater. This fresh water is vital for agricultural, industrial, ecological, water conservation and drinking water functions. An essential first step for managing the usable water properly is to know the location of the fresh–saline groundwater interface. Traditional salinity mapping with ground‐based vertical electrical soundings, electrical cone penetration tests or chloride measurements from groundwater samples is time‐consuming and, therefore, expensive to cover large areas. Airborne electromagnetics, which is fast and can cover large areas in short time, is an efficient alternative. Therefore, a consortium of BGR, Deltares and TNO conducted the project FRESHEM Zeeland during 2014–2017. An area of more than 2000 km² was surveyed using BGR's helicopter‐borne geophysical system totalling 9640 line‐km. The helicopter‐borne electromagnetic data, after inversion to resistivity–depth models, served as baseline information for further interpretation. Without information on lithology, however, an accurate discrimination between fresh and saline groundwater applying fixed resistivity thresholds would fail if clayey sediments exist. Therefore, a probabilistic Monte Carlo approach was developed within the FRESHEM project. This approach combines helicopter‐borne electromagnetic resistivities, 3D geological model (GeoTOP), laboratory results (formation factor and surface conductivity) and local in situ groundwater measurements for the translation of resistivity data to chloride concentration. As such detailed information is generally not available, another approach, which uses only helicopter‐borne electromagnetic results to derive the thicknesses of the freshwater lenses from smooth inversion models, is presented in this paper. The corresponding fresh–saline groundwater interfaces are derived from steepest resistivity–depth (log–log) gradients appearing within a certain resistivity range. The bounds of this range are defined by resistivity values, which predominantly correlate with fresh or saline water, nearly independent of the lithology type. The results of this approach are checked using both synthetic and field data. The latter are compared with electrical cone penetration test measurements, the common threshold approach and the 3D chloride distribution of the FRESHEM results, particularly in an evaluation area where the transition of fresh to saline groundwater is relatively sharp. The fresh–saline groundwater interfaces derived by all methods are quite similar on average with deviations in the order of a metre. Locally, however, greater deviations occur, particularly close to the coast and along creek ridges or dunes, where the elevation of the fresh–saline groundwater interface varies notably.

Analysis of Aquifer Pumping Test Data to Determine Deep Groundwater Security in Southeastern Bangladesh

In southeastern Bangladesh, where water quality in the upper aquifers is a serious constraint, future development will likely be confined to deep fresh groundwater. Owing to the importance and pervasive use of deep groundwater, the sustainability of water use has received extensive attention. However, excessive extraction from deep aquifers may pose a threat to the storage as well as the quality of water due to the high susceptibility to salinization and arsenic contamination from upper aquifers. Hence, determining the extension of aquifer units and the characterizing aquifer sediments are very important to ensure sustainable development and management of limited fresh groundwater resources. The study area extends over six districts of the southeastern coastal region of Bangladesh. In order to assess and monitor deep fresh groundwater potential in the study area, aquifer pumping tests were performed at six locations with up to 72 h of constant-discharge prior to recovery. Different methods were used to analyze the drawdown and recovery data considering aquifers as confined or leaky-confined. Based on transmissivity values it was found that the studied deep aquifers have moderate to high potential for potable water supply. However, this deep fresh groundwater may not be safe for a longer period where upper aquifer units contain saline groundwater and where there is no significant aquitard encountered above or below the deep aquifer. Irrigation extraction of the deep groundwater is not recommended.

Impacts of Sea Level Rise and Groundwater Extraction Scenarios on Fresh Groundwater Resources in the Nile Delta Governorates, Egypt

As Egypt’s population increases, the demand for fresh groundwater extraction will intensify. Consequently, the groundwater quality will deteriorate, including an increase in salinization. On the other hand, salinization caused by saltwater intrusion in the coastal Nile Delta Aquifer (NDA) is also threatening the groundwater resources. The aim of this article is to assess the situation in 2010 (since this is when most data is sufficiently available) regarding the available fresh groundwater resources and to evaluate future salinization in the NDA using a 3D variable-density groundwater flow model coupled with salt transport that was developed with SEAWAT. This is achieved by examining six future scenarios that combine two driving forces: increased extraction and sea level rise (SLR). Given the prognosis of the intergovernmental panel on climate change (IPCC), the scenarios are used to assess the impact of groundwater extraction versus SLR on the seawater intrusion in the Delta and evaluate their contributions to increased groundwater salinization. The results show that groundwater extraction has a greater impact on salinization of the NDA than SLR, while the two factors combined cause the largest reduction of available fresh groundwater resources. The significant findings of this research are the determination of the groundwater volumes of fresh water, brackish, light brackish and saline water in the NDA as a whole and in each governorate and the identification of the governorates that are most vulnerable to salinization. It is highly recommended that the results of this analysis are considered in future mitigation and/or adaptation plans.

Groundwater Resources and Their Role in Water Supply to Crimea

The processes of formation and distribution of the resources of fresh groundwater and surface water in the territory of Crimea Peninsula are considered. Water availability in the natural–historic and administrative regions of the republic is characterized. The proportions between different categories of groundwater resources are shown with their role in water supply to Crimea taken into account. The presentday development of groundwater resources is analyzed and the possible increase in water consumption meeting geoecological requirements is substantiated.

Competition for shrinking window of low salinity groundwater

Groundwater resources are being stressed from the top down and bottom up. Declining water tables and near-surface contamination are driving groundwater users to construct deeper wells in many US aquifer systems. This has been a successful short-term mitigation measure where deep groundwater is fresh and free of contaminants. Nevertheless, vertical salinity profiles are not well-constrained at continental-scales. In many regions, oil and gas activities use pore spaces for energy production and waste disposal. Here we quantify depths that aquifer systems transition from fresh-to-brackish and where oil and gas activities are widespread in sedimentary basins across the United States. Fresh-brackish transitions occur at relatively shallow depths of just a few hundred meters, particularly in eastern US basins. We conclude that fresh groundwater is less abundant in several key US basins than previously thought; therefore drilling deeper wells to access fresh groundwater resources is not feasible extensively across the continent. Our findings illustrate that groundwater stores are being depleted not only by excessive withdrawals, but due to injection, and potentially contamination, from the oil and gas industry in areas of deep fresh and brackish groundwater.

Hydrochemical behaviour of an underground dammed limestone aquifer in the subtropics

AbstractIn an island area with limited surface water resources, the conservation of fresh groundwater resources is important for the maintenance of the water supply and irrigation system to be used in agricultural activity. In a limestone aquifer used for irrigation on a subtropical island, the progress of the dissolution behaviour of the aquifer and the effects of CO2 storage and chemical weathering of the aquifer must be understood to ensure sustainable groundwater use. In this study, hydrochemical behaviour of the Ryukyu limestone aquifer was investigated using the residence time of slowly flowing groundwater, which is contained by a 2.3‐km‐long underground man‐made dam constructed in 2005 located at the southern edge of Okinawa Island, Japan. Groundwater dating and horizontal flow velocity measurements indicate that the groundwater horizontal flow is slow in the underground dam area, whereas the saturation index (SI) for calcite indicates that the majority of the limestone exists in a supersaturated condition. The range of SI for gypsum was indicative of subsaturation, and the SI increased with the groundwater residence time, suggesting that the dissolution of CaSO4 tends to proceed slowly through the common ion effect. The dissolution of CaCO3, however, tends to be in suspension within about a residence time of 20 years. The apparent dissolution rate of Ca in the Ryukyu limestone aquifer in this area was estimated to be approximately 2.70–4.06 nmol cm−2 year−1, a value much lower than that of the early stages of the limestone dissolution. The estimated groundwater CO2 (gas) concentrations are two order high (about 0.3–7%) relative to atmospheric CO2 (about 0.04%), and the groundwater pH shows a tendency to decrease from 7.4 to 6.9 over the last approximately 20 years, indicating that the hydration reaction of CO2 occurs in the Ryukyu limestone aquifer. These findings imply that high CO2 produced in the subtropical zone is consumed slower than CO2 production during limestone dissolution, with the exclusion of the early stage of the chemical weathering process, and causes groundwater acidification in the underground dammed limestone aquifer.

Drivers, patterns and velocity of saltwater intrusion in a stressed aquifer of the East African coast: Joint analysis of groundwater and geophysical data in southern Kenya

Fresh groundwater resources in coastal East Africa are crucial for the region's socio-economic development but are under threat of salinization caused by changes in recharge patterns and increasing abstraction. With the aim of establishing the drivers behind saltwater intrusion and its current spatial extent, we studied the Kenyan South Coast aquifer, a representative, strategic aquifer under increased pressure. Investigations included electrical resistivity tomography (ERT) surveys and in-situ groundwater measurements (water table and basic quality) together with the analysis of available long-term climatic and borehole monitoring data. Over the last 40 years, groundwater electrical conductivity values at the well field increased by about three times and groundwater levels declined by 1–3 m over the last decade. When put in perspective with the long-term climate (rainfall, temperature) and abstraction records, these trends in groundwater appear to be primarily driven by increased borehole abstraction (+400 m3/day per year in average), whereas observed increasing temperature (+0.02 °C per year) and decreasing rainfall (−0.8 mm per year) could potentially act as a secondary control through reduced recharge. However the low statistical significance obtained for both rainfall and temperature trends over the observation period suggests that no clear conclusion can be made with regards to long-term climate impact on groundwater. Groundwater quality mapping showed that proximity to the ocean, presence of abstraction well-fields and regional geology control groundwater salinity patterns at regional scale. Locally, geophysical data showed that, saltwater intrusion spatial patterns are controlled by local aquifer lithology, groundwater abstraction and freshwater recharge in floodplains. Comparison with previous (1984) resistivity data showed that the saltwater front has advanced toward the well-field by up to 2 km and rose by up to 80 m over the last 30 years, which corresponds to a maximal velocity of about 60 m/y horizontally and 2 m/y vertically. Implementation of groundwater management strategies such as sustainable groundwater exploitation, sourced alternative water supply, and managed aquifer recharge are required to mitigate the effects of seawater intrusion along the East African coastal strip.

Large-scale, probabilistic salinity mapping using airborne electromagnetics for groundwater management in Zeeland, the Netherlands

Seawater intrusion has often resulted in scarce fresh groundwater resources in coastal lowlands. Careful management is essential to avoid the overexploitation of these vulnerable fresh groundwater resources, requiring detailed information on their spatial occurrence. Airborne electromagnetics (EM) has proved a valuable tool for efficient mapping of ground conductivity, as a proxy for fresh groundwater resources. Stakeholders are, however, interested in groundwater salinity, necessitating a translation of ground conductivity to groundwater salinity. This paper presents a methodology to construct a high-resolution (50 × 50 × 0.5 m3) 3D voxel model of groundwater chloride concentration probability, based on a large-scale (1800 km2, 9640 flight line kilometres) airborne EM survey in the province of Zeeland, the Netherlands. Groundwater chloride concentration was obtained by combining pedotransfer functions with detailed lithological information. The methodology includes a Monte Carlo based forward uncertainty propagation approach to quantify the inherent uncertainty in the different steps. Validation showed good correspondence both with available groundwater chloride analyses, and with ground-based hydrogeophysical measurements. Our results show the limited occurrence of fresh groundwater in Zeeland, as 75% of the area lacks fresh groundwater within 15 m below ground surface. Fresh groundwater is mainly limited to the dune area and sandy creek ridges. In addition, significant fresh groundwater resources were shown to exist below saline groundwater, where infiltration of seawater during marine transgressions was hindered by the presence of clayey aquitards. The considerable uncertainty in our results highlights the importance of applying uncertainty analysis in airborne EM surveys. Uncertainty in our results mainly originated from the inversion and the 3D interpolation, and was largest at transition zones between fresh and saline groundwater. Reporting groundwater salinity instead of ground conductivity facilitated the rapid uptake of our results by relevant stakeholders, thereby supporting the necessary management of fresh groundwater resources in the region.

Forest fire effects on groundwater in a coastal aquifer (Ravenna, Italy)

AbstractWe examined the fire‐induced changes in groundwater recharge rate. This aspect is particularly important in the case of large forested areas growing over a coastal aquifer affected by saltwater intrusion. In the Ravenna coastal area (Italy), pine forests grow on coastal dune belts, overlying a sandy unconfined aquifer, which is strongly affected by marine ingression. Three groundwater profiles across the forest and perpendicular to the coastline were monitored for groundwater level, physical, and chemical parameters. The aims were to define groundwater quality, recharge rate, freshwater volume, and highlight change, which occurred after a forest fire with reference to pre‐fire conditions. Analytical solutions based on Darcy Law and the Dupuit Equation were applied to calculate unconfined flow and compare recharge rates among the profiles. The estimated recharge rates increased in the partially and completely burnt areas (219 and 511 mm year−1, respectively) compared with the pristine pine forest area (73 mm year−1). Although pre‐fire conditions were similar in all monitored profiles, a post‐fire decrease in salinity was observed across the burnt forest, along with an increase in infiltration and freshwater lens thickness. This was attributed to decrease canopy interception and evapotranspiration caused by vegetation absence after the fire. This research provided an example of positive forest fire feedback on the quantity and quality of fresh groundwater resources in a lowland coastal aquifer affected by saltwater intrusion, with limited availability of freshwater resources. The fire provided an opportunity to evaluate a new forest management approach and consider the restoration and promotion of native dune herbaceous vegetation.

Peoples’ Perception of the Water Salinity Impacts on Human Health: A Case Study in South-Eastern Coastal Region of Bangladesh

The salinity intrusion into fresh groundwater is a serious problem in coastal regions of Bangladesh. It has both direct and indirect effects on human well-being. This study was carried out in two coastal villages of south-eastern part of Bangladesh with the aim of examining peoples’ perception of the water salinity impacts on human health. Data were collected from randomly selected 153 semistructured household interviews, 10 key-informant interviews and two group discussions. The water salinity was measured for shallow tube-well (STW) and pond in three distinct seasons. The mean water salinity of STW varied from 5.11 to 6.48 dS/m, while pond water salinity level was in the range of 0.11–3.12 dS/m. The salinity level varied depending on depth of tube-well and distance from the sea. Due to the use of saline water, villagers suffered from several diseases including skin diseases, hair loss, diarrhea, gastric and high blood pressure. In one village high salinity restricted villagers to practice agriculture on limited agricultural land. Increasing salinity due to adverse climatic conditions in coastal areas would pose a serious threat on household water supplies. Suggestions are made to improve the management of fresh surface water and groundwater resources in salt-affected areas and to explore rainwater harvesting as a sustainable solution.

Numerical simulation of seawater intrusion to coastal aquifers and brine water/freshwater interaction in south coast of Laizhou Bay, China

Seawater intrusion and brine water/freshwater interaction have significantly affected agriculture, industry and public water supply at Laizhou Bay, Shandong Province, China. In this study, a two-dimensional SEAWAT model is developed to simulate the seawater intrusion to coastal aquifers and brine water/fresh water interaction in the south of Laizhou Bay. This model is applied to predict the seawater intrusion and brine water/freshwater interface development in the coming years. The model profile is perpendicular to the coastal line with two interfaces, freshwater-saline water interface near the shore and inland brine water-saline water-seawater interface. The hydrogeological parameters in the SEAWAT-2000 model are calibrated by the head and salinity measurements. The precipitation infiltration coefficient, boundary conditions and thicknesses of aquifers are studied in a sensitivity analysis. The predicted results indicate that equivalent freshwater head in shallow freshwater-saline water area will decline 2.0 m by the end of the forecasting period, caused by groundwater over-pumping for farmland irrigation. The groundwater head in the brine-saline water area will also decrease about 1.8 m by the end of forecasting period, caused by excessive brine mining. Salinity finally decreases below 105 g/L in the brine area, but increases in other areas and contaminates fresh groundwater resources.

Using InSAR Coherence for Investigating the Interplay of Fluvial and Aeolian Features in Arid Lands: Implications for Groundwater Potential in Egypt

Despite the fact that the Sahara is considered the most arid region on Earth, it has witnessed prolonged fluvial and aeolian depositional history, and might harbor substantial fresh groundwater resources. Its ancient fluvial surfaces are, however, often concealed by aeolian deposits, inhibiting the discovery and mapping of potential groundwater recharge areas. However, recent advances in synthetic aperture radar (SAR) imaging offer a novel approach for detecting partially hidden and dynamic landscape features. Interferometry SAR coherence change detection (CCD) is a fairly recent technique that allows the mapping of very slight surface changes between multidate SAR images. Thus, this work explores the use of the CCD method to investigate the fluvial and aeolian morphodynamics along two paleochannels in Egypt. The results show that during wetter climates, runoff caused the erosion of solid rocks and the rounding of sand-sized grains, which were subsequently deposited in depressions further downstream. As an alternating dry climate prevailed, the sand deposits were reshaped into migrating linear dunes. These highly dynamic features are depicted on the CCD image with very low coherence values close to 0 (high change), while the deposits within the associated ephemeral wadis show low to moderate coherence values ranging from 0.2 to 0.4 (high to moderate change), and the country rocks show a relative absence of change with high coherence values close to 1. These linear dunes crossed their parent’s stream courses and dammed the runoff to form lakes during rainy seasons. Part of the dammed surface water would have infiltrated the ground to recharge the permeable wadi deposits. The alternation of fluvial and aeolian depositional environments produced unique hydromorphometrically trapped lakes that are very rare in arid regions, but of great interest because of their significance to groundwater recharge.

Geographic mapping of tube wells and assessment of saltwater intrusion in the coastal areas of la union

A large number of coastal aquifers are threatened by saltwater intrusion. Over-abstraction due to high demands for domestic water supply is the main cause of saltwater intrusion. This can also be accelerated by the rise in sea level due to climate change and global warming. This reduces the fresh groundwater resources. With the impact of sea level rise and over-pumping combined together, the problem becomes even more serious.A large part of the province of La Union in the Ilocos Region, Northern Philippines is lying along the coastline, with its community stakeholders depending on wells for their source of water. Considering the safety of users, the study aimed to determine the incidence of saltwater intrusion in the coastal communities of La Union. In this study, the descriptive-qualitative research design was used. A questionnaire was formulated to determine the perceptions of the community stakeholders on the quality of water they are using but their responses were verified by the use of salinity meter to test the actual water salinity from the tube wells. Through the use of handheld Global Positioning System (GPS), the geographical coordinates depicting the location of the wells included in the study were identified. There was a total of 42 barangays selected as study sites. Using quota sampling, a total of 420 tube wells were subjected to analysis. A geographical map of tube wells showing the affected areas served as an output of the study.The research revealed that salt intrusion already exists into tube wells along coastal areas of La Union. Community stakeholders had already resorted to other sources/means for their water consumption.