Contribution of seismic profiles, historical maps, and digital elevation model to define buried geomorphological features in the Venice Lagoon subsoil (Italy)

Federica Rizzetto; Luigi Tosi; Massimo Zecchin; Giuliano Brancoli-ni and Luca Baradello

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CONTRIBUTION OF SEISMIC PROFILES, HISTORICAL MAPS, AND DIGITAL ELEVATION MODEL TO DEFINE BURIED GEOMORPHOLOGICAL FEATURES IN THE VENICE LAGOON SUBSOIL (ITALY)

Federica Rizzetto (1); Luigi Tosi (1); Massimo Zecchin (2); Giuliano Brancolini (1) and Luca Baradello (2)

(1) Institute of Marine Sciences - National Research Council. Castello 1364/a, 30122 Venice, Italy. (2) National Institute of Oceanography and Experimental Geophysics. Borgo Grotta Gigante 42/c, 34010 Sgonico (Trieste), Italy.

KEY WORDS: Venice Lagoon, geomorphology, paleochannels, paleo-coastlines.

INTRODUCTION

Recently, the integrated analysis of Very High Resolution Seismic (VHRS) profiles, satellite images, aerial photographs, maps, and topographic/bathymetric data has given an important contribution to the identification of buried geomorphological features in the Venice lagoon subsoil down to about 30 m b.s.l. (Figure 1). Investigations allow to attribute these features to the Late Pleistocene and the Holocene and to point out their relation with the evolution of the lagoon basin.

Results of this study are also assuming great importance in relation to coastal environmental problems. Relict sandy geomorphological features, characterized by high permeability, act as preferred pathways for groundwater flow and solute transport, enhancing saltwater intrusion in the watershed (Carbognin & Tosi, 2003; Carbognin et al., 2005; Pousa et al., 2007). Furthermore, salinization process can also trigger land subsidence induced by clayey particles rearrangement (Meade, 1964).

In addition, the different kinds of deposits that characterize geomorphological features are responsible for a differential lowering of the territory (Teatini et al., 2005).

MATERIALS AND METHODS

Aerial photograph and satellite image interpretations, analysis of historical and recent maps, field surveys, and topographic/bathymetric investigations were first used to identify the main buried and surface geomorphological features. Afterwards, an important contribution to the present study was given by a single channel VHR seismic system, optimized for surveys in shallow water less than 1 m depth (Brancolini et al., 2006; Brancolini et al., 2007).

Seismic profiles were calibrated and validated using geological information obtained from existing cores.

The detailed reconstruction of the seismic-morpho-stratigraphic units present in the subsoil of the Venice Lagoon is still in progress. It is obtained integrating results of the investigations previously described with sedimentological, stratigraphic, geotechnical, mineralogical, textural, and paleoenvironmental data, and 14C dating (Serandrei Barbero et al., 2006; Tosi et al., 2007a; Tosi et al., 2007b).

RESULTS AND DISCUSSION

The combined interpretation of results obtained from remote sensing investigations, topographic/bathymetric measurements, VHRS surveys, and analysis of multidisciplinary geological data allowed the discovery and characterization of buried paleoriver beds, ancient tidal channels, and paleobeach ridges (Figure 2) and pointed out the relation among geomorphological features occurring in the lagoon basin and in the watershed.

In fact, most of the features recognized in the mainland, which apparently come to an end in correspondence to the lagoon margin, continue into the lagoon basin, where their identification is made difficult by the presence of water and by depositional/erosive processes active in this kind of environment.

Data show that relict geomorphological features composed of high permeability deposits provide the hydraulic connection between freshwater aquifers and the sea. In particular, results of the present study point out that well developed paleoriver systems, intersecting the southern lagoon margin and the nearby coastline and characterized by permeable sediments, represent preferential way of communication among waters having different salinity. By contrast thick silty-clayey layers preclude the salty pollution in the aquifers from the lagoon and the sea.

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Figure 1 – Digital Elevation model (a) and network of seismic lines (b) carried out in the southern Venice Lagoon. An enlargement of the studied area, characterized by clear evidences of paleo-coastlines, is displayed in a separate window (c). The maps indicated as (d) and (e) represent the lagoon setting in 1556 and 1780, respectively.

As pointed out close to the lagoon margin (Rizzetto et al., 2003), the different kinds of deposits, related to the presence of distinct geomorphological features, contribute to the differential lowering of the lagoon basin (Teatini et al., 2005). In particular, organic soils correspond to highly sinking areas, whereas sandy-silty sediments, which constitute fluvial and beach ridges, are more stable.

Future investigations have to be addressed to the quantitative geomorphological analysis aimed to know the past hydrologic conditions of the drainage systems, and to analyze the formative processes that control the morphological setting and evolution of lowland fluvial river and tidal creek systems.

ACKNOWLEDGEMENTS

This study was performed in the framework of the following projects: Co.Ri.La. Linea di Ricerca 3.16; VECTOR-Cliven Linea 5, attività 3; CNR-Ricerca Spontanea a Tema Libero n. 809.

Figure 2 – Paleochannels and paleo-coastlines identified in the area of Figure 1c using multidisciplinary investigations.

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Figure 3 – Example of geomorphological features recognized in a seismic profile realized across the southern Venice Lagoon.

REFERENCES BRANCOLINI, G., TOSI, L., RIZZETTO, F., DONDA, F.,

BARADELLO, L., NIETO, D., FANZUTTI, F., WARDELL, N., TEATINI, P., AMOS, C., BONARDI, M., 2006. New very high resolution seismic surveys in shallow water to study the subsurface in the Venice Lagoon. In: CAMPOSTRINI, P. (ed.), Scientific Research and Safeguarding of Venice 2005, CORILA Research, Research Program 2004-2006. Multigraf Industria Grafica Editrice, Spinea, Venezia, 417-427.

BRANCOLINI, G., TOSI, L., BARADELLO, L., BRATUS, A., DONDA, F., RIZZETTO, F., ZECCHIN, M., 2007. Preliminary results of the high resolution seismic surveys in the Venice lagoon. In: CAMPOSTRINI, P. (ed.), Scientific Research and Safeguarding of Venice 2006, CORILA Research Program 2004-2006, 2005 Results. Multigraf Industria Grafica Editrice, Spinea, Venezia, 333-346.

CARBOGNIN, L., RIZZETTO, F., TEATINI, P., TOSI, L., 2005. L’intrusione salina nel comprensorio lagunare veneziano. Il bacino meridionale. Giornale di Geologia Applicata, 2, 119-124.

CARBOGNIN, L., TOSI L., 2003. Il Progetto ISES per l’analisi dei processi di intrusione salina e subsidenza nei territori meridionali delle province di Padova e Venezia. Grafiche Erredici, Padova, 96 pp.

MEADE, R.H., 1964. Removal of water and rearrangement of particles during the compaction of

clayey sediments-review. U.S., Geol. Surv., Prof. Pap. 497-B, 23 pp.

POUSA, J., TOSI, L., KRUSE, E., GUARAGLIA, D., BONARDI, M., MAZZOLDI, A., RIZZETTO, F., SCHNACK, E., 2007. Coastal processes and environmental hazards: The Buenos Aires (Argentina) and Venetian (Italy) littorals. Environmental Geology, International Journal of Geosciences, vol. 51, 8, 1307-1316.

RIZZETTO F., TOSI L., CARBOGNIN L., BONARDI M. TEATINI P., 2003. Geomorphological setting and related hydrogeological implications of the coastal plain south of the Venice Lagoon (Italy). In: SERVAT E., NAJEM W., LEDUC C., SHAKEEL A. (eds), Hydrology of Mediterranean and Semiarid Regions, IAHS Publication no. 278, 463-470.

SERANDREI BARBERO, R., ALBANI, A., DONNICI, S., RIZZETTO, F., 2006. Past and recent sedimentation rates in the Lagoon of Venice (Northern Italy). Estuarine, Coastal and Shelf Science, 69(1-2), 255-269.

TEATINI, P., TOSI, L., STROZZI, T., CARBOGNIN, L., WEGMÜLLER, U., RIZZETTO, F., 2005. Mapping regional land displacements in the Venice coastland by an integrated monitoring system. Remote Sensing of Environment, 98, 403-413.

TOSI, L., RIZZETTO, F., BONARDI, M., DONNICI, S., SERANDREI BARBERO, R., TOFFOLETTO, F., 2007a. Note illustrative della Carta Geologica d’Italia alla scala 1:50.000. 128-Venezia. APAT, Dipartimento

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Difesa del Suolo, Servizio Geologico d’Italia, Roma, Casa Editrice SystemCart, 164 pp.

TOSI, L., RIZZETTO, F., BONARDI, M., DONNICI, S., SERANDREI BARBERO R., TOFFOLETTO, F., 2007b. Note illustrative della Carta Geologica d’Italia alla scala 1:50.000. 148-149 - Chioggia-Malamocco. APAT, Dipartimento Difesa del Suolo, Servizio Geologico d’Italia, Roma, Casa Editrice SystemCart, 164 pp.

Proceedings Volume IRevised Digital Edition

Munich | Bavaria, Germanyjune 9th | 12th 2009

EUropeanCongresson REgional GEOscientific Cartography andInformation Systems

Earth

and

Man

Freistaat Bayern Catalunya

6th EUREGEO

6th European Congress on Regional Geoscientific Cartography and Information Systems EUREGEO

Earth and ManProceedings Volume IRevised Digital Edition

Editor: Bayerisches Landesamt für UmweltReferat GeoForum Bayern, GeotopkatasterBürgermeister-Ulrich-Straße 160D-86179 AugsburgTelefon: +49 821 90 71 0Telefax: +49 821 90 71 55 56e-Mail: poststelle@lfu.bayern.dehttp://www.lfu.bayern.dePrinted by Landesamt für Vermessung und Geoinformation, Alexandrastraße 4, 80538 München

We express our gratitude to Natalie Graf, Gisela Poesges, Christa Schindelmann, Erwin Geiß, Albrecht Jahn, Joachim Lindlbauer and Rudolf Wicke for their enthusiastic assis-tance.

Also, we thank the Cartography and Layout Units of the Bavarian Environment Agency and the Bavarian Agency for Surveying and Geoinformation.

Special thanks go to the Bavarian Agency for Surveying and Geoinformation for printing the proceedings and the programme.

The congress organization received generous support by Bayerischer Industrieverband Steine und Erden, München Conterra GmbH, Münster ESRI Geoinformatik GmbH, Kranzberg GAF AG Gesellschaft für Angewandte Fernerkundung, München Mineralientage München Fachmesse GmbH, Oberhaching

Finally, it is our concern to thank Ogarit Uhlmann, Maik Netzband and the team of F&U Confirm for the careful organization and technical assistance.

Promoting Committee

Horst Seehofer Bayerischer Ministerpräsident

Markus Söder Bayerischer Staatsminister für Umwelt und Gesundheit

Vasco Errani Presidente della Regione Emilia-Romagna

Marioluigi Bruschini Assessore alla Sicurezza territoriale. Difesa del Suolo e della Costa. Protezione civile. Regione Emilia-Romagna

José Montilla President de la Generalitat de Catalunya

Joaquim Nadal Conseller de Política Territorial i Obres Públiques de la Generalitat de Catalunya

SCientifiC Committee

Freistaat Bayern Emilia-Romagna Catalunya Albert Göttle Michela Grandi Xavier Berástegui Ulrich Lagally Raffaele Pignone Antoni Roca

European Commission EuroGeoSurveys Luca Montanarella Luca Demicheli

LoCaL organizing Committee

Albert Göttle, Ulrich Lagally, Ulrich Teipel, Roland Eichhorn, Stefan Glaser, Wolfgang Köhler, Peter Köstner, Georg Loth, Karl Mayer, Robert Reichel and Marcus Wandinger

III

Bayerisches Landesamt für Umwelt