Groundwater Flow Patterns Research Articles

Characterisation of fractured carbonate aquifers using ambient borehole dilution tests

Fractured carbonate aquifers derive their transmissivity essentially from a well-developed network of solutionally-enhanced fractures and conduits that can lead to high groundwater velocities and high vulnerability to contamination of water quality. Characterisation of the variation of hydraulic properties with depth is important for delineating source protection areas, characterising contaminant fate and transport, determination of the effectiveness of aquifer remediation, and parameter estimation for models. In this work, ambient open borehole uniform and point injection dilution tests were conducted on observation boreholes in the unconfined Cretaceous Chalk aquifer of East Yorkshire, UK, and interpreted in conjunction with other data via the implementation of a new work flow. This resulted in the characterisation of flow in these boreholes and the inference of properties such as groundwater flow patterns and velocities in the surrounding aquifer formation. Our workflow allowed sections of open boreholes showing horizontal versus vertical flow to be distinguished, and the magnitude of such flows and exchanges with the aquifer to be determined. Flow within boreholes were then used to characterise: i) presence and direction of vertical hydraulic gradients; ii) nature and depth distribution of flowing features; iii) depth interval porosity and permeability estimation of the flowing features from overall borehole transmissivity and geophysical image or caliper logs; iv) groundwater velocity estimation in the surrounding aquifer. Discrete flowing features were distributed across the range of depths sampled by the observation boreholes (typically up to 45–60 mbgl), but the majority were located in the zone of water table fluctuation marked by solutionally enlarged flow features. Quantitative interpretation of both uniform injection (tracer distributed throughout the open borehole section) and point injection (slug of tracer introduced at targeted depth) yielded vertical velocities within the borehole water column in broad agreement with those measured by flow logging. Depth specific fracture kinematic porosities inferred from the ambient dilution data combined with long-interval pump test and geophysical log data ranged between 3.7 × 10−4–4.1 × 10−3 with an average of 2.1 × 10−3; these values were in excellent agreement with those from other methods applied to the same aquifer such as larger scale pumping tests. A new approach to estimation of groundwater velocities from the dilution test data using externally measured hydraulic gradients gave inferred horizontal groundwater velocities ranging between 60 and 850 m/day, in full agreement with those from previously conducted borehole-to-borehole tracer tests. These results confirm that the studied aquifer is karstic, with rapid preferential pathways which have implication for flow and transport modelling, and pollution vulnerability. Our study results indicate that ambient single-borehole dilution approaches can provide an inexpensive and reliable approach for the characterisation of fractured and karstic aquifers.

Influence of lakebed sediment deposit on the interaction of hypersaline lake and groundwater: A simplified case of lake Urmia, Iran

Lake Urmia, which was once the second-largest saline lake in the world, has been shrinking dramatically. Moreover, Lake Urmia has become supersaturated with total salinity averaging more than 350 g/l. Salt precipitation and dissolved materials brought by inflowing rivers have formed a layer of sediment with low hydraulic conductivity on the lakebed. Considering the flat bathymetry of Lake Urmia, we conducted a series of numerical simulation scenarios to study the groundwater flow pattern in the vicinity of the hypersaline Lake Urmia using COMSOL Multiphysics®. In the first step, we performed the simulations in steady-state conditions. Secondly, we simulated the lake level fall in 10 years at a rate of −35 cm/year followed by a lake level rise at a rate of 35 cm/year for another 10 years. The steady-state results demonstrate that decreasing sediment hydraulic conductivity layer and increasing its thickness lead to a less intense saltwater intrusion, with lower saltwater flux from the lake to the aquifer. As the lake level begins to fall, in cases with high sediment hydraulic conductivity, incoming saltwater from the lake decreases and reaches nearly zero values through the time; instead, the lake begins to get recharged. On the other hand, as the lake level begins to rise after the falling period, the saltwater flux from the lake to the aquifer increases and finally reaches a value of nearly two times greater than steady-state results. In low sediment hydraulic conductivity cases, incoming saltwater from the lake to the aquifer remains negligible through both rising and falling scenarios.

Hydrogeological characterization of crystalline aquifer in the Hout River Catchment, Limpopo province, South Africa

This study attempted to conceptualize the hydrogeological setting of the Hout River Catchment, located in the Limpopo River Basin, using multiple methods that include groundwater flow patterns, structural analysis, stable (18O, 2H and 13C) and radiogenic (14C) isotopes of water and Water Table Fluctuation methods. The hydrogeological system of the catchment is represented by fractured crystalline basement aquifer as the main host for groundwater and is overlain by weathered rocks that act as a vadose zone and shallow aquifer in various places. Groundwater from the fractured basement rocks is the main source of water for large-scale irrigation and domestic use. Potential aquifers in the area are evident within the Hout River granitic gneiss and the Goudplaats granitic gneiss besides the younger granites as a result of fracturing and weathering. Groundwater flow map shows a flow pattern from the southern part of the catchment towards the north-eastern part of the catchment dictated by dolerite dykes and tectonic lineaments that trend in the ENE and E direction (088° and 075°) with the dip angle of 50° to 55°. The deeper aquifer in the southern and central part of the catchment contain old groundwater with high salinity due to long residence time. The stable isotopes further confirmed the limited possibility of local recharge, with rather dominance of regional groundwater circulation into the catchment. The northern part of the catchment seems to be receiving recent recharge with the groundwater of high 14C content derived from the mountains that border the catchment.

Recharge Estimation Using CMB and Environmental Isotopes in the Verlorenvlei Estuarine System, South Africa and Implications for Groundwater Sustainability in a Semi-Arid Agricultural Region

Groundwater recharge remains one of the most difficult hydrogeological variables to measure accurately, especially for semi-arid environments where the recharge flux is much smaller than in humid conditions. In this study, groundwater recharge was estimated using chloride mass balance (CMB) in the Verlorenvlei catchment, South Africa where the effects of recent severe drought conditions in an already semi-arid environment have impacted both agricultural activity as well as the RAMSAR-listed Verlorenvlei estuarine system. Chloride, 18O and 2H tracers were used to improve understanding of the groundwater flow patterns and allowed the fresh parts of the groundwater system, defined by Ca2+-HCO3− groundwater types, to be separated from those where additional salts were being introduced through groundwater mixing, and thus characterized as Na+-Cl− groundwater types. Recharge rates calculated from CMB in the fresh parts of the system were between 4.2–5.6% and 11.4–15.1% of mean annual precipitation for the headwater valley and mountains of the Krom Antonies and are largely consistent with previous studies. However, much lower recharge rates in the valleys where agriculture is dominant contrasts with previous results, which were higher, since groundwater-mixing zones were not recognised. Although the chloride concentration in precipitation is based on only one year of data between 2015 and 2016, where 2015 had on average 28% less precipitation than 2016, the results provide a snapshot of how the system will respond to increasing drought frequency in the future. The results suggest that low rates of groundwater recharge under dry spell conditions will impact on low flow generations which are required to sustain the Verlorenvlei estuarine lake system. Overall, the study highlights the importance of combining hydrochemical tracers such as bulk chloride and stable isotopes with numerical modelling in data-scarce catchments to fully understand the nature of hydrological resilience.

Geochemical Evolution and Groundwater Flow System in Batujajar Groundwater Basin Area, West Java, Indonesia

DOI:10.17014/ijog.7.1.87-104Batujajar and its surrounding areas, situated in the west of the Bandung Basin, are geologically composed of various Tertiary rock formations with complex fold and fault systems. Springs and drilled wells in sandstone aquifers, tuffaceous sand, and tuffaceous breccias mark the development of their aquifer systems. This study aimed to determine the characteristics of the hydrogeochemistry by analyzing major ions and stable isotopes (18O and 2H) of thirty-four hydrogeological objects. The groundwater flow pattern in this area is controlled by northwest-southeast lineament, as indicated by the emergence of springs along the transition zone between areas with high and low lineament density. In order of dominance, the groundwater facies are as follows:Ca-Mg-HCO3>Ca-HCO3>Ca-Na-Mg-HCO3>Na-Ca-HCO3. Hydrochemical evolutions were detected from the change of cations from Ca2+ to Mg2+ and then Na+, and this is believed to be the product of cation exchange and dissolution of silicate minerals. However, evolutions toward anion changes were not apparent yet, meaning that HCO3- ions still prevail, or in other words the groundwater flow system is local. Nevertheless, the geological and hydrogeochemical analyses, along with the relative compositions of stable isotopes, revealed that the groundwater had three systems, namely shallow, intermediate, and deep groundwater flows; all of which were segmented in three subgroundwater basins (Sub-GWB). Aquifer systems with shallow to intermediate groundwater flow were found in Sub-GWB-A, Sub-GWB-B, and Sub-GWB-C, while the other ones with deep groundwater flow system were identified in Sub-GWB-B and Sub-GWB-C.Fracture system has an important role as a connector between recharge system in hilly areas and discharge system in plain areas.

Lagged rejuvenation of groundwater indicates internal flow structures and hydrological connectivity

AbstractLarge proportions of rainwater and snowmelt infiltrate into the subsurface before contributing to stream flow and stream water quality. Subsurface flow dynamics steer the transport and transformation of contaminants, carbon, weathering products and other biogeochemistry. The distribution of groundwater ages with depth is a key feature of these flow dynamics. Predicting these ages are a strong test of hypotheses about subsurface structures and time‐varying processes. Chlorofluorocarbon (CFC)‐based groundwater ages revealed an unexpected groundwater age stratification in a 0.47 km2 forested catchment called Svartberget in northern Sweden. An overall groundwater age stratification, representative for the Svartberget site, was derived by measuring CFCs from nine different wells with depths of 2–18 m close to the stream network. Immediately below the water table, CFC‐based groundwater ages of already 30 years that increased with depth were found. Using complementary groundwater flow models, we could reproduce the observed groundwater age stratification and show that the 30 year lag in rejuvenation comes from return flow of groundwater at a subsurface discharge zone that evolves along the interface between two soil types. By comparing the observed groundwater age stratification with a simple analytical approximation, we show that the observed lag in rejuvenation can be a powerful indicator of the extent and structure of the subsurface discharge zone, while the vertical gradient of the age‐depth‐relationship can still be used as a proxy of the overall aquifer recharge even when sampled in the discharge zone. The single age stratification profile measured in the discharge zone, close to the aquifer outlet, can reveal the main structure of the groundwater flow pattern from recharge to discharge. This groundwater flow pattern provides information on the participation of groundwater in the hydrological cycle and indicates the lower boundary of hydrological connectivity.

Evaluation of vertical groundwater flux from borehole temperatures: a case study in the Leizhou Peninsula, South China

A least-square solver is presented for groundwater flux estimation using the one-dimensional conduction–advection equation, which was numerically solved using the MacCormack scheme. This approach was utilized to estimate groundwater fluxes from observed borehole temperatures under conditions of surface warming in both rural and urban areas in Leizhou Peninsula, China. The estimated groundwater recharge rate is 0.423 m/year, while the discharge rate is 0.269 m/year. The groundwater recharge rates were obtained in the north part of the study area, and the discharge locations were on Nansan, Donghai and Luzhou Islands, which fit favorably with the regional groundwater flow pattern. Relatively high correlations and low root mean square errors were detected between observed and computed borehole temperature–depth profiles, indicating the estimation is reasonable. The misfit between the observed and computed data might be associated with the uneven distribution of ground surface temperature (GST) and vertical soil heterogeneity. The urban heat island effect contributes an increment of 0.006 °C per year to the GST in the study area, which induces a 0.96 °C higher subsurface temperature in both recharge and discharge areas. The utilization of surface air temperature (SAT) as the upper boundary might underestimate groundwater fluxes, which might lead to inaccurate information for regional groundwater resource management.

The influence of connected heterogeneity on groundwater flow and salinity distributions in coastal volcanic aquifers

Geological heterogeneity is a key factor affecting rates and patterns of groundwater flow and the evolution of salinity distributions in coastal aquifers. The hydrogeologic systems of volcanic aquifers are characterized by lava flows that can form connected geologic structures in the subsurface. Surface-based geostatistical techniques were adopted to generate geologically-realistic, statistically equivalent model realizations of a hydrogeologic system based on that of the Big Island of Hawaii (conduit models). The density-dependent groundwater flow and solute transport code SEAWAT was used to perform 3D simulations to investigate subsurface flow and salt transport through these random realizations. Statistically equivalent geological systems generated with sequential indicator simulation (SIS) and equivalent homogeneous systems were also simulated for comparison. Simulation results show that conduit realizations tend to have more complex salinity distributions with larger mixing zones for which the center of mass is farther offshore compared to homogeneous and SIS realizations. The zone of groundwater discharge is also farther offshore than for homogeneous and SIS models, with higher point fluxes of both fresh and saline water and greater spatial variability. This highlights the importance of the geometry of geologic features in coastal groundwater flow and solute transport processes in highly heterogeneous aquifers. It also points to the importance of preferential flow, with implications for both coastal groundwater resource management and solute fluxes to the ocean.

STUDY OF SHALLOW GROUNDWATER CHARACTERISTICS IN SANGIRAN DOME, KALIJAMBE DISTRICT

<p><em>The purpose of this study are knowing the shallow groundwater flow patterns and characteristics in the Sangiran Dome. This research uses descriptive qualitative method, carried out with survey methods that are analyzed with spatial approach. Unit analysis of this studied is the landform unit the result of a overlay between the Geological’s Map, Genesis’s Process, and Slope’s Map, the result is 15 landform units. Data analysis techniques is to determine the pattern of shallow groundwater flow using the three point problem method. Data analysis is to determine the characteristics of groundwater by using the parameters of power oh Hydrogen (pH), temperature, and Electrical Conductivity (DHL). The results of this study are the shallow groundwater flow patterns in the Sangiran Dome are concentrated in the Kalibeng Formation, the diffuse flow patterns are in the Pucangan Formation and irregular flow patterns are found in Kabuh Formation and Noropuro. The characteristics of shallow groundwater in the Sangiran Dome, based on pH. Neutral classification are found in the Notopuro Formation, the lower Pucangan Formation; base pH classification found in Kabuh Formation, upper Pucangan Formation, and Kalibeng Formation; acidic pH classification is found in the Notopuro Formation. The low DHL classification is found in Notopuro Formation, Kabuh Formation, and Pucangan Formation while the moderate DHL classification is in the Kalibeng Formation.</em></p>

Direct measurement of groundwater flux in aquifers within the discontinuous permafrost zone: an application of the finite volume point dilution method near Umiujaq (Nunavik, Canada)

Permafrost thaw is a complex process resulting from interactions between the atmosphere, soil, water and vegetation. Although advective heat transport by groundwater at depth likely plays a significant role in permafrost dynamics at many sites, there is lack of direct measurements of groundwater flow patterns and fluxes in such cold-region environments. Here, the finite volume point dilution method (FVPDM) is used to measure in-situ groundwater fluxes in two sandy aquifers in the discontinuous permafrost zone, within a small watershed near Umiujaq, Nunavik (Quebec), Canada. The FVPDM theory is first reviewed, then results from four FVPDM tests are presented: one test in a shallow supra-permafrost aquifer, and three in a deeper subpermafrost aquifer. Apparent Darcy fluxes derived from the FVPDM tests varied from 0.5 × 10−5 to 1.0 × 10−5 m/s, implying that advective heat transport from groundwater flow could be contributing to rapid permafrost thaw at this site. In providing estimates of the Darcy fluxes at the local scale of the well screens, the approach offers more accurate and direct measurements over indirect estimates using Darcy’s law. The tests show that this method can be successfully used in remote areas and with limited resources. Recommendations for optimizing the test protocol are proposed.

QUALITY AND GROUNDWATER FLOW AT DEGAN, BANJARARUM, WEST PROGO

This research is a hydrogeological survey activity with the aim to determine the quality and pattern of groundwater flow in the Degan and surrounding areas, Banjararum Village, Kalibawang, West Progo District. The research method is carried out by hydrogeological surveys to collect groundwater data and groundwater quality in the form of pH, TDS and EC. The research area is included in the Dome of the Kulon Progo physiography, where this area is a non CAT area. The geomorphology of the study area in the north and west is dominated by relatively coarse landscapes forming hills, while in the central, eastern and southern parts it is a weak wavy landscape to the plains. The results showed that shallow groundwater depth of 1.2 - 10.8 m (under surface). The pattern of groundwater flow is to the east / southeast, with boundary conditions H5 and V1. Groundwater aquifers are composed of colluvium deposits and weathered - medium weathered rock. The pH value of water in the study area ranges from 6.7 -7.1; TDS is 165 - 901 ppm, while EC ranges from 187 - 1240 µS / cm. Thus, groundwater in the Degan area is neutral and tasteless.

Investigating karst aquifers in tectonically complex alpine areas coupling geological and hydrogeological methods

In this work, a reliable understanding of the storage patterns and flow dynamics of a tectonically complex karst system is attained by means of the combined analysis of results derived from geological and karst-specific -i.e. hydrogeological- approaches (hydrodynamic, hydrochemical, hydrothermal and isotopic). The pilot site comprises rocks belonging to six different complexes within the Betic Cordillera: External Zone (1), Flysch Complex (1) and the Internal Zone (4). Quick and sharp variations in natural responses after rainfall were recorded in the overflow springs located in the External Zone. In contrast, groundwater drained by permanent springs placed in the Internal Zone present high mineralization and temperature values, as well as lagged and buffered responses to precipitation events. At a first glance, one could assume that two independent systems with different behaviors are at work, following a classical interpretation: conduit flow-type functioning for Jurassic limestones (External Zone) and diffuse-flow behavior for the Triassic calcareous rocks (Internal Zone). However, integration of results with those derived from the water budget and geological observations leads us to propose a sole aquifer, formed by rocks belonging to several geological domains, but hydrogeologically connected, where shorter and longer water–rock interactions along flow paths coexist. Overthrust surfaces and the subsequent normal faults involve diverse low permeable formations imbricated within a tectonic suture, inducing strong heterogeneities in groundwater flow patterns. The geological complexity and the inner geometry at the southeast border of the aquifer jointly modulate the global signal coming from the External Zone, which is attenuated before arriving at the permanent springs found in the Internal Zone. We conclude by emphasizing that a continuous transfer of feedback from geological to hydrogeological approaches, and vice versa, enhances knowledge in both directions, helping us to avoid misinterpretations about the hydrogeological behaviors of aquifers and, ultimately, to better evaluate and manage water resources.

Pemodelan airtanah dan Neraca Airtanah Dampak Penambangan Batubara Open Pit pada Lipatan Sinklin di Daerah Muara Lawa, Kabupaten Kutai Barat, Provinsi Kalimantan Timur

Ch a n g e s in land use impacts on groundwater availability both in quality and quantity. Study of geological, hydrogeological conditions, hydrological, hydrogeological boundary conditions contribute to determine the presence of groundwater in the groundwater basin and determine the natural groundwater flow modeling patterns. Location of the study are in Muara Lawa, including the formation Pulaubalang, Pamaluan, and Balikpapan on Lampanan syncline structure. Exploration drilling results indicate, that the hydrogeological study area into the aquifer system of folded sedimentary rocks consisting of seven aquifer layers alternating between akuitar, aquifers, and the base layer in the form of akuiklud. The area bounded by the limits of the model study of surface water in two major rivers, the Lawa River (east) and the Perak River (west), as well as the groundwater divide with the highest head (north and south. The results of the analysis of the type of regional aquifers aquifer models including the category of semi depressed with aquitards dominance in the surface layer. The pattern of groundwater flow and head height can be predicted by modeling using Visual Modflow. There is an increase zone budget is almost five times higher than the natural condition to the active mining conditions, particularly in the green zone, that of the natural conditions of 1,502 m3 day-1 to 12,930 m3 day-1 in the active mining. This is due, in the mining area there is a change in land use and hidrostratigrafi, namely the formation of pits that reach depths of 70 meters.

Groundwater flow patterns and hydrochemical facies of Kendal groundwater basin, Central Java Province, Indonesia

Information on groundwater flow patterns is very important in groundwater conservation efforts. The patterns of groundwater flow will also affect the groundwater chemistry. However, information on this issue in some areas is often neglected or not yet available such as in Kendal district, Central Java Province, Indonesia. This paper presents the groundwater investigations in the Kendal groundwater basin area of Kendal district. The investigations cover geological survey, including 114 points of observation and measurements of shallow wells and deep wells. Groundwater sampling also carried out at 15 points that distributed evenly for groundwater chemical analysis. The results showed that the groundwater flow patterns in Kendal are generally flowed from south to north direction, for both the unconfined aquifer and confined aquifer. Based on the trilinear piper diagram, the groundwater facies for unconfined aquifer consists of magnesium bicarbonate, calcium chloride and mixed types. Whereas in the confined aquifer, the results obtained are of sodium chloride, calcium chloride and mixed types. Some similarities of groundwater facies found between the unconfined aquifer and confined aquifer, indicating an interaction of both aquifers. In addition, ion enrichment from the recharge area to the discharge area found due to the interaction of groundwater with aquifer material based on the stiff diagrams.

Fill and Spill Hillslope Runoff Representation With a Richards Equation‐Based Model

AbstractIntegrated surface‐subsurface hydrological models (ISSHMs) are well established numerical tools to investigate water flow and contaminant transport processes over a wide range of spatial and temporal scales. However, their ability to correctly reproduce the response of hydrological systems to natural and anthropogenic forcing depends largely on the accuracy of model parameterization, including the level of detail in the representation of the bedrock. This latter is typically incorporated in some way via the bottom boundary of the model domain. Issues of bedrock topography, variable soil depth, and the resulting hillslope storage distribution representation in ISSHMs are vitally important but to date have received little attention. A standard treatment of the bottom boundary, especially in large catchment and continental scale applications, is to model it as a flat or inclined (e.g., parallel to the surface) impermeable base (sometimes with some simple leakage term). This approach does not allow the model to correctly reproduce bedrock‐controlled threshold responses such as the fill and spill process, as observed across many hillslope and catchment scale field studies. It is still unclear whether Richards equation‐based numerical models are actually able to generate such responses. Here we use a Richards equation‐based model (CATHY) to simulate internal transient subsurface stormflow dynamics observed at the well‐characterized Panola experimental hillslope in Georgia (USA). Soil and bedrock properties were calibrated starting from values reported in previous studies at the site. Our simulation results show that the model was able to reproduce threshold mechanisms, which in turn affected both the integrated and distributed hydrologic responses of the Panola hillslope. We then developed a set of virtual experiments with modified boundary conditions and base topography at the soil‐bedrock interface to explore the bedrock boundary control on transient groundwater flow patterns. Our results show that accurate representation of the lower boundary is crucial for ISSHM simulations of hillslope‐scale storm runoff and for connectivity of transient groundwater. We summarize our findings with the development of a new bedrock topographic wetness index that takes into account the unsaturated infiltration dynamics. The index is able to help represent the spatial variability of water table response over the bedrock surface compared to standard surface topography‐based indices. This new index may be useful in larger‐scale ISSHM applications where an exact bedrock topography representation is not feasible or possible.

基于砂槽试验的开采和人工补给条件下潜水含水层地下水流路径模拟

Understanding the impacts of managed abstraction and recharge, i.e. artificial regulation of groundwater, on flow dynamics contributes to water resources planning and effective management of river basins. Based on the hydrogeological conditions of the aquifer in the Tailan River Basin, northwestern China, a two-dimensional sand-tank physical model and the corresponding numerical model were conceptualized and developed to investigate the influence of such regulation on the moisture content, groundwater flow patterns, groundwater age, residence time distributions, and groundwater flow paths in the groundwater reservoir. Four scenarios were examined at laboratory scale. The results showed that groundwater flow was influenced significantly by artificial regulation and that the depth of influence greatly increased depending on the regulation modes. Abstraction mainly alters the groundwater flow paths and moisture content at the ground surface in the core area of the depression cone and reduces the groundwater age in the entire aquifer. Groundwater flow lines are gradually parted by artificial recharge at different depths. Groundwaters of different ages have different behavior under the different artificial recharge depths and artificial recharge modes. Saddle points (kind of stagnation points) appeared at different locations, which were highly dependent on the modes of artificial regulation. Some of the lessons learned, and some management strategies, are proposed based on the results. Despite the dimensionality and scale of the model adopted, resulting in a relatively very large capillarity zone unrepresentative of field conditions, these findings nonetheless have important implications for understanding groundwater flow dynamics impacted by highly intensive human activities.

Characterisation of groundwater flow and recharge in crystalline basement rocks in the Talensi District, Northern Ghana

A numerical groundwater flow model, calibrated under equilibrium conditions to characterise the spatial variation of key hydraulic parameters and groundwater flow pattern in a crystalline aquifer in the Upper East Region of Ghana has been developed. The development of groundwater flow model was to provide the baseline information to assist in assessing the impacts of population growth and climate change scenarios on large scale development of groundwater resources for various uses. The results revealed an apparent dominant northeast–southwest flow pattern influenced mainly by the hydraulic conductivity field, with estimated values ranging between 0.001 and 58 m/day, and local flow systems which are controlled mainly by local variations in the topography in the area. The estimated average groundwater recharge from the calibrated model and chloride mass balance technique: 2.00% and 2.07% of the annual precipitation respectively has a direct positive correlation with elevation. The low recharge rate is evident in the high evaporation rates as revealed by stable isotope (δ2H and δ1⁸O) analysis of sampled water sources. The study also reveals the aquifer is being partly recharged by the White Volta River. This gives an indication that the area holds good groundwater fortunes for potential commercial groundwater development as predicted by scenario analysis which suggests that the aquifer can sustain increased abstractions by more than 100% of the current rate provided the current recharge rate is maintained. However, for the aquifer to sustain large scale abstractions beyond 100% of the current rate under conditions of reduced vertical recharge by more than 40% of the current rate, deliberate efforts would have to be made to enhance artificial vertical recharge to augment the natural recharge.

PENYUSUNAN ZONA KONSERVASI DAN PEMANFAATAN AKUIFER BEBAS PADA CEKUNGAN AIRTANAH PAGATAN KABUPATEN TANAH BUMBU, KALIMANTAN SELATAN

Pagatan groundwater basin is located on Tanah Bumbu Regency, South Kalimantan Province with 506.714 Ha or 13,5% from South Kalimantan total area. The increasing of population also affect the water demand as a human primary need. As one of the best sources for clean water, groundwater is being intensively extracted to fulfill the need of clean water until it becomes uncontrollable and damage the supply and demand equilibrium. This groundwater extraction has been turning uncontrollaby and decreasing the quantity and quality of groundwater. The purpose of this study is to know the water tables, to know the quality of groundwater, to determine the category of conservation zone and areas to be protected, and suitability of spatial planning of the region with conservation zone of research area. The method for this research is qualitative observation and descriptive. The method of observation is the measurement of water table, and sampling of wells, while the method of analysis is data processing which is done based on primary and secondary data obtained on field research data to determine the zone of conservation and groundwater utilization in in research area.The result showed that unconfined groundwater aquifers have groundwater flow pattern spreading flow towards South and Southwest. From the 150 groundwater samples, there are 9 samples that do not meet the requirements for drinking water.The construction of groundwater conservation zone is based on groundwater availability factor, the similarity of groundwater damage.

Development of a conceptual groundwater model for a complex basement aquifer system: The case OF OSUN drainage basin in southwestern Nigeria

Sound knowledge of hydrogeological setting is required for effective groundwater resource management and protection. In the basement environment where groundwater occurrence is discontinuous and highly heterogeneous, hydrogeological conceptual model is required to understand the occurrence and flow pattern of groundwater. This study presents an integrated 2D and 3D GIS method for conceptual modeling of the hydrogeological setting of a basement complex aquifer system in Osun Drainage Basin, Southwestern Nigeria. The efficiency of conjunctive use of RockWorks, Suffer and ArcGIS for surface and subsurface 3D hydrogeological modeling of a basement aquifer system was evaluated.Three distinct aquifers (Weathered Layer Aquifer (WLA), Unconfined Fractured Aquifer (UFA) and Confined Fractured Aquifer (CFA)) were delineated. WLA is characterized by low hydraulic conductivity (K = 0.34–27.54md−1, mean = 4md−1), hence low yield potential. Transmissivity (T) range and mean (0.6–1368 m2d−1, 85 m2d−1) indicate restricted flow within WLA. UFA is hydraulically connected to the underlying multi-layered CFA in the contact zones. The occurrence of UFA is localized within meta-sedimentary environment and it acts as the recharge redistributing medium, connecting the deep seated aquifers with the highly porous surface flaggy rubbles. CFA is characterized by relatively high mean K (0.2–91md−1, mean = 11md−1) and relatively high T (1.6–7185 m2d-1, mean = 483 m2d−1). Comparative analyses of aquifers’ hydraulic properties and spatial pattern of occurrence affirm that regional groundwater flow only takes place within CFA. The variation of hydraulic properties along fault lines is attributed to alternating occurrence of bedrocks of different structural and physico-chemical characteristics. Three distinct groundwater flow systems were identified in the study basin: i) the radially concentric localized shallow groundwater flow systems that occur within the overburden, ii) the W-E oriented regional flow system that feeds the source of Ikogosi Warm Spring in the adjourning basin, and iii) the NNE-SSW trans-current flow system that traverses the study basin at the center. While the first flow system is controlled by surface topography and the hydraulic properties of the vadose zone, the second and third flow systems are structurally controlled. The efficiency and efficacy of the methodology presented in this study is sufficient to develop hydrogeological conceptual model for highly heterogeneous, discontinuous basement aquifer system. Therefore, the developed conceptual model could be transformed to a numerical model of the study basin.

Identifying the groundwater flow systems in a condensed river-network interfluve between the Han River and Yangtze River (China) using hydrogeochemical indicators

Hydrogeochemistry and environmental isotopes were used to gain insight into the recharge processes, water–rock interactions, and groundwater residence time, and to identify groundwater flow systems (GFSs) in an interfluve between the Han River and Yangtze River in the eastern Jianghan Plain (China), an alluvial-lacustrine plain in the middle reaches of the Yangtze River. Because of carbonate mineral weathering, groundwater in the plain is predominantly HCO3-Ca or HCO3-Ca-Mg type. The decrease in typical ions and isotopic depletion with increasing depth indicates that the GFSs were divided into local and regional GFSs with an approximate depth limitation of 20 m. The consistent variations are attributable to complex anthropogenic activities, water–rock interactions and groundwater flow patterns. The multiple independent local GFSs exhibited a pattern in which groundwater was discharged into surface waters during the non-flood season. Groundwater age of local GFSs is modern according to the 3H concentrations, so the hydrodynamic circulation is active. Furthermore, the regional GFS pattern is controlled by slow lateral flow from west or northwest to east, eventually discharging into the Yangtze and Han rivers. The distribution of δ18O indicated three zones in regional GFSs that are likely dominated by the altitude effect of recharge areas. The groundwater age of regional GFSs varied from hundreds of years to 5000 years, estimated by 14C isotope data, revealing that the hydrodynamic circulation of regional GFSs is slow to relatively stagnant. The hydrodynamic characteristics and hydrochemical distributions corroborated the mixing zones of differently hierarchical GFSs in the discharge area of the Jianghan Plain.