The Morphological Evolution of a Step–Pool Stream after an Exceptional Flood and Subsequent Ordinary Flow Conditions

Abstract

Mountain streams are frequently characterized by step–pool morphology that provides stability and energy dissipation to the channel network. Large flooding events can overturn the equilibrium of the step–pool condition by altering the entire configuration. This work focuses on the impact of the “Vaia” storm (27–30 October 2018) on a step–pool mountain stream (Rio Cordon, Northeast Italy) and on its evolution after two years of ordinary flow conditions. To achieve the aims, this work uses both remote sensing data (LiDAR and UAV) and direct field measurements (i.e., longitudinal profiles and grain sizes distributions) performed pre-event, post-event, and 2 years later (current conditions). The results show a significant widening (width +81%, area +68%) and the creation of a new avulsion after the storm and a substantial change between the number of units (51 in the pre-event, 22 post-event, and 51 in the current conditions) and characteristics of step–pool sequences between pre- and post-conditions. Furthermore, it proves the ongoing processes of morphological stabilization since the current step–pool sequences parameters are heading back to the pre-event values. Such results suggest clear susceptibility of step–pool to exceptional events and fast recovery of such setting during barely two years of ordinary flow conditions.

Assessment of Flood-Induced Geomorphic Changes in Sidere Creek of the Mountainous Basin Using Small UAV-Based Imagery

“…On the other hand, for a long time, soil erosion with the associated sedimentation in surface water has been one of the main concerns for researchers, not only from a water quality perspective but also for the aquatic life living in the respective environment. The erosion/deposition processes in stream channels and their floodplains are significantly affected by high stream stages and/or flash floods that cause major changes in the stream bed, banks, width and longitudinal aspects, and adjacent corridors within the riparian zone [7][8][9][10]. Most of the hydro-morphological changes in the riverscapes usually take place during the high stages of floods [5,11], where the sedimentary characteristics of the stream bed and the pattern of flood events [12] also damage aquatic habitats [13], agricultural areas, and residential areas [14].…”

“…Alterations of the morphological features of the mountainous river channel on spatial and temporal scales due to floods can be an indicator of channel disequilibrium [9]. Therefore, the continuous monitoring of the physical and hydrological conditions of the riverscapes is an important step for identifying and analyzing the key elements of controlling factors of the channel response and habitat quality [20][21][22].…”