Surface water-groundwater exchange in transitional coastal environments
by airborne electromagnetics: The Venice Lagoon example
P. Teatini
Dept. Mathematical Methods and Models for Scientific
Applications, University of Padova, Padova, Italy
L. Tosi
Istituto di Scienze Marine, CNR, Venezia,
Italy
A. Viezzoli
Aarhus Geophysics APS, Aarhus, Denmark
L. Baradello, M. Zecchin
National Institute of Oceanography and Experimental Geophysics, Sgonico (TS), Italy
S. Silvestri
MARTE Srl, Venice, Italy
ABSTRACT
The occurrence of alternating dry/wet conditions in transitional environments, such as wetlands, deltas,
and lagoons, usually challenges the use of traditional direct and geophysical surveys for comprehensive
hydrogeologic investigations. Moreover, significant mixing between continental fresh groundwater and
marine salty surface waters generally takes place in these flat coastal areas. Airborne electromagnetics
(AEM) is a promising tool in this respect, as it provides, in a fast and cost effective manner, large-scale
distribution of bulk electrical conductivities that can be used profitably to develop hydrogeologic models.
The results of a SkyTEM AEM survey in the Venice Lagoon, Italy, show the capability of this technique to
significantly improve the knowledge of the hydrogeologic setting of the lagoon and nearby coastland sub-surface,
irrespective of the different features characterizing the area. The environment consists of salt
marshes, mud flats, shallows, tidal channels, islands, together with reclaimed farmlands crossed by nat-
ural watercourses and drainage channel networks. In particular, the AEM shows (i) the presence of fresh
water (with resistivity larger than 20 Ω m) underneath the central part of the lagoon at depths from 10 to
25 m below m.s.l., (ii) the interface between different relevant stratigraphic units, e.g., the clayey layer
bounding the Holocene-Pleistocene sedimentation, and (iii) the occurrence of areas with possible submarine
fresh groundwater discharge. Moreover, the source and inland extent of the saltwater contamination
in the shallow coastal aquifers along the southern margin of the lagoon are clearly revealed.
AEM data were complemented with very high resolution seismic (VHRS) acquisitions. The integrated
analysis of the two data sets allows distinguishing between lithostratigraphic heterogeneity and variability
of the subsurface fluids.
