Hydraulic Transmissivity Research Articles

Investigation of fractured rock aquifer in South China using electrical resistivity tomography and self-potential methods

Assessment of fractured rock aquifers in many parts of the world is complicated given their strong heterogeneity. Delineation of the subsurface geological formation in the weathered terrain is essential for groundwater exploration. To achieve this goal, 2D electrical resistivity tomography (ERT) and self-potential (SP) in combination with joint profile method (JPM) and boreholes have been carried out to delineate the subsurface geological units, detect the fracture/fault zones in hard rock, monitor the groundwater flow, and estimate the groundwater reserves contained within the weathered terrain at a complex heterogeneous site of Huangbu, South Guangdong of China. The integration of resistivity images with the borehole lithology along three profiles delineates three subsurface distinct layers namely topsoil cover, weathered and unweathered layers. The incorporation of ERT and SP with JPM reveal five fractures/faults, i.e., F1, F2, F3, F4 and F5. 2D ERT models interpret the less resistive anomalies as the fractures/faults zones, and high resistive anomalies as the fresh bedrock. The inversion program based on the smoothness-constraint is used on the resistivity field data to get more realistic three layered model. SP measurements are obtained along the same electrical profiles which provide the negative anomalies clearly indicating the groundwater preferential flow pathways along the fracture/fault zones. Hydraulic parameters namely hydraulic conductivity and transmissivity were determined to estimate the groundwater resources contained within the fractures/faults. The integrated results suggest that the fractures/faults zones are most appropriate places of drilling for groundwater exploration in the investigated area. Geophysical methods coupled with the upfront borehole data provides better understanding about the conceptual model of the subsurface geological formations. The current investigation demonstrates the importance of the integrated geophysical methods as a complementary approach for groundwater assessment in the hard rock weathered areas.

Quantitative estimations of aquifer properties from resistivity in the Bolivian highlands

Abstract Resistivity data constitute the largest part of the available information to assess the hydrogeological characteristics of the aquifer system near Oruro, in the central part of the Bolivian Altiplano. Two aquifers are part of this system; top unconsolidated sediments storing fresh water in their granular voids, overlying fractured hard rock formations where saline water was detected in connection to some faults. This study proposes an indirect and cost-effective way to estimate aquifer hydraulic properties for the groundwater management in the region. Hydraulic conductivity and transmissivity in the top aquifer were estimated using an empirical linear relationship between hydraulic conductivity and resistivity. This latter parameter, as well as the aquifer thickness, were obtained from the inverted models corresponding to the geoelectrical tests performed in the study area (electrical resistivity tomography, transient electromagnetic soundings and vertical electrical soundings). The highest estimated transmissivity values are ∼4.0 × 10−2 m2/s located in the centre of the study area, the lowest values are ∼3.4 × 10−3 m2/s, located around thermal intrusions to the south and where the top of the bedrock is shallow (∼20 m depth) to the west. The methodology presented in this study makes wider use of resistivity measurements to identify promising groundwater production sites.

Evaluation of aquifer hydraulic characteristics using geoelectrical sounding, pumping and laboratory tests: A case study of Lokoja and Patti Formations, Southern Bida Basin, Nigeria

AbstractThe hydraulic characteristics of aquifers in Lokoja and Patti Formations were investigated using combination of vertical electrical sounding (VES), pumping and laboratory tests. A total of 20 VES (10 each in areas underlain by Lokoja and Patti Formations) were carried out at different locations with 5 pumping tests around VES stations in order to determine the geoelectric layers, thickness, depths to water table and groundwater potential of the area. 21 samples extracted fromaquiferous units of surface outcrops were also subjected to laboratory constant head and falling head permeameter tests in order to determine hydraulic conductivity (K) values using the Darcy’s law of liquid flow. The results of VES for areas underlain by Lokoja and Patti Formations revealed 4-5 geo-electrical layers. The depths to water table vary from 5.91-40.8 m. Thickness values are within the range of 7.37-27.3 m for aquiferous units of Lokoja Formation, and 10.8-20.1 m for the Patti Formation. The results of aquifer characteristics using Dar-Zarrouk Parameter gave hydraulic conductivity (K) values between 1.92-91.7 m/day and 2.15-31.8 m/day for aquifers of Lokoja and Patti Formations respectively. Transmissivity (T) values of the aquiferous units of Lokoja Formation fall within 24.97-2117 m2/day, while those of Patti Formation vary from 27.9-456.91 m2/day. There is a strong correlation between the values of measured and calculated hydraulic conductivity and transmissivity between measured and calculated transmissivity for the five wells (R2 = 0.99 and 0.92, respectively). Based on the results obtained and interpretations proffered, aquiferous units in both formations are capable of yielding optimum groundwater for private consumption and partly to small communities, and to some extent can supply water for great regional use. It is suggested that similar study should be carried out in other sedimentary basins where to aid regional planning and management of groundwater resource.

Hydrogeological Parameter Determination in the Southern Catchments of Taiwan by Flow Recession Method

The understanding of hydrogeological characteristics and groundwater flow processes in aquifers is crucial for the determination of sustainable groundwater resource development as well as hydrological management and planning. In the past, information on hydrogeological characteristics was mainly acquired through point field measurement such as borehole geophysical techniques and field aquifer hydraulic testing. However, in view of the cost limitations and scale applicability of these methods, low-flow recession analysis techniques that utilize streamflow data can be used as alternative low-cost methods to reversely back-calculate hydrogeological parameters based on the hydrological processes by which groundwater from aquifers is naturally discharged to rivers. We chose Southern Taiwan as the study area for the estimation of the recession index (K), which is representative of catchment discharge behavior during both the dry and wet seasons, to determine seasonal differences in the aquifer flow regime and to estimate the following three hydrogeological parameters: hydraulic conductivity (k), specific yield (Sy), and transmissivity (T). Based on the field test reports of the locations of groundwater observational wells on the Chianan and Pingtung plains, the study area was divided into the Chianan sub-area (Zengwun, Yanshui, and Erren river basins) and the Kaoping sub-area (Kaoping, Donggang, and Linbian river basins). The estimation results of the present study were compared to the field test results. The results showed significant differences in the recession index K between the dry and wet seasons. Slight differences between the estimated hydrogeological parameters and the field test results were also observed for the two sub-areas because of differences in scale. Furthermore, regional differences in the estimation results were found to be consistent with the distribution of geological structures, which indicates a high degree of feasibility in the application of flow recession methods for catchment-scale hydrogeological parameter determination.

Estimation of hydraulic parameters using electrical resistivity tomography (ERT) and empirical laws in a semi‐confined aquifer

ABSTRACTThe estimation of hydraulic parameters is critical for the rational use of water resources and the development of reliable hydrogeological models. However, the cost of such estimation can be very high and the data are limited to the area near the pumping well. For this reason, complementary methods for estimating hydraulic conductivity and transmissivity have become increasingly important in recent years, such as the adjustment of empirical relationships between geoelectrical and hydraulic parameters. In this paper, two linear relationships were tested, combining resistivity measurements from well logging profiles and hydraulic conductivity values from pumping test data, in a semi‐confined fluvial aquifer in the province of Buenos Aires, Argentina. Furthermore, these relationships were used to obtain two‐dimensional (2D) hydraulic conductivity and transmissivity sections from electrical resistivity tomography using a high‐definition electrode array. Predicted values were compared with traditional pumping test in a near well showing very good agreement with both methods. Results showed that it would be possible to quantify the 2D variation of hydraulic parameters in aquifers and to identify high‐ or low‐productivity areas. By knowing this information in advance, it is possible to reduce the number of failures or unexpected results when drilling a well. These 2D sections also provide additional information about hydraulic parameters and their lateral variability, and can improve hydrogeological models without drilling new wells.

Evaluation of groundwater potential in Kabirwala area, Pakistan: A case study by using geophysical, geochemical and pump data

ABSTRACTKnowledge of hydraulic parameters (hydraulic conductivity and transmissivity) is essential for the delineation of groundwater potential zones. Conventionally, these parameters are measured using pumping tests carried out on boreholes. However, pumping tests are costly, labour intensive and require a considerable amount of equipment. The integration of geophysical methods with pumping tests provides efficient and cost‐effective alternative to calculate hydraulic parameters. Fifty electrical resistivity soundings were carried out in the study area using Schlumberger inter‐electrode configuration to obtain hydraulic characteristics that are estimated through the pumping tests. To apply this approach successfully, sufficient number of boreholes are used. Part of the boreholes, in which pumping tests were carried out, is used for both to constrain resistivity inversions and to establish the empirical relationship between the interpreted geophysical and hydraulic parameters. The rest of the boreholes without pumping tests are still used for constraining the inversions. Initially, aquifer parameters were measured using pumping tests at 12 water wells. Afterwards, transmissivity (T) and hydraulic conductivity (K) were correlated with transverse resistance (Tr) and the bulk resistivity (ρo) of the aquifer at other sites where pumping tests had not been conducted. In this way, the entire study area was covered to assess the groundwater reserves. The hydraulic properties obtained by the geophysical method fit pretty well to both the pumping and physicochemical data of the investigated area. The integrated study reveals five layers (i.e. topsoil, clay, clay sand, sand and gravel sand) and three potential zones (i.e. high, medium and low potential aquifer zones) with specific ranges of T, K, Tr and ρo. The results suggest that, in case of sparse well data, the aquifer parameters can be estimated using the relations depending on the specifications of the area.

Estimation of hydraulic transmissivity from MRS by varying the porosity exponent in detrital aquifers of the Iberian Peninsula

ABSTRACTTo this date, estimation of hydraulic transmissivity with magnetic resonance sounding (MRS) requires transmissivity values from pumping tests in nearby wells in order to determine a calibration constant from the relationship between both types of data. The use of this technique is limited due to the fact that reported values of this calibration constant are highly variable, even within the same type of aquifer. In order to minimize this shortcoming, a new methodology, which has been developed and presented here, is used to estimate the transmissivity of detrital aquifers with heterogeneous behaviour based only on the results obtained by MRS. The exponents applied to decay time and free porosity used in the expression to compute MRS transmissivity have conventionally been fixed values. In contrast, the work presented here aims to improve the applicability of this technique using a variable exponent for free porosity in each type of aquifer, obtained only from MRS results. In order to achieve this goal, previously published MRS data from four detrital aquifers in the Iberian Peninsula have been used and a relationship between the porosity exponent and a function of decay times and free porosities has been developed. This approach eliminates the need to drill and perform pumping tests in additional boreholes, which has cost and time implications, once the correct expression is determined for a given type of aquifer. The range of values thus obtained for the porosity exponent is similar to that reported in the literature. The deviation of the results obtained with this methodology regarding the results of pumping test is similar to the deviation with conventional process. This suggests that the proposed methodology is appropriate for the aquifers considered, and the approach may be expanded to study other types of aquifers. The drawbacks of the proposal related to the conventional equivalence are explored.

Three dimensional thermo-hydraulic modelling for KBS-3H alternative

The KBS-3H disposal alternative is composed by horizontally placed supercontainers comprising the canisters with the spent nuclear fuel surrounded in both drift axis and radial directions by compacted bentonite blocks (buffer) enclosed in a perforated shell. The different internal gaps between the supercontainer components and the one between the buffer blocks and the host rock have direct effects on the buffer behaviour. This paper presents a Thermo-Hydraulic (TH) Three-Dimensional (3D) numerical model developed to analyse a particular geometry assuming three different gap state conditions and providing results of the temperature, liquid pressure, and evolution of the degree of saturation.The material parameters, constitutive models, and assumptions made were carefully selected with regards to laboratory measurements reported in directly-related bibliography. The modelling settles the importance of understanding the groundwater flow through the rock mass and from fractures in the rock in order to achieve reliable predictions regarding buffer saturation, since it is known that the saturation times could range from few years to one thousand years depending on the hydrogeological conditions in the rock. The obtained results lead to full saturation times of 50 to 100 years. In addition to the rock hydraulic conductivity and fracture transmissivity, the saturation process was directly affected by the material properties of the buffer and gap presence between the buffer blocks and the host rock. Finally, in connection with thermal evolution, the thermal conductivity of repository components and the behaviour of air gaps in the buffer were key variables.

Geophysical, geological, and hydrogeological characterization of a tributary buried bedrock valley in southern Ontario

Buried bedrock valleys infilled with Quaternary-aged sediment have the potential to become productive aquifers owing to prevalent sand and gravel deposits often associated with these topographic lows. In areas where groundwater is drawn from the underlying bedrock aquifer, buried bedrock channels may significantly affect the spatial distribution of recharge and localized contaminant pathways. Therefore, understanding the form, distribution, and the nature of Quaternary infill sediments within these buried bedrock river valleys, and their relationship to hydraulically transmissive bedrock features is an important aspect of groundwater resource management. Here, we evaluate the effectiveness of electrical resistivity and seismic refraction collected over a partially urbanized 150 ha area with variable vegetation, roads, and structures, to map the spatial distribution of sediments and delineation of a channel segment associated with a regional bedrock valley. Electrical resistivity and seismic refraction was performed along 13 (covering ∼11.6 km) and seven transects (covering ∼0.9 km), respectively, to map and characterize the bedrock surface morphology beneath a variable thickness of unconsolidated deposits. Three continuously cored holes and downhole geophysical logs, supplemented with four nearby water well records captured the in-channel as well as adjacent Quaternary stratigraphy (∼15–40 m). Cores recorded multiple glacial till deposits and ice-marginal processes associated with ice advances and retreats. Hydraulic transmissivity of the bedrock around the valley feature was evaluated using a FLUTe hydraulic transmissivity profiling technique. This study demonstrates the potential of combining several surface geophysical methods with sedimentological analysis of continuous cores and hydraulic data for characterizing tributary bedrock channel morphology and Quaternary infill at a scale relevant to localized studies of municipal production well recharge zones and contaminant transport and fate.

Refinement indicators for estimating hydrogeologic parameters

ABSTRACTWe identify simultaneously the hydraulic transmissivity and the storage coefficient in a ground water flow governed by a linear parabolic equation. Both coefficients are assumed to be functions which are piecewise constant in space and constant in time. Therefore, the unknowns are the coefficient values as well as the geometry of the zones where these parameters are constant. The identification problem is formulated as the minimization of a misfit least-square function. Using refinement indicators, we refine the parameterization locally and iteratively. We distinguish the cases where the two parameters have the same parameterization or different parameterizations.

Hybrid Inversion Method to Estimate Hydraulic Transmissivity by Combining Multiple-Point Statistics and a Direct Inversion Method

Inversion methods that rely on measurements of the hydraulic head h cannot capture the fine-scale variability of the hydraulic properties of an aquifer. This is particularly true for direct inversion methods, which have the further limitation of providing only deterministic results. On the other hand, stochastic simulation methods can reproduce the fine-scale heterogeneity but cannot directly incorporate information about the hydraulic gradient. In this work, a hybrid approach is proposed to join a direct inversion method (the comparison model method, CMM) and multiple-point statistics (MPS), for determination of a hydraulic transmissivity field T from a map of a reference hydraulic head $$h^\mathrm {(ref)}$$ and a prior model of the heterogeneity (a training image). The hybrid approach was tested and compared with pure MPS and pure CMM approaches in a synthetic case study. Also, sensitivity analysis was performed to test the importance of the acceptance threshold $$\delta $$ , a simulation parameter that allows one to tune the influence of $$h^\mathrm {(ref)}$$ on the final results. The transmissivity fields T obtained using the hybrid approach take into account information coming from the hydraulic gradient while simultaneously reproducing some of the fine-scale features provided by the training image. Furthermore, many realizations of T can be obtained thanks to the stochasticity of MPS. Nevertheless, it is not straightforward to exploit the correlation between the T maps provided by the CMM and the prior model introduced by the training image, because the former depends on the boundary conditions and flow settings. Another drawback is the growing number of simulation parameters introduced when combining two diverse methods. At the same time, this growing complexity opens new possibilities that deserve further investigation.

Influence of Normal and Shear Stress on the Hydraulic Transmissivity of Thin Cracks in a Tight Quartz Sandstone, a Granite, and a Shale

AbstractTransmissivity of fluids along fractures in rocks is reduced by increasing normal stress acting across them, demonstrated here through gas flow experiments on Bowland shale, and oil flow experiments on Pennant sandstone and Westerly granite. Additionally, the effect of imposing shear stress at constant normal stress was determined, until frictional sliding started. In all cases, increasing shear stress causes an accelerating reduction of transmissivity by 1 to 3 orders of magnitude as slip initiated, as a result of the formation of wear products that block fluid pathways. Only in the case of granite, and to a lesser extent in the sandstone, was there a minor amount of initial increase of transmissivity prior to the onset of slip. These results cast into doubt the commonly applied presumption that cracks with high resolved shear stresses are the most conductive. In the shale, crack transmissivity is commensurate with matrix permeability, such that shales are expected always to be good seals. For the sandstone and granite, unsheared crack transmissivity was respectively 2 and 2.5 orders of magnitude greater than matrix permeability. For these rocks crack transmissivity can dominate fluid flow in the upper crust, potentially enough to permit maintenance of a hydrostatic fluid pressure gradient in a normal (extensional) faulting regime.

Spatial Variation of Aquifer Parameters from Coastal Aquifers of Sindhudurg District, Maharashtra Using Pore-water Resistivity and Bulk Resistivity

Estimation of hydraulic parameters in coastal aquifers is an important task in groundwater resource assessment and development. An attempt is made to estimate these parameters using geoelectrical data in combination with pore-water resistivity of existing wells. In the present study, 29 resistivity soundings were analysed along with 29 water samples, collected from the respective dug wells and boreholes, in order to compute hydraulic parameters like formation factor, porosity, hydraulic conductivity and transmissivity from coastal region of north Sindhudurg district, Maharashtra, India. The result shows some parts of the study area reveal relatively high value of hydraulic conductivity, porosity and transmissivity. Further, a negative correlation is seen between hydraulic conductivity and bulk resistivity. The hydraulic conductivity is found to vary between 0.014 and 293 m/day, and the transmissivity varied between 0.14 and 11,722 m2/day. The transmissivity values observed here are in good correspondence with those obtained from pumping test data of Central Ground Water Board. These zones also have high aquifer thickness and therefore characterize high potential within the water-bearing formation. A linear, positive relationship between transverse resistance and transmissivity is observed, suggesting increase in transverse resistance values indicate high transmissivity of aquifers. These relations will be extremely vital in characterization of aquifer system, especially from crystalline hard rock area.

Identification of Groundwater in Hard Rock Terrain Using 2D Electrical Resistivity Tomography Imaging Technique: Securing Water Scarcity at the Time of Seasonal Rainfall Failure, South Andaman

Like many of the tropical islands, the population of Andaman and Nicobar Islands, though not directly, relies predominantly upon rain water harvesting to quench their need and also depends on the groundwater sources. In the background of climate change, severity of hydrological cycle is much anticipated which may cause more extreme and unusual precipitation. It is quite essential to have other alternatives. Accordingly, groundwater could be exploited as a potential alternative. The present study intends to find out the potential groundwater source and estimate aquifer parameters in Kodiyaghat (KD) and Burmanallah (BN). As these areas are composed of very hard rock, Wenner-Schlumberger array has been used to carry out a 2D Electrical Resistivity Tomography survey to find out the fracture zone as well as to delineate the aquifer. KD and BN show maximum resistivity of 25,416 Ωm and 5985 Ωm indicate very hard rock terrain. Similarly, the minimum values of resistivity (21.6 Ωm and 30.4 Ωm) were observed at KD and BN define the presence of freshwater aquifers respectively. The aquifer identified was found to be at a depth of 5 m to 19.9 m at KD and 2.5 m to 20 m at BN. The calculated Hydraulic conductivity (14.85 m/day and 30.14 m/day), transmissivity (86.25 m2/day and 271.27 m2/day) and porosity (28.7% and 31.24%) values at KD and BN confirmed that, the located aquifer was of fresh ground water quality and can be utilized for drinking and house hold purposes. According to the results, almost 70% of the study area is hard rock terrain and 30% comes under potential aquifer zone. The results also show that, both the areas were characterized by Horst and Graben topography and suggest possible groundwater sources for future exploration.

Estimation of groundwater potential using surficial resistivity measurements: A case study from parts of Makurdi Benue State Nigeria

A geophysical survey involving vertical electrical sounding (VES) was carried out at Makurdi, Benue State Capital which is in the North Central of Nigeria using Schlumberger electrode array. The results show that the area is characterized by 4–5 geoelectric subsurface layers. The measured aquifer thickness ranges from 6 to 69 m, with an average value of 36.7 m and the aquifer resistivity ranges from 7 to 378 Ωm with an average of 133.8 Ωm. The aquifer thickness and aquifer resistivity were used to compute the values of the hydraulic conductivity and transmissivity. The aquifer thickness and aquifer resistivity along side with the estimated hydraulic conductivity and Transmissivity were used as indices for evaluation of groundwater potentials. The groundwater productivity potential in the area has been classified into two zones namely; high and intermediate. This study has revealed that no single index determines the groundwater productivity potential but a combination of two or more factors.

Study of aquifer characteristics in northern Paiko, Niger State, Nigeria, using geoelectric resistivity method

Vertical electrical soundings technique was used to evaluate the aquifer characteristics and distribution in the northern part of Paiko in Nigeria. A total of thirty vertical electrical soundings were carried out using ABEM SAS4000 Terrameter, and the data was analyzed both manually and with software (Resist software). The result revealed the aquifer resistivity and thickness to vary from 10.9 to 80,368 Ωm, and 1.06 to 72 m, respectively. Also, hydraulic conductivity ranges from 0.010267 to 41.61928 m/day while transmissivity values range from 0.035215 to 70.09302 m2. The hydrogeological maps (hydraulic conductivity and transmissivity image maps) showed the variations of these parameters in the study area and that the southwestern part of the area has prolific aquifer.

Re-evaluation of Shallow Floodplain Aquifers Groundwater Potentials and Storage of Sokoto Basin, Northwestern Nigeria

Floodplains of Sokoto Basin with covering about 280,000 hectares of land was assessed for its shallow groundwater potentials. Data on pumping test of tube wells, logs and drilled tube wells were utilized for this study. Storativity was determined from known lithology of tube wells. Results of this study gives the ranges and averages of Hydraulic parameters for the shallow alluvial aquifers of hydraulic conductivity, transmissivity, specific capacity and storativity to be 6.66 - 1316 m/day and 214,044 m/day, 40 – 3950 m2/day and 799.5 m2/day, 12.25 – 5763.6 m3/day and 1,031m3/day and 1×10-5 - 6×10-3 and 5×10-4 respectively, While the Yields range of 0.3- 7 l/s was obtained with 90% of tube wells evaluated having yields of 2.2 l/s and above. Lithologic Aquiferous units vary from medium sands, sands, coarse sands to gravel with thickness range of between 0.3 to 15 m. Computed hydraulic conductivity indicates the aquifer materials to be gravels and alluvial sands of high permeability. Specific capacity values indicated the wells to be of high productivity when compared with standard values, Transmissivity average revealed the area to be of high groundwater transmission potentials. Overall assessment of the yields of tube wells studied indicated that 90% of the wells have yields that are above the minimum required for irrigation; the low average drawdown of 0.41 m recorded is an indication that the aquifers have high efficiency and high performance as regards storage and transmission of water. Recharge of the alluvial aquifers is mainly through surface river flow and precipitation, climate change have recently threaten the recharge potential s owing to the drying up of some of these streams and rivers at the peak of dry season as well reduction in rainfall. Statistical analysis has shown a good linear relationship between Specific capacity with yield, Transmissivity and hydraulic conductivity while Transmissivity is linearly related with yield and Conductivity. Generally the study revealed that the Sokoto basin Fadama land to be of high groundwater potentials, with storage coefficient values of confined and high yielding aquifers with capabilities of sustaining withdrawals for long period without recharge from external sources. Standard procedures are highly recommended to reduce or avoid the case of drilling abortive or low yielding wells.

A self-organizing map approach to characterize hydrogeology of the fractured Serra-Geral transboundary aquifer

Abstract The aim of this work is to understand the exchange of water between the Serra Geral aquifer system (SGAS) and Guarani aquifer system (GAS). The objectives are two-fold. First, introduce the capability of the modified self-organizing maps (MSOM) as an unbiased nonlinear approach to estimate missing values of hydrochemistry and hydraulic transmissivity associated with the SGAS, a transboundary groundwater system spanning parts of four South American countries. Second, identify areas with potential connectivity of the SGAS with the GAS based on analysis of the spatial variability of key elements and comparison with current conceptual models of hydraulic connectivity. The MSOM is employed to calculate correlations (trends) between 27 variables from 1,132 wells. Hydraulic transmissivity is calculated from specific capacity values from well-pump tests in 157 locations. Hydrochemical facies estimates appear unbiased and consistent with current conceptual-connectivity models indicating that vertical fluxes from GAS are influenced by geological structure. The MSOM provides additional spatial estimates revealing new areas with likely connections between the two aquifer systems.

Classifying zones of suitability for manual drilling using textural and hydraulic parameters of shallow aquifers: a case study in northwestern Senegal

A method is proposed that uses analysis of borehole stratigraphic logs for the characterization of shallow aquifers and for the assessment of areas suitable for manual drilling. The model is based on available borehole-log parameters: depth to hard rock, depth to water, thickness of laterite and hydraulic transmissivity of the shallow aquifer. The model is applied to a study area in northwestern Senegal. A dataset of boreholes logs has been processed using a software package (TANGAFRIC) developed during the research. After a manual procedure to assign a standard category describing the lithological characteristics, the next step is the automated extraction of different textural parameters and the estimation of hydraulic conductivity using reference values available in the literature. The hydraulic conductivity values estimated from stratigraphic data have been partially validated, by comparing them with measured values from a series of pumping tests carried out in large-diameter wells. The results show that this method is able to produce a reliable interpretation of the shallow hydrogeological context using information generally available in the region. The research contributes to improving the identification of areas where conditions are suitable for manual drilling. This is achieved by applying the described method, based on a structured and semi-quantitative approach, to classify the zones of suitability for given manual drilling techniques using data available in most African countries. Ultimately, this work will support proposed international programs aimed at promoting low-cost water supply in Africa and enhancing access to safe drinking water for the population.

CONTRIBUTION TO HYDRAULIC CHARACTERISTICS OF PLIO-PLEISTOCENE DEPOSITS OF THRIASSION PLAIN OF ATTICA

The geological structure of Thriassion Plain is generally complex and has been affected at different times by many tectonic activities. The last ones are the neotectonic, which caused horsts and grabens structures. Geologic and tectonic structures have influenced the hydrogeological conditions and the groundwater flow. Hydraulic characteristics of Plio-Pleistocene deposits differ throughout their extent. In this study, pumping tests in Plio-Pleistocene deposits are represented and the hydraulic characteristics transmissivity T, storativity S and hydraulic conductivity K are assigned. Pumping tests, in 8 totally wells, were conducted in the dry period. Methods as Cooper-Jacob’s, Theis’s, Papadopoulos Cooper’s and Neuman’s and last the Recovery method, are used to assign the hydraulic characteristics. These tests highlighted the Recovery method as the most reliable. Transmissivity T: 18-279.1 m2/d, storativity S: 2.5*10-3 3*10-2and hydraulic conductivity K: 0.4-25.1 m/d. Specific capacity is also determined ranging between 16-360 m3/d/m. This study contributes, essentially, in the approach of hydrogeological conditions of Thriassion Plain.