Hydrochemical classification and multivariate statistical analysis of groundwater from Wadi Sahba area in central Saudi Arabia

The central region of Saudi Arabia is underlain by thick sedimentary formations belonging to the Mesozoic and Cenozoic era. These sedimentary formations form a prolific aquifer supplying groundwater for agricultural and domestic usage in and around Riyadh. The region south of Riyadh City is well known for agricultural activities. Wadi Sahba, which is an eastward extension of Wadi Nisah, has readily available groundwater resources in the Cretaceous Biyadh sandstone aquifer to sustain agricultural activities. The objective of the present study was the hydrochemical assessment of groundwater in the area to understand the main hydrological processes which influence groundwater chemistry. To achieve this objective, 20 groundwater samples were collected from agricultural farms in the Wadi Sahba in central Saudi Arabia, and the major physiochemical constituents were analyzed and interpreted. The average TDS value of the analyzed samples is 1578.05 mg/l, whereas the average EC concentration is 3220.05 μS/cm. Groundwater facies classification inferred from the Piper plot shows that groundwater in the study area belongs to the Ca-SO₄-Cl type and Ca-Na-SO₄-Cl type. The Ca-SO₄-Cl type of groundwater facies is influenced mainly by gypsum dissolution and base ion exchange, whereas the Ca-Na-SO₄-Cl type is influenced by gypsum and halite dissolution. All the groundwater samples are undersaturated with respect to these two principal mineral phases. The Q-mode cluster analysis results in two main groups of groundwater samples, mainly based on the TDS content. Cluster 1 has an average TDS value of 1980 mg/l, whereas cluster 2 has an average TDS of 1176 mg/l. The groundwater facies identified through the Piper plot reflects the major hydrological processes controlling groundwater chemistry in the area and was found to be more useful in this study as compared to cluster analysis.     

Using multivariate statistical analyses to evaluate groundwater contamination in the northwestern part of Saudi Arabia

Chemical characteristics of groundwater in the Midyan Basin (northwestern Saudi Arabia) were investigated and evaluated. A total of 72 water samples were collected from existing shallow wells and analyzed for different elements. Two multivariate statistical methods, hierarchical cluster analysis (HCA) and principal components analysis (PCA), were applied to a subgroup of the data set in terms of their usefulness for groundwater classification, and to identify the processes controlling groundwater geochemistry. The subgroup consisted of 46 water samples out of 72 samples and 24 variables included major elements (Ca²⁺, Na⁺, Mg²⁺, K⁺, Cl^?, HCO₃ ^?, NO₃ ^?, SO₄ ^2?), minor and trace element (SiO₂, Al, As, B, Ba, Cd, Cr, F, Fe, Mo, P, Pb, Sb, Sn, Ti, and V). For water samples, four geochemically distinct clusters (i.e., C1, C2, C3 and C4) have been observed by hierarchical cluster analysis. Cr, F and Pb are the dominant ions in cluster C2. Al, As, Cd, Mo, Sb and Ti are the dominant ions in cluster C3, while B, Ca, Cl, HCO₃, K, Mg, Na, SO₄ and V are identified as dominant ions in the cluster C4. In the PCA, a total of five components are extracted form the data set, which explained 73.37 % of the total data variability. Among them the first component reveals strong associations between As, B, Cd, Cr, F, Mo, Pb, Sb and Ti. The second component reveals the associations between Ca, Cl, HCO₃, Mg, Na, SO₄ and V.     

Hydrogeology and hydrochemistry of a shallow alluvial aquifer,western Saudi Arabia

A hydrogeological and hydrochemical study was conducted on a shallow alluvial aquifer, Wadi Wajj, in western Saudi Arabia to assess the influence of protection measures on groundwater quality. The hydrochemistry was assessed up-gradient and down-gradient from potential contamination sources in the main city in dry and wet seasons prior to and after the installation of major drainage and wastewater facilities. Wadi Wajj is an unconfined aquifer where water is stored and transmitted through fractured and weathered bedrock and the overlying alluvial sediments. Natural recharge to the aquifer is about 5% of rainfall-runoff. Hydrochemistry of the aquifer shows temporal and seasonal changes as influenced by protection measures and rainfall runoff. Both groundwater and runoff showed similar chemical signature, which is mostly of chloride-sulfate-bicarbonate and sodium-calcium type. Groundwater downstream of the city, though of poorer quality than upstream, showed significant improvement after the installation of a concrete runoff tunnel and a wastewater treatment plant. Concentrations of many of the groundwater quality indicators (e.g., TDS, coliform bacteria, and nitrate) exceed US Environmental Protection Agency drinking-water standards. Heavy metal content is, however, within allowable limits by local and international standards. The chemical analyses also suggest the strong influence of stream runoff and sewage water on the groundwater quality.

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Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.

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Résumé Une étude hydrogéologique et géochimique a été menée sur l’aquifère phréatique alluviale Wadi Wajj dans l’Ouest de l’Arabie Saoudite afin d’évaluer l’influence de mesures de protection sur la qualité de l’eau souterraine. L’hydrogéochimie de l’eau a été étudiée en amont et en aval de sources potentielles de contamination dans la ville principale, pendant les saisons sèches et humides, avant et après l’installation de réseaux majeurs de drainage et d’eaux usées. L’aquifère Wadi Wajj est libre, l’eau est stockée et s’écoule dans les sédiments alluviaux et dans le socle fracturé et altéré sous-jacent. La recharge naturelle de l’aquifère représente 5% des eaux de pluie et de ruissellement. L’hydrogéochimie de l’eau de l’aquifère montre que les changements saisonniers et temporaires sont influencés par les mesures de protection et par le ruissellement des eaux pluviales. L’eau souterraine et l’eau de ruissellement ont présenté le même faciès chimique, de type bicarbonatée-sulfatée-chlorée et calco-sodique. En aval de la ville, l’eau souterraine, bien que de moins bonne qualité qu’en amont, a présenté une nette amélioration après l’installation d’un système de récupération et d’une station de traitement des eaux usées. Les concentrations de plusieurs paramètres indicateurs de la qualité de l’eau (tels que la charge totale dissoute, les coliformes, et les nitrates) dépassent les normes de potabilité de l’eau de consommation de l’agence américaine de la protection de l’environnement. Les teneurs en métaux lourds en revanche n’excèdent pas les normes locales et internationales. Les analyses chimiques indiquent aussi l’influence importante de l’écoulement par ruissellement et des eaux usées sur la qualité de l’eau souterraine.

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Resumen Un estudio hidrogeológico e hidroquímico fue hecho en un acuífero somero de Wadi Wajj, en Arabia Saudi oeste para evaluar la influecia de medidas de protección en la calidad del agua subterránea. La hidroquímica fue evaluada gradiente-arriba y gradiente-abajo de las fuentes potenciales de contaminación de la ciudad principal durante las estaciones seca y lluviosa, antes y después de la instalación de sistemas principales de drenaje y aguas servidas. Wadi Wajj es un acuífero no-confinado donde el agua es almacenada y transmitida a través de roca fracturada y meteorizada, y los sedimentos aluviales que le sobreyacen. La recarga natural del acuífero es de cerca del 5% de la precipitación-escorrentía. La hidroquímica del acuífero muestra cambios temporales y estacionales influenciados por las medidas de protección y la escorrentía de precipitación. Ambas, agua subterránea y escorrentía mostraron composición química similar, siendo mayoritariamente de tipos cloruro-sulfato-bicarbonato y sodio-calcio. El agua subterránea aguas arriba de la ciudad, aunque de calidad más pobre que aguas abajo, mostró significante mejoría después de la instalación de un tunel de concreto para escorrentía y una planta de tratamiento de aguas servidas. Las concentraciones de muchos de los indicadores de calidad de agua subterránea (e.g., STD, coliformes, y nitrato) exceden los estándares de la Agencia de Protección Ambiental USA para agua potable. El contenido de metales pesados está, sin embargo, dentro de los límites permisibles de los estándares locales e internacionales. Los análisis químicos también sugieren la fuerte influencia de la escorrentía y aguas residuales en la calidad del agua subterránea.

     

Aeromagnetic data over Harrat Lunayyir and surrounding areas,western Saudi Arabia

Harrat Lunayyir is one of the smaller lava fields in western Saudi Arabia that is of current interest due to a dike intrusion episode in 2009, an ongoing swarm of earthquakes and the possible hazard that pose. In addition to seismology, other geophysical data have been used to study the structure of the area, and the available aeromagnetic information is shown and discussed here. The reduced to the pole (RTP) magnetic grid and its enhancements have been used to define some of the main anomalies, and these have been correlated with the known geology, including the Red Sea coastal dike system. There are numerous linear features that are possibly related to the dikes or faulting, but within the area of the harrat, details due to the underlying structure are largely obscured by the magnetic surface lavas. Northeasterly trends in the magnetic data may indicate old zones of weakness that intersect one of the main coastal dikes at the location of the recent seismic activity and surface fissure, suggesting that this is a point of weakness resulting in the volcanism and seismicity that also appears to be largely limited to two of the NE trends. The association of the recent seismicity with a known geological and aeromagnetic feature is important in determining the seismic hazard for the region, especially if the location of future activity can be used to reduce overall uncertainty in the analysis by identifying potential fault sources. Here, the seismicity appears to lie on one of the NNW-trending coastal dikes that have been reactivated recently along a section between two NE-trending older faults.     

Geohazard assessment of sand dunes between Jeddah and Al-Lith, western Saudi Arabia

Serious hazards have taken place in urban areas and road construction in Saudi Arabia because of the presence of accumulations of drifting sand dunes. Several researches, which carried out investigative work to solve this problem, were reviewed. Three locations of dune fields along the area between Jeddah and Al-Lith were investigated. The dune forms was identified. Detailed field investigations showed that barchan dunes are dominant in the area. The sands from the studied locations were found to be similar in grain size and shape parameters. Mineralogically, the sand reflects the composition of the surrounding igneous and metamorphic rocks. Regression analyses were performed and empirical relationships between dune height, width, windward length, slip-face length, and rate of movements were developed. Relatively strong relations exist between these parameters. The most important geometric parameter controlling dune movement with wind speed and direction is determined to be the dune height. A reasonable similarity occurs between the barchan dunes in the study area and those existing in Al Nufud, Al Jafurah sand seas, and Khulays area. The studied dune fields pose some natural hazards on the roads, and the surrounding buildings and constructions in the villages along the area between Jeddah and Al-Lith, especially during wind storms.     

Evaluation of the water resources potential at Dahaban region, western Saudi Arabia

Shallow renewable groundwater sources have been used to satisfy the domestic needs and the irrigation in many parts of Saudi Arabia. Increased demand for water resulting from accelerated development activities has placed excess stress on the renewable sources especially in coastal aquifers of the western region of Saudi Arabia. It is expected that the current and future development activities will increase the rate of groundwater mining of the coastal aquifer near the major city Jeddah and surrounding communities unless management measures are implemented. The current groundwater development of Dahaban coastal aquifer located at alluvial fan at the confluence of three major Wadis is depleting the shallow renewable groundwater sources and causes deterioration of its quality. Numerical models are known tools to evaluate groundwater management scenarios under a variety of development options under different hydrogeological regimes. In this study, two models are applied—the MODFLOW for evaluating the hydrodynamic behaviors of the aquifer and MT3D salinity distribution to the costal aquifer near Dahaban town. The models’ simulation evaluates two development scenarios—the impact of excessive abstraction and the water salinity variation keeping abstraction at its current or increases in levels with or without groundwater recharge taking place. The simulation evaluated two scenarios covering a 25-year period—keeping the current abstraction at its current and the other scenario is increasing the well abstraction by 50% for dry condition (no recharge) and wet condition (with recharge). The analysis reveals that, under the first scenario, the continuation of the current pumping rates will result in depletion of the aquifer resulting in drying of many wells and quality deterioration at the level of 2,500 ppm. The results are associated with the corresponding salinity distribution in the region. Simulation of salinity in the region is a density-independent problem as salt concentration does not exceed 2,000 ppm, which is little value compared with sea salinity that amounts to 40,000 ppm. It is not recommended to increase the pumping rate than the current values. However, for the purpose of increasing water resources in the region, it is recommended to install new wells in virgin zones west of Dahaban main road. Maps of high/low potential groundwater and maps of salinity zones (more or less than 1,000 ppm) are provided and could be used to identify zones of high groundwater potential for the four studied scenarios. The implemented numerical simulation of Dahaban aquifer was undertaken to assess the water resources potential in order to reduce the depletion of sources in the future.     

Overview of some geological hazards in the Saudi Arabia

The Saudi Arabia has harsh environmental conditions which enhance some geomorphologic/geological processes more than in other areas. These processes create different geological hazards. The general physiography of the Saudi Arabia is characterized by the Red Sea coastal plains and the escarpment foothills called Tihama, followed by the Arabian Shield Mountains, the Arabian Shelf plateau and finally the Arabian Gulf coastal plains. These types of geological hazards can be categorized into sand accumulations, earth subsidence and fissures, flash floods, problematic soils, slope stability problems, and karst problems. The current study gives an overview of all these hazards with examples, as well as develops a geo-hazard map for the Saudi Arabia. Our findings indicate that the desert environment needs much concern and care. National and international agencies have to join together with other people to keep the system balanced and to reduce the resulting geological hazards. Also, remedial measures should be proposed to avoid and reduce these natural hazards.     

An empirical assessment and illustration of some multivariate morphometric techniques

An artificial data set is used to illustrate the morphologic properties of some common multivariate techniques and consideration of three common situations. The first concerns a sample showing no obvious groupings. In this situation principal components (or coordinates) and factor analyses give a logical ordination of form variation; cluster analysis produces sizedominated groups. The second situation considers an homogeneous sample where size and shape have important implications. Principal components are tested for association with size and shape, both of which can be isolated if isometry exists; if allometry is present, isolation of shape is possible only by size elimination, e.g., conversion to ratios. The third situation examines a sample of unknown groupings in which shape variation is the only interest. Aside from ratios, two other methods which produce shape-dominant clusters are assessed. Some of the options available in cluster analysis are also examined.     

Seismic risk analysis of western Arabia

Based on the seismicity and tectonics of the western part of the Arabian Peninsula, a set of potential earthquake sources are identified and the relationships between magnitude and frequency of occurrence are determined. Using available attenuation laws,the individual influences of potential sources are integrated into the probability distribution of maximum annual intensity and peak ground acceleration.The results are presented in the form of seismic risk maps for various return periods, cumulative distribution functions and intensity zone graphs. Based on the results of this study, it is concluded that the seismic hazard potential for the central region is moderate but it is high for the northern and southern provinces.     

The statistical analysis of the sand grain size distribution of Al- Ubay-lah barchan dunes,Northwestern Ar-Rub-Alkhali desert,Saudi Arabia

The paper analyses the statistical parameters of the sand grain size distribution of Al-Ubaylah barchan dunes applying the sieving technique and Folk and Ward, and Trask's equation. The results of the sieving analysis divulged that nearly over 90% of the sand particles fall in the size ranging between 1.50ø and 3.ø. Insignificant amount of sand grains also fall in the size ranging from 0.0ø to 1.50ø and from 3.0ø to 4.0ø respectively. The statistical analysis reveals that the sand is characteristically fine grained, moderately to moderately well sorted with an average diameter of 2.4ø and a standard deviation of 0.64ø. The sand distribution is positively fine skewed and mesokurtic to leptokurtic in nature. No significant variation in the statistical parameters (median, mean, sorting, skewness and kurtosis) of the sand grains samples used in this research is detected. The sand grain size distribution of all the samples can also be considered symmetrical and unimodal in nature. Those abovementioned characteristics are found to be nearly similar to that of other Saudi dune deserts. The miscroscopic investigation undertaken by this researcher displays that quartz represents often more than 99% of the samples. Felsic, mafic and calcium carbonates minerals represent less than 1% of the mineralogical constituents. The sand grains are subrounded to subangular and iron and calcium carbonates coated.     

Geographic analysis of manufacturing industry in Saudi Arabia

The study focuses on the analysis of manufacturing industry in Saudi Arabia by examining development, structure and spatial distribution. The analysis has shown that Saudi manufacturing is basically of recent development and is highly capital- and energy-intensive, particularly the hydrocarbon-based groups. Perhaps the most conspicuous weakness of Saudi industrialization is the almost total dependence on expatriate labour. Foreign capital and expertise share in the building and development of the industrial sector by providing technical, managerial, and marketing skills. Saudi industry is heavily subsidized by the government, and the public sector plays a commanding role in industrial development. Large-scale basic industries are owned and run by the government, while light manufacturing of the import-substitution type is dominated by the private sector. One of the main characteristics of manufacturing industry is that it is scantily diversified, modestly concentrated and remarkably linked geographically but not functionally or structurally. Although the authorities are exerting tremendous efforts to achieve a regional balance in industrial development, Saudi manufacturing industry is significantly polarized, urban-oriented and highly associated with the major axes of population scatter. Like all developing countries beginning to industrialize, Saudi manufacturing industry faces certain problems which have to be resolved so as to lay the foundations for a sound and prosperous industrial future. The paper goes on to indicate problems and to suggest solutions.     

Hydrologic behavior and flood probability for selected arid basins in Makkah area, western Saudi Arabia

In arid regions, flash floods often occur as a consequence of excessive rainfall. Occasionally causing major loss of property and life, floods are large events of relatively short duration. Makkah area in western Saudi Arabia is characterized by high rainfall intensity that leads to flash floods. This study quantifies the hydrological characteristics and flood probability of some major wadis in western Saudi Arabia, including Na’man, Fatimah, and Usfan. Flood responses in these wadis vary due to the nature and rainfall distribution within these wadis. Rainfall frequency analysis was performed using selected annual maximums of 24-h rainfall from eight stations located in the area. Two of the most applied methods of statistical distribution, Gumbel’s extreme value distribution and log Pearson type III distribution, were applied to maximum daily rainfall data over 26 to 40 years. The Gumbel’s model was found to be the best fitting model for identifying and predicting future rainfall occurrence. Rainfall estimations from different return periods were identified. Probable maximum floods of the major wadis studied were also estimated for different return periods, which were extrapolated from the probable maximum precipitation.     

Hydrogeology of Al-Lith Sabkha,Saudi Arabia

In Saudi Arabia, coastal sabkhas cover extensive areas along the coasts of the Red Sea and Arabian Gulf in addition to the continental sabkhas scattered in many places inland. Al-Lith sabkha is one of the typical coastal sabkhas located along the Red Sea coast. Sabkhas, in general, pose a number of geotechnical problems and need to be carefully investigated before being urbanized.A generalized geologic section in Al-Lith sabkha indicates a salty crust at the surface followed by yellowish brown silt and silty sand, olive gray silt and sandy silt and bottomed by coralline reefal limestone. Within this succession, there are several isolated lenticular bodies of sandy silt, silty sand and shelly silty sand. The clay minerals constituting the fine-grained portion of the soil are, in decreasing order, kaolinite, illite and montmorillonite in addition to minor chlorite.The depth to groundwater in 17 observation wells ranged from 0.18 to 1.81 m with a maximum fluctuation of 0.60 m between summer and winter. The permeability of the top silt layer was found to be very low with an average of 5.4×10⁻⁴ m/day. A pumping test was performed in a deep well penetrating the coralline limestone. The measured permeability is 1.1×10² m/day and the estimated storage coefficient is 4×10⁻⁵.Soil water evaporation was measured using a lysimeter constructed with undisturbed soil samples having different depths to the water level. The rate of evaporation ranges from 2.8 to 27.8 ml/day decreasing with an increase in depth to the water level.Groundwater samples were analyzed for their major anions and cations. Salt concentrations show a general increase toward the sea except for the calcium and carbonates that show a landward increase. The groundwater could be classified as a Cl+SO₄ brine. The salinity of the groundwater was determined at different depths in the pumping well and was found to be low in the top 4 m. It sharply increases until it reaches a value approximately 10 times the salinity of the top layer indicating groundwater intermixing with freshwater and salt-water intrusion. The change in the salinity during pumping was erratic but within a range of 2%.     

Segregation and seclusion: the case of compounds for western expatriates in Saudi Arabia

In discussions on the “fragmented city” and the boom of private and guarded neighbourhoods, several authors have stressed the importance of a growing differentiation of lifestyles and “cultural” orientations for this trend. The compounds for western foreigners in Saudi Arabia are explicitly based on the idea of a spatial seclusion of social groups with different “cultural” backgrounds. This study presents an overview of the development of these western enclaves. Narrative interviews with former expatriates provide insights into their daily life, their social relations within the compound, and to the Saudi Arabia behind the gates.     

Estimation of source parameters and attenuation using digital waveforms of Al-Ays 2009 earthquake,Saudi Arabia

On 19 May 2009, an earthquake sequence of M _w?=?4.8 occurred at 25.20°N 37.76°E about 60 km onshore of the Red Sea coastline, Saudi Arabia. In the present study, the digital waveform data from the largest four events were used to estimate the source parameters and attenuation characteristics along the source-to-station path in the Arabian Shield. A grid search technique, combined with an assumption of circular source model, was applied to find the best-fit spectral amplitude over the space parameters: long period spectral level (Ω ₀), corner frequency (f ₀) and asymptotic high-frequency fall-off (γ). Consequently, the spectral parameters were used to estimate source parameters: seismic moment, fault radius (assumed circular rupture model) and stress drop. Seismic moments are founded to be within the range of 2.34E+14 to 2.83E+16 Nm and their corresponding moment magnitudes range from 3.5 to 4.8; the fault radius ranges from 369 to 1,498 m, and stress drops are observed in the range of 8.7 to 32.0 b. The spectral slopes beyond the corner frequency displayed ω ^?2.4 to ω ^?2.6 behaviours in contrast with Brune's source model of ω ^?2. This finding requires more detailed investigations on large data sets to distinguish the behaviour mechanism of the spectral slopes at high frequencies. By taking the ratio between observed and calculated spectra, the attenuation curves for P and S waves were derived along the source-to-station paths. The preliminarily results exhibited high quality factors of Q _α?=?3,883 and Q _β?=?3,530 for P and S waves, respectively. To this end, the ratio Q _β/Q _α is founded to be slightly less than unity indicating that the body waves from source-to-station paths crossed a crustal volume that is partially saturated with fluids causing lower attenuation effect on P waves than on S waves in the Arabian Shield.     

Interpretation of a seismic-refraction survey across the Arabian shield in western Saudi Arabia

In February 1978 seismic-refraction profiles were recorded by the U.S. Geological Survey along a 1000 km line across the Arabian Shield in western Saudi Arabia. This report presents a traveltime and relative amplitude study in the form of velocity-depth functions for each individual profile assuming horizontally flat layering. The corresponding cross section of the lithosphere showing lines of equal velocity reaches to a depth of 60–80 km.The crust thickens abruptly from 15 km beneath the Red Sea Rift to about 40 km beneath the Arabian Shield. The upper crust of the western Arabian Shield yields relatively high-velocity material at about 10 km depth underlain by velocity inversions, while the upper crust of the eastern Shield is relatively uniform. The lower crust with a velocity of about 7 km/s is underlain by a transitional crust-mantle boundary. For the lower lithosphere beneath 40 km depth the data indicate the existence of a laterally discontinuous lamellar structure where high-velocity zones are intermixed with zones of lower velocities. Beneath the crust-mantle boundary of the Red Sea rift most probably strong velocity inversions exist. Here, the data do not allow a detailed modelling, velocities as low as 6.0 km/s seem to be encountered between 25 and 44 km depth.