The study area is a part of the Arabian Shield rocks of west central part of Saudi Arabia (150 km to the northeast of Jeddah). Geologically, the study area comprises five main geologic units i.e. 1) Layered basic volcanics and related volcaniclastics which are composed mainly from intercalated basalts and andesites and the related volcaniclastic derivatives, 2) Acidic volcanics and related volcaniclastics which are composed from layered and laminated dark and light acidic to intermediate igneous rocks, quartz and chert and marbles, 3) The Tertiary sedimentary succession which of volcaniclastic red beds and the intercalated clays; 5) Tertiary volcanics of Harrart, and 4) The Quaternary wadi fill deposits which are composed from friable pebble supported conglomerates, sandstones and clays. Hydrogeologically, the groundwater aquifer of Wadi Qudaid is present mainly in two main horizons i.e. i) unconfined shallow aquifer (13 - 37 m) within the well porous and permeable conglomerates of the Quaternary Wadi deposits, ii) The deep confined aquifer of the bedded tuffaceous sandstones and mudstone of the Tertiary sedimentary succession of Ash Shumaysi Formation. The water samples are analyzed for major elements i.e. Ca, Mg, Na, Cl, SO 4, HCO 3 and the results show the normal content of these elements. The study related the addition and depletion of many elements during the running trip of the groundwater from the northeast (recharge area) to the southwest (downstream) area.
The study area lies within the western province of Saudi Arabia between latitudes 20˚54'00'' and 21˚57'23''N and longitudes 39˚1709'' and 40˚00'57''E (
The climatic conditions all over the study area may play an important role in defining the hydraulic response of the watersheds and groundwater quality existing in the region. Generally, the climate is typically arid and the rainfall is irregular and has torrential nature. The rainfall occurs during winter season, while in the autumn and spring the area is subjected to isolated events. The average annual rainfall is about 60 mm in the lowland areas. Where, moving towards the eastern direction the rainfall increases to more than 170 mm/year. Such variation in the rainfall amount can be attributed to the orographic effects of the Red Sea escarpment. Rainfall distribution over the study area was characterized in time and space. Data from the five rainfall gauges were used to establish the rainfall distribution.
The variation of rainfall in the spatial dimension reflects the topographic effects, since the highest values were recorded at the highest stations. The average monthly rainfall was computed in order to give an approximate idea of the seasonal variation in the local rainfall patterns. All effective rainfall is concentrated between November and April (with very minor exceptions in early May). Wadi Qudaid lies within the Arabian Shield rocks of the western area of Saudi Arabia. The following discussion on geology aspect will be based on the previous works available and the field observations.
Wadi Qudaid area is located N to NE of Jeddah City (about 150 km) along Al Madinah asphaltic road (
(
Several earlier studies (e.g. [
The present study aims to shed light on the general geology and hydrogeology of Wadi Qudaid Area. The study also aims to clarify the integration between the geologic parameters and the variation in the hydrochemistry of the groundwater.
The study is based mainly up on the following methods of studies: 1) Detailed field work including the preparation of the geologic maps and satellite images of the study area; 2) Hydrogeologic field works including the location of the water samples, collection of the groundwater samples; 3) Geological field work including the field description of the different rock units, the sampling of the rock units, measuring stratigraphic sections and the strike and dip of the bedded strata; 4) Lab works including preparation of the water samples for chemical analyses, the megascopic description of the rock samples, selection of the samples for thin section preparation, description and photocopying of the prepared thin sections and finally 5) Office works including the description and interpretation of the different results, their integration and writing of the manuscript.
13 water samples have been collected from wells scattered all over the study area, all samples have been fully analyzed for Major constituents. The Major constituents are: Ca2+, Mg2+, Na+, K+, HCO3−, CO 3 2 − , SO 4 2 − and Cl−. Beside the determination of pH, E.C., T.D.S and T. Hard., The results are shown in
The study area is a part of the Arabian shield of the west control Saudi Arabia. Generally, the study area comprises four main rock units (
succession of volcaniclastic red beds and the intercalated clays (
conglomerates, sandstones and clays (
The Quaternary deposits (groundwater aquifer) are mainly present with the main Wadi and its tributaries. Most of the private farms and drilled water well are within the fine loamy yellowish while clays (flood plain lakes) of the different sheet flood periods (
In some sections, the succession becomes bedded of well observed coarse clast-supported conglomerates and fine laminated siltstone and sandstone horizons. This succession is typically representing alluvial fan section of fining-upward cycles. The fine laminated horizon also contains sporadically distributed pebbles.
EC ms/cm | PH | Alkalinity | Cl− | HCO 3 − | CO 3 − | SO 4 2 − | K+ | Na+ | Mg2+ | Ca2+ | Water depth/m | Depth to water/m | Longitude | Latitude | Sample No. |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
2.4 | 7.77 | 275.22 | 470.4 | 335.5 | 0 | 112.87 | 1.4 | 310 | 53.504 | 88.176 | 32 | 19.8 | 39.3264 | 22.3484 | 1 |
5.72 | 8.04 | 975.78 | 1402.25 | 1189 | 0 | 179.63 | 12.64 | 540 | 169.27 | 304.608 | 27 | 17.5 | 39.32889 | 22.3496 | 2 |
2.38 | 8.04 | 320.26 | 337.3 | 390 | 0 | 108.55 | 2.19 | 300 | 38.912 | 56.112 | 20 | 14 | 39.33438 | 22.3632 | 3 |
4.73 | 7.8 | 237.69 | 461.5 | 289.75 | 0 | 1112.4 | 2.8 | 505 | 121.6 | 264.528 | 25 | 13.4 | 39.32265 | 22.3568 | 4 |
4.85 | 6.91 | 250.2 | 958 | 305 | 0 | 617 | 4.5 | 446 | 102.144 | 360.72 | 21 | 14.2 | 39.30653 | 22.3531 | 5 |
2.6 | 7.85 | 650.52 | 391 | 793 | 0 | 110 | 12.38 | 255.2 | 58.368 | 128.256 | 28 | 21.4 | 39.34372 | 22.2723 | 6 |
2.72 | 7.72 | 275.72 | 550.3 | 336.11 | 0 | 125.84 | 3.9 | 311 | 77.824 | 120.24 | 37 | 27 | 39.34602 | 22.3766 | 7 |
3.6 | 7.48 | 725.58 | 701.12 | 884.5 | 0 | 303 | 10.5 | 386 | 97.28 | 152.304 | 30.8 | 27.5 | 39.3547 | 22.3949 | 8 |
4.8 | 7.68 | 225.43 | 1411.124 | 274.8 | 0 | 504 | 7.3 | 520 | 170.24 | 280.56 | 32 | 21.8 | 39.34014 | 22.3706 | 9 |
1.3 | 7.56 | 125.6 | 177.677 | 153.12 | 0 | 101 | 3.4 | 180 | 29.135 | 56.192 | 31 | 24.8 | 39.36417 | 22.405 | 10 |
3.77 | 7.55 | 276.22 | 763.18 | 336.72 | 0 | 691 | 8.3 | 370 | 138.624 | 212.424 | 56 | 46 | 39.37632 | 22.412 | 11 |
3.39 | 7.92 | 240.44 | 621.23 | 293.105 | 0 | 442.5 | 7.6 | 420 | 107.008 | 168.336 | 62 | 36.5 | 39.387 | 22.4134 | 12 |
3.66 | 7.93 | 252.7 | 744.711 | 308.3 | 0 | 560 | 8.6 | 476 | 46.208 | 184.368 | 23 | 16.23 | 39.39456 | 22.415 | 13 |
From the sedimentologic points of views, the succession is of typical alluvial fan. The conglomerates of the successive fining-upward cycles are slightly disorganized which indicates its proximal position within the site of deposition and it also indicates rapid sedimentation.
Towards, the upper part of the succession, the section become finer and composed mainly from thick laminated fine sandstone/mudstone alternated with one clast thick thin beds (
The drainage lines of Wadi Qudaid area are shown in
The Quaternary deposits of the study area represent superimposed alluvial fan deposits formed during progressive humid climate periods. The lower and middle parts of these alluvial fan deposits are composed from clast- and matrix- supported conglomerates overlained by cross-bedded and cross-laminated sandstones and siltstones. The distal facies of the alluvial fans are composed from massive and bedded silts and clay deposits. During the different flooding periods, the deposited alluvial material become removed and reworked and redeposited in new areas which led to the desertification and destruction of the private farms of the different villages of Wadi Qudaid area.
The penetrated well of the study area are present in three main rock units: a) some wells are shallow and the bottom of the wells are within the Quaternary alluvial deposits. b) Most of the wells are penetrated within the Quaternary deposits and the underlying Tertiary red beds of Ash Shumaysi Formation. The microscopic description of the yellowish white staff extracted around the well walls revealed its composition from tuffaceous sandstone of angular to subrounded quartz grains embedded in chloritized tuffaceous materials hematitized in parts (
Some wells are penetrated within the hard and generally green metavolcanics of Samran Group. The field and microscopic description of the samples revealed its composition from metavolcanics, tuffs and volcanogenic massive sulphides in intermediate tuffs and andesitic tuffs (
The water samples are collected from the aforementioned wells (
The plotting of the data on variation diagrams revealed that: The Ca content of the different water samples (
The distribution of SO4 within the different water samples (
(
It is evident that, the pH distribution of the water samples (
The electro conductivity of the groundwater samples (
The plotting of Na against Cl also shows a positive relation (
The plotting of Ca against SO4 show somehow positive relation which support gypsum dissolution and releasing of Ca and SO4 (
The durov diagram show the dominant water type in Wadi Qudaid area in Na Cl type where the dominant cation is Na and the dominant anion is Cl (
The present study revealed that, the groundwater of W. Qudaid area is present in two main horizons: a) Quaternary alluvial gravels, conglomerates and sandstones, b) The Tertiary succession that composed from highly weathered basalts (harrat) and the underlying red ferruginous sandstones and clays of Usfan and Khulays formations. The recharge area of Wadi Qudaid is represented by the high mountainous Arabian shield rocks of the north and northeastern part of Wadi Qudaid.
The Quaternary groundwater aquifer of Wadi Qudaid area is represented by the wadi deposits of the main course and the tributaries of the wadi. These deposits are composed from successive fining-upward cycle of clast-and matrix-supported conglomerates, pebbly sandstones, siltstones and flood plain clays and represent successive alluvial fan sedimentation during the humid and arid periods. The low lands of Wadi Qudaid area represent downthrown faulted blocks where the drilled wells begin by Quaternary wadi deposit, black basalts, clastic sedimentary rocks and finally layered igneous rocks at the base of the wells. The groundwater bearing horizons varied according to the level of erosion and denudation processes where some water wells produce from the Quaternary deposits while other produce from the clastic sedimentary rocks and small number of wells produce from the layered igneous rocks. The present study revealed the presence of very clear relationship between the geology of the study area and the chemistry of the ground waters. The ground water quality appears very good and normal level for irrigation purposes.
Wadi Qudaid area represents one of the main NE trending wadies in the west central part of Saudi Arabia. It represents a good exposure site for the different rock units of this part of the Arabian shield. The Precambrian rocks of the study area are represented by layered slightly metamorphosed basic and acidic volcanics and the intercalated volcaniclastics. The Tertiary sedimentary is succession of Khulays and Usfan formations rest unconformably on the denudated Precambrian rocks and are composed from bedded mudstones and sandstones. The Tertiary rift-related volcanics are present as a horizontal sheet capping the Tertiary sedimentary succession. The floor of Wadi Qudaid is now occupied by many small villages surrounded by green cultivated private farms. The water supply of the human populations is comping from many wells of the Saudi ministry of agriculture as well as on private wells. Most of the wells are recharged from the loose Quaternary wadi fill (gravels and sandstones). Some wells are deep and recharged from the Tertiary sedimentary succession. During the stormy periods, the private farms in the central part of the wadi become destructed and subjected to abrupt removal as a result of the lateral migration of sheet flood water. The present study confirms normal major and trace elements content of the groundwater of the study area and also the major and trace elements become of low level towards the NE (recharge upstream) part of Wadi Qudaid.
The project was funded by the Deanship of Scientific research (DSR), King Abdulaziz University, Jeddah, under grant No. 351/145/1433. The authors, therefore, acknowledge with thanks DSR technical and financial support.
Sonbul, A.R., Sharaf, M.A. and Mesaed, A.A. (2017) Hydrogeology of Wadi Qudaid Area, Northeast Jeddah, West Central Arabian Shield, Saudi Arabia. Open Journal of Geology, 7, 1749-1766. https://doi.org/10.4236/ojg.2017.712117