Because the term ‘‘rippled scour depression’’ is associated with the genetic, cross-shelf process interpretation of Cacchione et al. (1984), and because the most recent surveys have shown that they are not simple depressions, we adopt the term ‘‘sorted bedforms’’ to describe the features off Wrightsville Beach and elsewhere.

Swift and Freeland (1978)referred to similar features off the northern North Carolina coast as bedforms, but suggested no general mechanism to generate the marked sorting of sediment sizes associated with them. They referred to an analytical model for the growth of topographic bed- forms in a unidirectional current (Smith, 1970). However, inner-shelf sorted features are primarily compositional phenomena, exhibiting very subtle topographic expression with relief on the order of a meter over widths on the order of hundreds of meters. If topographic interactions drove the development of the features, they would be expected to attain more than subtle relief in at least some locations.

The widespread occurrence of sorted bedforms on the shoreface and inner continental shelf suggests that oceanographic processes are responsible for their formation and evolution. They are apparently independent of geologic factors, such as underlying stratigraphic framework or sediment supply, although both factors may play an important role in the overall settings in which they occur. Studies off Wrightsville Beach suggest that these features are not ephemeral, and indeed persist through a wide range of storm and fairweather conditions over interannual and long- er time scales.

In the next section we describe observations that, along with those above, motivate a hypothesis for a mechanism that could lead to the self- organization of sorted bedforms. (‘‘Self-organization’’ refers to pattern formation caused by interactions within a system, as opposed to being dictated by the patterns of the forcing or the initial conditions.) This conceptual model postulates that sorted bedforms are a robust result of the interaction of waves, mean currents, and poorly sorted bed material, in a moderately high-energy environment (outside the surf zone).

Quoted from: A new hypothesis and exploratory model for the formation of large-scale inner-shelf sediment sorting and ‘‘rippled scour depressions’’