Hydrogeophysical Investigations Using DC Resistivity Survey to Assess the Water Potentialities of the Shallow Aquifer Zone in East of Dakhla Oasis, Egypt

Abstract

In the Egyptian Western Desert oases as an example of arid environment, groundwater is considered the key source for agricultural and national development projects. The Dakhla Oasis has been a part of the national agriculture projects in the last years therefore, the unplanned pumping of groundwater leads to dropping of water table in the shallow wells. In such cases, the sustainable management and continuous assessment of groundwater is considered as a noteworthy challenge to reduce the impact of the excessive exploitation from the upper zone of the Nubian aquifer system. The present work aims to assess the groundwater potentialities in the shallow aquifer which is structurally controlled by faults. In this study, the DC resistivity sounding survey was integrated with borehole logs and TDS data to delin-eate the impact of the local faults on the recharge system and water quality in the shallow wells, east of Dakhla area. Forty-Six Schlumberger resistivity soundings were measured to determine the geometry, position, and properties of the upper aquifer zone in the area. In addition, sixteen borehole logs were employed to adjust the resistivity models and determine the accurate boundaries of subsurface layers. The obtained resistivity models were integrated with TDS measurements of the collected water samples from 60 water wells to assess water quality in the upper aquifer zone. Geoelectric cross-sections have been developed to represent plainly the diverse litho-logic units and the structural components (essentially faults). Moreover, the inferred true resistivity map of the aquifer layer reflects the water quality and demonstrates that this aquifer resistivity ranges from 11.4 to 337 .m indicating fresh to brackish nature. The anomalous TDS of shallow groundwater in southern parts is referred mainly to, the drained irrigation water (unconfined aquifer) and the low values of K. 261 262 K. S. Gemail et al. transmissivity which retards the velocity of groundwater up-flow through vertical faulting zones and lead to the increasing of leaching processes of salts.