Impact of morpho-sedimentary heterogeneities on the evolution of coastal meandering rivers (Brenta River, Italy)

Abstract

Over time, alluvial coastal plains are formed as rivers evolve and alter the landscape by eroding and depositing various morpho-sedimentary bodies. These bodies contribute to creating morphological, lithological, and topographic heterogeneities in the floodplain, which can in turn influence river dynamics by providing preferential areas for erosion and river avulsion. While the influence of differential changes in floodplain elevation on river dynamics has been explored in relation to the interaction between rivers and tectonics, there is still a significant gap in understanding the effects of subtle elevation changes produced by the distribution and composition of buried sedimentary bodies.This study examines the response of an ancient river channel to morphological and sedimentological heterogeneities in the floodplain substrate. It focuses on a 14 km long paleo-channel belt located in the southern Venetian Plain (northeast Italy), using field analyses such as sediment coring and geophysical investigations, as well as remote sensing for morphometric analyses. The results indicate that the paleo-channel belt underwent changes as it crossed an ancient sandy beach ridge, which is still visible as a relative high point in the present-day floodplain. Variations in floodplain gradient and substrate erodibility brought about morphometric changes in the paleo-channel, with downstream impacts on the grain-size distribution. This study emphasizes how heterogeneous substrates in alluvial and coastal plains have the potential to induce significant alterations of river morpho-sedimentary processes.