Quantification of Groundwater ‐ Saline Surface Water Interaction in a Small Coastal Plain in North‐East Tunisia using Multivariate Statistical Analysis and Geophysical Method

Abstract

Amultivariate statistical analysis used with geophysical investigation enabled the assessment of interaction between saline surface water and groundwater in the coastal plain of Wadi Al Ayn and Daroufa in CapBon peninsula, north-east Tunisia. The application of the Principal Component Analysis (PCA) identified the end members which contribute to groundwater recharge: the wastewater infiltrated from Wadi Al Ayn, the oilfield brine infiltrated to the aquifer through the sandy bed of Wadi Al Ayn, the intruded seawater near Wadi Daroufa in the downstream region and the fresh groundwater flowing from the upstream region. The contribution of wastewater in groundwater recharge varies from 1.4% in the upstream region of Wadi Al Ayn to 77% near its downstream part. The fraction of oilfield brine mixed with groundwater in the alluvial aquifer under Wadi Al Ayn varies from 1% to 13%; whereas the fraction of intruded seawater into the coastal part of the aquifer near Daroufa region varies from 2% to 21%.

Using Analytical Hierarchy Process and Multi-Influencing Factors to Map Groundwater Recharge Zones in a Semi-Arid Mediterranean Coastal Aquifer

“…The main compressive structures that bend in the northeast-southwest direction (Figure 2a) were generated during the Atlasique phase of the Upper Miocene [5,6,10,40]. These structures include: (1) Djebel Sidi Abderrahmene anticlinal, an elongated antiform parallel to the atlasic folds along the northeast-southwest direction; (2) Dakha synclinal, which contains the Korba coastal aquifer; (3) Menzel Temime anticlinal, which stretches along the Northeast-Southwest direction, beginning in the north of Nabel due to seismicity and ending at Korba.…”

“…Demand for fresh water resources is noticeably increasing as a result of growing agricultural water demand, population growth and rapid industrialization. Therefore, groundwater abstraction has become an integral component of many water management plans worldwide, including in rural areas of the Western Mediterranean region [4][5][6][7][8].…”

“…The Korba coastal area in northeastern Tunisia is faced with groundwater over-pumping, causing seawater intrusion and degradation of groundwater quality. In this region, groundwater is the primary water source for domestic and agricultural purposes for about 90% of the rural population [2,[5][6][7][8][9] and 50% of urban residents [6,9,10], putting pressure on the aquifer to cope with the rising demand [2,5,9,10]. Groundwater overdraft was identified as a problem in the early 1980s when the Tunisian government called for a reduction of water pumping by encouraging farmers to adopt drip irrigation systems by covering up to 60% of the installation cost [11].…”

“…Since then, groundwater levels have continued to decline and seawater intrusion is steadily progressing in most of the coastal areas with the expansion of agricultural lands despite efforts to implement water conservation policies, build recharge dams, transfer water from the north, stop drilling new wells and encourage the re-use of treated wastewater [4,8]. Most of the deficit is observed in the central part of the Korba area where 53% of croplands are irrigated [2,[5][6][7]11].…”

“…The accuracy of the AHP and MIF techniques was evaluated using a receiver operating characteristic (ROC) curve based on the area under the ROC curve (AUC), which includes all the possible decision thresholds from field observations of well yield data and water level depth. Although many investigations have assessed the groundwater resources of the Korba area [2,[5][6][7][8]10,11] none of them have used remotely derived data to demarcate GWRZs in this region. The GWRZ maps facilitate groundwater management through better water balance calculations based on improved estimates of recharge-precipitation ratios to quantify percolation.…”