FIRST DATA ON THE COASTAL DYNAMICS AND THE SEDIMENTARY CHARACTERISTICS OF THE AREA INFLUENCED BY THE RIVER IRMINIO BASIN (SE SICILY)

The various lithological outcrops in the drainage basin of the River I rminio are described for their contribution to the riverborne material and therefore to the sedimentary balance of the coastal strip. The ma in contribution to the present sedimentary balance of the subaqueous d elta cannot be attributed to the River Irminio, owing to the extreme d ifference between fluvial and marine sediments. The river's hydraulic characteristics have not always been constant but have tended to decre ase in three stages: the first, with a strong competence, shown by the Quaternary alluvial sediments with pebbles; the second, up to 1985, o f medium competence, shown by sandy-gravelly deposits in the coastal s trip and by finer sediments in the distal areas; the third, at the pre sent day, with low competence, shown by a prevalently suspended load s ediment with practically no fluvial influence and with a sedimentation dominated by the littoral currents; this is because between the 1960s and 1970s, owing to interventions along the river channel, the sedime nts from the basin were reduced to the point of non-existence and a ne w sedimentary cycle was set up on the delta with allochthonous sedimen ts, exclusively made up of quartz clasts, whereas in the distal zones the mineralogical and compositional characteristics of the ancient riv er mouth were maintained. (C) 1997 Elsevier Science B.V.