Application of airborne electromagnetics to effective
hydrogeological modelling of delicate coastal areas
A. Viezzoli
Aarhus Geophysics APS, Aarhus, Denmark
P. Teatini
Dept. of Civil, Environmental and Architectural Engineering, University of Padova, Padova,
Italy
L. Tosi
Institute of Marine Sciences, CNR, Venezia,
Italy
ABSTRACT
Lagoon environments are very important for groundwater modeling in costal areas, they are
delicate and in rapid evolution due to global climatic changes. Airborne electromagnetics (AEM)
is a very valuable methodology that can provide high density, high quality data to produce 3D
hydrogeological models to depths in excess of hundred meters below surface water column.
We present the results from the SkyTEM Venice lagoon survey of 2009, integrated with data from
very high resolution seismic survey. The AEM data results enhance greatly the understanding of
the hydrogeology and surface-groundwater interactions in the lagoon area, where indirect measurements
abound but wells are missing. For example, there is clear evidence of fresh water aquifers underneath
the central part of the lagoon, at depth of about 40 m. The near surface part of the AEM data compare
well with seismic data, showing that main reflectors come from the interface between the superficial
Late Pleistocene looser, saline water saturated sediments and the deeper, more compact and fresher
Holocene sediments. There is also clear evidence of submarine groundwater discharge in the lagoon,
of paleorivers, and a possible indication of gas seepage trough shallow sediments. Seismic and AEM
provide complimentary datasets to discriminate between pore water salinity, lithology and gas. Seismic
horizons can actually be included during inversion of AEM data, producing more robust output. AEM data
from the southern part of the survey that crosses the shore line and continued also onshore allow a
clear mapping of the saline water intrusion inland, and highlight the relationship between pore water
salinity of the lagoon sediments and spatial distribution of salt marshes. The latter seem to act like
salt sinks, increasing sediments electrical conductivity.
