ENVIRONMENTAL EFFECTS OF CHANNEL-HARBOR MODIFICATIONS AT PESCARA RIVER MOUTH (ADRIATIC SEA, ITALY)

Pescara river is a 130 km long stream draining into the Adriatic sea a mean volume of 50 m3/sec of water from a 3200 km2 wide catchment on the eastern side of the central Apennines neogenic orogenic chain. The river outlet, surrounded by the city of Pescara, has been used for more than a century as a harbor for fishermen boats. In the last decades, a number of artificial changes have dramatically altered the environmental conditions, in particular sediment budget and dynamics and concentration of polluting agents near shore. First of all, dams and borrow pits along stream have limited the sediment load at the outlet. Then, due to the will to improve the harbor and recreation capabilities, nearshore breakwaters, and a breakwater ca. 800 m long defending the river outlet from northerly storms have been realized. This has determined significant changes in the flow paths accumulating fine sediments and polluted fresh water along the northern beach and eroding the southern one, which has resulted in lower frequentation in the summer season and significant economic losses. In this work we show how a combined use of an appropriate numerical method, field surveys, historical data on shoreline evolution and remote sensing techniques can address toward the most effective practical solution, either from the coastal engineering and environmental protection viewpoints, to force the river flow outward at Pescara channel-harbor (removal or re-orientation of the large breakwater, or new marine structures). The numerical results are obtained applying a model developed at ANPA, based on 2D shallow water equations implemented by a finite difference method. 3D flow structures can be neglected here, being the water depth rather low (less than 8 m). The vertical pressure distribution is assumed to be hydrostatic and the flow is considered barotropic. Complex geometry boundary description (breakwater, shorelines) is implemented by a body force approach. The breakwater-induced environmental effects resulting from the unsteady interaction between river mouth flow and marine structures have been compared to field experimental data, consisting of repeated surveys of sea bottom morphology, infrared remote sensing images, water quality parameters from samples taken close to the shoreline.