Simple Conceptual Explanation of Down‐Drift Offset Inlets

Abstract

A very simple, conceptual explanation of the cause of down‐drift offset inlets is presented. Sheltering of a time‐varying wave climate by the inlet's ebb‐tidal shoal causes the offset. Wave sheltering is defined to include all of the nearshore wave transformations that occur across the ebb‐tidal shoals, including wave refraction, diffraction, shoaling, breaking, and other forms of attenuation. Sheltering tacitly includes the effect of the shoal on the directional spread of incident wave energy. This explanation of down‐drift offsets is better than the oft‐quoted explanation of refraction around the ebb shoal for two reasons: (1) The present explanation, sheltering of a variable wave climate, specifically includes the factor of time, which is obviously important in geomorphologic feature development; and (2) there is little justification for explaining the current reversal only in terms of wave refraction. All that is needed to create a down‐drift offset inlet is an ebb shoal and a wave environment with a dominant direction of littoral drift and periods of reversal.