Water shortage and quality are major issues in many places, particularly arid and semi-arid regions such as Makkah Al-Mukarramah province, Saudi Arabia. The current work was conducted to examine the geochemical mechanisms influencing the chemistry of groundwater and assess groundwater resources through several water quality indices (WQIs), GIS methods, and the partial least squares regression model (PLSR). For that, 59 groundwater wells were tested for different physical and chemical parameters using conventional analytical procedures. The results showed that the average content of ions was as follows: Na+ > Ca2+ > Mg 2+ > K+ and Cl− > SO42− > HCO32− > NO3− > CO3−. Under the stress of evaporation and saltwater intrusion associated with the reverse ion exchange process, the predominant hydrochemical facies were Ca-HCO3, Na-Cl, mixed Ca-Mg-Cl-SO4, and Na-Ca-HCO3. The drinking water quality index (DWQI) has indicated that only 5% of the wells were categorized under good to excellent for drinking while the majority (95%) were poor to unsuitable for drinking, and required appropriate treatment. Furthermore, the irrigation water quality index (IWQI) has indicated that 45.5% of the wells were classified under high to severe restriction for agriculture, and can be utilized only for high salt tolerant plants. The majority (54.5%) were deemed moderate to no restriction for irrigation, with no toxicity concern for most plants. Agriculture indicators such as total dissolved solids (TDS), potential salinity (PS), sodium absorption ratio (SAR), and residual sodium carbonate (RSC) had mean values of 2572.30, 33.32, 4.84, and −21.14, respectively. However, the quality of the groundwater in the study area improves with increased rainfall and thus recharging the Quaternary aquifer. The PLSR models, which are based on physicochemical characteristics, have been shown to be the most efficient as alternative techniques for determining the six WQIs. For instance, the PLSR models of all IWQs had determination coefficients values of R2 ranging between 0.848 and 0.999 in the Cal., and between 0.848 and 0.999 in the Val. datasets, and had model accuracy varying from 0.824 to 0.999 in the Cal., and from 0.817 to 0.989 in the Val. datasets. In conclusion, the combination of physicochemical parameters, WQIs, and multivariate modeling with statistical analysis and GIS tools is a successful and adaptable methodology that provides a comprehensive picture of groundwater quality and governing mechanisms.

Abstract. This paper investigates the development of waterlogging in the cultivated and arable areas within typical dryland closed drainage basins (e.g. the Farafra and Baharia Oases), which are located in the Western Desert of Egypt. Multi-temporal remote sensing data of the Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper (ETM+) were collected and processed to detect the land cover changes; cultivations, and the extent of water ponds and seepage channels. The Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM) has been processed to delineate the catchment morphometrical parameters (i.e. drainage networks, catchment divides and surface areas of different basins) and to examine the spatial distribution of cultivated fields and their relation to the extracted drainage networks. The soil of these closed drainage basins is mainly shallow and lithic with high calcium carbonate content; therefore, the downward percolation of excess irrigation water is limited by the development of subsurface hardpan, which also saturates the upper layer of soil with water. The subsurface seepage from the newly cultivated areas in the Farafra Oasis has revealed the pattern of buried alluvial channels, which are waterlogged and outlined by the growth of diagnostic saline shrubs. Furthermore, the courses of these waterlogged channels are coinciding with their counterparts of the SRTM DEM, and the recent satellite images show that the surface playas in the downstream of these channels are partially occupied by water ponds. On the other hand, a large water pond has occupied the main playa and submerged the surrounding fields, as a large area has been cultivated within a relatively small closed drainage basin in the Baharia Oasis. The geomorphology of closed drainage basins has to be considered when planning for a new cultivation in dryland catchments to better control waterlogging hazards. The "drydrainage" concept can be implemented as the drainage and seepage water can be conveyed through the inactive alluvial channels into certain abandoned playas for evaporation.

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The Nubian Sandstone Aquifer (NSSA) is the main groundwater resource of the El-Bahariya Oasis, which is located in the middle of the Western Desert of Egypt. This aquifer is composed mainly of continental clastic sediments of sandstone with shale and clay intercalations of saturated thickness ranging between 100 and 1500 m. Vulnerability assessment to delineate areas that are more susceptible to contamination from anthropogenic sources has become an important element for sustainable resources management and land use planning. Accordingly, this research aims to estimate the vulnerability of NSSA by applying the DRASTIC model as well as utilising sensitivity analyses to evaluate the relative importance of the model parameters for aquifer vulnerability in the study area. The main objective is to demonstrate the combined use of the DRASTIC and the GIS techniques as an effective method for groundwater pollution risk assessment, and mapping the areas that are prone to deterioration of groundwater quality and quantity. Based on DRASTIC index (DI) values, a groundwater vulnerability map was produced using the GIS. The aquifer analysis in the study area highlighted the following key points: the northeastern and western parts of the NSSA were dominated by 'High' vulnerability classes while the northwestern and southeastern parts were characterised by 'Medium' vulnerability classes. The elevated central part of the study area displayed 'Low' aquifer vulnerability. The vulnerability map shows a relatively greater risk imposed on the northeastern part of the NSSA due to the larger pollution potential of intensive vegetable cultivation. Depth-to-water, topography and hydraulic conductivity parameters were found to be more effective in assessing aquifer vulnerability.