Fractal dimension of drainage network geometry of some Mediterranean-type river basins in California, Spain and Italy: a geomorphologic key to interpretation

By applying fractal geometry analysis to the drainage network of three large river basins in America and Europe, 2D-fractal dimensions through the correlation integral have been calculated. Preliminary results have been compared with classical geomorphic-quantitative indexes to highlight fluvial dynamics. The basins of Russian River in northern California, Ebro River in northeastern Spain and Volturno River in southern Italy, in present-day Mediterranean climate and with different geologic history and tectonic styles, have been analyzed. Preliminary results show an average fractal dimension slightly above unity. This suggest that basins have experienced concurrent overlay of secondary modeling processes, resulting from morphoselective erosion in a climate different from the present, on the primary tectonic processes, responsible for both the current structuration of inherited landscapes and degree of structural control. Tectogenesis was intense in the Plio-Pleistocene, although currently very active in some of these basins, while morphogenesis mainly occurred in the Late Quaternary and its effects are well preserved. The different fractal degree would indicate river basin evolution at certain periods was controlled by glacial fluctuations, at others by intense effects related to Plio-Quaternary tectonics and locally to Pleisto-Holocene volcano-tectonic activity. Finally, in historical times such phenomena appear to have been overlain by fluvial dynamics.