In arid climates, conventional water resources are severely limited and stressed in the face of rapid population growth and future climate change. So, it is necessary to find alternative non-conventional water resources for use in drought situations. Additionally, the non-conventional water resources in these areas are not sufficient to meet future water demand. Therefore, non-conventional water resources can be adopted as a strategic reserve to bridge the gap between water supply and demand in case of emergency and drought events. These resources might include rainwater harvesting, treated wastewater, and desalinated seawater. Managed aquifer recharge (MAR) can be applied to store these resources in the hydrogeological system using Geo information System—Multi Criteria Decision Analysis (GIS-MCDA) approach for determining the suitable MAR location for storage. North-west Kingdom of Saudi Arabia area was chosen for this study because it is extremely arid, has high potential for social and economic development, and it has newly constructed non-conventional water infrastructures distributed throughout the area including water desalination plants, Tertiary Sewage Effluent (TSE) waste water plants, and flash-flood storage dams. To identify the suitable MAR site location and structure, different data related to aquifer hydrogeology, surface hydrology, hydrometeorology, and water quality were applied. Then, GIS-MCDA holistic approach was applied with aid of ordered weighting average (OWA) technique. Finally, two maps were created to show the MAR location and structure type. Potential map indicates that ~ 18.85% of the area is suitable for MAR installations. About 0.17% of the total area exhibited very high potential, where infiltration ponds can be applied, 1.86% had high potential for construction of check dams with diversion channels, and 16.82% had moderate potential for installation of recharge wells. Additionally, 56 MAR structures were proposed and a map showing their locations has been created. Thus, results indicated that the study area is promising for MAR installation. These maps could aid the decision makers to propose a sustainable development plan for the future water resources of the area.

Four surface geophysical techniques were utilized to study the geological and hydrogeological settings of highly saline a coastal aquifer system to the north-east of River Nile Delta, Egypt. These techniques include SP, DC-Resistivity, TDIP and TDEM methods. The first target was to determine the geological stratification as a differentiation among clay, clayey, sand and sandy layers of high saline water. These techniques reflect that there is a complicated lateral and vertical difference in sediments along study area. The surface layers with depth down to ~120 m have low to medium content of clay that change with depth. Then, the second target was the differentiation laterally and vertically for salinity with depth down to ~250m as an interesting hydrogeological setting. These techniques reported that the sediments consist of thin and thick clay and silts, clayey sand, and sandy clay strata. Investigation depth was up to ~210m due to high salinity and clay content effect. At shallow depths, soil texture (down to ~100m and sometimes down to ~160m) consists of clay and silt with sand intercalation. The TEM data indicate a zone of less saline water and low clay content starting from ~40 to ~100m. There may be an evidence for a significant high to medium clay content after these depths down to ~250m. All four methods were calibrated with each other. Accordingly, good matching between the inversion model of TEMSs and composite logs of new drilled well was found, especially in lithological layers identifications. Also, this calibration confirmed that the area was complicated regarding the geological and hydrogeological conditions and the TDIP and TEM are the best methods in studying the environmental, geological and hydrogeological settings as primary important engineering implications for studying coastal highly saline aquifers.

Determining the type and properties of saturated groundwater for complex sedimentary facies, as well as the various properties of these sedimentary facies, requires extensive geological, hydrogeological, and geophysical studies. Therefore, identifying the different types of subsurface deposits and their physical properties as well as their geological, hydrogeological, and structural settings are the interesting features in this study which play an important role in achieving its objectives. To achieve these objectives, the Direct Current (DC) resistivity method and the Direct Current Time-Domain Induced Polarization (DC-TDIP) method were used. These two methods were applied because they are complementary methods, one of which is more accurate in sediments saturated with fresh water (the DC resistivity method) and the other in sediments saturated with salt water (DC-TDIP method). Also, the DC-TDIP method was applied to avoid ambiguity in the resistivity results, as well as their results were compared with the available geological and hydrogeological field data. Accordingly, 2D and 3D resistivity values were designed to describe the hydro-lithological environment of the recorded sediments, and their hydrogeoelectric properties and groundwater zones were also identified and divided. Also, 2D and 3D chargeability values were designed to distinguish between sediments, their depositional facies, and their saturated water properties. These values also succeeded in separating clay from non-clay layers, and clay layers from layers containing salt water. Therefore, it was found that the integration between the two methods helped in identifying and visualizing the characteristics of the sediments and determining their facies and their water content, which helped in understanding the complex sedimentary facies recorded in the study area as well as identifying the types and characteristics of groundwater contained in these facies. Therefore, it can be recommended to apply the previous methodology and include the two geophysical methods and their results to study complex facies deposits and determine their water content and type, especially in similar depositional environments that are located next to a source of salt water mixed with other types of water.

Studying and determining the physical properties and hydraulic parameters of vadose zone sediments is an important key to evaluate the infiltration rate into them and assessing the extent to which aquifer sediments benefit from rainwater harvesting in arid and semi-arid areas. Due to the lack of sufficient data on the characteristics of this zone depths, a numerical modeling was used to simulate the electrical resistivity of these sediments by applying the electrical resistivity method, because it is the most affected by the physical properties of dry and wet sediments. This study was applied as a proposal for application in northwestern KSA to calculate the vertical hydraulic conductivity and transmissivity for the vadose zone. This was implemented by assuming a three-layer model using COMSOL Multiphysics model with different electrical resistivity values depending on some in situ electrical resistivity measurements for shallow depths. Hence, the infiltration rate of sediments in this area can be predicted with depth and its effect on aquifer recharge. The focus was on calculating the vertical hydraulic parameters of the most widespread surface sediments with depth and comparing the results of calculating these parameters for some sediments laboratory-wise to ensure their accuracy. Then, their infiltration rate was inferred separately with depth, predicting their ability to aquifer recharge and make the most of rainwater harvesting. Finally, this study can be considered as a preliminary study to determine the expected forward model of electrical resistivity and hydraulic parameters values for the vadose zone sediments with depth along the area and in any other areas, and then apply them accurately in situ to estimate the extent of its usefulness in rainwater harvesting, especially aquifer recharge.

Exploration and determination of the hydro-geo-electrical characteristics of an aquifer can be done by applying the forward (initial multi-layers), and the inverse (final layered) models for interpreting the DC-resistivity (VES) and TEM data. So, 22 VES using Schlumberger configuration (AB/2 = 500–700m) and 12 TEMS using in-loop configuration (square, ℓ = 200m) were carried out at the West El-Minia selected area for studying the Oligocene Clastic and Carbonate aquifers. VESs were interpreted for studying the shallow resistive and conductive layers, as well as faults delineation. TEMs were interpreted for shallow and deep conductive layers discrimination. The VES and TEM inverse models were examined with the drilling data and construed the subsurface into four units; dry Oligocene Clastics (173–467 Ω.m), dry limestone (273–374 Ω.m), saturated Oligocene Clastics (Oligocene aquifer) (2–107 Ω.m), then saturated fractured Eocene limestone to shaly limestone (5–188 Ω.m). Groundwater depths (62–131m) and thicknesses variation were estimated, as well as the faults location. Two hydro-geo-electrical sections were built for simulating the resistivity values and their connotations, and managing in choosing the promised locations for drilling wells. The ramp-off time effect was studied and found that ∼50–∼100m shallow high resistive thickness didn't defined from the TEM data in which the max penetration depth was 672m. The available well logging data were analysed to reveal the pure saturated zones, the volume of shale of 0%–100% and the porosity values of ∼9%–∼35% in the Oligocene aquifer and of ∼4%–∼15.5% in the carbonate aquifer. So, the forward and inverse models application and soundings integration are considered robust tools for estimating and simulating the aquifer characteristics.

In this study, the SP, DC-Resistivity and DC-TDIP methods were used and included 21 sites for determining the groundwater conditions and visualizing the aquifer sediments, surface water seepage, and groundwater flow in 2D and 3D. The results indicated the occurrence of Quaternary and Tertiary deposits, as well as shallow aquifer of Eocene fractured limestone and Quaternary deposits. The resistivity, chargeability and SP values were compared with each other and 2D and 3D visualization models were designed for these values to understand the sediment distribution and its geological and hydrogeological implications. High to medium, low and very low chargeability values indicated the compact sediments with high shale content, water-bearing layers and freshwater zones and dry sediments, respectively, and varied with the water amount, salinity and effective porosity. Low to very low values of SP indicated the occurrence and high accumulation of groundwater and an increase in shale, permeability and groundwater flow and source, and possibly salinity. The results showed that the resistivity, chargeability and SP values had an important role in separating the dry and saturated sediments and defining the fault zone, determining the source of surface water seepage, classifying the depths of high, medium and low groundwater accumulation and flow and permeability. The IP depended highly on the water amount and shale content and it was interesting in groundwater exploration with resistivity and in differentiating between groundwater and clays. The SP assisted in delineating the surface water seepage and groundwater source and flow direction, and predicting the sediments permeability.