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Seasonal Monitoring of Saline Intrusion in an Unconfined Coastal Aquifer in New Zealand Using DC Resistivity Traversing
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, Near Surface Geoscience 2015 - 21st European Meeting of Environmental and Engineering Geophysics, Sep 2015, Volume 2015, p.1 - 5
Abstract
Long term time-lapse DC resistivity measurements along six 155 to 275 meter long traverses at the Kapiti Coast in New Zealand have been made to image a seasonal cycle in the saline interface movement. Two-monthly repetition of the measurements showed a continuous decrease of the bulk resistivity at depth and over an extended horizontal area when coming into the drier summer season. This observation is somewhat contradictory to the expectations and has its origin most possibly in a decrease of the fluid resistivity, likely due to a lower fresh water flow coupled with saltwater intrusion. Although, the changes from time step to time step are not always major on all profiles, ERT time-lapse monitoring proved itself a suitable tool to image the saline interface shape and movement along with changes in the subsurface resistivity distribution in an unconfined coastal sand aquifer and in a seasonal time frame.