Integrated subsurface thermal regime and hydrogeochemical data to delineate the groundwater flow system and seawater intrusion in the middle Nile Delta, Egypt

Abstract

Several aquifers around the world are situated in the coastal zones and influenced by seawater intrusion. The development of populace in coastal territories and the conjugate increment in human, farming, and industrial activities have forced an increase in the needs for freshwater. The Quaternary aquifer in the Nile Delta is among the biggest groundwater aquifers in the world. Along its northern side, the aquifer is highly affected by the Mediterranean Sea. Because of the inordinate pumping in the course of the most recent couple of decades, the groundwater quality in the northern parts of the Nile Delta has been decreased extensively. Therefore, this chapter aims to trace the groundwater flow system and seawater intrusion in the study area using the multi-tracing technique. The integration between borehole temperatures and groundwater chemistry was good to conduct the aim of this study. Borehole temperature was measured in eight boreholes, and the groundwater was sampled from the same wells but sometimes from the shallow and deep zones. Tala well located to the south of the study area indicated the recharged fresh groundwater with downward flux of 0.8 m/year. The fresh groundwater started to discharge from south Tanta City till south Kafr Elsheikh City where the calculated upward fluxes were −0.1 to −0.5, − 0.35, and −0.23 m/year for Kafelarab, Nawag, and Elkarada wells. Hydrochemically, the groundwater in the area northern Kafr Elsheikh City is highly affected by seawater intrusion, and the measured temperature profiles are of discharge type, and their calculated upward fluxes were −0.6, −1.2, and −2.8 m/year for Kafr Mesaaed, Elhadady, and Motobes wells, respectively. In comparison, temperature profile (Motobes well) affected by seawater intrusion has higher upward flux, while the freshwater recharge-type profile (Tala well) has lower downward flux. Hydrochemically, the seawater intrusion highly affected the wells from ElKarada wells to Motobes wells (northern Kafr Elsheikh City) and close to the Mediterranean Sea. Two types of saline water were recognized. The shallow groundwater is highly affected by seawater intrusion (TDS around 20 g/l), and the deeper groundwater is of hypersaline characters (80 g/l). These two types of saline water could deteriorate the groundwater quality in the Nile Delta in case of unresponsible severe pumping rates.