Geomorphological survey for lagoon and coastal pond management projects: the Lagoon of Venice and the Orbetello coastal pond study cases

摘要

RIASSUNTOQuesto lavoro riporta l'applicazione del rilevamento geomorfologico attraverso misure plano-altimetriche e batometriche ad alta risoluzione per differenti problematiche ambientali in due aree costiere: la Laguna di Venezia e lo stagno costiero di Orbetello. La programmazione di un piano di gestione e salvaguardia degli ecosistemi ha richiesto, per la laguna di Venezia, il monitoraggio delle tendenze evolutive' dei principali elementi morfologici, mentre per Orbetello la naturalizzazione di alcune casse di colmata. I rilevamenti topografici e batimetrici di dettaglio sono stati effettuati sia mediante strumenti e metodologie tradizionali sia mediante GPS in modalità statica-differenziale e cinematica-differenziale che ha permesso la visualizzazione dei dati in tempo reale ottenendo un diretto controllo delle misure. Queste metodologie, per il rilevamento topografico di alcuni limiti ed elementi morfologici inaccessibili,sono state integrate dal telerilevamento con foto aeree mentre, per la progettazione degli interventi di modella mento delle casse di colmata,dalla mappa tura dei sedimenti superficiali. Infine, la valutazione dei tassi erosivi e deposizionali, è stata effettuata sia con rilevamenti topografici stagionali sia con il confronto di una serie storica di cartografie e di foto aeree.ABSTRACTEnvironment management plans for lagoonal ecosystems require highly detailed geomorphological maps that cannot be obtained with the standard topographical survey. High resolution topographic and bathymetric measurements were carried out in the Lagoon of Venice and in the Lagoon of Orbetello (ItaIy) both with traditional methods and instrumentation and with DGPS (Differential Global Positioning System) in static and kinematic differential modes, with the purpose of providing the ecosystem management plans for the two lagoons, with detailed geomorphological data. For the Lagoon of Venice the detailed topographic and bathymetric surveys were required for the recognition and quantification of erosion and/or deposition processes active in the Venetian basin survey. The comparison of topographic and bathymetric surveys, since 1931, of aerial photographs and of all available information on the geomorphology of the area, has allowed the recognition and quantification, on a decadal scale, of the rate and trend of erosion and sedimentation and has made it possible to de fine those morphological boundaries impossible to survey due to the inaccessible soft mud. Three field measurements done during the 1996-1997 period have made possible the identification of the present erosion rate in a selected area of a salt marsh subjected to wave action. For the Lagoon of Orbetello very low scale topographic measurements were needed for the "naturalization" of manmade mud flats and salt marshes. The naturalization plan of five artificial islets, made with dredged sediments, required the detailed topographic measurements at very low scale of all the morphological elements in order to recreate a natural environment for a rich transitory, nesting or permanent bird life. In addition, sever l small creeks have been dredged for improve the hydrodynamics of the lagoon and the water exchallge between shallows in the 111art made islets and the main channels and to protect the bird life by making it inaccessible for man and other predacious animals. Overall the combination of traditional survey methods with DGPS and the use of all in house developed software has proved to be very efficient for producing the required for detailed topographic and bathymetric maps of the two study areas. Furthermore the study has provided the management plans for the two different ecosystems with geomorphological data otherwise not available.