Groundwater Lenses Research Articles

Impacts of the 2004 tsunami on groundwater resources in Sri Lanka

The 26 December 2004 tsunami caused widespread destruction and contamination of coastal aquifers across southern Asia. Seawater filled domestic open dug wells and also entered the aquifers via direct infiltration during the first flooding waves and later as ponded seawater infiltrated through the permeable sands that are typical of coastal aquifers. In Sri Lanka alone, it is estimated that over 40,000 drinking water wells were either destroyed or contaminated. From February through September 2005, a team of United States, Sri Lankan, and Danish water resource scientists and engineers surveyed the coastal groundwater resources of Sri Lanka to develop an understanding of the impacts of the tsunami and to provide recommendations for the future of coastal water resources in south Asia. In the tsunami‐affected areas, seawater was found to have infiltrated and mixed with fresh groundwater lenses as indicated by the elevated groundwater salinity levels. Seawater infiltrated through the shallow vadose zone as well as entered aquifers directly through flooded open wells. Our preliminary transport analysis demonstrates that the intruded seawater has vertically mixed in the aquifers because of both forced and free convection. Widespread pumping of wells to remove seawater was effective in some areas, but overpumping has led to upconing of the saltwater interface and rising salinity. We estimate that groundwater recharge from several monsoon seasons will reduce salinity of many sandy Sri Lankan coastal aquifers. However, the continued sustainability of these small and fragile aquifers for potable water will be difficult because of the rapid growth of human activities that results in more intensive groundwater pumping and increased pollution. Long‐term sustainability of coastal aquifers is also impacted by the decrease in sand replenishment of the beaches due to sand mining and erosion.

Screening level modeling of long-term impact of petroleum hydrocarbon contamination on fresh groundwater lenses in the Arabian Gulf region

The Gulf War in 1991 created an environmental catastrophe, one of the major consequences of which was setting several oil wells on fire in the Arabian Gulf area. The total oil spilled as a result of the damaged wells was about 3.5 × 106 m3. Out of these, 3.3 × 106 m3 of oil was recovered and exported. The rest was left behind as it was not economical to collect. The oil left behind was subject to severe weathering over the past ten years. Soil and subsurface contamination pose a serious risk to the quality of the already scarce fresh groundwater resources in the area which was subject to oil spill in the study region. This paper presents the computer modeling activities carried out towards simulating the transport of the hydrocarbon contamination of the fresh groundwater resources at a study area in the Arabian Gulf region, and predicting the contamination levels at the fresh groundwater lenses in the area in the future, should current contamination levels persist in the soil and groundwater. The modeling activities relied on both semi-analytical and numerical flow and transport models.

Contamination of groundwater under cultivated fields in an arid environment, central Arava Valley, Israel

The purpose of this study is to obtain a better understanding of groundwater contamination processes in an arid environment (precipitation of 50 mm/year) due to cultivation. Additional aims were to study the fate of N, K, and other ions along the whole hydrological system including the soil and vadose zone, and to compare groundwater in its natural state with contaminated groundwater (through the drilling of several wells). A combination of physical, chemical, and isotopic analyses was used to describe the hydrogeological system and the recharge trends of water and salts to the aquifers. The results indicate that intensive irrigation and fertilization substantially affected the quantity and quality of groundwater recharge. Low irrigation efficiency of about 50% contributes approximately 3.5–4 million m 3/year to the hydrological system, which corresponds to 0.65 m per year of recharge in the irrigated area, by far the most significant recharge mechanism. Two main contamination processes were identified, both linked to human activity: (1) salinization due to circulation of dissolved salts in the irrigation water itself, mainly chloride, sulfate, sodium and calcium, and (2) direct input of nitrate and potassium mainly from fertilizers. The nitrate concentrations in a local shallow groundwater lens range between 100 and 300 mg/l and in the upper sub-aquifer are over 50 mg/l. A major source of nitrate is fertilizer N in the excess irrigation water. The isotopic compositions of δ 15N–NO 3 (range of 4.9–14.8‰) imply also possible contributions from nearby sewage ponds and/or manure. Other evidence of contamination of the local groundwater lens includes high concentrations of K (20–120 mg/l) and total organic carbon (about 10 mg/l).

Vulnerability of groundwater resources from agricultural activities in southern Kuwait

Kuwait is an arid country situated in the northwestern corner of the Arabian peninsula, which suffers from limited natural water resources. Groundwater in Kuwait is mostly saline, except for some freshwater lenses in the northern part and some brackish zones existing in the south and southwest. With an annual average rainfall of 120 mm and evapotranspiration of around 2266 mm, the recharge of aquifers by rainfall is negligible. Fresh groundwater lenses with total dissolved solids (TDS) less than 1000 mg/l are exploited for potable purpose, and brackish groundwater with TDS between 1000 and 5000 mg/l is used for irrigation. The objective of this study was to assess the impact of irrigation on the salinity and the drawdown of groundwater in the Al-Wafra farms area in southern Kuwait. As a result of the gradual increase of the groundwater extraction for irrigation, the quality and quantity of the groundwater in the aquifers have been depleted. Water levels in the southern part of Kuwait have declined and the maximum declination of 20 m was observed at the center of the farm area. About 35% of the irrigated water was lost due to evapotranspiration, and the rest infiltrated back to the aquifer through the vadose zone, resulting in an increase in the TDS level in the groundwater up to 14,000 mg/l. Such an increase was observed at several locations within the farming area. As a part of this study, two numerical models were developed to predict the groundwater quality as well as the drawdown. The relation between the well locations, decline in water levels, variations in groundwater quality and the transmissivity distribution were interpreted, and the results of the numerical simulations were compared and scaled with field observations. It is estimated that, in the next 5 years, if irrigation is continued at the present rate, then only about 20% of the existing wells will have a TDS level of less than 7500 mg/l.

A thick lens of fresh groundwater in the southern Lihue Basin, Kauai, Hawaii, USA

A thick lens of fresh groundwater exists in a large region of low permeability in the southern Lihue Basin, Kauai, Hawaii, USA. The conventional conceptual model for groundwater occurrence in Hawaii and other shield-volcano islands does not account for such a thick freshwater lens. In the conventional conceptual model, the lava-flow accumulations of which most shield volcanoes are built form large regions of relatively high permeability and thin freshwater lenses. In the southern Lihue Basin, basin-filling lavas and sediments form a large region of low regional hydraulic conductivity, which, in the moist climate of the basin, is saturated nearly to the land surface and water tables are hundreds of meters above sea level within a few kilometers from the coast. Such high water levels in shield-volcano islands were previously thought to exist only under perched or dike-impounded conditions, but in the southern Lihue Basin, high water levels exist in an apparently dike-free, fully saturated aquifer. A new conceptual model of groundwater occurrence in shield-volcano islands is needed to explain conditions in the southern Lihue Basin.

Extracting relatively-fresh groundwater from aquifers underlain by salty groundwater

The native groundwater in the central regions of the doabs of the Indus basin of Pakistan is deep and salty because of the marine origin of the hydrogeologic formation. Percolation of fresh irrigation waters has formed a relatively-fresh groundwater lens above the underlying native salty groundwater layer. The thickness of this relatively-fresh groundwater lens varies from a few meters to 150 m. The costs involved in the installation of horizontal subsurface drains to extract the water are prohibitive. Alternatively, shallow wells with small discharge rates, commonly known as the skimming wells, can be used to extract the relatively-fresh groundwater. Extraction of this water from inappropriate depths and at inappropriate rates will cause ‘upconing’ of the ‘interface’ between the relatively-fresh groundwater lens and salty groundwater layer, and draw marginal quality water to the root zone, resulting in an increase in salinity and sodicity. In this paper, two numerical models, MODFLOW ( McDonald and Harbough, 1988) and MT3D ( Zheng, 1990) were used to model the interface movement in an unconfined aquifer in Punjab, Pakistan. Data collected by Kemper et al. (1976) was used to calibrate and validate the models. Subsequently, the sensitivity of the depth to watertable, discharge rate, thickness of the relatively-fresh groundwater lens, well penetration ratio, and daily operating hours on the salinity of pumped groundwater was studied. The results show that skimming wells of 10–18 l/s discharge rates can be installed and operated successfully with 60–70% well penetration ratio for an operating time of 8–24 h per day from an unconfined aquifer with 15–18 m thick relatively-fresh groundwater lens.

Some Hydrogeological Peculiar to Various Types of Problems Small Islands

AbstractThere are many problems associated with the investigation of small island hydrogeology, including (i) the availability of data and the distribution of both spatial and temporal data sets, (ii) the dynamics of the groundwater to sea‐water interface and the shape of the so‐called groundwater lens, and (iii) the difficulties of evaluating recharge to groundwater and of calculating the volume of groundwater discharge to the sea. These issues are compounded by (a) the ratio of coast to area in small islands, (b) the problems of extreme topography, and (c) the identification of baseflow to rivers and streams. A simple classification of island types assists in evaluating hydro‐geological regimes, and the importance of groundwater in an island context cannot be over‐emphasised.

Formation of fresh ground-water lenses in northern Kuwait

In Kuwait, an arid country with a low annual average rainfall of about 115 mm, fresh ground-water lenses are found at Raudhatain and Umm Al-Aish fields, in the northern part of the country. These lenses are formed due to a combination of unique conditions that include short duration, high intensity rainfall; geomorphology; and lithology that enables rapid infiltration to the underlying ground-water. Large depressions and playas, paleodrainage patterns, and catchment areas, which are necessary for the accumulation of large amounts of water during flash foods, were mapped from aerial photographs, Landsat Thematic Mapper (TM) imagery, and digital elevation model (DEM) datasets. From historical pumping and water quality variation data acquired between 1963 and 1977, the sustainable extraction rate for Raudhatain and Umm Al-Aish is estimated to be 5·5 and 3·5 Ml day−1, respectively. These rates are fundamental to the delicate management required to extract freshwater from the lenses and yet avoid upconing of the deeper saline water.

Implications of Electrical Resistivity Data Regarding Ground-Water Lenses on San Salvador Island, Bahamas

Fresh ground-water lenses in the Bahamas may be mapped using electrical resistivity surveys utilizing the large resistivity contrast between fresh-water and salt-water saturated carbonate rock. Ideally, this contrast is a factor of 18 or more; however, porosity variations introduce even larger resistivity variations. The relevant resistivity-porosity relationship determined for surficial rock samples from San Salvador Island is R o = 1.04 R w /Φ 219 , where R o and R w are the resistivities of rock and pore water, and Φ is the porosity. These criteria were used to determine the depth of the fresh-water/salt-water interface of fresh-water lenses in the Sandy Point area of San Salvador Island, based on interactive inversion of vertical electrical sounding (VES) data collected during the past 15 years. The resulting computed resistivity layer models indicate a major fresh-water lens of maximum thickness of approximately 30 m under the peripheral hills of Sandy Point with little or no fresh water in the low-lying interior of the region. Pseudo-depth sections and high-resistivity layers at depth suggest confined fresh-water aquifers at depth beneath brackish near-surface ground water in parts of the interior, with fresh-water recharge from the peripheral hills. A resistivity profiling survey of the interior indicates possible conduits connecting several of the brackish blue holes.

Impact of irrigation on brackish ground water lenses in northern Kuwait

Kuwait is an arid country with very few natural water resources. Ground water in Kuwait is mostly saline with some brackish zones existing in the southwestern region. With an annual average rainfall and evapotranspiration of about 105 mm and 2270 mm, respectively, recharge of aquifers by rainfall is negligible. However, in northern Kuwait, unique geomorphologic conditions and lithological formations have contributed to the formation of fresh to brackish ground water lenses. Fresh ground water lenses with total dissolved solids (TDS) less than 1000 p.p.m. were exploited for potable purposes. Brackish ground water with TDS between 1000 and 5000 p.p.m. was used for irrigation. Ground water extraction for irrigation has increased gradually since the 1960s and reached about 200 Ml day −1 in 1989. About 30% of irrigated water was lost as evapotranspiration and the rest infiltrated back to the aquifer. As a result, the TDS of ground water at several locations within the farming region increased to about 8000 p.p.m. in 1989. The maximum decline in ground water levels owing to pumping was about 3–5 m in the central farming region. It is estimated that in the next 10 years, if irrigation were to be continued at the 1989 rate, then only about 10–25% of the existing wells will have TDS levels less than 7500 p.p.m.

Results Of An Artificial Recharge Test And A Double Pumping Test As Preliminary Studies For Optimizing Water Supply In The Western Belgian Coastal Plain

In the western Belgian coastal plain, a major part of the water demand is supplied by catchments in the dune belt, where water is extracted from fresh groundwater lenses in the unconfined aquifer. Because of overexploitation, mainly in summer, the water catchments are threatened by salt-water encroachment. Artificial recharge of the catchments could be considered since, in winter, a large amount of fresh surface water of the polder area is evacuated to the sea. A proposal for an improved water management of the region is formulated. Preliminary studies consisted of two tests: an artificial recharge test in the dune area and a double pumping test in a sandy ridge near a canal in the polder area. The tests are interpreted by means of inverse models. Results of the artificial recharge test demonstrate that recharge is feasible for the water catchment area of Koksijde. Results of the double pumping test show that the Avekapelle creek ridge in the polder area is very well suited as an intake area.

Groundwater lens dynamics of Atoll Islands

A variable‐density groundwater model is used to analyze the effects of various controls on the size of the freshwater lens, the structure of the transition zone, and the propagation of tidal fluctuations in a two‐layer atoll island groundwater system. Modeling results indicate that mixing of fresh water and saltwater occurs primarily as a result of oscillating vertical flow due to tidal fluctuations and depends to a lesser extent on transverse dispersion along the dominantly horizontal recharge‐discharge path of flow. The controls on the amount of mixing are: (1) the accumulated vertical distance, which increases with tidal range and is restricted by vertical permeabilities, and (2) vertical longitudinal dispersion. Comparison of cross‐sectional simulations of atoll islands using nontidal and tidal models shows that the nontidal model must use artificially high values of transverse dispersivity to compensate for the lack of tidally driven, vertical mixing processes. Although the tidal model has high computational requirements, it can be used to calibrate vertical permeabilities and is best suited for problems dealing with groundwater resource evaluations, hydrologic events, and hydrologic processes. The limitations of the nontidal model are that it cannot be used for calibration of vertical permeabilities and will not realistically simulate those cases in which transition zones are thick or recharge low.

The hydrogeology of complex lens conditions in Qatar

The emirate of Qatar lies on a peninsula extending northward from the mainland of Saudi Arabia into the Arabian Gulf. The peninsula is underlain by sedimentary rocks ranging from late Cretaceous to Holocene age but only two Lower Tertiary units are identified as aquifers. The groundwater distribution in these units is seen to be controlled by facies distributions related to tectonically controlled sedimentation and subsequent dissolution. Dissolution has created permeability, in the Umm er Rhaduma limestones and in the overlying Rus anhydrites. In the latter case the dissolution has lead to extensive surface collapse which has provided a mechanism for recharge from runoff. Despite very low rainfall and high evaporation rates, recharge related to storm runoff has resulted in the establishment of a complex fresh groundwater lens in both aquifer units. The lens is constrained by saline groundwaters which in the lower unit are controlled by heads in eastern Saudi Arabia but in the upper unit by the Arabian Gulf sea level. Groundwater abstraction is shown to be distorting the fresh groundwater lens configuration, and estimates of the resultant flow responses affecting the lens are given.

A GROUND WATER RESOURCES STUDY OF A PACIFIC OCEAN ATOLL ‐ TARAWA, GILBERT ISLANDS1

ABSTRACT: The geology and fresh ground water lens development in a typical Pacific atoll are described together with a method for hydrogeological investigation. The fresh water resources of such lenses are investigated using Tarawa as an example. It is shown that simple steady state solutions cannot be realistically applied, and that despite the paucity of hydrogeological data, which is considered typical of such islands, practical nonsteady state solutions allow resource assessments. The susceptability of lens resources to drought conditions is demonstrated.

The Study of Local Waters in the Deserts of the USSR

AbstractA review of potential local fresh-water sources in the deserts for the use of livestock herds, herders' settlements, and extractive and other industrial enterprises. One of the most promising approaches is held to be the use of takyrs [clay pans] as catchment areas for ephemeral runoff of precipitation, which is then directed into natural aquifers or artificial underground storage cisterns. Another potential source of water is large perched ground-water lenses that could be tapped by paired wells to prevent the intrusion of salt water from below. Artesian waters in the desert which are far from areas of recharge are found to be largely saline.

RADIO-WAVE METHOD OF GEOLOGICAL MAPPING

Practical methods of using radio waves in geological mapping are considered. The history and basic principles of the method are briefly outlined. When transmitted radio waves penetrate the earth to a definite depth, they induce currents in the heterogeneous geological structures encountered (ore veins, contacts of different rocks, ground-water lenses, for example). The electromagnetic fields of these currents superimposed on the primary radio signal cause local anomalies qualitatively and quantitatively depending on the nature of the heterogeneity and the interrelations between the electromagnetic parameters (∊, ρ, μ) and the surrounding medium. The results of field measurements by the radio-wave method of geological mapping in different regions are described. The author's work and experiments of other investigators indicate the feasibility of radio-wave methods for large-scale geological mapping and exploration. The portable measuring apparatus, PINP-1, is a high-selective microvoltmeter measuring 3-10 m...

GEOLOGY OF KAPINGAMARANGI ATOLL, CAROLINE ISLANDS

Research Article| March 01, 1958 GEOLOGY OF KAPINGAMARANGI ATOLL, CAROLINE ISLANDS EDWIN D MCKEE EDWIN D MCKEE UNITED STATES GEOLOGICAL SURVEY, GEOLOGIC DIVISION, FEDERAL CENTER, DENVER, COLORADO Search for other works by this author on: GSW Google Scholar Author and Article Information EDWIN D MCKEE UNITED STATES GEOLOGICAL SURVEY, GEOLOGIC DIVISION, FEDERAL CENTER, DENVER, COLORADO Publisher: Geological Society of America First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1958, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1958) 69 (3): 241–278. https://doi.org/10.1130/0016-7606(1958)69[241:GOKACI]2.0.CO;2 Article history First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation EDWIN D MCKEE; GEOLOGY OF KAPINGAMARANGI ATOLL, CAROLINE ISLANDS. GSA Bulletin 1958;; 69 (3): 241–278. doi: https://doi.org/10.1130/0016-7606(1958)69[241:GOKACI]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Kapingamarangi Atoll of the Caroline Islands consists of a peripheral reef, 1000–4000 feet across, surrounding a nearly circular lagoon which is 5 by 6 nautical miles in area and about 240 feet at maximum depth. Thirty-three islands, most of which are less than half a mile in length, are scattered along the eastern half of the peripheral reef. At least 75 patch reefs, most of which are small, nearly symmetrical mounds, rise to the surface of the lagoon.The peripheral reef and the patch reefs, composed largely of the stony structures of corals and coralline algae, have flat upper surfaces, apparently the result of bevelling by waves during a recent lowering of sea level. The islands on the peripheral reef are formed of partially consolidated stratified sediments composed of clastic limestone particles and the shells of marine animals. These islands are migrating lagoonward across the reef flat because of erosion on the seaward sides and the growth of beaches and bars on the opposite sides.Soils on the islands are poorly developed and retain much of the texture, structure, and composition of the parent rock or sediment. They consist chiefly of mechanical mixtures of carbonaceous material and lime gravel, lime sand, or lime mud. Phosphorite is present on some islands and is still forming locally where apatite derived from bird guano is reacting with limestones.The tidal fluctuation of ground-water lenses, determined on islands of several sizes, ranges from about 4 to 18 inches. In one very small island where the water is brackish, the rise is much greater. The time lag between tidal movements and the rise and fall of fresh water in the islands ranges from a few minutes on very small islands up to 5 hours on some large ones. This time lag is controlled by the permeability of rocks composing an island and varies from one area to another according to the distribution of rock types.The lagoon contains six concentric belts of bottom sediment; in each, the composition and texture depend on the depth of water in which it occurs. Lime sand and lime gravel derived for the most part from the shells of animals form most of the sediment, but a lime mud covers the bottom of the deepest parts of the lagoon. Waves and currents cause gradation between types of sediment to a depth of about 30 feet, but little mixing was detected at greater depths. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Geology of Kapingamarangi Atoll, Caroline Islands

Kapingamarangi Atoll of the Caroline Islands consists of a peripheral reef, 1000–4000 feet across, surrounding a nearly circular lagoon which is 5 by 6 nautical miles in area and about 240 feet at maximum depth. Thirty-three islands, most of which are less than half a mile in length, are scattered along the eastern half of the peripheral reef. At least 75 patch reefs, most of which are small, nearly symmetrical mounds, rise to the surface of the lagoon. The peripheral reef and the patch reefs, composed largely of the stony structures of corals and coralline algae, have flat upper surfaces, apparently the result of bevelling by waves during a recent lowering of sea level. The islands on the peripheral reef are formed of partially consolidated stratified sediments composed of clastic limestone particles and the shells of marine animals. These islands are migrating lagoonward across the reef flat because of erosion on the seaward sides and the growth of beaches and bars on the opposite sides. Soils on the islands are poorly developed and retain much of the texture, structure, and composition of the parent rock or sediment. They consist chiefly of mechanical mixtures of carbonaceous material and lime gravel, lime sand, or lime mud. Phosphorite is present on some islands and is still forming locally where apatite derived from bird guano is reacting with limestones. The tidal fluctuation of ground-water lenses, determined on islands of several sizes, ranges from about 4 to 18 inches. In one very small island where the water is brackish, the rise is much greater. The time lag between tidal movements and the rise and fall of fresh water in the islands ranges from a few minutes on very small islands up to 5 hours on some large ones. This time lag is controlled by the permeability of rocks composing an island and varies from one area to another according to the distribution of rock types. The lagoon contains six concentric belts of bottom sediment; in each, the composition and texture depend on the depth of water in which it occurs. Lime sand and lime gravel derived for the most part from the shells of animals form most of the sediment, but a lime mud covers the bottom of the deepest parts of the lagoon. Waves and currents cause gradation between types of sediment to a depth of about 30 feet, but little mixing was detected at greater depths.