Controls on local scour and deposition induced by obstacles in fluvial environments

Obstacles in fluvial environments cause flow separation and the emergence of three-dimensional flow fields that can lead to scour and deposition, even when no general sediment transport at the bed occurs. Resulting forms are commonly denoted as ‘fluvial obstacle marks’. The morphology and dynamics of these forms is depended on obstacle-, flow- and sediment characteristics. As no generally approved approach for analysis of these forms exists yet, a process-based method is developed that relates certain dependent morphometric variables to an adapted obstacle Reynolds number. The novel approach was applied by conducting experiments in a laboratory flume and validated against other laboratory and field data. The results of this work have shown a significant relationship between the morphometry of fluvial obstacle marks and obstacle Reynolds number, especially when morphometric variables were combined. Further validation, calibration and extension and of this approach will help to adequately asses the influence of obstacles in the fluvial environment on micro- and meso-scale processes of sediment transport.

Research highlights
► We experimentally investigate local scour and deposition at obstacles in rivers.
► Corresponding bedforms are classified as complex geomorphic systems.
► Local scour depth is identified as a key order parameter.
► Local scour depth is modelled using an obstacle Reynolds number approach.
► The analytical model is validated with bridge scour field data.