Groundwater balance in the Khor Arbaat basin, Red Sea State, eastern Sudan

The Khor Arbaat basin is the main source of potable water supply for the more than 750,000 inhabitants of Port Sudan, eastern Sudan. The variation in hydraulic conductivity and storage capacity is due to the heterogeneity of the sediments, which range from clay and silt to gravely sand and boulders. The water table rises during the summer and winter rainy seasons; it reaches its lowest level in the dry season. The storage capacity of the Khor Arbaat aquifer is estimated to be 21.75?×?10⁶ m³. The annual recharge through the infiltration of flood water is about 1.93?×?10⁶ m³. The groundwater recharge, calculated as underground inflow at the ‘upper gate’, is 1.33?×?10⁵ m³/year. The total annual groundwater recharge is 2.06?×?10⁶ m³. The annual discharge through underground outflow at the ‘lower gate’ (through which groundwater flows onto the coastal plain) is 3.29?×?10⁵ m³/year. Groundwater discharge due to pumping from Khor Arbaat basin is 4.38?×?10⁶ m³/year on average. The total annual groundwater discharge is about 4.7?×?10⁶ m³. A deficit of 2.6?×?10⁶ m³/year is calculated. Although the total annual discharge is twice the estimated annual recharge, additional groundwater flow from the fractured basement probably balances the annual groundwater budget since no decline is observed in the piezometric levels.     

Developing conceptual hydrogeological model for Potsdam sandstones in southwestern Quebec,Canada

A hydrogeological study was conducted in Potsdam sandstones on the international border between Canada (Quebec) and the USA (New York). Two sandstone formations, arkose and conglomerate (base) and well-cemented quartz arenite (upper), underlie the study area and form the major regional aquifer unit. Glacial till, littoral sand and gravel, and marine silt and clay discontinuously overlie the aquifer. In both sandstone formations, sub-horizontal bedding planes are ubiquitous and display significant hydraulic conductivities that are orders of magnitude more permeable than the intact rock matrix. Aquifer tests demonstrate that the two formations have similar bulk hydrologic properties, with average hydraulic conductivities ranging from 2?×?10^?5 to 4?×?10^?5 m/s. However, due to their different lithologic and structural characteristics, these two sandstones impose rather different controls on groundwater flow patterns in the study area. Flow is sustained through two types of fracture networks: sub-horizontal, laterally extensive fractures in the basal sandstone, where hydraulic connectivity is very good horizontally but very poor vertically and each of the water-bearing bedding planes can be considered as a separate planar two-dimensional aquifer unit; and the more fractured and vertically jointed system found in the upper sandstone that promotes a more dispersed, three-dimensional movement of groundwater.     

Assessing groundwater storage in the Kairouan plain aquifer using a 3D lithology model (Central Tunisia)

The aquifer of the semi-arid Kairouan plain has been exploited for decades to supply the growing irrigated agriculture and the need of drinking water. In parallel, the major hydraulic works drastically changed the natural groundwater recharge processes. The continuous groundwater level drop observed since the 1970s naturally raises the question of groundwater storage sustainability. To date, hydrogeological studies focused on groundwater fluxes, but the total amount of groundwater stored in the aquifer system has never been fully estimated. This is the purpose of the present paper. A complete database of all available geological, hydrogeological and geophysical data was created to build a 3D lithology model. Then, the lithological units were combined with the hydraulic properties to estimate the groundwater storage. Over the 700 km² of the modelled area, the estimated storage in 2013 was around 18?×?10⁹ m³ (equivalent to 80 times the annual consumption of 2010) with a highly variable spatial distribution. In 45 years (1968–2013), 12% of the amount of groundwater stored in the aquifer has been depleted. According to these results, individual farms will face strong regional disparities for their access to groundwater in the near future.     

Groundwater budget for the upper and middle parts of the River Gash Basin, eastern Sudan

The River Gash Basin is filled by the Quaternary alluvial deposits, unconformably overlying the basement rocks. The alluvial deposits are composed mainly of unconsolidated layers of gravel, sand, silt, and clays. The aquifer is unconfined and is laterally bounded by the impermeable Neogene clays. The methods used in this study include the carry out of pumping tests and the analysis of well inventory data in addition to the river discharge rates and other meteorological data. The average annual discharge of the River Gash is estimated to be 1,056?×?10⁶ m³ at El Gera gage station (upstream) and 587?×?10⁶ m³ at Salam-Alikum gage station (downstream). The annual loss mounts up to 40% of the total discharge. The water loss is attributed to infiltration and evapotranspiration. The present study proofs that the hydraulic conductivity ranges from 36 to 105 m/day, whereas the transmissivity ranges from 328 to 1,677 m²/day. The monitoring of groundwater level measurements indicates that the water table rises during the rainy season by 9 m in the upstream and 6 m in the midstream areas. The storage capacity of the upper and middle parts of the River Gash Basin is calculated as 502?×?10⁶ m³. The groundwater input reach 386.11?×?10⁶ m³/year, while the groundwater output is calculated as 365.98?×?10⁶ m³/year. The estimated difference between the input and output water quantities in the upper and middle parts of the River Gash Basin demonstrates a positive groundwater budget by about 20?×?10⁶ m³/year     

Groundwater flow in a transboundary fault-dominated aquifer and the importance of regional modeling: the case of the city of Querétaro,Mexico

The city of Querétaro, located near the political boundary of the Mexican states of Querétaro and Guanajuato, relies on groundwater as it sole water supply. Groundwater extraction in the city increased from 21?×?10⁶ m³/yr in 1970 to 104?×?10⁶ m³/yr in 2010, with an associated drawdown of 100 m in some parts of the aquifer. A three-dimensional numerical groundwater-flow model has been developed that represents the historical evolution of the aquifer’s potentiometric levels and is used to simulate the effect of two scenarios: (1) a 40 % reduction in the extraction rate from public water supply wells in early 2011 (thus reducing the extraction to 62?×?10⁶ m³/yr), and (2) a further reduction in 2021 to 1?×?10⁶ m³/yr. The modeling results project a temporary recovery of the potentiometric levels after the 40 % reduction of early 2011, but a return to 2010 levels by 2020. If scenario 2 is implemented in 2021, the aquifer will take nearly 30 years to recover to the simulated levels of 1995. The model also shows that the wells located in the city of Querétaro started to extract water from part of the aquifer beneath the State of Guanajuato in the late 1970s, thus showing that the administrative boundaries used in Mexico to study and develop water resources are inappropriate, and consideration should be given to physical boundaries instead. A regional approach to studying aquifers is needed in order to adequately understand groundwater flow dynamics.     

Hydrogeological studies on the Nubian sandstone aquifer in El-Bahariya Oasis, Western Desert, Egypt

The current study aimed to evaluate hydrogeologically the Nubian sandstone aquifer in El-Bahariya Oasis. It represents the main water-bearing horizon in the study area and consists of continental elastic sediments, mainly sandstone alternating with shale and clays. The general flow lines are directed from SW to NE direction, as detected from the constructed potentiometric head contour map. The piezometric surface reaches 149 m in El-Heiz area at the southern part, while it reaches 90 m at the northern, reflecting higher pressure head of the aquifer in the southern part. The map also illustrates that the southern part is considered as the most promising location for development. The structural elements play an important role in the deposition and distribution of the sedimentary succession of the Nubian sandstone sediments. Consequently, this sedimentary pattern affects the occurrences and movements of the groundwater within the aquifer system. Along the structurally high areas, in the study area, the piezometric head increases, while the reverse is recorded along the structurally low areas. The step-drawdown tests data were carried out by calculating the aquifer loss coefficient (B) and the well loss constant (C). The B values are smaller compared with C values, indicating that the aquifer under pressure has a behavior of leaky aquifer; therefore, it shows hydraulic connection with surrounding formation. The values of well efficiency range from 78.50% to 87.76%. Analysis of 12 pumping test data (constant discharge tests) was carried out in order to calculate the Nubian aquifer hydraulic parameters (transmissivity, hydraulic conductivity, and storage coefficient). The transmissivity values decrease from 3,045 m²/day in the southern part (El-Heiz area) to 236 m²/day in the northeastern part (El-Harra area). Accordingly, the aquifer classified as a high to moderate potentiality. Transmissivity contour map observes gradual increase of transmissivity values from the southern to northeastern direction. This may be due to the increase of shale or clay content in the concerned aquifer in that direction. The storage coefficient values range between 1.04 × 10^?4 and 5.22 × 10^?3, as obtained from the results of pumping test analysis, which ensure that the Nubian sandstone aquifer is classified as semi-confined to confined aquifer type. The S values show a decrease from southwest to northeast direction as detected from S-map. The hydraulic conductivity values vary from to 0.46 m/day in the northern part to 10.88 m/day in the southern part with an average of 5.67 m/day. According to the classification based on K values, the aquifer is mainly composed of coarse sand.     

Hydrogeologic characteristics of the alluvial tuff aquifer of northern Sahand Mountain slopes, Tabriz, Iran

The Tabriz area is a densely populated area of northwestern Iran (more than 1.5 million in population) with a large proportion of its drinking, domestic, industrial and agricultural water supplied from groundwater resources. The average rate of drinking and industrial water use in the city of Tabriz is about 3.45 m³ s^–1. The Plio-Pleistocene unconfined alluvial tuff aquifer (about 1,275 km²), the most important aquifer in the area, has been known for many years as a reliable resource. The greatest estimated thickness of the alluvial tuff lies in the Saidabad area, with 350 m thickness. There are 994 deep and 284 shallow active pumping wells and 83 qanats operate in the alluvial tuff aquifer. The total water withdrawal from all these artificial discharge points has been measured at 72, 3.8 and 17 million m3/year, respectively. Analytical and numerical methods have been applied to the constant rate pumping test data from the Saidabad wellfield (eight pumping and three observation wells). The values of electrical conductivity in the groundwater of alluvial tuff aquifer range from 203 to 960 μS cm^–1 and bicarbonate type water dominates.     

Interactions between the surface water and groundwater in the western shoreline of Lake Nasser, Upper Egypt

The present study indicates that the factors controlling the hydraulic relation between surface water and groundwater at the western lake shoreline change from one locality to another. This depends upon the lithological characteristics and the major structures. In the southern sectors, sedimentation at the bottom and sides of the lake prevents the water movement to the Nubian sandstone aquifer. The potentiometric map reveals that the water level altitudes range between 170 m in the vicinity of the lakeshore line and 110 m west of the lake. The groundwater flow lines show that the main recharge to the aquifer comes from the southwest direction, as well as from the lake inland to variable distances (about 30 Km). During the present study, Darcy’s law was applied to calculate the recharge from the western shoreline of Lake Nasser to the adjacent Nubian aquifer. The maximum value of seepage was at Garf Hussein (27.71?×?10⁶ m³/year), which may be related to high permeability and hydraulic gradient. Also, it may be related to the N–S strike faults that cut the area on both sides of the Lake, and the groundwater is expected to have free circulation through the faults of this trend. The minimum value was recorded in Adindan section (0.61?×?10⁶ m³/year). This may be related to the limited recharge from the lake to the aquifer, due to the sedimentation that dislocates this recharge.     

Estimation of Groundwater and Nutrient Fluxes to the Neuse River Estuary, North Carolina

A study was conducted between April 2004 and September 2005 to estimate groundwater and nutrient discharge to the Neuse River estuary in North Carolina. The largest groundwater fluxes were observed to occur generally within 20 m of the shoreline. Groundwater flux estimates based on seepage meter measurements ranged from 2.86?×?10⁸ to 4.33?×?10⁸ m³ annually and are comparable to estimates made using radon, a simple water-budget method, and estimates derived by using Darcy’s Law and previously published general aquifer characteristics of the area. The lower groundwater flux estimate (equal to about 9 m³ s^?1), which assumed the narrowest groundwater discharge zone (20 m) of three zone widths selected for an area west of New Bern, North Carolina, most closely agrees with groundwater flux estimates made using radon (3–9 m³ s^?1) and Darcy’s Law (about 9 m³ s^?1). A groundwater flux of 9 m³ s^?1 is about 40% of the surface-water flow to the Neuse River estuary between Streets Ferry and the mouth of the estuary and about 7% of the surface-water inflow from areas upstream. Estimates of annual nitrogen (333 tonnes) and phosphorus (66 tonnes) fluxes from groundwater to the estuary, based on this analysis, are less than 6% of the nitrogen and phosphorus inputs derived from all sources (excluding oceanic inputs), and approximately 8% of the nitrogen and 17% of the phosphorus annual inputs from surface-water inflow to the Neuse River estuary assuming a mean annual precipitation of 1.27 m. We provide quantitative evidence, derived from three methods, that the contribution of water and nutrients from groundwater discharge to the Neuse River estuary is relatively minor, particularly compared with upstream sources of water and nutrients and with bottom sediment sources of nutrients. Locally high groundwater discharges do occur, however, and could help explain the occurrence of localized phytoplankton blooms, submerged aquatic vegetation, or fish kills.     

Groundwater sustainability and groundwater/surface-water interaction in arid Dunhuang Basin,northwest China

The Dunhuang Basin, a typical inland basin in northwestern China, suffers a net loss of groundwater and the occasional disappearance of the Crescent Lake. Within this region, the groundwater/surface-water interactions are important for the sustainability of the groundwater resources. A three-dimensional transient groundwater flow model was established and calibrated using MODFLOW 2000, which was used to predict changes to these interactions once a water diversion project is completed. The simulated results indicate that introducing water from outside of the basin into the Shule and Danghe rivers could reverse the negative groundwater balance in the Basin. River-water/groundwater interactions control the groundwater hydrology, where river leakage to the groundwater in the Basin will increase from 3,114?×?10⁴ m³/year in 2017 to 11,875?×?10⁴ m³/year in 2021, and to 17,039?×?10⁴ m³/year in 2036. In comparison, groundwater discharge to the rivers will decrease from 3277?×?10⁴ m³/year in 2017 to 1857?×?10⁴ m³/year in 2021, and to 510?×?10⁴ m³/year by 2036; thus, the hydrology will switch from groundwater discharge to groundwater recharge after implementing the water diversion project. The simulation indicates that the increased net river infiltration due to the water diversion project will raise the water table and then effectively increasing the water level of the Crescent Lake, as the lake level is contiguous with the water table. However, the regional phreatic evaporation will be enhanced, which may intensify soil salinization in the Dunhuang Basin. These results can guide the water allocation scheme for the water diversion project to alleviate groundwater depletion and mitigate geo-environmental problem.     

Integrated geophysical interpretation for the area located at the eastern part of Ismailia Canal, Greater Cairo, Egypt

The integrated geophysical interpretation for the different geophysical tools such as resistivity and gravity is usually used to define the structural elements, stratigraphic units, groundwater potentiality, and depth to the basement rocks. In the present work, gravity and resistivity data were utilized for detecting the groundwater aquifer and structural elements, as well as the upper and lower surfaces of the subsurface basaltic sheet in an area located at the eastern side of Ismailia Canal, northeastern Greater Cairo, Egypt. Two hundred and ten gravity stations were measured using an Autograv instrument through a grid pattern of 50?×?50 m. The different required corrections were carried out, such as drift, elevation, tide, and latitude corrections. The final corrected data represented by the Bouguer anomaly map were filtered using high- and low-pass filters into regional and residual gravity anomaly maps. The resulting residual gravity anomaly map was used for gravity modeling to calculate the depths to the upper and lower surfaces of the basaltic sheet. The resulting gravity models indicated that the depths to the upper surface of the basaltic sheet are ranged between 26 and 314 m, where the shallower depths were found around the southern and eastern parts. The depths to the lower surface of the basaltic sheet are varied from 86 to 338 m, and the thickness of the basaltic sheet is ranged from 24 to 127 m, where the biggest thicknesses were found around the southern and northern parts of the study area. Forty-two vertical electrical soundings (VES) were carried out using Schlumberger configuration with AB/2 spacings ranged from 1.5 to 500 m. 1D quantitative interpretation was carried out through manual and analytical interpretations. The VES data were also inverted assuming a 3D resistivity distribution. The results from the 3D resistivity inversion indicated that the subsurface section consists of sand, sandstone, and sandy–clays of Miocene deposits overlying the basalts. Such basaltic features (of Oligocene age) are underlain by Gabal Ahmar Formation of Oligocene deposits, which are composed of sand and sandstone. Therefore, two aquifers were deduced in the area. The first is the Miocene aquifer (shallower) and the other is the Oligocene aquifer (deeper).     

Study of the water saving potential of an irrigation area based on a remote sensing evapotranspiration model

To estimate the water saving potential of an irrigation area and create a scientific water saving plan, the irrigation water use efficiency and water productivity of the Hulanhe irrigation area for 2007–2014 were calculated, and the water saving potentials of different water saving plans were determined from the perspectives of engineering and crop water saving. The results showed that the evapotranspiration calculated from the surface energy balance algorithm for land model (SEBAL) agreed well with the measured results. The irrigation water use efficiency in the Hulanhe irrigation area was positively correlated with precipitation of irrigated land and was negatively correlated with the net irrigation water volume. The engineering water saving potential ranges for periods of 5, 8, 11, and 15 years were (1.702?×?10⁸, 5.103?×?10⁸) m³, (1.783?×?10⁸, 5.184?×?10⁸) m³, (1.865?×?10⁸, 5.266?×?10⁸) m³, and (2.301?×?10⁸, 5.702?×?10⁸) m³, respectively, and the water saving potential increased year over year. Low amounts of precipitation of irrigated land corresponded with small amounts of net irrigation water and greater water saving potential. Based on the cumulative frequency of the water productivity calculated for the Hulanhe irrigation area from 2007 to 2014, the target water productivity for short (50% of the multi-year average cumulative water productivity) and long (70% of the multi-year average cumulative water productivity) terms were 1.03 kg/m³ and 1.22 kg/m³, respectively, and the cumulative crop water saving potentials for short and long terms were 1.18?×?10⁸ and 2.74?×?10⁸ m³, respectively. These results provided a theoretical reference for creating water saving plans for irrigation areas.     

An assessment of the potential and impacts of winter water banking in the Sokh aquifer, Central Asia

The dynamics of artificial recharge of winter surface flows coupled with increased summer groundwater use for irrigation in the Sokh aquifer (Central Asia) have been investigated. Water release patterns from the giant Toktogul reservoir have changed, as priority is now given to hydropower generation in winter in Kyrgyzstan. Winter flows have increased and summer releases have declined, but the Syr Darya River cannot pass these larger winter flows and the excess is diverted to a natural depression, creating a 40?×?10⁹m³ lake. A water balance study of all 18 aquifers feeding the Fergana Valley indicated the feasibility of winter groundwater recharge in storage created by summer abstraction. This modeling study examines the dynamics of the process in one aquifer over a 5-year period, with four scenarios: the current situation; increased groundwater abstraction of around 625 million (M) m³/year; groundwater abstraction with an artificial recharge of 144 Mm³/year, equivalent to the volume available in low flow years in the Sokh River; and with a larger artificial recharge of 268 Mm³/year, corresponding to high flow availability. Summer surface irrigation diversions can be reduced by up to 350 Mm³ and water table levels can be lowered.     

Characterization of the shallow groundwater system in an alpine watershed: Handcart Gulch,Colorado, USA

Water-table elevation measurements and aquifer parameter estimates are rare in alpine settings because few wells exist in these environments. Alpine groundwater systems may be a primary source of recharge to regional groundwater flow systems. Handcart Gulch is an alpine watershed in Colorado, USA comprised of highly fractured Proterozoic metamorphic and igneous rocks with wells completed to various depths. Primary study objectives include determining hydrologic properties of shallow bedrock and surficial materials, developing a watershed water budget, and testing the consistency of measured hydrologic properties and water budget by constructing a simple model incorporating groundwater and surface water for water year 2005. Water enters the study area as precipitation and exits as discharge in the trunk stream or potential recharge for the deeper aquifer. Surficial infiltration rates ranged from 0.1–6.2×10^?5 m/s. Discharge was estimated at 1.28×10^?3 km³. Numerical modeling analysis of single-well aquifer tests predicted lower specific storage in crystalline bedrock than in ferricrete and colluvial material (6.7×10^?5–2.0×10^?3 l/m). Hydraulic conductivity in crystalline bedrock was significantly lower than in colluvial and alluvial material (4.3×10^?9–2.0×10^?4 m/s). Water budget results suggest that during normal precipitation and temperatures water is available to recharge the deeper groundwater flow system.     

Analysis of low-flow characteristics for catchments in Dongjiang Basin, China

Low-flow indices have been determined from long-term daily streamflow data for 13 catchments in Dongjiang Basin in southern China. The Brutsaert-Nieber method was applied to estimate catchment-scale effective groundwater parameters; representative values were 4.5?×?10^?4 m² s^?1 for the hydraulic diffusivity; 3.19?×?10^?5 m² s^?1/2 for the hydraulic desorptivity; 2.27?×?10^?4 m s^?1 for the hydraulic conductivity; and 0.2617 for the drainable porosity. The response constants correlate well with the total stream length and catchment area. Solutions of the linearised Boussinesq equation were used to guide the development of regional multivariate regression models for estimating low-flow indices from the catchment-scale effective parameters. Results showed that these catchments exhibit similar low-flow characteristics. The 7-day lowest average streamflows with return periods of 10 and 2 years (7Q10 and 7Q2) are highly correlated with the catchment-scale response constants. The low-flow ratio Q95/Q50 (ratio of daily streamflow exceeded 95 and 50% of the time, respectively) varied between 0.3 and 0.5, indicating a high proportion of groundwater in the streamflow. The advantage of the regional regression model is its conceptual basis and use of the catchment-scale effective parameters. The method has the potential to be applied to ungauged catchments for estimating low-flow statistics from stream length and catchment area.     

Large-scale hydraulic conductivity distribution in an unconfined carbonate aquifer using the ocean tidal propagation

The hydraulic conductivity of an unconfined carbonate aquifer at the uplifted atoll of Minami-Daito, Japan, was evaluated by a combination of cross-spectral analysis, analytical solution, and density-dependent groundwater modeling based on observed groundwater levels in 15 wells and at sea level. The island area was divided into 10 subregions based on island morphology and on inland propagation of ocean tides. The hydraulic conductivity was obtained for each subregion using analytical solutions based on phase lags of M₂ constituents of ocean tides at each well by assuming two aquifer thicknesses (300 and 1,800 m) and two effective porosities (0.1 and 0.3). The density-dependent groundwater model evaluated the hydraulic conductivity of the subregions by reproducing observed groundwater levels. The hydraulic conductivity in the subregions was estimated as 3.46?×?10^?3 to 6.35?×?10^?2 m/s for aquifer thickness of 300 m and effective porosity of 0.1, and as 1.73?×?10^?3 to 3.17?×?10^?2 m/s for aquifer thickness of 1,800 m and the effective porosity of 0.3. It was higher in southern and northern areas, and higher in interior lowland than in the western and eastern areas. Fissures and dolomite distributions on the island control differences of the omnidirectional ocean tidal propagation and cause these differences in hydraulic conductivity. The method used for this study may also be applicable to other small islands that have few or no data for hydraulic conductivity.

     

Comparison of groundwater recharge estimation methods for the semi-arid Nyamandhlovu area, Zimbabwe

The Nyamandhlovu aquifer is the main water resource in the semi-arid Umguza district in Matebeleland North Province in Zimbabwe. The rapid increase in water demand in the city of Bulawayo has prompted the need to quantify the available groundwater resources for sustainable utilization. Groundwater recharge estimation methods and results were compared: chloride mass balance method (19–62 mm/year); water-table fluctuation method (2–50 mm/year); Darcian flownet computations (16–28 mm/year); ¹⁴C age dating (22–25 mm/year); and groundwater modeling (11–26 mm/year). The flownet computational and modeling methods provided better estimates for aerial recharge than the other methods. Based on groundwater modeling, a final estimate for recharge (from precipitation) on the order of 15–20 mm/year is believed to be realistic, assuming that part of the recharge water transpires from the water table by deep-rooted vegetation. This recharge estimate (2.7–3.6% of the annual precipitation of 555 mm/year) compares well with the results of other researchers. The advantages/disadvantages of each recharge method in terms of ease of application, accuracy, and costs are discussed. The groundwater model was also used to quantify the total recharge of the Nyamandhlovu aquifer system (20?×?10⁶–25?×?10⁶ m³/year). Groundwater abstractions exceeding 17?×?10⁶ m³/year could cause ecological damage, affecting, for instance, the deep-rooted vegetation in the area.     

Groundwater flow dynamics of weathered hard-rock aquifers under climate-change conditions: an illustrative example of numerical modeling through the equivalent porous media approach in the north-western Pyrenees (France)

A numerical groundwater model of the weathered crystalline aquifer of Ursuya (a major water source for the north-western Pyrenees region, south-western France) has been computed based on monitoring of hydrological, hydrodynamic and meteorological parameters over 3 years. The equivalent porous media model was used to simulate groundwater flow in the different layers of the weathered profile: from surface to depth, the weathered layer (5?·?10^?8?≤?K?≤?5?·? 10^?7 m s^?1), the transition layer (7?·?10^?8?≤?K?≤?1?·? 10^?5 m s^?1, the highest values being along major discontinuities), two fissured layers (3.5?·?10^?8?≤?K?≤?5?·?? 10^?4 m s^?1, depending on weathering profile conditions and on the existence of active fractures), and the hard-rock basement simulated with a negligible hydraulic conductivity (K = 1 10 ^?9 ). Hydrodynamic properties of these five calculation layers demonstrate both the impact of the weathering degree and of the discontinuities on the groundwater flow. The great agreement between simulated and observed hydraulic conditions allowed for validation of the methodology and its proposed use for application on analogous aquifers. With the aim of long-term management of this strategic aquifer, the model was then used to evaluate the impact of climate change on the groundwater resource. The simulations performed according to the most pessimistic climatic scenario until 2050 show a low sensitivity of the aquifer. The decreasing trend of the natural discharge is estimated at about ?360 m³ y^?1 for recharge decreasing at about ?5.6 mm y^?1 (0.8 % of annual recharge).     

Development of a Darcy-Brinkman model to simulate water flow and tracer transport in a heterogeneous karstic aquifer (Val d’Orléans, France)

Darcy’s law is the equation of reference widely used to model aquifer flows. However, its use to model karstic aquifers functioning with large pores is problematic. The physics occurring within the karstic conduits requires the use of a more representative macroscopic equation. A hydrodynamic model is presented which is adapted to the karstic aquifer of the Val d’Orléans (France) using two flow equations: (1) Darcy’s law, used to describe water flow within the massive limestone, and (2) the Brinkman equation, used to model water flow within the conduits. The flow equations coupled with the transport equation allow the prediction of the karst transfer properties. The model was tested by using six dye tracer tests and compared to a model that uses Darcy’s law to describe the flow in karstic conduits. The simulations show that the conduit permeability ranges from 5?×?10^?6 to 5.5?×?10^?5?m² and the limestone permeability ranges from 8?×?10^?11 to 6?×?10^?10?m². The dispersivity coefficient ranges from 23 to 53 m in the conduits and from 1 to 5 m in the limestone. The results of the simulations carried out using Darcy’s law in the conduits show that the dispersion towards the fractures is underestimated.