Time-lapse photography of the edge-of-water line displacements of a sandbar as a proxy of riverine morphodynamics

A simple methodology to track the displacements of a sandbar from a fixed video camera, extracting its morphological features and deriving the associated fluvial morphology is presented, using a small reach of the Po River in Italy as a case study. A camera fixed on a bridge pier acquired images every twelve hours while hourly water levels are derived from a radar hydrometer located upstream of the study area. The quantification of the fluvial bathymetry is achieved by mapping multiple edge-of-water lines of a sandbar before and after high flow conditions in December 2017. Both from video information and 2-D numerical simulations, it is evident that flooding waves can easily remove sediments that accumulated on bars during low flow conditions in this area, redistributing them across the river channel. This video-based methodology-which confirms to be economically attractive if compared to more traditional monitoring systems-proves to be a valuable system to monitor long-term fluvial processes providing detailed indications on how to better plan river management activities.