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Vincenzo Simeone, Politecnico di Bari (Italy)
Alessandro Guerricchio, Università della Calabria (Italy)
Alessandro Biasi, Politecnico di Bari (Italy)
Rosa Maria Lacertosa, Consultant Engineer (Italy)
Davide Mancarella, Politecnico di Bari (Italy)
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The morphology of Cigno stream and of the final tract of Biferno river (downstream Liscione bridge Dam) is strongly conditioned by a deep seated gravitational deformation. It has deformed the right Biferno riverside upstream the confluence with Cigno stream and created the valley in which flows Cigno stream. The Cigno stream develops along an ample arch concave towards west, down to the confluence with Biferno. In this tract the valley exhibits a remarkable asymmetry: to the hydrographic right the alluvial deposits are indeed bounded by a steep clayey scarp extending up to form a topographic water divide of the watershed; on the other hand to the hydrographic left, after a short clayey scarp, the valley is delimited by an extended morphologic terrace, lowered with respect to the upper edge of the scarp on the hydrographic right. This observation leads to believe that the river bed should lay right at the edge toe of the great scarp of the Deep Seated Gravitational Deformation The Biferno river downstream the Dam of Liscione Bridge, undertakes two different morphological outlines: pseudo-meandering upstream the confluence with cigno stream shifting from right riverside to left, and, subsequently, getting typically meandering from the confluence to the sea.
Right after the dam the Biferno river shifts to the right river bank as a result of pivoting of the valley towards SE due to the swelling of the DSGSD toe. The latter indeed affects the left side of the valley and forces the river bed to occupy the right side. The motion occurs before the confluence with Cigno stream and therefore cannot be ascribed to solid transport processes of the latter, but mainly to the presence of pseudo-terraces in the area. They appear as an anomaly in the plane surrounding landscape and are aroused by the gravitative deformation as they are located at the fulcrum of it.
The river Biferno, when approaching this zone, is disturbed in its regular flow by the obstacle and tends to regain energy from the right bound to the left, trying to "go round" the obstacle. Downstream the confluence with Cigno stream the Biferno river bed gets meandering and shifts from the left riverside to the right. In order to go beyond the morphological threshold that is upstream the confluence, the river has to regain energy by flowing with lower gradients, and dissipate it afterwards in the meandering area downstream the confluence. While ordinary flows can easily run along the meandering paths of the river bed, floods can hardly get canalized in this meanders and overflow in the entire Biferno valley that is therefore characterized by a high hydraulic vulnerability.
The Engineering Faculty of Taranto of the Technical University of Bari has financially supported the participation of the authors at the Meeting, using funds of Provincia di Taranto for the support the Faculty's didactic and scientific activities.
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