ORIGINAL PAPER

Hydrogeophysical investigation of groundwater potentialin the El Bawiti, Northern Bahariya Oasis, Western Desert,Egypt

Mohamed El Kashouty & Aiman Abdel Aziz &Mamdouh Soliman & Hany Mesbah

Received: 3 June 2010 /Accepted: 30 November 2010 /Published online: 4 January 2011# Saudi Society for Geosciences 2010

Abstract The future development of agriculture, industry,and civil activity planned to be in the Western Desert. Thisstrategy need to the groundwater resource. Vertical electri-cal soundings (VES) and electromagnetic (TEM) measure-ments conducted in the El Bawiti, northern Bahariya Oasis.The measurements give detailed information about thegeometry of the different hydrogeological layers in theaquifer system and depth to them. A total of 22 VES andTEM were carried out within El Bawiti area. Thirty-one subsoil samples were collected from eight sites to determinethe chemical characteristics and address the effects oflithogenic source and anthropogenic activity on them. Thegeoelectrical measurements and borehole information indi-cate the presence of five geoelectrical units, from top tobase; the surface cover, sand and shale, upper aquifer(Nubian sandstone), sand and shale, and lower aquifer(Nubian sandstone). Surface cover was equally distributedin thickness and composed of dry sand, gravel, and claydeposits. The regional resistivity of the upper aquiferincreased in the southwestern part and decline in thenorthern, eastern, southern, and western parts. The declinein the resistivity reflects the high water yields andpotentiality, as well as low salinity. The resistivity of thelower aquifer increased due the northwestern part and thesouthwestern part. The information collected during this

research provides valuable data for estimating the fresh- tobrackish-water resources and for development of a ground-water management plan. The integrated analyses carried outrepresent a significant and cost-effective method fordelineating the main aquifer in this area. In turn, futurewell locations can be placed with more confidence thanbefore, in accordance with the evaluation of the potentialityof the groundwater aquifers in the area. The electricalconductivity of the soil ranges from 302 to 8,490 S/cm,increases in the western and central-northern parts. It isattributed to the location from the salt-affected soils (playa),the relatively lower elevation units (depressions) and theposition in landscape in the Oasis. Sodium adsorption ratioranges from 0.44 to 11 and the exchangeable sodium ratioranges from 0.11 to 5. The estimated magnesium hazardfluctuated below 50%. The statistical analyses wereaccomplished in soil chemistry and discussed.

Keywords Geophysical methods . Groundwaterexploration . Soil salinity . Nubian sandstone . Agriculture

Introduction

The Bahariya Oasis occurs in the heart of the WesternDesert at a distance of about 370 km to the southwest ofCairo. It lies between latitudes 28o 00 and 28o 50 N andlongitudes 28o 20 and 29o 10 E (Fig. 1). The Bahariyadepression comprises a total area of approximately2,250 km2 and is one of the five large oases in the WesternDesert. The area falls under the arid condition as the totalrainfall ranges from 3 to 6 mm/year. Springs and wells arethe main two-groundwater resources for irrigation and civicpurposes (Salem 1987). Egypt is facing greatly increasing

M. El Kashouty (*)Faculty of Science, Geology Department, Cairo University,Giza, Egypte-mail: mohamedkashouty@yahoo.com

A. A. Aziz :M. Soliman :H. MesbahNational Research Institute of Astronomy and Geophysics,Helwan,Cairo, Egypt

Arab J Geosci (2012) 5:953970DOI 10.1007/s12517-010-0253-8

demands for water due to a rapidly growing population.Surface water resources originating from the Nile are nowfully exploited (Hvidt 1999). Great attention is now focusedon groundwater extraction from the desert. Recently, therehas been a development program of progressive reclama-tion and urbanization of the desert including the investigat-ed northern Bahariya Oasis (El Bawiti). In some localities,the drilling program continued without taking the aquifergeometry and potential yields into consideration. Measuredelectrical data, in combination with some borehole geo-physical data and the lithological information from thedrilled wells, have been reinterpreted in the present work toreveal the subsurface geological and hydrological condi-

tions. Two geophysical methods used in this research wereelectrical and electromagnetic. The main objective was todetermine the aquifer configuration.

Soil salinity limits food production in many countries ofthe world. There are mainly two kinds of soil salinity:naturally occurring dry land salinity and human-inducedsalinity caused by the low quality of water. In both cases,the development of plants and soil organisms are limitedleading to low yields. In Bahariya Oasis, where more than10% of the land is affected by salt, groundwater andinadequate drainage conditions are the major causes ofsalinization. Generally, the classical soil survey methods offield sampling, laboratory analysis and interpolation of

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Fig. 1 Location map of the vertical electrical soundings (VES) and electromagnetic (TEM)

954 Arab J Geosci (2012) 5:953970

these field data for mapping, especially in large areas isrelatively expensive and time consuming. Conventionally(Soil and Plant Analysis Council 1992) soil salinity isdetermined by laboratory analysis (electrical conductivityof the saturated soil paste extract ECe). This procedure isexpensive and time consuming, and provides an incom-plete view of the extent of soil salinity. An alternative tolaboratory analysis is to assess soil salinity in the field bydetermining the apparent electrical conductivity (ECa).This can be done using sensors such as the four-electrodeprobes (Rhoades and van Schilfgaarde (1976)) or byelectromagnetic induction instruments (McNeil 1980).This procedure is cheaper and less time-consuming,enabling a more intensive survey of the study area. InBahariya, it is found that the main unsuitability criteriaeliminating more extend of cultivation areas is the excessof salts. The mapping of saline soils is the first task beforeany reclamation effort conducted and is important issue inprecision agriculture.

The geology

The stratigraphic setup from base to top is as follows (ElShazly et al. 1993): (1) Pre-Cambrian (basement complex)(1,8231,843 m below ground surface). It is composed ofmetamorphosed porphyritic andesites and metamorphoseddolerite. Granodiorite was injected in fissures in thedolerites. (2) Paleozoic (Cambrian) (1,3651,823 m belowthe ground surface). It is predominantly sandstone with clayintercalation in the upper 90 m and a clay bed between1,722 and 1,744 m. The sandstone consists of fine-grainedquartz with a siliceous, dolomites and micaceous matrix.(3) Mesozoic/and or Paleozoic (Lower Cretaceous or older)(7071,365 m). The upper 258 m consist of clay andsandstone. (4) The Cenomanian section (Lower-UpperCretaceous) is the presently exploitable aquifer system. Itconsists of fine to coarse-grained loose sand, alternate withthin clay. The intervals between 350 and 580 m arerepresented by fine-grained sandstone and grey green clay.The Cenomanian layer is the floor of the Bahariyadepression and is exposed along the pass of the surroundingescarpment. The total thickness of the Cenomanian includ-ed Al Heiz Fm. on top and Al Bahariya Fm. below, reachesabout 1,155 m. The stratigraphic setup of the Cenomaniansection is from base to top is as follows:

(1) El Bahariya Fm. is composed of sandstone andvariegated shale and is fluviomarine sediments. It repre-sents the floor of the depression. (2) El Hefhuf Fm. iscomposed of limestone and dolomite at the base and shaleand clay at the top. It is exposed at the southern part of thedepression (El Heiz village). (3) Chalk is exposed at thewestern part of the depression and extended to the Farafra

Oasis. (4) Chalky plateau is composed of numiliticlimestone of Middle Eocene. (5) Dolertic extrusion (thebasaltic rocks) distributed in the depression, e.g., at G.Missura, northern of G. El Hefhuf, western of G. Qala, andG. Aqouza. A new geologic map was constructed for theBahariya Oasis using aerial photographs (scale 1:40,000)(Khalifa et al. 2002) (Fig. 2). The boundaries of El HefhufFm. and the new introduced rock unit, Naqb Es Sillim Fm.were placed. The El Hefhuf Fm. was traced at G. Hammadand Tibnia for the first time, because it was not traced onformer geologic map by El Akkad and Issawi (1963)(Khalifa et al. 2002). The Bahariya Oasis is considered oneof the late active structure evolutions in the Western Desert.Its evolution took place during the Turonian or UpperCretaceous starting from Cenomanian onwards. The struc-ture includes regional anticlines all over the Bahariya Oasisor local anticlines and synclines within the depression andstructural highs and lows.

The hydrogeology

The major aquifer is made up of intercalated layers ofLower Cenomanian sands and sandstone with some claylenses in between, with thickness is about 705 m. Studieson El Bahariya Fm. (Desert Research Center 1990)indicate that the deposits have simultaneous to fluviatilesands transpo