GNGTS 2013 - Atti del 32° Convegno Nazionale

erosive processes and on the degree of evolution of the basin. Index A represents the number of anomalous fluvial segments. Hierarchical anomaly index ( Δa ) allows to better quantify drainage anomalies. First order flow density ( D1 ) indicates possible areas suffering uplift due to dip slip movements. Also, we calculated some morphometric indexes indicating possible basin asymmetry (Asymmetry factor, AF ; Transverse topography asymmetry, T ) and basin differential uplift (Basin elongation Ratio, Re ; hypsometric curve and Stream length-gradient index, SL ). Finally, a morphostructural study allowed us to evaluate the relationship between the geometry of the hydrographic network and the trend of the tectonic structures. Morphometric indexes are very sensitive to lithological change, thus each parameter has been punctually related to the rock type cropping out, classified on the basis of the erosion susceptibility (Fig. 2). A class includes the crystalline terrains of the metamorphic massif, that is the most resistant lithology. B class represents the terrains of Tortonian, Pliocene and Lower Pleistocene age, made of conglomerates, sandstones, sands and clays with mid/low resistance to the erosion. C class includes clays, sands and poorly cemented conglomerates of Pleistocene age and Holocene alluvial deposits. These terrains have low degree of strengthened and are easy to erosion. In some cases, the Catona Fiumara and Petrace Fiumara have been divided in sub-basins with the aim to examine in depth possible perturbation of their drainage. Results. The basin of the Catona Fiumara is 67.47 km 2 wide; most of the drainage flows on the crystalline terrains of the metamorphic massif (A class) and on Pleistocene marine and continental deposits (C class), in the lower sector. Trunk stream flows towards NW and changes running towards SW in the final tract (Fig. 2). Fluvial network reaches the V hierarchical Strahler’s order and shows parallel shape pattern and trellis pattern as it regards the I order branches. Fig. 2 – Sketch map of the Catona Fiumara and Petrace Fiumara. Drainage is divided into hierarchical orders according to Strahler (1957) ordering. Terrains are classified on the basis of their susceptibility to erosion. 105 GNGTS 2013 S essione 1.1