Monitoring of seawater intrusion in coastal aquifers: Basics and local concerns

Monitoring of seawater intrusion is essential to determine and predict groundwater deterioration, and assess other managerial activities in coastal aquifers. Monitoring involves designing strategy and methodology of field surveys for choosing the most effective means towards obtaining the most reliable possible data. The monitoring of seawater intrusion may consist of direct and indirect methods. Direct methods include measurement of groundwater salinity profiles and groundwater sampling of observation and active wells. Such sampling can involve single-chamber apparatus or multi-layer samplers. Indirect methods can use geoelectromagnetics and more specifically the time domain electromagnetic method (TDEM). Until recently, seawater intrusion monitored within the framework of the Israeli national groundwater monitoring network, was based upon observation wells. Many of these wells are no longer in operation. Therefore, monitoring activity based upon a reduced number of observation wells yields uncertain indications as regards seawater intrusion into the Coastal Plain aquifer. For more accurate insight, the TDEM has been involved recently to enhance the conventional seawater intrusion network. Experience in Israel indicates that a combination of TDEM and direct well observation appears an optimal means of assessing intrusion of seawater into coastal aquifers. In future, more geophysical means ought to be involved. (C) 1997 Academic Press Limited.