The effect of the Messinian Deep Stage on karst development around the Mediterranean Sea. Examples from Southern France

It is difficult to explain the position and behaviour of the main karst springs of southern France without calling on a drop in the water table below those encountered at the lowest levels of Pleistocene glacio-eustatic fluctuations. The principal karst features around the Mediterranean are probably inherited from the Messinian period (“Salinity crisis”) when sea level dropped dramatically due to the closing of the Straight of Gibraltar and desiccation of the Mediterranean Sea. Important deep karst systems were formed because the regional ground water dropped and the main valleys were entrenched as canyons. Sea level rise during the Pliocene caused sedimentation in the Messinian canyons and water, under a low hydraulic head, entered the upper cave levels.

The powerful submarine spring of Port-Miou is located south of Marseille in a drowned canyon of the Calanques massif. The main water flow comes from a vertical shaft that extends to a depth of more than 147 m bsl. The close shelf margin comprises a submarine karst plateau cut by a deep canyon whose bottom reaches 1,000 m bsl. The canyon ends upstream in a pocket valley without relation to any important continental valley. This canyon was probably excavated by the underground paleoriver of Port-Miou during the Messinian Salinity Crisis. Currently, seawater mixes with karst water at depth. The crisis also affected inland karst aquifers. The famous spring of Fontaine de Vaucluse was explored by a ROV (remote observation vehicle) to a depth of 308 m, 224 m below current sea level. Flutes observed on the wall of the shaft indicate the spring was formerly an air-filled shaft connected to a deep underground river flowing towards a deep valley. Outcroppings and seismic data confirm the presence of deep paleo-valleys filled with Pliocene sediments in the current Rhône and Durance valleys. In the Ardèche, several vauclusian springs may also be related to the Messinian Rhône canyon, located at about 200 m below present sea level. A Pliocene base level rise resulted in horizontal dry cave levels. In the hinterland of Gulf of Lion, the Cévennes karst margin was drained toward the hydrologic window opened by the Messinian erosional surface on the continental shelf.     

Geologic controls of submarine groundwater discharge: application of remote sensing to north Lebanon

Typical of Mediterranean countries, the Lebanese shoreline is well known for its littoral and offshore groundwater discharges, the so-called submarine springs. The tectonic framework of the terrain explains its interruption by dense geologic structures, i.e., fracturing, faulting, karstic routes, as well as acute dips of rock strata seaward. All of these structures serve as hydrologic agents transporting groundwater to the sea. The study aims to locate these groundwater discharges, and to interpret their geologic controls on land. For this purpose, two major lines of approach were followed. The first is an airborne thermal infrared (TIR) survey using radiometers to identify thermal anomalies, thereby determining the exact location of submarine groundwater discharges (SGDs). The second line of approach is the analysis of satellite images (Landsat 7ETM⁺) to delineate the geologic features that govern the mechanism of water flow, thereby determining their sources on land. Twenty-seven major SGDs were identified, 10 of these being offshore springs, the others littoral springs. The springs show a large variety of discharge configurations and extents, mainly parallel or perpendicular to the shoreline or rounded. Three major structural controls were identified to contribute to the transport of groundwater to the sea. These are karstic galleries, faults, and tilted rock strata, their contributions being 48, 37, and 15%, respectively. The SGDs associated with linear passageways, i.e., karstic galleries and faults, are connected with land aquifer formations several kilometers away from the shoreline. Moreover, the presence of impervious rock formations at many localities along the coastline results in a confined hydrologic system, promoting the flow of SGDs into the sea.     

The use of hydrochemical techniques to estimate the discharge of Ovacık submarine springs on the Mediterranean coast of Turkey

Shallow submarine springs along the Mediterranean coast of Turkey discharge most available groundwater via highly developed karstic (buried channels) systems towards the Mediterranean Sea before interception for domestic and agricultural uses. This phenomenon takes place in OvacLk-Silifke village, one of the most intensive touristic places on the Mediterranean coast of Turkey. This study reports on the hydrochemical tests and dye-tracing techniques that were used to measure the amount of water discharge along the OvacLk coastline. Comparison of the electrical conductivity (EC) of the karst springs, which have a background concentration of 500 µS/cm, with the EC of the coastal and submarine discharges is an important tool for identifying the percentage of available freshwater from the shallow submarine springs.     

The groundwater discharge in the Mediterranean karst coastal zones and freshwater tapping: set problems and adopted solutions. Case studies

In the karstic regions of the Mediterranean coastal zones the groundwater discharge and its outcrops—the coastal and submarine springs—represent the most typical natural phenomena of littoral karst, the economic potential of which is significant. The case studies discussed in this paper concern the problems of freshwater tapping in karst coastal zones along the Mediterranean littoral. Owing to the geological and hydrogeological approach, the set problems and adopted solutions involve two most important tasks: (1) the regulation of groundwater flow in the tapping facilities and (2) the control system of saltwater encroachment in a larger protection zone, between the coast and the site of tapping facilities.     

Temporal variability of freshwater and pore water recirculation components of submarine groundwater discharges at Baffin Bay,Texas

Submarine groundwater discharges (SGDs) are an important source of freshwater as well as nutrients and other chemicals to bays and estuaries. SGDs are particularly important for coastal bodies in arid and semi-arid regions that are not fed by perennial streams. The Baffin Bay, TX is a shallow coastal water body that is weakly connected to the Gulf of Mexico and has no major rivers or streams draining into it. A year-long submarine groundwater discharge measurement study was carried out at the Loyola Beach of the Baffin Bay during the months of July 2005–June 2006. A total of 23 synoptic SGD sampling events were carried out with most events collecting SGD data continuously over a period of 24 h at a 1-min temporal resolution using an ultrasonic seepage meter. The median SGD was noted to be 3.83 cm/d with an inter-quartile range (IQR) of 11.36 cm/d. Four sampling events had anomalously high SGD values (~27–48 cm/d) which are hypothesized to be due to the geologic heterogeneity of the sea bed and meteorological effects. Eight of the 23 sampling events had a negative average SGD flux indicating landward flow. The short-term diurnal variability of SGD was comparable or sometimes higher than the longer-term and between-events variability. No long-term trend could be inferred. In the short-term, SGD measurements showed considerable persistence and the effective sample size analysis indicated each sampling event (consisting of over 1,000 samples) yielded only a handful of statistically independent measurements of SGD. The measured SGD values exhibited both negative (hydraulically controlled) and positive (wave set-up controlled) correlations with the bay water levels. Marine controls appeared to be the most significant SGD drivers and are in turn controlled by prevailing aeolian forcings. The salinity of the SGDs were estimated from measured sonic velocities and used in conjunction with the end-member mixing models to estimate fresh (meteoric) and re-circulated pore-water fractions. The freshwater fraction of the SGD was estimated to vary between nearly 4 and 89 % with a median value of 9.96 % and an IQR of 7.16 %. Three events were noted to have abnormally high freshwater fractions (~28, 50 and 84 %) which are likely artifacts caused by bay water freshening from rainfall and plausible thermal expansion. The meteoric and pore-water partitioning was sensitive to the assumed end-member concentrations. This study provides preliminary estimates for SGDs along the South Texas coast line and is useful for calibrating groundwater flow models and understanding the relative importance of terrestrial and marine controls on SGD. However, the heterogeneous nature of the sedimentary geology of the Texas Gulf Coast implies the SGD fluxes are likely to exhibit considerable spatial variation that has not been characterized yet. Therefore, the study provides useful insights for such future data collection and monitoring activities. The measured SGD values at Baffin Bay, TX are comparable to those reported at other parts of the Gulf of Mexico.     

Analysis of drivers governing temporal salinity and temperature variations in groundwater discharge from Altug Submarine Karst Cave (Kas-Turkey)

Salinity and temperature variations in groundwater discharge from the Altug submarine karst cave have been observed at 28 m below sea level for every 10 min between November 2004 and August 2005 to determine the drivers that govern the salinization. Comparisons between temporal trends of salinity and temperature with those of precipitation, air pressure, sea level and wind velocity revealed an apparent dominance of precipitation regime on the salinity and temperature variations. Spectral analyses applied to observations showed that the air pressure and sea level oscillations are affected by sun and moon tides which do not have an appreciable impact on the salinity and temperature variations. Annual rate of salinization in Altug cave seems inversely related to the inland groundwater head so that the maximum and minimum fresh water contributions occur at mid-spring and late-summer, respectively.     

Stable isotopic and geochemical data for inferring sources of recharge and groundwater flow on the volcanic island of Rishiri,Japan

An isotopic and chemical study was conducted on precipitation, spring water, streams, groundwater wells and submarine groundwater discharge (SGD) to constrain the recharge areas and flow paths of SGD. The isotopic values of precipitation were used to determine the local meteoric water lines (LMWLs) of Rishiri Island. The d-excess values of precipitation showed seasonal variation, with lows of 2.5‰ in the summer and highs of 24.2‰ in the winter. The d-excess values of spring water, streams, groundwater wells and SGD ranged from 12.5‰ to 23.0‰, indicating that the resulting waters were a mix of two seasons of precipitation. The isotopic composition of the groundwater wells sampled along the coast and SGD showed more negative values than that of the spring water sampled along the coast. This indicated that SGD recharged at high altitudes and flowed into the sea. The isotopic and chemical composition of SGD indicated unidirectional flow from land to sea.     

Environmental isotopic and hydrochemical study of water in the karst aquifer and submarine springs of the Syrian coast

The groundwater of major karst systems and submarine springs in the coastal limestone aquifer of Syria has been investigated using chemical and isotopic techniques. The δ¹⁸O values of groundwater range from ?6.8 to ?5.05‰, while those for submarine springs vary from ?6.34 to +1.08‰ (eastern Mediterranean seawater samples have a mean of +1.7‰). Groundwater originates from the direct infiltration of atmospheric water. Stable isotopes show that the elevation of the recharge zones feeding the Banyas area (400–600 m a.s.l.) is higher than that feeding the Amrit area (100–300 m a.s.l.). The ¹⁸O_extracted (¹⁸O content of the seawater contribution) for the major submarine springs suggests a mean recharge area elevation of 600–700 m a.s.l., and lower than 400 m a.s.l. for the spring close to Amrit. Based on the measured velocity and the percentage of fresh water at the submarine springs outlet, the estimated discharge rate is 350 million m³/year. The tritium concentrations in groundwater (1.6–5.9 TU) are low and very close to the current rainfall values (2.9–5.6 TU). Adopting a model with exponential time distribution, the mean turnover time of groundwater in the Al-sen spring was evaluated to be 60 years. A value of about 3.7 billion m³ was obtained for the maximum groundwater reservoir size.     

古喀斯特岩岸的地质意义：以黔中贵阳乌当志留纪岩岸为例

本文记述黔中乌当地区志留纪的喀斯特岩岸，是我国前第四纪岩岸实例的首次报道。志留纪海水始于Ｌｌａｎｄｏｖｅｒｙ世Ａｅｒｏｎｉａｎ晚期浸漫本区并逐级超覆在奥陶纪不同时代的地层之上，形成了一个穿时性喀斯特不整合面，这是宜昌运动和其后长期风化剥蚀，产生强烈地形高差的结果。根据地层发育及不整合面上的沉积和生物特征，肯定喀斯特岩岸在本区的存在，推断岩岸的生物生存环境，海平面升降变化以及宜昌运动牟对贵州中，南部     

Sustainable yield of a karst aquifer system: a case study of Jinan springs in northern China

Based on the long-term monitoring data of rainfall, groundwater levels, groundwater abstraction, spring flow rates and groundwater quality, an assessment has been undertaken of the sustainable yield of a karst aquifer system in Shandong Province, northern China, to maintain perennial outflow of the karst springs while meeting water demands. One of the fundamental indicators for sustainable yield of groundwater is identified as maximum allowable water-level drawdown. A regional three-dimensional finite-difference numerical model has been developed to optimize the schemes associated with well fields and their locations and sustainable yields, in the Jinan spring catchment and its adjacent karst groundwater catchments, with the aim of maintaining the water level higher than the allowable lowest water level of 27.5?m above sea level. Furthermore, measures necessary to move towards sustainable use of the karst groundwater are outlined, drawing on contingency plans of water-source replacement and artificial recharge, dual water supply (based in water quality), use of the spring waters themselves, and groundwater quality protection.     

Impacts of sea-level rise and urbanization on groundwater availability and sustainability of coastal communities in semi-arid South Texas

The sea levels along the semi-arid South Texas coast are noted to have risen by 3–5 mm/year over the last five decades. Data from General Circulation Models (GCMs) indicate that this trend will continue in the 21st century with projected sea level rise in the order of 1.8–5.9 mm/year due to the melting of glaciers and thermal ocean expansion. Furthermore, the temperature in South Texas is projected to increase by as much as 4 °C by the end of the 21st century creating a greater stress on scarce water resources of the region. Increased groundwater use hinterland due to urbanization as well as rising sea levels due to climate change impact the freshwater-saltwater interface in coastal aquifers and threaten the sustainability of coastal communities that primarily rely on groundwater resources. The primary goal of this study was to develop an integrated decision support framework to assist land and water planners in coastal communities to assess the impacts of climate change and urbanization. More specifically, the developed system was used to address whether coastal side (primarily controlled by climate change) or landward side processes (controlled by both climate change and urbanization) had a greater control on the saltwater intrusion phenomenon. The decision support system integrates a sharp-interface model with information from GCMs and observed data and couples them to statistical and information-theoretic uncertainty analysis techniques. The developed decision support system is applied to study saltwater intrusion characteristics at a small coastal community near Corpus Christi, TX. The intrusion characteristics under various plausible climate and urbanization scenarios were evaluated with consideration given to uncertainty and variability of hydrogeologic parameters. The results of the study indicate that low levels of climate change have a greater impact on the freshwater-saltwater interface when the level of urbanization is low. However, the rate of inward intrusion of the saltwater wedge is controlled more so by urbanization effects than climate change. On a local (near coast) scale, the freshwater-saltwater interface was affected by groundwater production locations more so than the volume produced by the community. On a regional-scale, the sea level rise at the coast was noted to have limited impact on saltwater intrusion which was primarily controlled by freshwater influx from the hinterlands towards the coast. These results indicate that coastal communities must work proactively with planners from the up-dip areas to ensure adequate freshwater flows to the coast. Field monitoring of this parameter is clearly warranted. The concordance analysis indicated that input parameter sensitivity did not change across modeled scenarios indicating that future data collection and groundwater monitoring efforts should not be hampered by noted divergences in projected climate and urbanization patterns.     

Electrical resistivity tomography (ERT) of a coastal carbonate aquifer (Port-Miou, SE France)

As part of a larger regional research program “KarstEAU”, the authors have applied electrical resistivity tomography (ERT) techniques to characterize heterogeneities in the Port-Miou coastal karst aquifer (Cassis, SE France). Field surveys were carried out on intensely fractured and karstified Urgonian carbonates. Extensive research has characterized macro- and micro-scale geology of the Port-Miou area and particularly underground water-filled conduits and fault/fracture and karst systems within a former quarry. The authors applied 2D ERT along two surface profiles of length 420 and 595 m to test capability for delineating subsurface conduits and possibly relationship between conduit and fault/fracture/karst orientation; and 3D ERT with a dense 120 electrode array at 1 m spacing (11 × 10 m) was applied over an area of the quarry that had been profiled using 3D georadar and which has had intensive nearby structural geological interpretation. The 2D profiling imaged several underground conduits at depths to >50 m below ground surface and below sea level, including possibly the main Port Miou submarine spring and smaller springs. The 2D profiling within the quarry provided a better understanding of the connectivity between major fractures and faults on the quarry walls and secondary springs along the coast supporting flow of the secondary springs along interpreted fracture orientations. In addition, 2D inversion-derived conductivity models indicate that high resistivity zones above sea-level are associated with non-saturated zones and low resistivity anomalies in the non-saturated zone are associated with residual clays in paleokarsts. A partitioned lower resistivity zone below sea-level can be associated with a higher porosity/permeability zone with fractures and karstic features. Inversion models of the dense 3D ERT data indicate a higher resistivity volume within the larger surveyed block. The survey characterized the non-saturated zone and the ERT resistivities are correlated with karst features interpreted by 3D georadar and visible in the inferior wall of the quarry.     

咸淡水界面位置确定的综合方法(TEcG)及其应用

准确确定咸淡水界面位置是评价咸水入侵范围的前提。对于咸淡水界面位置的确定,传统研究以水化学法和物探法为主。为克服单一使用传统方法造成的人力、物力和财力的大量浪费,以莱州湾西南岸广饶县小清河以南咸水入侵区为研究对象,在综合分析研究区地下水开采现状、水化学监测结果的基础上,选择3个典型断面,采用水化学法中的野外现场电导率法,快速判断咸淡水界面大致位置（某两眼监测井之间）;再在一咸一淡的两眼监测井之间,采用高密度电阻率法快速、准确地确定咸淡水界面的空间分布。结果表明：该地区的地下水电导率若大于1.61 mS/cm,即可认为此处受到咸水入侵;咸淡水界面位置的视电阻率特征值为11~13 Ω·m,咸淡水界面附近咸水体呈舌状入侵并主要发生在地表以下13 m内的浅层地下水中。     

广西布泉地下河发育特征及连通性分析

为查明广西布泉地下河岩溶发育规律和分布特征,在1∶5万水文地质调查的基础上,对该区地下水水位动态进行长期观测和示踪,研究布泉地下河地表和地下岩溶发育特征,分析布泉河上游和中游各支流间的连通性。该区地表主要为峰丛洼地,溶蚀强烈,地下河管道主要沿断层展布,平面形态呈树枝型,剖面形态呈阶梯型。地下河中下游管道的地下水水位动态对降雨的响应滞后,上游管道及远离管道区的地下水水位动态对降雨的响应敏感。地下河上游和中游地下水平均流速分别为1 166 m/d和1 079 m/d,地下水总体径流速度较快,上游地下水的水力坡度大于中游。地下河上游管道分支较多,地下水连通性较复杂,中游主管道明显,连通性较好。     

New type of tsunami barrier

Tsunami impact on a coast can be reduced by applying a submerged vertical barrier to reflect tsunami before the catastrophic waves are built up near the coast. However, construction of such long walls by conventional submarine technology is difficult. In this paper, the construction of extended submarine walls at a depth of between 50 and 500 m below sea level by a relatively simple and efficient technology is described. The submarine walls can consist either of high-strength steel fences with anchors or two parallel steel fences with distance holders, lowered into the sea and fixed with rocks inserted from top. Alternatively, the barriers could be built from gabions (prefabricated steel net baskets filled with rocks) and lowered into the sea. The space between these tsunami barriers and the coast can be filled with solid material, thus allowing reclamation of new land, or this gap can be used for fish farming. These barriers can contribute to preservation of beaches and natural ecosystems at the coast.     

Groundwater investigation in Kuala Selangor using vertical electrical sounding (VES) surveys

Integrated geoelectrical and hydrochemical surveys were used to investigate and delineate different types of groundwater in the Kuala Selangor alluvial aquifer. Previous hydrogeological borehole investigation showed that this aquifer contains several types of groundwater in relation to its salinity. The high salinity of the groundwater in some areas is believed to be due to either saltwater intrusion from the nearby sea or river infiltration during high tide season. The vertical electrical sounding (VES) method was employed to study and map the subsurface variation of resistivity in the area. For each sounding measurement, a total spread length of 300 m was obtained with a vertical depth penetration of about 60 to 75 m. Chemical analysis of the groundwater samples taken from both shallow and deep boreholes was carried out for the water quality determination. A total of 45 VES stations were succesfully established along three parallel roads with a direction almost perpendicular to the coastal line. The distance between stations varies from 1 to 2 km with a maximum length of about 60 km surveyed line. Results of the vertical electrical soundings as well as the hydrochemistry of the groundwater samples show that the soil and groundwater in the study area can be grouped into fresh and brackish water zones. The subsurface resisitivity sections derived from the VES study suggest that the area is dominated by brackish soil and groundwater zones, especially in the area towards the coast. This result appears to agree well with the groundwater pumped from boreholes scattered around in the area. Water drawn from boreholes near the coast showed higher salinity compared to the water pumped from inland boreholes. Chloride values greater than 250 mg/L are considered to represent the brackish zones whilst values less than 250 mg/L represents zones of fresh soil and groundwater.     

Using radon-222 to study coastal groundwater/surface-water interaction in the Crau coastal aquifer (southeastern France)

Radon has been used to determine groundwater velocity and groundwater discharge into wetlands at the southern downstream boundary of the Crau aquifer, southeastern France. This aquifer constitutes an important high-quality freshwater resource exploited for agriculture, industry and human consumption. An increase in salinity occurs close to the sea, highlighting the need to investigate the water balance and groundwater behavior. Darcy velocity was estimated using radon activities in well waters according to the Hamada “single-well method” (involving comparison with radon in groundwater in the aquifer itself). Measurements done at three depths (7, 15 and 21 m) provided velocity ranging from a few mm/day to more than 20 cm/day, with highest velocities observed at the 15-m depth. Resulting hydraulic conductivities agree with the known geology. Waters showing high radon activity and high salinity were found near the presumed shoreline at 3,000 years BP, highlighting the presence of ancient saltwater. Radon activity has also been measured in canals, rivers and ponds, to trace groundwater discharges and evaluate water balance. A model of the radon spatial evolution explains the observed radon activities. Groundwater discharge to surface water is low in pond waters (4 % of total inputs) but significant in canals (55 l/m²/day).     

Groundwater level fluctuation in the Waimea Plains, New Zealand: changes in a coastal aquifer within the last 30 years

Data for the Waimea Plains, New Zealand indicate that the lower confined groundwater aquifer is hydraulically homogeneous and that shallow groundwater levels inland are affected mostly by anthropogenic processes, while those near the coast are affected more by sea level variation. Analysis of long-term data for New Zealand indicates that sea level has increased continuously, but trends are not spatially uniform. Results from non-parametric trend analysis show that rising trends for groundwater levels are predominant in the shallow aquifer both inland on the Waimea Plains and, for recent years, near the coast, while decreasing trends are evident in the underlying confined aquifer near the coast. Groundwater level change in the shallow aquifer appears to be more affected by climate change than the lower confined aquifer. Correlation analysis indicated that groundwater levels are more affected by rainfall during the rainy season than the dry season and more influenced by rainfall inland than near the coast. Groundwater level declines in the lower confined aquifer near the coast, which has its major recharge area inland in the catchment, may be substantially affected by groundwater abstraction in inland areas as well as sea level variation, but there are little evidences of seawater intrusion. Meanwhile, groundwater recharge over the catchment area has great influence on rising groundwater levels in the shallow aquifer and its recharge is estimated to be 417.8 mm/year using chloride concentrations of precipitation and groundwater.     

Current Status of Scientific Deep-diving Investigations in Submarine Canyons

Submarine canyons represent one of the most important geomorphologic features in continental margins, act as one of the most important conduits of seafloor sediment transporting from shallow waters into the deep sea, and are also biodiversity hotspots. Submarine-canyon investigations are therefore significant for seafloor scientific research, submarine mineral and resource exploitation, and the construction and safety operation of submarine infrastructures. Deep-sea diving by manned submersibles and robot submersibles represented by Remotely Operated Vehicles (ROV) and Autonomous Underwater Vehicles (AUV) provides an important approach to the investigation of modern submarine canyons. The biggest advantage of manned submersibles is that they can bring scientists to the deep sea for in-place observations and precise sampling, while the robot deep-sea diving has the advantages of low cost, high efficiency, no personnel safety concerns, and the ability to reach the extreme sea areas that are difficult for humans to reach. Deep-sea diving has found broad applications in the geo-scientific research of submarine canyons. These studies cover seafloor topography and geomorphology, seafloor sediments, erosional and depositional bedforms, mass transport processes and flow dynamics, cold springs, cold-water corals and other biological habitats, as well as seafloor biological erosion. The research experience and scientific findings in scientific diving investigation of submarine canyons accumulated by the developed countries in Europe and the United States over the past 70 years are of great reference and significance to the emerging scientific deep-sea diving in China.     

Flandrian sea-level changes in the Fenland. I: The geographical setting and evidence of relative sea-level changes

The Flandrian sediments of the Fenland record the infilling of the Wash embayment on the east coast of England, UK. Since at least 6500 BP changes in sea level have been a major control on the rate and pattern of sediment accumulation. New data are presented from the area which together with published information allow the reconstruction of palaeoenvironments from 6500 to 2500 BP. The major environmental changes involved alternations between freshwater fen and intertidal marine sedimentation. Each episode was characterised by transitional changes as vegetation and sediment zones shifted over large areas. Marine/brackish sediments are found up to 45 km inland of the present coast. Radiocarbon dated sea-level index points, with relevant stratigraphic and micropalaeontological data, ranging from 6415 BP at ?8.17m OD to 2595 BP at +1.45m OD, are described.