The interaction between the catchment basin of the Tevere river and the structural evolution in the Umbria area

We present a preliminary tectonic and geomorphologic analysis of the Tevere river network of the Umbria Region in order to define the relationship between tectonic setting and drainage basin evolution looking at the erosion, transport and sedimentation process. Due to the coarse variability of the climate and of the lithology of the area geological and geomorphological offsets of river basin drainages are used to constrain the deformation and the basin change rates. The research highlights and investigates the relationship between catchments basin and the main evolution of the area at the short-medium timescale while taking account of local tectonic changes. In the research project we look at the Tevere river between the confluence of River Afra (300m a.s.l.) and the confluence of River Paglia (90m a.s.l.). We divided this area in three zones: the upper part of the Valtiberina valley (between the Montedoglio dam and the gorge of Città di Castello), the valley until the confluence of the Chiascio-Topino, and the valley until the Corbara lake. 1. in the upper part of the Valtiberina valley the drainage network is characterized by an high edge scarp erosion that lead the migration of the Apennine thresholds toward est. Furthermore the continuous increase of the local scarp create a bigger stream velocity and transportation leading to a prograding alluvial fan area. Consequently this condition contrasts the Tevere river “tectonic” trend to drift toward east (Sansepolcro – Città di Castello basin over heading). 2. In the middle part of the Umbrian Tevere the basin is included between very steep slopes. The hills structure derives from the activity of boundering fault systems. The Tevere river network leans against the boundering faults: westward, along the valley as far as Perugia/P.te S. Giovanni town and eastward from Torgiano to Todi village. Wide relict terrains, made up of ancient continental deposits, lay at the foot of the opposite side of the basin. 3. Tevere river leans against the east side of the basin also in the lowest branch of the profile (Martani Mountains chain) whereas ancient continental deposits, cut by pleistocenic faults, characterize the opposite side of the basin. The distribution of the areas subject to erosion and of the low regions (toward the Tevere river and its tributaries converge) defines different basins, evolved in distinct times and with different ways before of getting together in the present valeey system of Tevere river.