Oblique second-order sand transport pathways on an intertidal sand flat in a natural tidal inlet system

A detailed digital elevation model (DEM) of an intertidal sand flat in the Knudedyb tidal inlet in the Danish Wadden Sea, derived from high-resolution Light Detection And Ranging (LiDAR) data, reveals a large elongated bedform field with complex bedform morphologies and drainage channel networks. This indicates distinct second-order sand transport pathways oblique to the main tidal transport pathways. A conceptual model for the development of the bedforms and channels is presented, which comprises hypotheses of the hydrodynamic forcing of the different second-order sand transport pathways. During flood tide, sand is transported along ESE-oriented pathways across the intertidal flat towards the inner tidal basin. During the late stages of ebb tide, sand is transported in drainage channels (WSW-oriented) from the intertidal flat towards the inlet channel. During storm events with winds from SW, wave-generated currents transport sand along a NE-oriented transport pathway from the inlet channel towards the intertidal flat.