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Abstract

A joint geophysical-hydrogeological experiment was performed to monitor groundwater level changes in a shallow aquifer caused by tidal loading. Electrical resistance tomographies (ERT) were recorded every 45 minutes for two days and consisted of a profile of 41 electrodes, using a 1-m spacing dipole-dipole array protocol. Eleven piezometers were installed with a separation of 10m; pressure data was recorded at 2 min interval. Other hydrogeological data included tide levels, temperature, water electrical conductivity, and porosity estimations. Time-lapse resistivity imaging shows subtle changes in resistivity close to the sea water front and in a region of large lateral gradient of resistivity thought to be the limit between waters of contrasting salinity. Reasons for the small water-induced vertical resistivity variations were investigated using numerical modelling. It is shown that ERT may not resolve changes smaller than 25 cm over a depth of 3m using the survey acquisition parameters. Coupling hydrogeological data with groundwater ERT allowed displaying a likely contact between saline and fresh groundwater. Measured hydraulic conductivities were used to model the effect of tidal loading on the piezometric level and the computed damping and time-lag of the tide induced effects with distance inland fit well with the observed data.

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/content/papers/10.3997/2214-4609.20144407
2011-09-12
2024-03-29
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http://instance.metastore.ingenta.com/content/papers/10.3997/2214-4609.20144407
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