Journal articles on the topic 'Hydrogeology, groundwater, modelling, Iraq'

The current study evaluated the hydrogeological conditions and hydraulic properties of the groundwater aquifers in Qaraqosh, Karamless and Bartella areas within Al-Hamdaniya district east Mosul. The depths and water tables of groundwater for 48 well were measured in October 2019, were ranged between 5 - 45 meters and 234 - 278.5 meters, respectively. The highest water table reaches in the center of the studied area north Qaraqosh and decreases gradually in all directions. A map of the flow net was drawn, and it was found that the general direction of water movement is from north to south, with local directions resulting by pumping from the aquifer, or due to the heterogeneity of the porous media. The results of the pumping test in Karamless area shows that the transmissivity was 107.671 m2/day and 100.682 m2/day according to Theis and Cooper-Jacob methods, respectively. The hydraulic conductivity of 157.65 m saturated thickness was found to be 0.683 m/day and 0.639 m/day using Theis and Cooper-Jacob methods, respectively. While the storage coefficient using Theis and Cooper-Jacob methods was 0.0023 and 0.0020، respectively. In Qaraqosh, the transmissivity was 87.1685 m2/day and 88.1004 m2/day according to the mentioned methods, respectively. While the hydraulic conductivity of saturated thickness of 71.07 m was found to be 1.24 m/day and 1.23 m/day using Theis and Cooper-Jacob methods, respectively. The values of storage coefficient using these methods was 0.00135 and 0.00115 respectively. The total dissolved solids (TDS) measured to conclude the hydrogeological system according to the quality of the groundwater aquifers, it was found that the concentrations of total dissolved solids are more than 3500 ppm in the mid of the study area and decreased towards all directions to the limits of 250 ppm. This wide variation in salinity may be because the wells in the central area penetrate the groundwater aquifers, represented by the layers of gypsum in Al-Fat'ha formation, which is hydraulically connected with the main aquifer of the Injana formation.

Review of more than 200 publications on numerical modelling in hydrogeology has been presented as a base for the presentation the progress and development of this widely used method, especially during the years 2004–2017. Three stages in the research methods of modelling has been noticed. The main trends in the field of modelling groundwater flow, the mass transport and pollutants migration, practical applications, research processes and improvement of the research method has been discussed. Highlighting the many benefits of this method are given some examples as well as indicated on the constraints and disadvantages during the groundwater modelling. At the end provides an overview of the most frequently used keywords. The nature of things the review is subjective descriptions based on the experience of the author and of literature review.

Groundwater pollution risk modelling is an important asset to improve groundwater management and protection. In this study, we assess the temporal dynamics of groundwater pollution risk at the continental scale, using the DRASTIC model. The approach was developed using continental-scale data on soil properties, topography, land use, geology, hydrogeology, and climate with a resolution of 15 × 15 km2. We compared continental-scale groundwater pollution risk for the years 1990, 2000, and 2010. The results showed significant inter-annual variations of the spatial distribution of pollution risk. Changes were mainly concentrated in the area of the Nile Delta, around the Lake Victoria, in North Africa, and in coastal West Africa (predominately in Nigeria). We found that the increase in pollution risk was mainly related to the increase in the population density in these regions. The proposed methodology for modelling the temporal dynamics of groundwater pollution risk could support the monitoring of the Sustainable Development Goal 6, which focus in particular on the preservation of the freshwater resources against future threats.

Groundwater is an important resource in Halabja Said Sadiq sab-basin, Sulaymaniyah district for agricultural and other uses. Continuous dramatic extraction of groundwater from legal and illegal wells led to a severe decline in the water table for the last thirty years. The objectives of this study are to delineate the groundwater productivity zones by combining the geographic information system and geoelectrical survey, which serves to recognize the locations of good groundwater storage and recharge zones. The Halabja Said Sadiq sub-basin has been selected as a case study to delineate the groundwater productivity zones. Four geoelectrical resistivity profiles conducted with electrode spacing 10 m and the length of the profiles is equal to 710 m. Themes such as hydrogeology, land use/land cover, topography, drainage density, soil type, slope, lineaments and rainfall maps are created. The thematic maps made with GIS platform and appropriate weights put to the attributes taking into account the influence on the storage potential of groundwater. The results of geoelectrical profiles revealed that the aquifer thickness is 150 m. Three zones of groundwater potential delineated which are low, moderate and high and cover 33 %, 24 %, and 42 % of the total area respectively. Spatially, the highest zone is located along with the Quaternary deposits which characterized by high lineament density, low slop, and pediment deposition The output of the groundwater potential model is verified by testing the discharge rate of the existing 580 wells. The results are revealed that most of the high yield wells are located within the high groundwater potential zone. Results of such verifications proved that the groundwater productivity areas recognized by GIS (AHP) and geoelectrical techniques are dependable and practical. http://dx.doi.org/10.25130/tjps.24.2019.112

Carbonate aquifers are the primary source of freshwater in Cuba. Unfortunately, coastal groundwater is often contaminated by seawater intrusion. The main aim of the present study was to test the efficacy of an experimental modelling approach, ranging from hydrogeology/geomorphology to microbiology, to better characterise both the hydraulic features and behaviour of a coastal carbonate aquifer and acquire useful information to prevent groundwater salinization. The interdisciplinary approach was an effective tool in order to understand (i) the hydraulic role played by some fault zones; (ii) the influence of discontinuous heterogeneities on groundwater flow and saltwater wedge shape; (iii) mixing processes between different water bodies (groundwater, surface water, seawater); (iv) the role of karst conduits in influencing the step-like halocline within the mixing zone between fresh groundwater and seawater.

The aim of this study is to the evaluation of the general hydrogeology condition of the Al-Khassa sub-basin area. Pumping test has been done for five wells in the area. The hydrogeological characteristics (transmissivity, hydraulic conductivity and storage coefficient) were determined in the area by input data which obtained from the pumping test process into the (AquiferWin32, Version 5) software program. The data were analyzed using Copper-Jacob, Theis and Hantuosh methods for pumping, the values of hydraulic characteristics range from: transmissivity (0.98 to 19.57) m²/day in (W7-W9-W10-W12) sites and 416 m²/day in W1, hydraulic conductivity (0.051 to 0.305) m/day in (W7-W9-W10-W12) sites and 5.012 m/day in W1, storage coefficient 0.021 to 0.065, intendment that the water is pumped from semi-confined aquifer. By using the lithological information, the saturated thickness of where the minimum thickness of 47 m is observed in site W4, and a maximum thickness of 83 m are obtained in site W1, with an average of 67 m. Groundwater flow was 0.364 MCM annually. The flow direction of groundwater was drawn by calculated head values of the eleven wells, it was from the recharge areas in northeast and southeast towards the discharging areas at west.

With the availability of Global Circulation Models (GCMs) it is now possible to apply hydrological and hydrogeological models and knowledge to assess environmental conditions in past climates. In the upper Kennet there is considerable interest in the development of the construction of the man-made hill at Silbury. Silbury was built in several stages over a period of time and the question arises as to the availability of water for the people who built Silbury. The current Kennet flows at Silbury are low and the current stream tends to be dry for on average 5 months of the year. The aim of the research has been to assess the palaeohydrology of the Silbury Hill and Avebury area and determine the flow rates, groundwater levels and hydrological conditions in 4,400 BP. This has been undertaken using hydrogeological mapping and modelling techniques, making use of outputs from a GCM to recreate past flows and groundwater levels in the upper Kennet at Avebury and Silbury. The modelling results indicate a past wetter climate in the area, with higher river flows and higher groundwater levels, which would have sustained the local populations through dryer summer months.

Indirect physical methods of assess groundwater recharge rely on the measurement or estimation of soil physical parameters, which along with soil physical principles; can be used to estimate the potential or actual recharge. However, the deep percolation method uses a daily water- budget approach to simulate deep percolation. In this method, the model computes daily fluxes of water into and out of a volume extending from the top of foliage to the bottom of the root zone and accounts for changes in water content. In most environments, deep percolation is destined to recharge the saturated systems that are tapped by wells. Deep percolation technique was deployed to determine the rate of ground water recharge in the Voinjama region of Liberia, and also establish points of lineaments where wells can be dug for water supply. The perimeter of the hypothesized basin is about 28.9km while the length of the thalweg of the mainstream is about 11km. the average width of the basin area is 5.9km while the circumference of the equivalent circular area is 25.33km and compactness coefficient (R) of the basin is computed at 1.14. The elongation ratio (Er) is computed at 0.73km. The diurnal recharge computed from Deep Percolation was 6712.21 cm3 /km2 per annum. In conclusion, this study aids the restoration of water supply system destroyed during the war periods emphasizing the abundant water in the hydrological system and viable ground water recharge adequate for exploitation in a near uniform geology. Several faults and crevices scattered abroad the area were recorded indicating good lineament distribution and abundant aquifer recharge.Keywords: Hydrogeology, Deep Percolation Method, Groundwater, Recharge

Abstract. Contamination of groundwater with nitrate poses a major health risk to millions of people around Africa. Assessing the space–time distribution of this contamination, as well as understanding the factors that explain this contamination, is important for managing sustainable drinking water at the regional scale. This study aims to assess the variables that contribute to nitrate pollution in groundwater at the African scale by statistical modelling. We compiled a literature database of nitrate concentration in groundwater (around 250 studies) and combined it with digital maps of physical attributes such as soil, geology, climate, hydrogeology, and anthropogenic data for statistical model development. The maximum, medium, and minimum observed nitrate concentrations were analysed. In total, 13 explanatory variables were screened to explain observed nitrate pollution in groundwater. For the mean nitrate concentration, four variables are retained in the statistical explanatory model: (1) depth to groundwater (shallow groundwater, typically < 50 m); (2) recharge rate; (3) aquifer type; and (4) population density. The first three variables represent intrinsic vulnerability of groundwater systems to pollution, while the latter variable is a proxy for anthropogenic pollution pressure. The model explains 65 % of the variation of mean nitrate contamination in groundwater at the African scale. Using the same proxy information, we could develop a statistical model for the maximum nitrate concentrations that explains 42 % of the nitrate variation. For the maximum concentrations, other environmental attributes such as soil type, slope, rainfall, climate class, and region type improve the prediction of maximum nitrate concentrations at the African scale. As to minimal nitrate concentrations, in the absence of normal distribution assumptions of the data set, we do not develop a statistical model for these data. The data-based statistical model presented here represents an important step towards developing tools that will allow us to accurately predict nitrate distribution at the African scale and thus may support groundwater monitoring and water management that aims to protect groundwater systems. Yet they should be further refined and validated when more detailed and harmonized data become available and/or combined with more conceptual descriptions of the fate of nutrients in the hydrosystem.

Groundwater modelling is particularly challenging in arid regions where limited water recharge is available. A fault zone will add a significant challenge to the modelling process. The Western Desert in Iraq has been chosen to implement the modelling concept and calculate the model sensitivity to the changes in aquifer hydraulic properties and calibration by researching 102 observations and irrigation wells. MODFLOW-NWT, which is a Newtonian formulation for MODFLOW-2005 approaches, have been used in this study. Further, the simulation run has been implemented using the Upstream-Weighting package (UPW) to treat the dry cells. The results show sensitivity to the change of the Kx value for the major groundwater discharge flow. Only about 7% of the models from the region can be irrigated utilizing greenhouses supported by external recharge.

A lab scale pellet reactor (PR) was designed and fabricated to carry out extensive investigations on the removal efficiency of the hardness of groundwater. The groundwater of 2200 – 2600 mg/L hardness was collected from Abdulla Ibnalhassan wells area located at the west desert of Al-Shinafiyah district (70 km to the southwest of Al-Dewaniyah city, Iraq). Both hydrodynamic parameters of the pellet reactor (porosity and fluidized bed height) and the parameters of calcium carbonate crystallization process (calcium carbonate equilibrium, pellet size, and density) were modeled and compared with the experimental results of the lab scale pellet reactor. The comparison showed that fair agreement between modeled and measured results was observed. The removal efficiency of both calcium and magnesium ions were 62.5-99% and 83-99% respectively. The removal efficiency was found to be strongly dependent on pH and the ratio of NaOH solution flow rate to the groundwater flow rate in the pellet reactor.

By 1980, coal production and coal recovery at the Whitewood mine, Alberta, were unacceptably low as a result of poor groundwater and surface water control at the mine. A feasibility study conducted to determine the most cost-effective method to reduce groundwater inflows into the mine pit and reduce pore-water pressures in the mine walls concluded that a vertical well dewatering system, which would be located behind the highwall, was the most suitable. A finite difference computer model was constructed and successfully applied to design the dewatering system. The flexibility and ease of application of the model made it possible to determine the optimum number, production schedules, and locations of the dewatering wells, in conjunction with evolving mine plans. The implementation of the dewatering well program and improvements in surface water and in-pit drainage have resulted in increased coal recovery, a significant decrease in mine wall failures, and improved coal quality. Key words: dewatering, modelling, groundwater, open-pit mining, hydrogeology, pumping wells, optimization, monitoring, coal recovery.

Abstract. Multiple-point geostatistical simulation (MPS) has recently become popular in stochastic hydrogeology, primarily because of its capability to derive multivariate distributions from a training image (TI). However, its application in three-dimensional (3-D) simulations has been constrained by the difficulty of constructing a 3-D TI. The object-based unconditional simulation program TiGenerator may be a useful tool in this regard; yet the applicability of such parametric training images has not been documented in detail. Another issue in MPS is the integration of multiple geophysical data. The proper way to retrieve and incorporate information from high-resolution geophysical data is still under discussion. In this study, MPS simulation was applied to different scenarios regarding the TI and soft conditioning. By comparing their output from simulations of groundwater flow and probabilistic capture zone, TI from both sources (directly converted from high-resolution geophysical data and generated by TiGenerator) yields comparable results, even for the probabilistic capture zones, which are highly sensitive to the geological architecture. This study also suggests that soft conditioning in MPS is a convenient and efficient way of integrating secondary data such as 3-D airborne electromagnetic data (SkyTEM), but over-conditioning has to be avoided.

Abstract. We investigate the degree of hydraulic interconnection between the different (regional to local) groundwater compartments with respect to the choice of boundary conditions and their impact onto the groundwater safety beneath the urban centre of Berlin, capital city of Germany. To this end, we carry out a systematic study based on 3-D hydrothermal models differing in terms of imposed parametric set-ups of the hydrogeology, as well as different surface forcing with respect to their impact on fresh groundwater production. The study area is part of the Northeast German Basin and consists of a thick sequence (up to 5 km) of differently consolidated sedimentary deposits. This sedimentary succession features a sequence of alternating aquifers (reservoirs) and aquitards which are connected to different degrees, each one depicting a specific composition of its mineralised pore water. The uppermost aquifer system (made up mainly of poorly consolidated siliciclastic rocks) acts as the main freshwater reservoir used for groundwater production by the municipal water supplier. This compartment is incompletely sealed from the brackish to saline aquifers extending at greater depths by a regional clay-enriched aquitard, the Oligocene Rupelian Clay. The latter shows a heterogeneous thickness distribution due to erosion during the latest glacial periods resulting in local discontinuities. This aspect opens to the potential risk of contamination of the drinking water reservoir from mixing with the saline groundwater upconing, locally enhanced by shallow pumping activities. Based on our results and their correlation with available isotopic and chemical analysis of water samples, we demonstrate how hydraulic connection between the different compartments is indeed likely to occur thus supporting the possibility of a contaminant rise from the saline aquifers below through either natural or anthropogenic (pumping) forcing.

A robust decision-making tool is needed to meet sustainability challenges and to manage water resources that are under development pressure, water scarcity, and climate change impact. To tackle such challenges, optimization modelling can be employed to explore regional sustainable management scenarios of groundwater exploitation. Multi-objective management modelling of various alternatives was developed for the Diyala River Basin in Iraq using Borg multi-objectives evolutionary algorithm (MOEA) and ε-DSEA algorithms. In almost all modelled cases, the upper aquifer storage is predicted to be depleted after 40 years due to large water demands and regional recharge scarcity. Hence, there is a need to develop a strategy to reduce water stresses by 45% to achieve sustainability within the next 25 years. Optimization modelling successfully generated future predictions that can be used by decision makers to manage the predicted groundwater shortages in the future.

AbstractTracer methods have been widely used in many fields of environmental and natural sciences, and also in human health sciences. In particular, tracers are used in the study of karst hydrogeology, typically focusing on phenomena such as sinkholes, sinking rivers and large karst springs. It is known that tracers have been used since antiquity. The aim of tracer tests has been to investigate underground flow paths, transport processes and water–rock interactions, and to get an insight into the functioning of a karst aquifer. In karst hydrogeology, tracer methods are the most important investigation tools beside conventional hydrological methods. In early times, tracer methods were applied only to investigate underground flow-paths. Later they were also used to elucidate transport processes associated with water flow, and today they are often the basis, together with detailed hydrological information, of groundwater protection investigations and aquifer modelling. Many substances (spores, microspheres, bacteriophages, salt tracers, fluorescent dyes, radioactive substances) have been investigated for their properties and potential usage in environmental investigations, in particular the often unknown and inaccessible underground systems of karst areas. A great number of analytical techniques is available. This includes instrumentation for laboratory applications and direct online, on-site or in-situ field measurements. Modern instruments have a high capability for data acquisition, storage and transmission in short intervals, as a basis for quantitative evaluation and modelling. This enables research on the hydrological and hydrochemical dynamics of aquifers and their response to different natural or anthropogenic impacts.

Abstract. Coastal aquifers in arid and semiarid regions are particularly at risk due to intrusion of salty marine water. Since groundwater is predominantly used in irrigated agriculture, its excessive pumping – above the natural rate of replenishment – strengthen the intrusion process. Using this increasingly saline water for irrigation, leads to a destruction of valuable agricultural resources and the economic basis of farmers and their communities. The limitation of resources (water and soil) in these regions requires a societal adaptation and change in behaviour as well as the development of appropriate management strategies for a transition towards stable and sustainable future hydrosystem states. Besides a description of the system dynamics and the spatial consequences of adaptation on the resources availability, the contribution combines results of an empirical survey with stakeholders and physically based modelling of the groundwater-agriculture hydrosystem interactions. This includes an analysis of stakeholders' (farmers and decision makers) behaviour and opinions regarding several management interventions aiming on water demand and water resources management as well as the thinking of decision makers how farmers will behave. In this context, the technical counter measures to manage the saltwater intrusion by simulating different groundwater pumping strategies and scenarios are evaluated from the economic and social point of view and if the spatial variability of the aquifer's hydrogeology is taken into consideration. The study is exemplarily investigated for the south Batinah region in the Sultanate of Oman, which is affected by saltwater intrusion into a coastal aquifer system due to excessive groundwater withdrawal for irrigated agriculture.

The search by SKB (Swedish Nuclear Fuel and Waste Management Co.) for a site to locate the deep geological repository for spent nuclear fuel in Sweden has involved geoscientific investigations at several locations since the 1970s. The objectives were to characterise geologically a bedrock volume as well as its hydrogeology and hydrochemistry. To acquire high-quality hydrogeochemical data, a complete system for groundwater sampling and analysis, as well as for interpretation strategies, has been developed through a continuous process of modification and refinement. Since the largest part of the Swedish bedrock is composed of granitoids, the site investigations had to adapt to the special difficulties of fractured crystalline rocks. This paper discusses the problems with groundwater sampling that are specific to fractured crystalline rocks and describes the solutions adopted and methods developed by SKB since the early 2000s during the site investigations. The methodology described in this paper for the characterisation of deep groundwaters in crystalline rocks is not only applicable in the context of radioactive waste disposal but also useful when sampling groundwaters for any purpose in such rocks. Sampling of groundwaters in fractured rocks at depth, often down to approximately 1,000 m, involves special challenges since the natural conditions of the groundwater are easily disturbed, especially by the initial drilling, but also by every subsequent activity performed in the borehole, including the actual groundwater sampling. The sampling strategy presented in this paper shows that planning of the sampling preferably starts already when the drilling procedure is decided. Each following step is described in detail and includes tracing the drilling fluid, selecting the best borehole sections to sample, procedures for the actual sampling, and selection of analytical protocol; all this with the goal of taking representative samples. Although the evaluation of the sampling uncertainties is not a straightforward procedure, an adequate categorisation routine has been established to classify groundwater samples regarding sample quality, representativeness, and suitability for further interpretations and modelling.

The interaction between fluids and tectonic structures such as fault systems is a much-discussed issue. Many scientific works are aimed at understanding what the role of fault systems in the displacement of deep fluids is, by investigating the interaction between the upper mantle, the lower crustal portion and the upraising of gasses carried by liquids. Many other scientific works try to explore the interaction between the recharge processes, i.e., precipitation, and the fault zones, aiming to recognize the function of the abovementioned structures and their capability to direct groundwater flow towards preferential drainage areas. Understanding the role of faults in the recharge processes of punctual and linear springs, meant as gaining streams, is a key point in hydrogeology, as it is known that faults can act either as flow barriers or as preferential flow paths. In this work an investigation of a fault system located in the Nera River catchment (Italy), based on geo-structural investigations, tracer tests, geochemical and isotopic recharge modelling, allows to identify the role of the normal fault system before and after the 2016–2017 central Italy seismic sequence (Mmax = 6.5). The outcome was achieved by an integrated approach consisting of a structural geology field work, combined with GIS-based analysis, and of a hydrogeological investigation based on artificial tracer tests and geochemical and isotopic analyses.

Abstract. While groundwater recharge is one of the most prominently covered subjects in hydrogeology, the spatial distribution of recharge has been given relatively little attention, especially in semi-arid, karstic aquifers. Under conditions of highly diverse geology, relief, vegetation and land use, the complexity and variability of spatially distributed hydrological processes remains a challenge in many regions around the world. This is particularly true for hitherto ungauged basins, such as Wadi Natuf, a 103 km2 large karstic Eastern Mediterranean watershed in the Palestinian upstream mountain and recharge area of the Western Aquifer Basin (WAB), which is shared with Israel in the coastal plain. In this first in a series of two papers, distributed recharge is estimated and represented, based on 7 years of extensive field observations and measurements and based conceptually on observable physical landscape features such as geology, land use and land cover (LU/LC) and especially soil conditions. For the first time in the WAB, a forward calculated soil moisture and percolation model (SMSP) was set up with parameters directly gained from field observations. The model was parameterised in a strictly parsimonious manner, as a one-dimensional model (a.k.a. “tank”, bucket or box model). This is based on dominant hydrological processes, in particular saturation excess in the soil column, and identifying patterns of linkage between different landscape features. Average soil thickness was encountered at the range of decimetres, rarely above one metre. Both soil thickness and LU/LC features, such as terraced olive groves or forests as well as grassland or barren rock outcrops, were found to be highly formation specific. This linkage allowed us to further simplify the model and its requirements in a realistic manner for eight soil moisture stations, chosen at six different geological formations with typical soil and LU/LC representations. The main result of the model was the determination of formation-specific recharge coefficients, spatially ranging between 0 % and almost 60 % of annual rainfall or up to 300 mm a−1 in Wadi Natuf's climate. The karstified main aquifers showed recharge coefficients (RC) above 40 % and even the less prominent slightly aquitardal local aquifers reached RC values above 30 %. The model was separately tested on two conceptual levels: on the level of basin form (soil moisture) and basin response (signatures of peak recharge and local spring discharge events) under well-controlled conditions in isolated sub-catchments. In principle, our approach is applicable in many of the scarcely gauged karstic groundwater basins around the world with a highly diverse landscape and geology.

Abstract. Management of water resources requires understanding of the hydrology and hydrogeology, as well as the policy and human drivers and their impacts. This understanding requires relevant inputs from a wide range of disciplines, which will vary depending on the specific case study. One approach to gain understanding of the impact of climate and society on water resources is through the use of an integrated modelling process that engages stakeholders and experts in specifics of problem framing, co-design of the underpinning conceptual model, and discussion of the ensuing results. In this study, we have developed such an integrated modelling process for the Campaspe basin in northern Victoria, Australia. The numerical model built has a number of components: Node/link based surface water hydrology module based on the IHACRES rainfall-streamflow model Distributed groundwater model for the lower catchment (MODFLOW) Farm decision optimisation module (to determine irrigation requirements) Policy module (setting conditions on availability of water based on existing rules) Ecology module (determining the impacts of available streamflow on platypus, fish and river red gum trees) The integrated model is component based and has been developed in Python, with the MODFLOW and surface water hydrology model run in external programs, controlled by the master program (in Python). The integrated model has been calibrated using historical data, with the intention of exploring the impact of various scenarios (future climate scenarios, different policy options, water management options) on the water resources. The scenarios were selected based on workshops with, and a social survey of, stakeholders in the basin regarding what would be socially acceptable and physically plausible options for changes in management. An example of such a change is the introduction of a managed aquifer recharge system to capture dam overflows, and store at least a portion of this in the aquifer, thereby increasing the groundwater resource as well as reducing the impact of existing pumping levels.

Hydrogeological models need to be supported by a clear understanding of the subsurface geology to provide effective assessment, flow modelling, or management of groundwater regimes. This paper illustrates how geophysical and sedimentological data can be used to significantly improve watershed-scale hydrostratigraphic models by advancing our understanding of the subsurface through regional hydrogeological investigations in the Greater Toronto Area. The example of a 3 km shallow seismic reflection survey that traverses a buried channel within Bowmanville Creek watershed, Oak Ridges Moraine, Ontario, illustrates a basis for linking geophysical and sedimentological properties to regional hydrostratigraphic parameters. Seismic reflection methods plus seismic stratigraphy and a well-constrained three-dimensional geological framework have helped to (i) identify regional hydrostratigraphic units, (ii) define properties and trends of these units–facies, (iii) improve depositional models that assist hydrogeological analysis, and (iv) establish a hydrostratigraphic framework within a watershed. The extent, proportions, boundaries, and variation in internal properties of major hydrostratigraphic units could be identified to greater than 100 m depth. Geostatistical analysis of seismic amplitudes was used to provide a quantitative measure of heterogeneity in a glaciofluvial aquifer with inadequate parameter support. Benefits to engineering practice include improved siting of monitors and tests from portrayal of the spatial organization, geometry, and variability of hydrostratigraphic units based on sedimentary architecture and environments of deposition. Hydrogeological modelling can be improved with better knowledge of the geometry of aquifers and aquitards and grid-cell boundaries that correspond with the defined sediment boundaries that control properties.Key words: Oak Ridges Moraine, hydrogeology, seismic stratigraphy, southern Ontario, sedimentology.

Abstract. Lacustrine groundwater discharge (LGD) can significantly affect lake water balances and lake water quality. However, quantifying LGD and its spatial patterns is challenging because of the large spatial extent of the aquifer–lake interface and pronounced spatial variability. This is the first experimental study to specifically study these larger-scale patterns with sufficient spatial resolution to systematically investigate how landscape and local characteristics affect the spatial variability in LGD. We measured vertical temperature profiles around a 0.49 km2 lake in northeastern Germany with a needle thermistor, which has the advantage of allowing for rapid (manual) measurements and thus, when used in a survey, high spatial coverage and resolution. Groundwater inflow rates were then estimated using the heat transport equation. These near-shore temperature profiles were complemented with sediment temperature measurements with a fibre-optic cable along six transects from shoreline to shoreline and radon measurements of lake water samples to qualitatively identify LGD patterns in the offshore part of the lake. As the hydrogeology of the catchment is sufficiently homogeneous (sandy sediments of a glacial outwash plain; no bedrock control) to avoid patterns being dominated by geological discontinuities, we were able to test the common assumptions that spatial patterns of LGD are mainly controlled by sediment characteristics and the groundwater flow field. We also tested the assumption that topographic gradients can be used as a proxy for gradients of the groundwater flow field. Thanks to the extensive data set, these tests could be carried out in a nested design, considering both small- and large-scale variability in LGD. We found that LGD was concentrated in the near-shore area, but alongshore variability was high, with specific regions of higher rates and higher spatial variability. Median inflow rates were 44 L m−2 d−1 with maximum rates in certain locations going up to 169 L m−2 d−1. Offshore LGD was negligible except for two local hotspots on steep steps in the lake bed topography. Large-scale groundwater inflow patterns were correlated with topography and the groundwater flow field, whereas small-scale patterns correlated with grain size distributions of the lake sediment. These findings confirm results and assumptions of theoretical and modelling studies more systematically than was previously possible with coarser sampling designs. However, we also found that a significant fraction of the variance in LGD could not be explained by these controls alone and that additional processes need to be considered. While regression models using these controls as explanatory variables had limited power to predict LGD rates, the results nevertheless encourage the use of topographic indices and sediment heterogeneity as an aid for targeted campaigns in future studies of groundwater discharge to lakes.

The excavation of tunnels below the water table causes variations in the hydraulic level, pore pressure and effective stresses. In this regard, rapid drawdown is considered as a destructive phenomenon as to the change in the flow regime which has mostly been studied for the reservoirs of embankment dams. The rapid drawdown occurred at the upstream shell of the dam gives rise to increase in the pore pressure at the upstream shell. This is as a result of the incompliance between the water loss inside the shell and the reservoir water level. Hence, it would be more likely to have instability and sliding at the upstream slope on account of decrease in the effective stress. Lack of sufficient studies performed on this matter in tunnelling projects on the one hand and the knowledge on the most important parameter for decreasing the destructive effects of this phenomenon on the other hand necessitates performing further studies on this matter. To this end, the reasons for the occurrence as well as the affecting parameters were studied by modelling the large subsidence of the inlet portal of Heybat Sultan twin tunnels located in Kurdistan-Iraq making use of the variations of the groundwater boundary conditions under Phase2 code. The modelling results depict the importance of the drawdown rate and the permeability coefficient of the surrounding rock mass. In the interim, the rapid loss in the hydraulic gradient caused by the drainage of a considerable volume of precipitations into the tunnels led to the rapid decrease in the pore pressure and increase in the effective stresses up to total stress. This has resulted in the consolidation settlement in the tunnel portal.

Abstract Variations in salinity and flow rate in the aerial, naturally salty spring of Almyros of Heraklion on Crete were monitored during two hydrological cycles. We describe the functioning of the coastal karstic system of the Almyros and show the influence of the duality of the flow in the karst (conduits and fractured matrix) on the quality of the water resource in the coastal area. A mechanism of saltwater intrusion into this highly heterogeneous system is proposed and validated with a hydraulic mathematical model, which describes the observations remarkably well. Introduction. – Fresh groundwater is a precious resource in many coastal regions, for drinking water supply, either to complement surface water resources, or when such resources are polluted or unavailable in the dry season. But coastal groundwater is fragile, and its exploitation must be made with care to prevent saltwater intrusion as a result of withdrawal, for any aquifer type, porous, fractured or karstic. In karstic zones, the problem is very complex because of the heterogeneous nature of the karst, which makes it difficult to use the concept of representative elementary volume developed for porous or densely fractured systems. The karstic conduits focus the major part of the flow in preferential paths, where the water velocity is high. In coastal systems, these conduits have also an effect on the distribution of the saline intrusion. As was shown e.g. by Moore et al. [1992] and Howard and Mullings [1996], both freshwater and salt-water flow along the fractures and conduits to reach the mixing zone, or the zone where these fluids are superposed in a dynamic equilibrium because of their differences in density ; but the dynamics of such a saltwater intrusion are generally unknown and not represented in models. Such coastal karstic systems are intensely studied at this moment in the Mediterranean region [Gilli, 1999], both as above sea-level or underwater springs, for potential use in areas where this resource would be of great value for economic development. This article discusses the freshwater-saltwater exchange mechanisms in the karstic aquifer of the Almyros of Heraklion aquifer (Crete) and explains the salinity variations observed in the spring. First, the general hydrogeology of the study site is described, then the functioning of the spring : a main conduit drains the freshwater over several kilometres and passes at depth through a zone where seawater is naturally present. The matrix-conduit exchanges are the result of pressure differences between the two media. These processes are represented in a mathematical model that confirms their relevance. General hydrogeology of the studied site. – The karstic coastal system of the Almyros of Heraklion (Crete) covers 300 km2 in the Ida massif whose borders are a main detachment fault, and the Sea of Crete in the north, the Psiloritis massif (highest summit at 2,456 m) in the south and west, and the collapsed basin of Heraklion filled in by mainly neo-geneous marl sediments in the east. The watershed basin consists of the two lower units of characteristic overthrust formations of Crete (fig. 1) : the Cretaceous Plattenkalk and the Cretaceous Tripolitza limestones. The two limestone formations are locally separated by interbedded flysch or phyllade units that form an impervious layer [Bonneau et al., 1977 ; Fassoulas, 1999] and may lead to different flow behaviour within the two karstic formations. Neo-tectonic activity has dissected these formations with large faults and fractures. The present-day climate in Crete is of Mediterranean mountain type, with heavy rain storms and snow on the summits in winter. Rainfall is unevenly distributed over the year, with 80 % of the annual total between October and March and a year-to-year average of 1,370 mm. The flow rate of the spring is high during the whole hydrologic cycle, with a minimum in summer on the order of 3 m3.s−1 and peak flow in winter reaching up to 40 m3.s −1. The water is brackish during low flow, up to a chloride content of 6 g.l−1, i.e. 23 % of seawater, but it is fresh during floods, when the flow rate exceeds 15 m3.s−1. During the 1999–2000 and 2000–2001 hydrologic cycles, the water was fresh during 14 and 31 days, respectively. The water temperature is high and varies very little during the year (see table I). In the areas of Kéri and Tilissos (fig. 1), immediately south of the spring, the city of Heraklion extracts water from the karstic system through a series of 15 wells with depth reaching 50 to 100 m below sea level. Initially, when the wells were drilled, the water was fresh, but nowadays the salinity rises progressively, but unequally from well to well (fig. 2). The relatively constant temperatures and salinities of the wells, during the hydrological cycle, contrast with the large salinity variations at the spring (fig. 2 and table I). They show that the karstic system is complex and comprises different compartments, where each aquifer unit reacts to its individual pressures (pumping, rainfall) according to its own hydrodynamic characteristics [Arfib et al., 2000]. The Almyros spring seems disconnected from the surrounding aquifer and behaves differently from that which feeds the wells (upper Tripolitza limestone). It is recharged by fresh water from the mountains, which descends to depths where it probably acquires its salinity. The spring would thus be the largest resource of the area, if it was possible to prevent its pollution by seawater. A general functioning sketch is proposed (fig. 3), which includes the different geological units of interest. Identification of the functioning of the Almyros spring through monitoring of physical and chemical parameters. – The functioning of the aquifer system of the Almyros spring was analysed by monitoring, over two hydrological cycles, the level of the spring, the discharge, the electric conductivity and the temperature recorded at a 30 min time interval. In the centre of the watershed basin, a meteorological station at an altitude of 800 m measures and records at a 30 min time interval the air temperature, rainfall, relative humidity, wind velocity and direction ; moreover, an automatic rain gauge is installed in the northern part of the basin at an altitude of 500 m. The winter floods follow the rhythm of the rainfall with strong flow-rate variations. In contrast, the summer and autumn are long periods of drought (fig. 7). The flow rate increases a few hours after each rainfall event ; the water salinity decreases in inverse proportion to the flow rate a few hours to a few days later. Observations showed that the water volume discharged at the Almyros spring between the beginning of the flow rate increase and the beginning of the salinity decrease is quite constant, around 770,000 m3 (fig. 4) for any value of the flow rate, of the salinity and also of the initial or final rainfall rates. To determine this constant volume was of the upmost importance when analyzing the functioning of the Almyros spring. The lag illustrates the differences between the pressure wave that moves almost instantaneously through the karst conduit and causes an immediate flow rate increase after rainfall and the movement of the water molecules (transfer of matter) that arrives with a time lag proportionate to the length of the travel distance. The variation of the salinity with the flow rate acts as a tracer and gives a direct indication of the distance between the outlet and the seawater entrance point into the conduit. In the case of the Almyros, the constant volume of expelled water indicates that sea-water intrusion occurs in a portion of the conduit situated several kilometres away from the spring (table II), probably inland, with no subsequent sideways exchange in the part of the gallery leading up to the spring. As the lag between the flow rate and the salinity recorded at the spring is constant, one can correct the salinity value by taking, at each time step, with a given flow rate, the salinity value measured after the expulsion of 770,000 m3 at the spring, which transforms the output of the system so as to put the pressure waves and the matter transfer in phase [Arfib, 2001]. After this correction, the saline flux at the spring, equal to the flow rate multiplied by the corrected salinity, indicates the amount of sea-water in the total flow. This flux varies in inverse proportion to the total flow rate in the high-flow period and the beginning of the low-flow period, thereby demonstrating that the salinity decrease in the spring is not simply a dilution effect (fig. 5). The relationship that exists between flow rate and corrected salinity provides the additional information needed to build the conceptual model of the functioning of the part of the Almyros of Heraklion aquifer that communicates with the spring. Freshwater from the Psiloritis mountains feeds the Almyros spring. It circulates through a main karst conduit that descends deep into the aquifer and crosses a zone naturally invaded by seawater several kilometers from the spring. The seawater enters the conduit and the resulting brackish water is then transported to the spring without any further change in salinity. The conduit-matrix and matrix-conduit exchanges are governed by the head differences in the two media. Mathematical modelling of seawater intrusion into a karst conduit Method. – The functioning pattern exposed above shows that such a system cannot be treated as an equivalent porous medium and highlights the influence of heterogeneous structures such as karst conduits on the quantity and quality of water resources. Our model is called SWIKAC (Salt Water Intrusion in Karst Conduits), written in Matlab®. It is a 1 D mixing-cell type model with an explicit finite-difference calculation. This numerical method has already been used to simulate flow and transport in porous [e.g. Bajracharya and Barry, 1994 ; Van Ommen, 1985] and karst media [e.g. Bauer et al., 1999 ; Liedl and Sauter, 1998 ; Tezcan, 1998]. It reduces the aquifer to a single circular conduit surrounded by a matrix equivalent to a homogeneous porous medium where pressure and salinity conditions are in relation with sea-water. The conduit is fed by freshwater at its upstream end and seawater penetrates through its walls over the length L (fig. 6) at a rate given by an equation based on the Dupuit-Forchheimer solution and the method of images. The model calculates, in each mesh of the conduit and at each time step, the head in conditions of turbulent flow with the Darcy-Weisbach equation. The head loss coefficient λ is calculated by Louis’ formula for turbulent flow of non-parallel liquid streams [Jeannin, 2001 ; Jeannin and Marechal, 1995]. The fitting of the model is intended to simulate the chloride concentration at the spring for a given matrix permeability (K), depth (P) and conduit diameter (D) while varying its length (L) and its relative roughness (kr). The spring flow rates are the measured ones ; at present, the model is not meant to predict the flow rate of the spring but only to explain its salinity variations. Results and discussion. – The simulations of chloride concentrations were made in the period from September 1999 to May 2001. The depth of the horizontal conduit where matrix-conduit exchanges occur was tested down to 800 m below sea level. The diameter of the conduit varied between 10 and 20 m, which is larger than that observed by divers close to the spring but plausible for the seawater intrusion zone. The average hydraulic conductivity of the equivalent continuous matrix was estimated at 10−4 m/s. A higher value (10−3 m/s) was tested and found to be possible since the fractured limestone in the intrusion zone may locally be more permeable but a smaller value (10−5 m/s) produces an unrealistic length (L) of the saline intrusion zone (over 15 km). For each combination of hydraulic conductivity, diameter and depth there is one set of L (length) and kr (relative roughness) calibration parameters. All combinations for a depth of 400 m or more produce practically equivalent results, close to the measured values. When the depth of the conduit is less than 400 m, the simulated salinity is always too high. Figure 7 shows results for a depth of 500 m, a diameter of 15 m and a hydraulic conductivity of 10−4 m/s. The length of the saltwater intrusion zone is then 1,320 m, 4,350 m away from the spring and the relative roughness coefficient is 1.1. All the simulations (table II) need a very high relative roughness coefficient which may be interpreted as an equivalent coefficient that takes into account the heavy head losses by friction and the variations of the conduit dimensions which, locally, cause great head losses. The model simulates very well the general shape of the salinity curve and the succession of high water levels in the Almyros spring but two periods are poorly described due to the simplicity of the model. They are (1) the period following strong freshwater floods, where the model does not account for the expulsion of freshwater outside the conduit and the return of this freshwater which dilutes the tail of the flood and (2) the end of the low-water period when the measured flux of chlorides falls unexpectedly (fig. 5), which might be explained by density stratification phenomena of freshwater-saltwater in the conduit (as observed in the karst gallery of Port-Miou near Cassis, France [Potié and Ricour, 1974]), an aspect that the model does not take into account. Conclusions. – The good results produced by the model confirm the proposed functioning pattern of the spring. The regulation of the saline intrusion occurs over a limited area at depth, through the action of the pressure differences between the fractured limestone continuous matrix with its natural saline intrusion and a karst conduit carrying water that is first fresh then brackish up to the Almyros spring. The depth of the horizontal conduit is more than 400 m. An attempt at raising the water level at the spring, with a concrete dam, made in 1987, which was also modelled, indicates that the real depth is around 500 m but the poor quality of these data requires new tests to be made before any firm conclusions on the exact depth of the conduit can be drawn. The Almyros spring is a particularly favorable for observing the exchanges in the conduit network for which it is the direct outlet but it is not representative of the surrounding area. To sustainably manage the water in this region, it is essential to change the present working of the wells in order to limit the irreversible saline intrusion into the terrain of the upper aquifers. It seems possible to exploit the spring directly if the level of its outlet is raised. This would reduce the salinity in the spring to almost zero in all seasons by increasing the head in the conduit. In its present state of calibration, the model calculates a height on the order of 15 m for obtaining freshwater at the spring throughout the year, but real tests with the existing dam are needed to quantify any flow-rate losses or functional changes when there is continual overpressure in the system. The cause of the development of this karstic conduit at such a great depth could be the lowering of the sea level during the Messinian [Clauzon et al., 1996], or recent tectonic movements.

Groundwater control is required to allow excavations and tunnels to be formed in stable and workably dry conditions below groundwater level. Representative and relevant conceptual models are an essential requirement for the successful development of groundwater control schemes. Prior to construction, conceptual models can aid the planning of ground investigations to help select borehole depths, borehole locations and hydrogeological testing methods. During construction the effectiveness of groundwater control techniques will vary with different hydrogeological conditions and the hydraulic conductivity of the strata. A sound conceptual model reduces the risk of designs being developed using inappropriate approaches to groundwater control. Common misconceptions include the assumption of a single aquifer (where multiple aquifers and aquitards exist) and cases where significant transmissive zones (which may act as aquifers) are not identified. Other errors include assuming that groundwater levels reported during site investigations are representative of maximum levels that may occur during construction, or not considering the risk of external impacts caused by groundwater control methods. A suggested framework to produce better models is problem–solution–technology–impacts. This framework can avoid some of the common misconceptions that have resulted in problems during the design and implementation of groundwater control schemes.Thematic collection: This article is part of the Ground models in engineering geology and hydrogeology collection available at: https://www.lyellcollection.org/cc/Ground-models-in-engineering-geology-and-hydrogeology

Groundwater management in the semi-arid areas is a crucial issue and requires more scientific study and techniques. Groundwater potential areas for part of the Chamchamal basin are determined using two techniques, the analytical hierarchy process (AHP) and a geographic information system (GIS). Several Input factors were used to produce a thematic map, including geology, structure, drainage density, land-use/landcover, slope steepness, lineament density, and hydrogeology. Based on the relative importance, the layers are ranked which control the groundwater potential areas. The factor classified into several zones builds upon the hydrogeological characteristics and the classes weighted based on the relative standing to the potential area of groundwater. The output of the analysis showed that there are four zones of groundwater potential, good, moderate, poor, and very poor. The zones cover 10.4, 38.7, 43.93, and 6.96% of the area, respectively. Furthermore, the results showed that the southwest part of the area is the most favorable area for groundwater existence. While the center and some parts of the northeast characterized by low groundwater potential zones. To verify the final potential zones, the yield rates of 38 wells are used. The verification process verified that the categories of groundwater potential areas are closed to the results obtained from (AHP) and (GIS).

The term groundwater resources was introduced to hydrogeology from economic geology similarly to the resources of ore bodies almost a hundred years ago. It has been used for the need of physical planning, investment in new water intakes, and water management. Discussion on the groundwater resources started in the past after implementation of new methods of their evaluation, e.g. analytical approaches, and physical and then numerical modelling techniques. The ecological aspects of water demand, indicated in the Water Framework Directive, oblige the EU countries to introduce a new idea for the estimation of groundwater resources. This idea is also presented in the water management plans for river catchment areas. Distribution of available groundwater resources in the country and comparison with the groundwater exploitation is the background of proper, sustainable management of its resources. Available groundwater resources of the country, understood as a total amount of disposable and prospective groundwater resources, is 36.4 million m3/day (as of December 31, 2015), including 21.4 million m3/day of disposable resources, and 15 million m3/day of estimated prospective resources.

The subsurface material in urban areas comprises the original geological succession together with anthropogenic modifications and deposits. The Geological Survey of Denmark previously performed geological mapping in selected Danish cities (e.g. Mertz 1974), but this practice stopped in the mid-1980s. The lack of recent systematic mapping in urban areas is apparent not only in Denmark but also in most other European countries (COST 2015). However, there is a growing demand for knowledge of the subsurface beneath our cities for a number of reasons: increased urbanisation, infiltration of excess surface water and other climate-change related measures, thermal storage, groundwater cooling and abstraction, subsurface infrastructure, infrastructure projects, etc. The physical properties of the subsurface material are in constant change due to urban growth and infrastructure development. This can strongly influence the geotechnical properties and handling of excess surface water. In order to manage both challenges and opportunities of the ground beneath the cities there is a growing need for 3D hydrogeological models that can encompass all relevant parts of the physical subsurface system and act as operational tools in its management. With the main focus on hydrogeology and the urban water cycle, the Municipality of Odense, the local waterworks (VandCenter Syd), the Geological Survey of Denmark and Greenland (GEUS) and two consultants (Alectia and I-GIS) have made a joint effort to systematically map the subsurface layers and build a 3D hydrogeological model of the subsurface of the city of Odense (Fig. 1). This paper provides an overview of the project rationale and an outline of the major results.

AbstractDuring the past few years, the number of regional and national assessments of groundwater quality in regard to saltwater intrusion in coastal aquifers has increased steadily. However, most of the international literature on saltwater intrusion is focused on coastal plains with aquifers in unconsolidated material. Case studies, modelling approaches and parameter studies dealing with saltwater intrusion in those systems are abundant. While the hydrogeology of fractured rock has been intensively studied with both modelling approaches and parameter studies—mainly in relation to deep-laying fractured crystalline bedrock as potential waste repositories—case studies on saltwater intrusion in shallow fractured rocks are still an exception. This review summarizes the actual knowledge on saltwater intrusion in fractured crystalline rock. In combination with short overviews of the processes of saltwater intrusion, flow in fractured systems and the genesis of these systems, the review highlights the importance of the fracture systems and its specific characteristics. Fracture properties are a direct consequence of the geological history as well as the current situation of the coastal area. A holistic assessment of water quality in coastal areas hosting fractured crystalline bedrock therefore requires the combination of different approaches in order to investigate the impact of saltwater intrusion through the fractured system.

ABSTRACTCalculations of risk or dose from the groundwater flow pathway are a central part of the assessment of post closure performance for a deep repository system for radioactive waste. These calculations need to be supported by a knowledge of the various components of the disposal system. Site characterisation provides a site specific geological database which can be used to build, test and refine numerical models of the geosphere and, to some extent, the biosphere components of the disposal system in order to evaluate its future evolution.Site characterisation programmes, and groundwater flow modelling within the performance assessment need to progress in an interactive manner to ensure that both remain focused on the resolution of key uncertainties which impact the overall performance assessment. The data derived from site investigations can be classified in terms of their application within the performance assessment: establishing the framework for numerical models; enabling the parameterisation of numerical models; testing model output; refining models; and demonstrating their credibility. Site characterisation programmes need to be established to provide the appropriate level of information for each of these stages. It is therefore not particularly useful to classify information into the traditional disciplines of geology, hydrogeology and geochemistry.A key issue for developing a geological and hydrogeological database for performance assessment is determining when sufficient information has been obtained. Primarily, this is dictated by the needs and sensitivities of the performance assessment and any regulatory requirements. However, radioactive waste disposal agencies work in a political environment that is strongly influenced by public perception. In order to progress, any programme must attain a broad measure of credibility and acceptability to other key “stakeholders”.The paper draws on examples and experiences from the extensive programme of work which has been performed by Nirex to understand the characteristics of a site near Sellafield in Cumbria, and to develop groundwater flow models to support the assessment of the post closure performance of a potential repository located at that site. Uncertainties important in influencing calculated risk within an interim assessment, published as the “Nirex 95 assessment” were used to develop further site-specific investigations. The resulting site characterisation activities generated an enhanced and refined site-specific geological and hydrogeological database for a subsequent assessment - the “Nirex 97 assessment”.