The role of dunes in coastal hydrology and integrated coastal zone management.

Dune characterization in coastal zones is important for planning coastal defenses, groundwater management, and tourism development. Dune protection should be one of the main goals of any Integrated Coastal Zone Management Plan (ICZM). Coastal dunes efficiently oppose saltwater intrusion: their topographic elevation and their excellent infiltration capacity provide freshwater recharge and a hydraulic head that protect from saline intrusion according to the Ghyben-Herzberg principle (Fetter, 2001). The lateral continuity of the dunes system is also important for creating a continuous freshwater lens along the coast. As part of the Interreg IIIc Beachmed – “PosiDune project”, a monitoring campaign for groundwater levels and quality is being conducted on some test sites along stretches of the Ravenna coast: P.to Corsini, Marina Romea, Marina di Ravenna, Bevano river mouth. Dunes are still preserved in these areas and they act as natural defenses against storms, erosion and wave attack (Caruso et al., 2004; Caruso et al. 2006). A monitoring network has been established in each test site by placing piezometers both on the back and the crest of the dune and by carrying out a VES (Vertical Electri Sounding) geophysical campaign. The two methods (giving the chance to compare direct – piezometers - and indirect – geoelectric - data) has allowed to characterize the thickness of the fresh groundwater lens and the depth of the freshwater-saltwater interface. These actions have been integrated using: 1. a G.I.S. for data management; 2. a topographic and bathymetric reconstruction of the area using a LIDAR (Light detection and Ranging) survey; 3. a systematic seasonal update of the topography base and geomorphology using DGPS and theodolite surveys; 4. a survey of the geomorphologic evolution of the area through the periodical (monthly) acquisition of aerial images (flight height at 300m). The techniques employed are aimed at a precise charactetrization of the morphologic and hydrogeologic framework of the study areas. In addition, the maintenance of the monitoring system in future years will allow a better understanding of the effects of vegetation, dune restoration, and climate change to coastal hydrology and to ecosystem development (Gabbianelli & Sangiorgi, 2004; Ranjan et al. 2006). A clear comprehension of the role of dunes, achieved with this project, will be helpful for the management of the sites studied, especially considering their naturalistic values and peculiarities (they all belong to the Ramsar Zones list, SIC/ZPS sites list, Regional Po Delta Park – Emilia Romagna Region areas).