Risk Assessment and Mitigation of the Seawater Intrusion Using Modeling Approach

Abstract

Groundwater is one of the most precious natural resources in the Gaza Strip as it is the only source of drinking water for the majority of the population. The increasing of salinity problem and the dropping in water level are two of the most important and widespread of the numerous potential groundwater problems. The salinity sources in the groundwater of Gaza Strip are from the intrusion of the seawater which caused by increased abstraction from the wells. The problem of high salinity concentrations in drinking water exceeded the WHO standards of 250 mg/l constitutes a major health risk to both humans and stock life. The chloride concentration reached to 1500 mg/l in some wells. The water level will drop to -10 M.S.L in some area in north of Gaza strip within 10 years if the levels of abstraction continues in this regime. Therefore, this work tried to study the increase of chloride concentration and the drop of level of groundwater in North of Gaza Strip area as a result of seawater intrusion. A coupled flow and transport model using a three-dimensional, finite difference simulation model (VMODFLOW Pro.) was applied to simulate the Northern part of Gaza coastal aquifer. Model application was carried out in two steps; (a) The calibrated flow and transport model was used to study management scenarios for the Seawater intrusion problem, (b) Simulation of chloride concentration and water level transport in the Northern part of Gaza Strip coastal aquifer to estimate transport parameters. The approach for selecting the management scenarios was carried out depending on the need to reduce the transport of chloride concentration and improving the water level into the aquifer system during the next 10 years. Six selected management scenarios were tested; (1) work as usual (zero scenario), (2) Management of the pumping to 50%, (3) Injection of treated wastewater to the aquifer, (4) combining the previous two scenarios together, (5) Reduction the abstraction to 20% and injection of treated wastewater (6) Injection of treated wastewater and stopping the abstraction from the aquifer. The best scenario to solve the increasing of chloride concentration and dropping in water level problems in the groundwater is the implementation of the sixth scenario from 2012 to 2020 which cause rising of water level and reversing the seawater toward west.