Ship-induced morphology along a maritime waterway in a micro-tidal environment

High-resolution bathymetry data from Kiel Bight, Western Baltic Sea, Germany, reveals distinct bedforms in water depths between 12 and 19 m, laterally confined to a ca. 3000 m wide band along an 18 km long stretch of a busy maritime waterway. The seabed displays entrenched channels with asymmetric current ripples, migrating dune-like sand bodies and scours and comet marks at boulders. The current direction indicated by these features aligns inversely with the direction of ship traffic on either side of the maritime route. The patterns suggest that the ship-induced flow from passing vessels changes seabed morphology and sedimentology, resulting in a more complex seabed structure than natural forcing allows. The critical shear stresses for mobilization of the sediments and the dimensions of the seabed features agree with empirical estimations of the propeller-induced shear stress footprints on the seafloor. A comparison of a recent survey with data from ten years before shows a cumulative impact on sediment transport. The spatial limitations of the distribution of the indicative features are used to establish thresholds for water depth and route density and used for an extrapolation beyond the observed occurrence to highlight other possible hotspots for this anthropogenic impact on the seafloor. • Propeller jets from ship traffic generate distinct bedforms on the seafloor. • Propeller-induced shear stress exceeds natural forces by orders of magnitude. • Bedforms and sediment sorting indicate persistent anthropogenic impact. • Thresholds for impact may help to identify other vulnerable shallow regions globally. • The findings highlight need for further ecological studies of ship-induced changes.