Author(s): Sandro Carniel; Mauro Sclavo; Andrea Bergamasco; Alvise Benetazzo; Davide Bonaldo; Francesco Marcello Falcieri; Marina Aurighi
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Keywords: Northern Adriatic sea; Artificial reefs; Sediment transport; Numerical modelling; Coastal circulation
Abstract: The sea reach offshore the Venice littoral (Italy) is an area of outstanding ecological importance due to the presence of several outcropping rocky systems (named Tegnue by locals) on a sandy-silty bottom, which creates significant habitat variability. In order to enhance sealife settlement and protect these strategic environments from trawl fishing, artificial reefs were deployed as an implementation of the regional coastal management and preservation policy. Such reefs are made of a number of monolithic structures, designed so to enhance fish colonization, and are located in the vicinity of the rocky outcrops. Within the MARINA (Modellistica ad Alta Risoluzione Integrata del Nord Adriatico, Integrated High-Resolution Modelling of the Northern Adriatic sea) project, funded by the Veneto Regional government (Regione Veneto - Geology and Geo-Resources Dept., Water Protection Unit), CNR-ISMAR integrated different scientific activities performed on the Northern Adriatic sea (NA) in a high-resolution modelling work for the study of the impacts of some reef systems on local hydrodynamics and sediment transport, with the final aim of providing a support tool for managing and planning the deployment of these structures, often located in the proximity of aquaculture sites. During the study, a three-level step activity was planned. Initially, a statistical characterization of the NA ocean circulation was obtained by means of a basin scale high-resolution (500 m) numerical modelling run. To simulate sea currents the Coupled Ocean - Atmosphere - Wave - Sediment Transport (COAWST) modelling system was used. COAWST relies on the ocean model ROMS (Regional Ocean Modeling System), the wave model SWAN (Simulating WAves Nearshore), and the CSTMS (Community Sediment Transport Modeling System) routines, and in this configuration received the atmospheric forcings from the meteorological COSMO-I7 model. Once the mesoscale hydrodynamic conditions on the Tegnue area were known, a set of super-high-resolution (having grid sizes variable between 0. 15 m and 4. 00 m) simulations was performed via the numerical model MIKE-3 to provide a detailed three-dimensional description of hydrodynamics and sediment transport processes close to a single submerged monolith, albeit in a simplified domain. For these runs, the hydrodynamic and geometric conditions, as well as the grain size representing the bottom properties, were chosen in order to cover the whole range of statistically relevant possible environmental conditions on the Tegnue area, as resulting from the first step of the activities. The results of the single-monolith runs were assembled by means of a superimposition approach in order to simulate the complex structure of the real systems. Last, the whole data set results, currently describing four Tegnue in different hydrodynamic and sedimentological conditions, were made available via a dedicated user-friendly graphical query tool. The overall results show that relevant suspended sediment concentration increases may occur only during severe storms and in presence of fine bottom material, suggesting that artificial reef systems in the NA, if properly deployed, do not generally produce harmful turbidity effects on the rocky outcrops.
Year: 2013