Piezometric Surface Research Articles

HIGH-RESOLUTION SURFACE AND BED TOPOGRAPHY MAPPING OF RUSSELL GLACIER (SW GREENLAND) USING UAV AND GPR

Abstract. This study presents the detailed survey of the northern marginal part of Russell Glacier, SW Greenland using the combination of unmanned aerial vehicle (UAV) photogrammetry and low-frequency ground penetrating radar (GPR) measurements. Obtained digital elevation model (DEM) and ice thickness data from GPR data allowed the generation of high precision subglacial topography model. We report uncertainties arising from GPR, GPS, and DEM suggesting sufficient accuracy for the reconstruction of glacier bed topography. GPR data and generated subglacial topography model does not reveal any possible Nye channel that could be incised into the bedrock, however, we were able to detect englacial tunnel that runs approximately parallel to the ice margin and possibly is a remnant of a tunnel that provided passage for ice-dammed lake waters during the latest jökulhlaups (2007, 2008). We also observe a radar-transparent layer up to 20 m from the glacier surface suggesting the boundary of cold/temperate ice or piezometric surface. The latter one is preferred due to the warm climatic conditions which are supposed to warm up possible winter cold wave.

Quantitative and Qualitative Appraisals of Aquifer Properties in Kachia Area of Kaduna State, Nigeria

Kachia Local Government Area (LGA) is located at the southern part of Kaduna State, Nigeria. Quantitative and qualitative appraisals were carried out in order to have proper understanding of the aquifer system and ensure sustainable development by using geophysical, geological and pumping test data obtained from 32 producing boreholes across the entire LGA. Hydraulic conductivity, transmissivity and storativity values were computed, piezometric surface map and the basement relief map were prepared, geoelectric layer characteristics were delineated and two geological profile sections were constructed. The hydraulic conductivity values were found to range from 0.021 m/day at Walijo to 1.391 m/day at Iddah-Hanya with an average of 0.42 m/day. The transmissivity values ranged between 0.90 m²/day at Walijo to 25.37m²/day at Iddah-Hanya, with average value of 6.31 m²/day. Storativity values were lowest at Walijo with a value of 89.42 and highest at Iddah-Hanya having a value of 2877 with an average of 929.82. The lowest values of these three aquifer constants were observed to converge at Walijo at the extreme eastern part and they all peaked at Iddah Hanya on the western border of the study area. The piezometric surface contour map showed that static water level is generally deeper around the central part of the study area than at the southern and western parts. The basement relief map revealed that the depth to Basement rock is generally deeper at the central part than at the eastern, western and southern boundaries of the study area. Three-layer geoelectric horizons delineated agreed with the drilled sections. The two profile sections 1 and 2 suggested that the weathered layer constituted the major aquiferous unit, and it occurred within a depth of 1 m to as much as 35 m, except Kurmin-Sara with 80 m thickness. Groundwater prospecting can therefore be targeted to an approximately uniform regolith thickness across the entire study area.

The Hydraulic Profiling Tool for Hydrogeologic Investigation of Unconsolidated Formations

AbstractThe hydraulic profiling tool (HPT) has become one of the basic tools for investigation of soils and unconsolidated formations over the last 10 years. The HPT is advanced into the subsurface using direct push methods. Clean water is injected into the formation from a small screened port on the side of the probe as it is steadily advanced into the subsurface. A downhole pressure sensor detects the pressure required to inject the water into the formation while an up‐hole flowmeter monitors the water flow rate. An electrical conductivity (EC) array included in the lower end of the probe provides a simultaneous EC log of the bulk formation. The EC log, HPT pressure, and flow rate are logged and displayed onscreen as the probe is advanced. These logs enable the investigator to evaluate vertical changes in relative formation permeability at high resolution. Pressure dissipation tests may be performed at selected depths in coarse‐grained materials to determine the piezometric pressure in saturated formations. This enables the operator to define the piezometric profile and determine the piezometric surface without a well. Post processing of the log in the viewing software provides for calculation of the corrected HPT pressure (Pc) and estimation of hydraulic conductivity (Est. K) within limits (~0.1 to 75 ft/d). In clean, coarse‐grained materials the tandem EC log may be used to estimate groundwater specific conductance based on an Archie's Law model. Cross sections of HPT logs provide an efficient means to define hydrostratigraphy. When combined with contaminant logging tools such as the membrane interface probe (MIP) the HPT data may help to define contaminant migration pathways or contaminated low permeability zones that may result in back diffusion. The HPT can be a useful tool for many geoenvironmental investigations in unconsolidated formations.

Climate change impact assessment on a carbonate aquifer under semi-arid climate: example of the Cenomanian-Turonian aquifer within Meskala-Ouazzi region (Essaouira Basin, Morocco)

This study aims to assess the climate change impact on water resources of the Essaouira Basin (Morocco). The rainfall index shows a significant interannual variability which is organized in an alternation of the excess period (1940–1956), two deficit periods (1956–1986 and 1998–2015) separated by a normal period (1986–1998). The statistical approach reveals the presence of a break in 1956 with a rainfall deficit of 14.45% and that the temperatures show a general upward trend with a warming of 2.3 °C for mean and minimum temperature and of 2.8 °C for maximum and this for the period 1987–2014. Flow rates show a slight upward trend that could be explained by a short and intense rainfall that characterizes our semi-arid environment. Concerning the piezometric approach, it shows a general descent in piezometric surface for the period of observation (reached 12 m in some wells). The downward evolution of piezometric surface due to the decrease of precipitation has resulted in the spatial and temporal degradation of the groundwater quality. A decrease in nitrate levels has been noted; this could be explained by the downward trend in precipitation by favoring the retention of nitrates in the superficial parts of the soil and by limiting their infiltration to the aquifer.

Vulnerabilidade dos Aquíferos do Município de Salvador, Bahia, Brasil, utilizando o Método GOD

Este trabalho investigou a vulnerabilidade dos aquíferos do município de Salvador, Bahia, Brasil, um sistema aquífero fissural nos domínios do Complexo Cristalino, e, granular, no domínio das rochas sedimentares. Esse sistema aquífero apresenta-se, em geral, livre e pouco profundo, com superfície piezométrica em torno de 6m, e zona não saturada dominada por materiais argilo-areno-siltosos e, eventualmente, arenosos finos. Utilizou-se a metodologia GOD para cálculo da vulnerabilidade intrínseca do aquífero, através da avaliação numérica dos parâmetros hidrogeológicos do sítio: G (tipo de aquífero), O (tipo de solo), D (profundidade até o aquífero), todos obtidos com base em interpretação das fichas de perfuração de poços tubulares dos bancos de dados da CERB e da CPRM/SIAGAS, e de alguns poços de pesquisa, perfurados até o ano de 2006. A metodologia GOD revelou que a vulnerabilidade natural dos aquíferos da cidade de Salvado é baixa à insignificante nos trechos mais argilosos e elevados; e, alta à extrema, nos trechos mais arenosos que ocorrem nos vales e baixadas. O mapa das classes de vulnerabilidade revelaram os trechos com potencial de água subterrânea não potável, devido a risco de contaminação por atividades antrópicas nelas instaladas.

Influence of Land Use Land Cover Change on Groundwater Recharge in the Continental Terminal Area of Abidjan, Ivory Coast

The process by which rainfall reaches the aquifer in a sedimentary area is infiltration. This process could be affected quantitatively or qualitatively by the changes in the land use land cover (LULC) as a result of anthropogenic activities which could affect groundwater reserves. This study focuses on the influence of LULC change on groundwater recharge in the context of urbanization and population growth. Four weather stations data and satellite image data were used in order to evaluate water infiltration which is the amount of water that reaches the piezometric surface from 1990 to 2016. The spatial-temporal LULC change in relation to urbanization sprawl was assessed based on a series of Landsat images for 1990, 2000 and 2016. The maximum likelihood pixel-based on classification method was used to analyze the spatial-temporal LULC dynamics. The Thiessen polygon method was used for the mean area precipitation computation. The recharge was determined using water balance method after determining the runoff based on the Soil Conservation Service curve number method. The results show an increase in built-up and agricultural land, while the forest and shrub areas declined with water body remaining unchanged over the period 1990-2016. The decline in forest could be imputed to the demographic and socio-economic growth as expressed by the expansion of agriculture and urbanization. Groundwater recharge and runoff results are respectively 34%, 20% in 1999; 21%, 46% in 2000 and 26%, 14% in 2016 of rainfall and show their strong dependence on precipitation and LULC change.

Appraising Hydro-dynamics of Alluvial Aquifers from Indo-Gangetic Plains

ABSTRACT Aquifer behaviour in alluvial plains is a complex phenomenon owing to the discrete lithological units, hydro-dynamics and erratic rainfall patterns. Therefore, the aquifer geometry, recharge and rainfall which define the hydro-dynamics of alluvial aquifers are important to understand in view of sustainable groundwater management. This study appraises the time series hydro-climatic data on daily basis during July-2008 to March-2011 in Indo- Gangetic plains, India. It includes field site monitoring of six piezometric wells installed with borehole data loggers and daily rainfall events. The temporal variations recorded for hydro-climatic (i.e. piezometric surface and rainfall) data sets are examined applying classical statistical tools. Results showed, a) the linear regression value R2 = 0.81−0.98 (mean: 0.94) calculated for consecutive three monsoons indicated the rise of static WL by 1.59 m/monsoon, b) the linear trend for three hydrological cycles denotes, rainfall deficit of 9.83 % and 14.10 % corresponds to WL decline by 0.914 m and 1.478 m, c) for an individual hydrological year, a negative response of rainfall to WL decline with correlation coefficient r=-0.921 indicates multiple variables of aquifer discharge. The derived negative linearity y=−1.196x+223.35 has assisted to simulate the declining mode of WL by 1.196 m/year. It assists to draw the similar results for alluvial aquifers in other regions of Indo-Gangetic plains.

Hydrogeological characterisation of regional faults and dolerite dykes in the Precambrian Basement and Karoo Supergroup (Tete Province, Mozambique)

Abstract Faults and dolerite dykes within Basement- and Karoo-aquifers in northern Mozambique may increase groundwater occurrence but may also be barriers to groundwater flow. Should observation boreholes drilled into regional and local faults as well as dykes show a response to aquifer testing, it would be deduced that these hydrogeological discontinuities are not barriers to groundwater flow. The approach adopted for this study included a sequential process involving data acquisition through a hydrogeological fieldwork programme consisting of geophysical surveys, borehole drilling, aquifer testing, and groundwater level monitoring. The Zambezi Border and geological contact faults were characterised by high variability in hydraulic properties. Aquifer testing resulted in drawdown in observation boreholes as well as a reduction in piezometric surface in the installed vibrating wire piezometers located in different aquifer units, indicating the Zambezi Border- and geological contact-faults were not barriers to groundwater flow. Not all the northwest-southeast trending dykes acted as barriers to groundwater flow, as there were discreet intervals with relatively high permeability present.

Hydrogeological characterization and assessment of anthropic impacts in the Lower Piura Sub-basin Aquifer in Peru

The Lower Piura Sub-basin Aquifer is a vital source of water in the north of Peru. Despite its importance, few local studies describe this formation. Most are limited to reporting hydraulic characteristics and abstraction rates, lacking a broader analysis. This article characterizes the aquifer, presenting the development of a conceptual and mathematical model with sparse data, completed using several assumptions and interpolations. The model will improve understanding of the aquifer system and the impacts of abstraction. The aquifer system includes an unconfined aquifer connected to a confined aquifer through an aquitard. Steady-state and transient-state models from 2004 to 2014 were used. The development and calibration of the model have led to proper identification of hydraulic parameters and boundary conditions, clarifying the dynamics of the system. In the unconfined aquifer, groundwater flows towards the south-west without significant variation in the water table. Conversely, the piezometric surface of the confined aquifer shows a cone of depression with a falling trend of 1.6 m/year between 2004 and 2014. Outflows include abstractions (48.42 × 106 m3/year), gaining surface waters (6.33 × 106 m3/year), and sea discharge (18.50 × 106 m3/year). Inflows are from irrigation return (34.67 × 106 m3/year) and from the Higher Piura Aquifer (27.23 × 106 m3/year). The imbalance of 11.24 × 106 m3/year is abstracted from aquifer storage leading to hydraulic head drops and flow changes, revealing a clearly unsustainable overexploitation scenario that impacts more intensively the confined aquifer. Model results provide the basis to understand how this is happening and help to suggest strategies to alleviate the current aquifer situation.

Potential Groundwater Extraction and Piezometric Surface Fluctuations in Puruliya, West Bengal – A GIS based study

Abstract. A majority of Indians living in rural areas still primarily depend on agriculture for their sustenance. The water requirement is thus constantly high with groundwater being the most widely used source for domestic, agricultural and industrial use. More than 90% of the rural and nearly 30% of the urban populations depend on groundwater for meeting their drinking and domestic requirements causing an ever-rising demand for groundwater resources, resulting in an increase of the stress on these reservoirs and their consequent pollution. Water resources development occupies a key place in India because of its role in stabilizing the Indian agro-economy. Groundwater is a dynamic and replenishable natural resource but in hard rock terrain availability of groundwater is of limited extent.This work attempts to present an overview of groundwater utilisation in the different blocks of Puruliya district, West Bengal and particularly within Puruliya Town (Municipality). Being a semi-arid district, Puruliya experiences hot and dry summers. Groundwater in the district occurs at shallow depths within the weathered mantle, fractural zones of hard rock, and narrow zones of unconsolidated sediments which are utilized by developing dug wells. During the peak of long and harsh summers, most of these openings dry out and there occurs a severe scarcity of water. The objectives are:Block-wise assessment of groundwater fluctuation (recharge & utilization), types of irrigation structures and present utilization status.To examine the groundwater abstraction and use in Puruliya town – the district headquarter.Remote sensing studies for locating weak zones and for understanding factors influencing groundwater movement in different geomorphologic setup.To highlight the problems associated with groundwater use and investigate possible solutions. The following study is mostly done based on secondary data collected from various Central and State Government offices. The various data used and their sources are as follows:District level groundwater reports from Central Groundwater Board, Eastern Region, Kolkata.District and ward level administrative, land use and land cover, geomorphology and groundwater maps and statistics from Puruliya Town Municipality.Shuttle Radar Topographic Mission Digital Elevation Model (SRTM DEM data for preparation of elevation and drainage maps along with Survey of India topographical maps (73E, 73I, 73J – R.F. – 1 : 250,000) for preparing several base maps.Lineament extraction and mapping using SRTM DEM to show possible fracture zones that might be used for future groundwater abstraction.Collating different reports together and preparing thematic maps to show the groundwater utilisation status of the different blocks in Puruliya district.The work analyzes the correlations between the physiography, geomorphology, geology, hydrogeology, soils, climate and land use – land cover of the region with the groundwater zones. The present level of groundwater utilization in the district is mapped. Amount and quality of groundwater extracted, the levels of groundwater abstraction development block-wise are examined along with the different types of mechanical structures related to this. The nature of groundwater level fluctuation throughout the district at the Block level, in the Pre-Monsoon and Post-Monsoon season is also depicted and the long term terns of the peizometric surface behaviour analysed from these maps. The Block level utilisation as well the ward level utilisation of groundwater in the District Headquarter, Puruliya Town is mapped. A small attempt is also made to delineate some potential groundwater zones through lineament mapping and correlation with the earlier mapped variables. Problems faced in groundwater exploitation here and its ambient quality is also examined.

Applying 3D Geostatistical Simulation to Improve the Groundwater Management Modelling of Sedimentary Aquifers: The Case of Doñana (Southwest Spain)

Mathematical groundwater modelling with homogeneous permeability zones has been used for decades to manage water resources in the Almonte-Marismas aquifer (southwest Spain). This is a highly heterogeneous detrital aquifer which supports valuable ecological systems in the Doñana National Park. The present study demonstrates that it is possible to better characterize this heterogeneity by numerical discretization of the geophysical and lithological data available. We identified six hydrofacies whose spatial characteristics were quantified with indicator variogram modelling. Sequential Indicator Simulation then made it possible to construct a 3D geological model. Finally, this detailed model was included in MODFLOW through the Model Muse interface. This final process is still a challenge due to the difficulty of downscaling to a handy numerical modelling scale. New piezometric surfaces and water budgets were obtained. The classical model with zones and the model with 3D simulation were compared to confirm that, for management purposes, the effort of improving the geological heterogeneities is worthwhile. This paper also highlights the relevance of including subsurface heterogeneities within a real groundwater management model in the present global change scenario.

Assessment of saltwater contamination extent in the coastal aquifers of Chaouia (Morocco) using the electric recognition

The coastal Chaouia, located on the Moroccan Atlantic coast, comports three aquifers: a first Plio-quaternary constitutes the cover, a second Cretaceous located at SW in the zone of Azemmour-Tnine Chtouka, and a third Primary located at SE in the zone of Tnine Chtouka-Casablanca. These reservoirs constitute the only exploitable water resource for the social and economic development of the region between Azemmour and Casablanca. These aquifers are unconfined, pellicular, and discontinuous. They feed by infiltration of rainwater and discharge at sea. Agricultural irrigation is carried out exclusively from the groundwater, which causes a drop of the piezometric surface and the intrusion of saltwater into the aquifer at the coast. The consequence is the abandonment of some wells contaminated by seawater leading to conflict situations and significant economic losses. Therefore, delineation of the freshwater/saltwater interface is very important in order to build a sustainable groundwater management system and to implement appropriate regulatory policies.The purpose of this study is to determine the extent and the geometric characteristics of the saltwater contamination extent in the coastal aquifers of the coastal Chaouia. To achieve this, 399 vertical electric soundings and 48 electrical resistivity tomography profiles were performed perpendicular to the ocean. Furthermore, the electrical conductivity and the piezometry were measured in 344 wells distributed over the study area.The study demonstrated the effectiveness of electrical methods for mapping seawater intrusion into coastal aquifers. In fact, the results of the interpretation of the VES and ERTs after calibration with the lithological data of the boreholes, as well as the values of the electrical conductivity, have shown that the length of the saltwater wedge penetration inland depends on the lithological nature of the aquifer formations. Thus, in the zone of Azemmour – Tnine Chtouka, characterized by the presence of Cretaceous terrains, the extension of the saltwater wedge exceeds 2 km towards the continent and its depth reaches 45 m. On the other hand, in the zone of Tnine Chtouka- Casablanca, characterized by the rise of the schists surmounted by the altered schists the seawater intrusion remains limited at 700 m from the coast and at 20 m of depth.

Application of the Electrical (Geophysical) Method for the Identification of the Sealed Bevel in the Coastal Region of Walidia Province of el Jadida – Morocco

The Walidia area knows a great development of agricultural, industrial, maritime activities and a very great demographic expansion. This development is accompanied by a growing demand for water. On the other hand, any intense abstraction of fresh water at a coastal aquifer capture field causes a decrease in groundwater flow and a lowering of the piezometric surface. There is therefore a danger of advancing towards the land of the saltwater bevel and salinization of groundwater which is gradually loaded into mineral salts and can reach abnormally high levels. This work deals with the application of geophysics by electrical sounding method to the in-depth study of the freshwater-salt water interface (salted bevel) on the one hand and the study of the lateral and vertical evolution of the geometry of the different aquifers. The principle of the method is, when performing an electrical survey, to research how varies, at a given point on the surface, the resistivity of the subsoil vertically. For this one executes in a same place a succession of measurements, increasing each time the dimensions of the device and thus the depth of investigation which is proportional to them. At this site, we explore a slice of ground increasingly thick and thus highlights the changes in geological constitution along the vertical. The electrical soundings were carried out with the classic Schlumberger device. The interpretation and the exploitation of the data of the electric soundings carried out made it possible to : Follow the evolution of the salted bevel roof, Draw the upstream limit (marine invasion) of salted bevel Hauterivian, on the one hand, and Valanginian and Jurassic on the other hand, Follow the roof structure of Dridrat limestone (Hauterivien) and limestones of Valanginien and Upper Jurassic, Draw the map of the marl roof of Safi (Hauterivian) constituting the impermeable substratum of Dridrat limestones.

Hydrodynamics and Recharge of the Aioune Sandstone Aquifer in the Taoudenni Transboundary Basin in Mauritania

In Mauritanian, 4/5 of the territory is subject to an arid climate, where groundwater resources are the main sources of drinking water for populations and livestock. The study area is located in south-eastern Mauritania and in the western part of the Taoudenni Transboundary Basin. A better knowledge of the hydrogeological system to ensure a sustainable and rational management is necessary for this vulnerable water resource. This pioneering study, based on the compilation of hydrogeological, geochemical and isotopic data, aims to characterize the hydrodynamics and recharge of this one layer aquifer system, composed of Aioune infracambrian sandstone. The piezometric surface exhibits relatively the same morphology of the soil topography, and computed effective velocity is 94 m/yr (Northeast area), and the direction of flow is generally from cliff to plains area. The chemical data show water types evolving between two poles namely the HCO3-Ca/Mg pole (low mineralized), and the Cl-Ca/Na pole; these waters are characterized by a high vulnerability to pollution, especially at shallow depth area (Douerare, Aioune). The dissolution of bicarbonate and evaporate minerals is likely the main source of mineralization. The isotopic tool used to support comprehension of the system functioning, evidences a local indirect recharge water localized at the cliff or Wadi zones. The age of the waters ranges from the present to 1060 year. The recharge rate calculated by 14C and the chloride masse balance is respectively 0.4 to 5 mm/year. This recharge compared to the water pumping rate is lower and hence this imbalance is likely the cause of water shortages particularly during summer season period.

Assessment of Groundwater Potential of Gandhinagar Region, Gujarat

ABSTRACT With burgeoning population, the groundwater demands of any area increased by many fold and therefore, it is essential to assess the groundwater potential to choose suitable sites for further groundwater development. Present study determines the groundwater potential of different parts of Gandhinagar region located at Gandhinagar district, Gujarat, India. Here, excluding city dwellers, all villagers are mostly dependent on groundwater for drinking and domestic purposes. With increasing population, there is a rise in daily human consumption and hence reduction in groundwater quantity. Various types of industries of Gandhinagar such as textile industries, food processing industries, ceramic industries etc. also require groundwater. Industrial discharges deteriorate the water quality of this region. Therefore, water level monitoring and quality assessment of groundwater in regular intervals is essential. The groundwater potential zoning is an indicator, which gives the overall idea about the groundwater condition. Overlay analysis in GIS using multiple criteria such as WQI, hydraulic conductivity, groundwater velocity, and depth to piezometric surface discloses that there are five groundwater potential zones in Gandhinagar region. This study reveals that majority of the study area is covered with medium potential zone. Different management plans such as treated surface water supply, reduction in tubewell operation time, development of rooftop rainwater harvesting system and artificial recharge system etc. are recommended for different potential zones for sustainable development of groundwater of Gandhinagar region.

Functioning of the Primary Aquifer Relating to the Maider Basin, Morocco: Case of the Ordovician aquifer.

The basin of Maider is limited northly by the vast ensemble Oriental Saghro-Ougnate, from the east by the Tafilalet plain, from the west by the oriental Jbel Bani, finally from the south and south-east by the Cretaceous Hamada of Kern-Kem. During last decades, groundwater in the basin of Maider, is confronting degradation in both cases: Quantitative and qualitative, as a result of the drought, the overexploitation and the salinization. The aim of this action research is to understand the current state of water resources in the area of stady. At the end of this work, we can get the following conclusions: the general flow of the ordovician aquifer is always directed from the north to the south-east of the basin by following the principal axes of the wadis:Taghbalt, Hssiya and Fezzou. The recharge of the aquifer is primarily done, either by the underground flow, or by the surface runoff of torrential waters from the upstream of Jbel Saghro. The piezometric anomaly noticed at the level of Ait Saàdane, explained by overexploitation linked to the needs of irrigation water. The physicochemical approach for the Maider basin identifies two essential factors of the salinisation of groundwater: the dissolution of the aquifer which is rich in minerals with high temperature on the one hand, and the decrease of the piezometric surface due to the overexploitation and drought on the other hand.

A vertical water exchange of the groundwater in the central part of Moscow artesian basin

The hydrogeological features of the central part of the Moscow artesian basin (MAB) under the natural conditions provided the existence of the downward vertical flows of the groundwater, the formation of the fresh underground waters of the Carboniferous complex, desalination of the Upper Devonian subterranean waters. The long exploitation of the Aleksin-Protvino horizon in the central part of the MAB led to the formation of a depression of the piezometric level with a depth of 80 m, as well as a change in the ratio of the absolute marks of the piezometric surfaces of the groundwater of the Lower Carboniferous and the Upper Devonian, and the creation of prerequisites for the changing of the orienfafion of the vertical wafer exchange between them. A map of the difference in pressures between the Aleksin-Protvino and the Upper Devonian horizons, compiled by the author, shows this situation. In a vast zone of the central part of the MAB, the pressure surface of the Alexin-Protvino horizon is 30-50 m below the upper Devonian horizon. Under these conditions, it seems important to study the Upper Devonian aquiferous complex as a possible source of the «contamination» of the groundwater of the Lower Carboniferous, especially in the zones of active lineaments of the Moscow syneclise.

Numerical Modelling of Mining-induced Inrushes from Subjacent Water Conducting Karst Collapse Columns in Northern China

Collapse columns are geological features formed by chimney caving of karst voids. Collapse columns can cut through the rock mass and introduce vast geological complexity in coalfields. When a collapse column becomes accessible to a confined aquifer, water inrush disasters can be triggered. In northern China, inrushes related to collapse columns occur in regions where extensive Ordovician limestone underlies the coal measures. This limestone is strongly karstified and holds large quantities of water. The piezometric surface can be considerably higher than the coal extraction level. Numerical simulation was used to explore how the water inrush pathway forms, based on a demonstration model. First, the evolution of the stress field, damage field, and flow volume within the coal floor was analysed. Then factors such as the column height, mechanical strength of the coal floor, and hydraulic pressure in the aquifer were considered. In the demonstration models, if the height of the collapse column exceeded 35 m and the initial thickness of the aquiclude was less than 15 m, an inrush definitely occurred, even when the strength of the floor strata was relatively high. Finally, a practical case of water inrush in the Fangezhuang coal mine related to a collapse column was numerically investigated. Modelling of the fracturing process provided insight into evolution of the fracture zone and inrush processes that cannot be observed in the field and are difficult to evaluate using static stress analysis.

NEW DATA REGARDING THE GROUND WATER LEVEL CHANGES AT THE AMYNTAIO BASIN- FLORINA PREFECTURE, GREECE

The site investigated is the Amyntaio basin where a productive semi-confined aquifer is developed at the quaternary deposits. In the present study, the piezometric curves which have been extracted before the beginning of the mine activity (1992), were compared with the recent ones (2015), aiming to study their diachronic changes. From the subtraction of the two aforementioned piezometric surfaces, a significant ground water drawdown that reaches 70 m near the mine was observed. This drawdown, during the last decades, proves that the aquifer has been overexploited by both the mine of PPC -to protect the slopes and to prevent the water outflow in the mine- and the wells for irrigation purposes. The level drop extends, on the west, to the villages of Valtonera and Anargyroi and the underground water flow directs towards the mine. The Amyntaio mine can be described as a well with a diameter up to a few kilometers. The interaction of the groundwater level drawdown with the intense fragmentation and the geotechnical characteristics of the geological formations of the region triggered extensive land subsidence phenomena damaging numerous villages, infrastructures and extensive farmlands.

GRANULAR AQUIFER SYSTEM OF WEST CHALKIDIKI AREA, REGION OF CENTRAL MACEDONIA, NORTHERN GREECE

The granular aquifer system of the western Chalkidiki peninsula covers an area of 667 Km2 occupying Neogene and Quaternary sediments. The present study deals with the hydrogeological and hydrogeochemical characterization of the granular aquifer system for the purposes of efficient utilization and management of groundwater resources. It is a multilayered formation, composed of unconsolidated to semi-consolidated sands, gravels, conglomerates, sandstones and marly limestones with intercalated impermeable to semi-permeable beds of clays, marls or mixed with pebbles and sands. The aquifer system is characterized by medium to moderate hydrocapacity and the pumped groundwater consumptions are 74*106 m3/yr. Piezometric studies carried out in the period of 2003-14, conclude that the piezometric surface decline is located in the S and SE parts of the aquifer system, while in the rest Central and NW parts there is a noticeable rising of the groundwater table. Groundwater is generally characterized by a good quality; however, groundwaters of the broader Triglia area, have excessively high contents of As (10 to 3400 μgr/l) and B (1.5 to 4.0 mg/l). Other natural pollutants are Fe and Mn. Salinization and high values of nitrate are mainly detected in water boreholes of Moudania-Portaria, Akrotiri-Epanomi and Agelochori areas.