Salt Water Intrusion

Water resource management along coastal areas is rapidly becoming an important requirement with increasing demands on freshwater resources and the threat of contaminating these supplies.  Excessive pumping rates on groundwater supplies can lead to changes in the freshwater – salt water gradients, resulting in salt water intruding landwards.  Geophysical methods can be used to characterize and monitor the subsurface in coastal areas to identify saline groundwater and map the changes in intrusions over time.  Electrical resistivity and electromagnetic methods lend themselves to imaging salt water intrusion due to the highly conductive nature of saline groundwater.  Geophysical surveys can be conducted at a range of scales and imaging depths, from 10’s to 100’s of meters, and in a variety of environments, including urban areas.

Geophysical methods can be used to characterize aquifers in coastal areas, and identify the freshwater – saltwater interface(s).  These surveys can be combined with additional information (geological cores, geochemical analyses, geophysical logging, etc) obtained from wells and boreholes to ‘fill in the gaps’ between these point sources of subsurface information.  Geophysical surveys can also be used to aid in planning well drilling campaigns to target salt water intrusions and mixing zones.  This can be especially useful in areas of complex geology where multiple aquifers are present, each with differing degrees of salt water intrusion.  In addition, geophysical surveys can be used to monitor the evolution of intrusions over time by conducting time-lapse imaging.  These can be implemented to monitor the effectiveness of mitigation campaigns or natural seasonal variations in the salt water – freshwater interface(s).

HGI has experience of conducting a range of surveys involving salt water intrusion.  These include, large scale characterization of salt water intrusions along coastal regions using time-domain electromagnetic and electrical resistivity methods.