Morphometric analysis of the drainage network in the Modena and Reggio Emilia Apennines (Northern Italy)

Abstract

This paper provides quantitative geomorphic analysis in the catchment basins of the rivers Secchia and Panaro, in the Modena and Reggio Emilia Apennines (northern Italy). The research is based on established methods applied in several Apennine basins of central Italy. The aim of the research is to carry out a preliminary morphometric characterisation of the Emilia basins that, if supported by sample monitoring, should allow the correct management of these fluvial basins. A Digital Elevation Model (DEM), based on contour line interpolation of the Regional Technical Maps at a 1:25,000 scale is used to calculate and extract landscape metrics. The DEM provide an objective means through which the drainage network was defined. The DEM is linked to a cartographic database, that spatially coordinates the calculation of metrics including: Frequency of channels (F), Length of channels (L), Area of catchment basins (A), Ratio between area and length, Drainage density (D). From these basic metrics the following ratios and indexes have been derived: Mean bifurcation ratio (Rb), Direct mean bifurcation ratio (Rbd), Bifurcation index (R), Hierarchic anomaly (Ga), Hierarchic anomaly density (ga), Hierarchic anomaly index (Da), Extension ratio (Re), and Circularity ratio (Rc). Subsequently, hypsometric analysis was carried out and finally, on the basis of established empirical relationships, the annual unitary stream load (Tu) has been assessed. The various parameters extracted have been compared with the lithological, structural and slope characteristics of the area, in the attempt to define the different role that the latter have played in relation to the morphodynamic evolution of the hydrographic network within the study area. The DEM has provided us with information on the type of geomorphological evolution of the basins in relation to both the structural and lithological characteristics of the area and the distribution of the prevailing modelling processes. The assessment of stream load is consistent with the scanty data experimentally measured along the main watercourses in the pre-war period.