Il contributo della idro-geomorfologia nella valutazione delle piene in Campania

Abstract

Italy and, in particular, the Campania region, has been exposed to Hydraulic Risk since long ago. In hydraulic risk analysis the definition of maximum flood discharge with a specific return time (T) is crucial and, to this aim, the VAPI- Campania procedure (1995) was adopted in the Campania region. The VAPI method is based on a geo-morphoclimatic model, identifying 7 climatic homogenous areas with respect to the rainfall probability density function and 3 classes of permeability for the rainfall-runoff transformation model. At the XXX National Congress on the Hydraulic and Hydraulic Engineering (IDRA 2006), the hydrological working group of Salerno University (Rossi and Villani (2006)), pointed out guidelines for up-dating the VAPI-Campania and, in particular the role of: orographic barriers in the evaluation of intensity and persistence of the extreme rainfalls; and the individuation of hydro-geomorphotypes for the rainfall-runoff modeling at the catchments and sub-catchments scales. In this framework, the present thesis gives a contribution to a hydro-geomorphological approach to achieve the two guidelines mentioned above. This research focuses first on the automatic individuation and objective delimitation of the orographic barriers in order to upgrade the heuristic delimitation (expert judgment) used in the simplified model of orographically induced rainfall of Rossi et al. (2005). The proposed procedure is based on the basic concepts of the hierarchic orometry (hierarchical mountain geomorphometry), prominence and parent relationships, to delineate the 'orographic mountain' in various spatial scale (hierarchical- multiscale approach). Also, the procedure defines the 'morphologic mountains' and its components (ridge, plain and hillslope) using slope, altitude, relief ratio and exposition with respect to the dominant perturbation fronts and its moving direction. The second topic of research deals with the individuation of the hydrogeomorphotypes. To this aim, the prototypal work of Guida et al. (2007), was taken into account as a guideline in the identification of the hydrogeomorphotypes and the decisional scheme of Scherrer and Naef (2003), here modify, allowed the identification of the three dominant runoff mechanisms on the Campania region. In particular, the prototypal procedure of Guida has been here objectified and automatized, defining the 9 elementary landscape forms (Troch et al., 2002), characterized in terms of sub-surface flow and soil moisture storage, under an objectbased GIS environment. The procedure here presented allowed identification on the hydro-geomorphological map, and of the runoff mechanisms: Hortonian overland flow for excess of saturation, subsurface flow, and deep percolation. In order to test the procedure some hydro-geomorphological analysis have been carried out based on data from two instrumented experimental catchments and on rainfall data from the Regional Functional Center of the Campania Civil Protection Sector. The results allowed to calculate the hydrologic index named Runoff Index, which improves the evaluation of the runoff coefficient (Cf) for un-gauged basins. Other analyses were performed on further 4 catchments with similar hydrologic and geologic behavior in order to extended the procedure to the whole Campania region. Also, conceptual discussions on the implementation of the Runoff Index in the rainfall-runoff transformation operated with a largely used hydrologic software, HECHMS, was made, in order to evaluate the feasibility of the procedure proposed in the present research and improve the RI in hydraulic risk evaluation at a regional scale. [edited by author]