Interactions between the surface water and groundwater in the western shoreline of Lake Nasser, Upper Egypt

The present study indicates that the factors controlling the hydraulic relation between surface water and groundwater at the western lake shoreline change from one locality to another. This depends upon the lithological characteristics and the major structures. In the southern sectors, sedimentation at the bottom and sides of the lake prevents the water movement to the Nubian sandstone aquifer. The potentiometric map reveals that the water level altitudes range between 170 m in the vicinity of the lakeshore line and 110 m west of the lake. The groundwater flow lines show that the main recharge to the aquifer comes from the southwest direction, as well as from the lake inland to variable distances (about 30 Km). During the present study, Darcy’s law was applied to calculate the recharge from the western shoreline of Lake Nasser to the adjacent Nubian aquifer. The maximum value of seepage was at Garf Hussein (27.71?×?10⁶ m³/year), which may be related to high permeability and hydraulic gradient. Also, it may be related to the N–S strike faults that cut the area on both sides of the Lake, and the groundwater is expected to have free circulation through the faults of this trend. The minimum value was recorded in Adindan section (0.61?×?10⁶ m³/year). This may be related to the limited recharge from the lake to the aquifer, due to the sedimentation that dislocates this recharge.     

Hydrogeochemical and isotopic evidence of groundwater evolution and recharge in aquifers in Beijing Plain, China

An investigation was conducted in Beijing to identify the groundwater evolution and recharge in the quaternary aquifers. Water samples were collected from precipitation, rivers, wells, and springs for hydrochemical and isotopic measurements. The recharge and the origin of groundwater and its residence time were further studied. The groundwater in the upper aquifer is characterized by Ca-Mg-HCO₃ type in the upstream area and Na-HCO₃ type in the downstream area of the groundwater flow field. The groundwater in the lower aquifer is mainly characterized by Ca-Mg-HCO₃ type in the upstream area and Ca-Na-Mg-HCO₃ and Na-Ca-Mg-HCO₃ type in the downstream area. The δD and δ¹⁸O in precipitation are linearly correlated, which is similar to WMWL. The δD and δ¹⁸O values of river, well and spring water are within the same ranges as those found in the alluvial fan zone, and lay slightly above or below LMWL. The δD and δ¹⁸O values have a decreasing trend generally following the precipitation → surface water → shallow groundwater → spring water → deep groundwater direction. There is evidence of enrichment of heavy isotopes in groundwater due to evaporation. Tritium values of unconfined groundwater give evidence for ongoing recharge in modern times with mean residence times <50 a. It shows a clear renewal evolution along the groundwater flow paths and represents modern recharge locally from precipitation and surface water to the shallow aquifers (<150 m). In contrast, according to ¹⁴C ages in the confined aquifers and residence time of groundwater flow lines, the deep groundwater is approximately or older than 10 ka, and was recharged during a period when the climate was wetter and colder mainly from the piedmont surrounding the plain. The groundwater exploitation is considered to be “mined unsustainably” because more water is withdrawn than it is replenished.     

A new model (DRASTIC-LU) for evaluating groundwater vulnerability in parts of central Ganga Plain,India

The study area is a part of central Ganga Plain which lies within the interfluve of Hindon and Yamuna rivers and covers an area of approximately 1,345 km². Hydrogeologically, Quaternary alluvium hosts the major aquifers. A fence diagram reveals the occurrence of a single aquifer to a depth of 126 m below ground level which is intercalated by sub-regional clay beds. The depth to water level ranges from 9.55 to 28.96 m below ground level. The general groundwater flow direction is northwest to southeast. Groundwater is the major source of water supply for agricultural, domestic, and industrial uses. The overuse of groundwater has resulted in the depletion of water and also quality deterioration in certain parts of the area. This has become the basis for the preparation of a groundwater vulnerability map in relation to contamination. The vulnerability of groundwater to contamination was assessed using the modified DRASTIC-LU model. The parameters like depth to water, net recharge, aquifer media, soil media, topography, impact of vadose zone, hydraulic conductivity of the aquifer, and land use pattern were considered for the preparation of a groundwater vulnerability map. The DRASTIC-LU index is computed as the sum of the products of weights and rating assigned to each of the inputs considered. The DRASTIC-LU index ranges from 158 to 190, and is classified into four categories, i.e., <160, 160–170, 170–180, and >180, corresponding to low, medium, high, and very high vulnerability zones, respectively. Using this classification, a groundwater vulnerability potential map was generated which shows that 2 % of the area falls in the low vulnerable zone, 38 % falls in the medium vulnerable zone, and 49 % of the area falls in the high vulnerable zone. About 11 % of the study area falls in the very high vulnerability zone. The groundwater vulnerability map can be used as an effective preliminary tool for the planning, policy, and operational levels of the decision-making process concerning groundwater management and protection.     

Water resources and geomorphological characteristics of Tushka and west of Lake Nasser, Egypt

The water level fluctuations and geomorphology of Lake Nasser reservoir in Tushka area, Egypt, has its own bearing on the local hydrogeological regime. Comparison of the available data concerning the submerged bottom elevations of Lake Nasser with the static water levels of the groundwater wells reaching the deeper horizons of the Nubia Sandstone aquifer, suggests that Lake Nasser acts mostly as an influent stream. However, in some cases, when the static water levels of some deep water-bearing horizons reach levels above those at the bottom of the lake, water flows from the groundwater reservoirs towards the river which acts as an effluent stream. The constructed equipotentiometric map confirms this conclusion as it indicated that the maximum potentiometric level was attained to the northwestern part of Lake Nasser area, whereas the minimum potentiometric level was encountered to the southeast of this area. Hence, the groundwater flow is generally towards Lake Nasser. However, in some instances, it also flows in an adverse direction. The Piper trilinear diagram revealed the existence of four hydrochemical facies reflecting the quality of the fresh water of Lake Nasser, the slightly saline original water quality of the Nubia aquifer and the mixing facies with no dominant water types.

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Resumen Las fluctuaciones del nivel de agua y la geomorfología del reservorio del Lago Nasser en el área de Tushka, Egipto, tienen su propia influencia sobre el régimen hidrogeológico local. La comparación de los datos disponibles acerca de las elevaciones del fondo sumergido de Lago Nasser, con los niveles estáticos de los pozos de agua subterránea que alcanzan los horizontes más profundos del acuífero de la Arenisca de Nubia, sugieren que el Lago Nasser actúa principalmente como una corriente influente. Sin embargo, en algunos casos, cuando los niveles estáticos de agua de algunos horizontes acuíferos profundos, alcanzan niveles por encima de aquellos del fondo del lago, el agua fluye desde los depósitos de agua subterránea hacia el río, que actúa entonces como una corriente efluente. El mapa equipotenciométrico construido confirma esta conclusión, pues indica que el nivel potenciométrico máximo estaba localizado en la parte noroccidental del área del Lago Nasser, mientras que el nivel potenciométrico mínimo se encontró al sudeste de esta área. Por lo tanto, el flujo del agua subterránea generalmente va hacia el Lago Nasser. Sin embargo, en algunos casos, también fluye en una dirección contraria. El diagrama trilinear de Piper, reveló la existencia de cuatro facies hidroquímicas que reflejan la calidad de agua dulce del Lago Nasser, la calidad de agua ligeramente salina original del acuífero de Nubia y las facies mezcladas sin tipos de agua dominantes.

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Résumé Les fluctuations du niveau d'eau ainsi que la géomorphologie du réservoir du lac Nasser dans la région de Tushka, Egypte influencent le régime hydrogéologique local. La comparaison de l'altitude des fonds du lac Nasser avec les niveaux phréatiques des puits qui atteignent les niveaux inférieurs de l'aquifère des grès Nubiens suggère que le lac Nasser agisse le plus souvent comme un cours d'eau infiltrant. Il arrive aussi, lorsque le niveau hydrostatique d'horizons aquifères profonds dépasse ceux de la base du lac, que l'eau des aquifères soutienne les eaux de la rivière qui agit alors comme un émissaire. Les cartes hydro isostatiques confirment cette conclusion en indiquant que le niveau maximum est atteint au Nord-Ouest de la région du lac Nasser et que le niveau minimum se trouve au Sud-Est de cette zone. Ainsi, les eaux souterraines se dirigent généralement en direction du lac Nasser. Mais, elles se dirigent parfois en direction inverse. Le diagramme de Piper montre l'existence de quatre faciès hydro chimiques, qui correspondent à l'eau douce du lac Nasser, à l'eau légèrement salée de l'aquifère Nubien, et les eaux mélangées sans types d'eaux dominants.

     

Hydrochemistry and isotope geochemistry as tools for groundwater hydrodynamic investigation in multilayer aquifers: a case study from Lomellina, Po plain, South-Western Lombardy, Italy

A multicriteria approach in studying hydrodynamics of a multilayer aquifer system has been used in the Lomellina region (Northern Italy). It involves the reconstruction of the hydrogeological framework coupled to the definition of the hydrochemical and isotopic features of the aquifers. A shallow phreatic aquifer, reaching depths of about 60–80 m from the surface, and deeper aquifers containing confined groundwater, were distinguished. Groundwater generally shows mineralisation decreasing with depth; dissolved ions depict calcium-bicarbonate hydrochemical facies and stable isotopes define the recharge mechanisms, the origin of groundwater, and the hydraulic confinement of deep aquifers. The phreatic aquifer is fed by local infiltration and by streams and irrigation channels. Tritium and Carbon-14 groundwater dating indicate long residence times (on the order of thousands of years) for confined aquifers. The confined aquifers show essentially passive hydrodynamic conditions and maintain a higher piezometric level than the phreatic aquifer. This inhibits the possibility of recent water penetrating far below the surface. The hydrogeological setting of the Lomellina region displays features which are common to other sectors of the Po plain. As a consequence, the results of this study, although conducted on a restricted area, are highly illustrative of groundwater hydrodynamics in large sedimentary aquifers.     

Geophysical characteristics of Wadi Hanifah water system, Riyadh, Saudi Arabia

Integrated geophysical techniques including resistivity image, vertical electrical sounding (VES), and seismic refraction have been conducted to investigate the Wadi Hanifah water system. The groundwater in Wadi Hanifah has problems caused by the high volumes of sewage water percolating into the ground. The combination of VES, resistivity image, and seismic refraction has made a valuable contribution to the identification of the interface between the contaminated and fresh water in Wadi Hanifah area. The contaminated groundwater has lower resistivity values than fresh groundwater due to the higher concentration of ions which reduces the resistivity. Resistivity image and sounding in this area clearly identified the nature of the lithological depth and proved useful at identifying water-bearing zones. Fresh groundwater was found in the study area at a depth of 100 m within the fractured limestone. Water-bearing zones occur in two aquifers, shallow contaminated water at 10 m depth in alluvial deposits and the deeper fresh water aquifer at a depth of about 100 m in fractured limestone. The interface between the contaminated water (sanitary water) and fresh water marked out horizontally at 100 m distance from the main channel and vertically at 20 m depth.     

Rate and budget of blown sand movement along the western bank of Lake Nasser,southern Egypt

Three sets of Landsat? satellite images for the years 1993, 1998, and 2003 show that the sand dunes at the southwestern Desert of Egypt are generally moving towards southeast direction with a mean annual creeping speed over ground attaining 15 m/year. The manual-stickled field measurements show that the net annual extension of the longitudinal dunes in the coastal area is between 4 and 5 m/year, while the inland longitudinal dunes showed a net movement ranging between 5 and 6 m/year. Seasonal variations of drift potential and sand movement refer to a strongly high energy wind desert environment in the spring season, high energy wind desert environment in the summer season, and relatively high to intermediate in the autumn and winter seasons, respectively. The total annual estimated volume of transported sand which falls down into Lake Nasser basin attains 16,225,808 m³ as calculated by Bagnold's equation and quantities of sand collected from the sand traps. Comparing this value with the total volume of Lake Nasser Basin, which attains 120?×?10⁹ m³, we can conclude that the sand sheets or sand accumulations may represent serious natural hazards to Lake Nasser in some locations. However, the sand drifting towards the lake may be obstructed by high contour topography hindrance, and the mean grain size of the sand sheets is bigger than 0.25 mm, which needs high wind velocity more than 4 m/s. In addition, the direction of the prevailing wind is N-NNW to S-SSE, and this direction sometimes is parallel to Lake Nasser in some places according to the meandering of the lake. The total lengths of hazardous areas along the western bank of Lake Nasser, which receive the most amounts of the drifted sands, attain 43.6 km only.     

Arsenic movement and traces in the groundwater from the Hetao area, Inner Mongolia

In the Hetao area of Inner Mongolia, Quaternary alluvial aquifers used for the water supply are contaminated by naturally occurring arsenic, which heavily affects the health of 200,000 local residents. This study on the isotopes of strontium and relevant elements contained in the groundwater as well as the arsenic in the groundwater and residents’ hair indicates that the arsenic originally derives from the upper reaches of this area where arsenic levels are high in groundwater, rock, and soil. Over, respectively, 44 km (work-line AA′) and 36 km (work-line BB′) away from there, the levels of arsenic in the water, corresponding to the trend of the residents’ arseniasis, decrease along the direction of the flow from 0.251 to 0.05 mg/L and 0.232 to 0.036 mg/L. The result of this research suggests that long-term strategies to deal with this arseniasis should involve finding hydrous terrains uncontaminated by water from the upper reaches and developing routes to prevent water from taking arsenic.     

变异条件下内蒙古呼包平原地下水演化趋势

重点探讨气候变异对内蒙古呼包平原地下水资源、地下水流场和动态的影响。在介绍呼包平原水文地质条件的基础上,运用地下水模型软件PMWIN 5.1建立了研究区双层地下水流模型,并根据1998年地下水动态观测和统测资料对模型进行识别。通过对近51 a降水量的分析,确定将连续出现的2个特枯年作为地下水的变异条件,运用地下水模型对变异条件下地下水状态进行模拟,结果表明：2年间对地下水的严重超采,使地下水亏空量达75 296.34 万m³,潜水和承压含水层的地下水位大幅度下降,潜水位最大下降4 m左右,承压水位最大下降17 m左右;漏斗中心主要集中在开采量大的呼和浩特和包头市区。     

Contribution to the hydrogeology of the Lower Cretaceous aquifer in east Central Sinai, Egypt

The present work deals with the groundwater aquifer of the Lower Cretaceous sandstone and its sustainable development in Sinai. The studied aquifer system is the most promising groundwater system in Sinai due to its wide extension, hug storage, and good quality. The objective of this paper aims to elucidate the hydrogeological characteristics of the Lower Cretaceous aquifer. The aquifer system occurs under confined conditions. The top surface of the Lower Cretaceous dips steeply towards the southwest direction with step faults. The average sand percent of the penetrated aquifer attains 54%. The main direction of groundwater flow is generally from southwest and locally is concentric to the center of study area related to the influence of the graben block. The aquifer has a hydraulic gradient generally reaches 0.0011 m/m and attains 0.0028 in central portion of study area. The aquifer parameters (effective porosity, transmissivity, and hydraulic conductivity) increase towards the northeast direction with increasing of the sand percentage. Durov diagram plot revealed that the groundwater has been a final stage evolution represented by a NaCl water type. The groundwater salinity increases towards the central of study area coinciding with groundwater flow. The groundwater salinity of the Lower Cretaceous aquifer is brackish water and varies from 2,510 to 5,256 ppm and unsuitable for drinking and domestic purposes.     

Constraining flow paths of saline groundwater at basin margins using hydrochemistry and environmental isotopes: Lake Cooper,Murray Basin,Australia

Solutes in saline groundwater (total dissolved solids up to 37 000 mg/L) in the Lake Cooper region in the southern margin of the Riverine Province of the Murray Basin are derived by evapotranspiration of rainfall with minor silicate, carbonate and halite dissolution. The distribution of hydraulic heads, salinity, percentage modern carbon (pmc) contents, and Cl/Br ratios imply that the groundwater system is complex with vertical flow superimposed on lateral flow away from the basin margins. Similarities in major ion composition, stable (O, H, and C) isotope, and ⁸⁷Sr/⁸⁶Sr ratios between groundwater from the shallower Shepparton Formation and the deeper Calivil – Renmark aquifer also imply that these aquifers are hydraulically interconnected. Groundwater in the deeper Calivil – Renmark aquifer in the Lake Cooper region has residence times of up to 25 000 years, implying that pre-land-clearing recharge rates were <1 mm/y. As in other regions of the Murray Basin, the low recharge rates account for the occurrence of high-salinity groundwater. Shallow (<20 m) groundwater yields exclusively modern ¹⁴C ages and shows a greater influence of evaporation over transpiration. Both these observations reflect the rise of the regional water-table following land clearing over the last 200 years and a subsequent increase in recharge to 10 – 20 mm/y. The rise of the regional water-table also has increased vertical and horizontal hydraulic gradients that may ultimately lead to the export of salt from the Lake Cooper embayment into the adjacent fresher groundwater resources.     

An integrated approach for groundwater assessment at the Northwestern Coast of Egypt (Ras El Hekma area): case study

Ras El Hekma area was chosen for the present study due to its special conditions; the area lacks water for human and agriculture proposes. This area represents one of the main headlands along the southern Mediterranean coast, where population growth and agricultural activities require the corresponding development of groundwater. The main objective of this paper is to monitor and record data about the current groundwater as well as to have a systematic understanding of the hydrogeological setting in the area of study. Also, one of the study objectives is to identify and assess the factors which affect the groundwater occurrence and quality. This assessment will contribute to groundwater protection. The study area has three aquifers: Holocene, Pleistocene, and Middle Miocene aquifers. The recharge to these aquifers comes from the direct infiltration of rainfall and from the surface runoff. Rock–water interaction and the effect of solution and leaching processes on the mineralization of groundwater are studied using the PHREEQC model. Seawater intrusion contributes effectively to the increase in water salinity. The present study clarifies the relationship between the depth to water, the sea level and salinity of water. The groundwater in the area of study is evaluated for drinking, domestic, livestock and agricultural purposes. The present study suggests some recommendations for developing the groundwater in the study area.     

Groundwater origin and flow along selected transects in Ethiopian rift volcanic aquifers

The disruption of lithologies by cross-cutting faults and the variability in volcanic structures make the hydrogeology of the rifted volcanic terrain in Ethiopia very complex. Along two transects, selected due to their hydrogeologic characteristics, groundwater flow, depth of circulation and geochemical evolution have been conceptualized. The groundwater flow continuity between the high rainfall plateau bounding the rift and the rift valley aquifers depends principally on the nature of the bounding faults. Up to 50% of recharge to the rift aquifers comes from the plateau as groundwater inflow where the rift is cross cut by transverse fault zones. Recharge from the mountains is found to be insignificant where the rift is bounded by marginal grabens; channel loss and local precipitation are the principal sources of recharge to the rift aquifers in such cases. At a regional scale, there is a clear zonation in the geochemical compositions of groundwaters, the result of aquifer matrix composition differences. The environmental isotope results show that the majority of the aquifers contain modern groundwaters. In a few localities, particularly in thermal groundwaters representing deeper circulation, palaeo-groundwaters have been identified. Deeper groundwaters in the rift floor have a uniform ¹⁴C age ranging between 2,300 and 3,000 years.     

Characteristic of groundwater potentialities in West Nile Valley South,Minia Governorate,Egypt

The main aim of the present study is to detect the status of groundwater resources in west Mallawi area which represented one of the new reclamation lands. In order to achieve this aim, the hydrogeological and hydrogeochemical studies are carried out, based on the results of 21 pumping tests and chemical analysis of 29 water samples. Two water-bearing units are detected in the study area, namely, the Eocene fractured limestone aquifer which occupies the east portion of the studied area. The second aquifer consists of friable sediments of sand and gravel and may be related to the late Oligocene–early Miocene age and overlies the limestone rocks in the west, and this aquifer were studied for the first time in this work. Regionally, the groundwater flow in the area under study occurs toward the north and east directions. There is a hydraulic connection between both aquifers through the structural pattern affected the area. The partial recharge of the both aquifers takes place through the upward leakage from deep aquifers and the Nile water. There is a general decrease in the water salinity from west to east direction. The groundwater of both aquifers was evaluated for the different purposes and concluded that, it is considered suitable for different uses.     

Numerical analysis of the hydrogeologic controls in a layered coastal aquifer system, Oahu, Hawaii, USA

 The coastal aquifer system of southern Oahu, Hawaii, USA, consists of highly permeable volcanic aquifers overlain by weathered volcanic rocks and interbedded marine and terrestrial sediments of both high and low permeability. The weathered volcanic rocks and sediments are collectively known as caprock, because they impede the free discharge of groundwater from the underlying volcanic aquifers. A cross-sectional groundwater flow and transport model was used to evaluate the hydrogeologic controls on the regional flow system in southwestern Oahu. Controls considered were: (a) overall caprock hydraulic conductivity; and (b) stratigraphic variations of hydraulic conductivity in the caprock. Within the caprock, variations in hydraulic conductivity, caused by stratigraphy or discontinuities of the stratigraphic units, are a major control on the direction of groundwater flow and the distribution of water levels and salinity. Results of cross-sectional modeling confirm the general groundwater flow pattern that would be expected in a layered coastal system. Groundwater flow is: (a) predominantly upward in the low-permeability sedimentary units; and (b) predominantly horizontal in the high-permeability sedimentary units. Received, October 1996 Revised, August 1997 Accepted, September 1997     

Groundwater occurrence and aquifer vulnerability assessment of Magodo Area,Lagos, Southwestern Nigeria

A combination of vertical electrical soundings (VES), 2D electrical resistivity imaging (ERI) surveys and borehole logs were conducted at Magodo, Government Reserve Area (GRA) Phase 1, Isheri, Southwestern Nigeria, with the aim of delineating the different aquifers present and assessing the groundwater safety in the area. The Schlumberger electrode array was adopted for the VES and dipole-dipole array was used for the 2D imaging. The maximum current electrode spread (AB) was 800 m and the 2D traverse range between 280 and 350 m in the east-west direction. The thickness of impermeable layer overlying the confined aquifer was used for the vulnerability ratings of the study area. Five lithological units were delineated: the topsoil, clayey sand, unconsolidated sand which is the first aquifer, a clay stratum and the sand layer that constitutes the confined aquifer horizon. The topsoil thickness varies from 0.6 to 2.6 m, while its resistivity values vary between 55.4 and 510.6 Ω/m. The clayey sand layers have resistivity values ranging from 104.2 to 143.9 Ω/m with thickness varying between 0.6 and 14.7 m. The resistivity values of the upper sandy layer range from 120.7 to 2195.2 Ω/m and thickness varies from 3.3 to 94.0 m. The resistivity of the clay layer varies from 11.3 to 96.1 Ω/m and the thickness ranges from 29.6 to 76.1 m. The resistivity value of the confined aquifer ranges between 223 and 1197.4 Ω/m. The longitudinal conductance (0.0017–0.02 mhos) assessment of the topsoil shows that the topsoil within the study area has poor overburden protective capacity, and the compacted impermeable clay layer shows that the underlying confined aquifer is well protected from contamination and can be utilized as a source of portable groundwater in the study area. This study therefore enabled the delineation of shallow aquifers, the variation of their thicknesses and presented a basis for safety assessment of groundwater potential zones in the study area.     

Characterisation of groundwater recharge conditions and flow mechanisms in bedrock aquifers of the Johannesburg area,South Africa

Groundwater is the major source of water and a critical resource for socioeconomic development in semi-arid environments like the Johannesburg area. Environmental isotopes are employed in this study to characterise groundwater recharge and flow mechanisms in the bedrock aquifers of Johannesburg, which is known for polluted surface water. With the exception of boreholes near the Hartbeespoort Dam, groundwater in the study area was derived from meteoric water that has undergone some degree of evaporation before recharge, possibly via diffuse mechanisms. Boreholes that tap groundwater from the Transvaal Supergroup Formation show depletion in δ¹⁸O and δ²H values. This is attributed to diffuse recharge through weathering fractures at high elevation that are undergoing deep circulation or recharge from depleted rainfall from the high-latitude moisture sources. The influence of focused recharge from the Hartbeespoort Dam was observed in the boreholes north of the dam, possibly as a result of the north–south trending fault lines and the north-dipping fractures in the bedding planes of quartzites. This is also supported by a reservoir water budget method which indicated a mean annual net flux of 2,084,131 m³ from Hartbeespoort Dam recharging groundwater per annum. Using tritium in the dam and boreholes located at 750 m and 5400 m downstream, average groundwater flow velocity was estimated as 202 m/year. An open system was observed in shale, andesite and granitic-gneiss aquifers indicating soil CO₂ as a dominant source of carbon (δ¹³C) in groundwater. A closed system was also observed in dolomitic aquifers indicating carbonate dissolution as the predominant source of carbon.     

Studying the impacts of groundwater evolution on the environment,west Qena city,Egypt

The current research has been conducted to evaluate groundwater aquifers qualitatively in the area located in the Western side of Qena city. The Quaternary aquifer represents the main groundwater source in the study area. It exists under unconfined to semiconfined conditions at depths varying between 4 m due North and 80 m in the South. The chemical analyses of the groundwater samples indicate that 77% of the total samples are fresh and 20% are brackish, while only 3% are saline. In addition, the iso-salinity contour map indicates that the salinity increases towards the central and northern parts of the study area. The total and permanent hardness increase as water salinity increases and vice versa in case of temporary hardness in the groundwater samples. The chemical water types and the ion ratios indicate meteoric origin of groundwater as well as the dissolution of terrestrial and marine salts. The contribution of recent recharge from the River Nile to a few groundwater wells in the study area varies from low to high. In addition, the most recharge sources are from the precipitation. Nitrate concentrations in groundwater increase towards the central and Northern areas significantly elevated in response to increasing anthropogenic land uses. Much of the solutes and physicochemical parameters in these waters are under the undesirable limits of World Health Organization (WHO) for drinking purpose, and a plot of sodium adsorption ratio versus EC shows that about 23% of the groundwater samples are good water quality, about 45% of groundwater samples are moderate quality, and 23% of the groundwater samples are intermediate water class, while the rest of samples (9%) are out of the range.     

A groundwater flow model for overexploited basaltic aquifer and Bazada formation in India

Recent changes in land use practices, such as increase in orange orchards in central India, has put undue pressure on the groundwater resources. Excess withdrawal from the aquifers has resulted in groundwater table decline. The stage of groundwater development in some watersheds has reached 155.85 %, converting these into overexploited watersheds. In the present research paper, a groundwater flow model has been developed to evaluate the groundwater system in a basaltic terrain with Bazada formation. A conceptual model has been developed and calibrated for steady and transient states and the sensitivity analysis was carried out. Future predictions, for current scenario where present practices are continued and for scenario with 20 % reduction in groundwater draft have been made, to select the best strategy for mitigating the problem. The modeling results show that the decline in groundwater level in basaltic and Bazada unconfined aquifers will result into drying up (water level more than 15 m bgl) of 243 km² area by 2020. To restore the groundwater level, it is simulated that the groundwater draft rate must be reduced by 20 % for next 10 years. It may be achieved by adopting groundwater management strategies, particularly for irrigation sector.     

Groundwater mixing in a sand-island freshwater lens: density-dependent flow and stratigraphic controls

This paper focuses on a small back-barrier sand-island on the southeast coast of Queensland. The freshwater lens in the study area exhibits anomalously high short-range salinity gradients at shallow depths, which cannot be explained using a standard seawater intrusion model. The island groundwater system consists of two aquifers: a semiconfined aquifer hosting saline to hypersaline groundwater and an overlying unconfined freshwater aquifer. The deeper aquifer is semiconfined within an incised paleovalley, and groundwater flow is restricted to an east – west direction. Tidal response observations show that the tidal signal propagates far more rapidly and is of much higher magnitude in the semiconfined aquifer than the unconfined aquifer. The tidal wave-pulse amplitude is also subject to greater attenuation in the unconfined aquifer. A conceptual hydrogeological model illustrates how upwelling of hypersaline groundwater, induced by density-dependent flow and tidal pumping, has contaminated the shallow groundwater resource. Salinisation at shallow depths is restricted to an area proximal to the paleovalley aquifer. The spatial distribution of lithological heterogeneity is an initial limiting control on the movement of the upwelling saline plume. The extent of shallow groundwater contamination is also limited by the presence of a baroclinic field, resulting from lateral variations in fluid density. Hydrochemical signatures have been used to support the model hypothesis and link the salinisation of fresh groundwater with the semiconfined aquifer as opposed to the surrounding estuarine surface water. The geometry and thickness of the freshwater lens are further controlled by the presence of the largely impermeable bedrock paleosurface between 9 and 12 m depth. The combination of hypersaline groundwater and hydraulically restrictive lithology at shallow depths has produced excessive thinning of the freshwater lens, demonstrating that the application of a model such as the Dupuit – Ghyben – Herzberg relationship would grossly overestimate the available groundwater resource.