Distribution and morphometry of buried inlet channels along a microtidal paraglacial coast: Indispensable role of GPR

Abstract

Breaching of coastal barriers, leading to the formation of ephemeral or permanent inlets, is an essential element of coastal evolution in many parts of the world. With time, some inlets migrate or close, leaving no surface signature of their existence. The challenge of locating these channels through coring is exacerbated by high gravel content and widespread anthropogenic development. Subsurface imaging using ground-penetrating radar (GPR) is often the only viable technique to overcome this limitation. GPR surveys carried out across microtidal baymouth barriers fronting salt ponds on Cape Cod, Massachusetts reveal a series of paleo-channels that lack any geomorphic expression. In some areas, channel fill comprises 50–80% of the barrier lithosome. The pre-closure dimensions of historic channels identified on charts and photographs spanning the past 170 years were measured in these subsurface records. In addition, records revealed eight previously unknown relict channel structures with widths (W) ranging between 25 and 100 m and depths (D) of 1–4 m. Based on minimum cross-sectional dimensions in GPR images, a W/D ratio of ~40 is characteristic of the natural (unstabilized) paleo-channels. This study demonstrates that the distribution and morphometry of buried channels based on high-resolution geophysical images can be used to reconstruct past equilibrium hydrodynamic conditions, with implications for locating important alongshore anomalies and assessing coastal vulnerability to breaching.