Structure and development of shell cheniers in Essex, southeast England, investigated using high-frequency ground-penetrating radar

The stratigraphy and internal structure of contemporary shell cheniers on the southern Essex coast, England were investigated using a high-frequency (900 MHz) ground-penetrating radar (GPR) system. The cheniers lie on the seaward edge of laterally eroding saltmarshes, at the junction with the tidal flats. Four main types of chenier are recognised, each with a characteristic morphology and dynamic status. Migrated radar reflection profiles obtained from each of the chenier types achieved a sub-decimetre vertical resolution. Ground-truthing data demonstrate that the radar profiles accurately delineate the subsurface stratigraphy and sedimentary structure of the cheniers. Interpretation of the radar stratigraphy derived from the radar reflection profiles allows various deposits to be identified. These have resulted from overwashing, overtopping, sedimentation across the whole of a seaward dipping beachface or berm ridge welding onto the upper beachface. Each chenier is characterised by a different spatial arrangement of these four basic depositional units. The results from the GPR surveys support the hypothesis that each of the chenier types represents a distinct phase in the development of these contemporary coastal landforms. However, a simple model involving a linear progression through chenier types 1–4 with time appears inappropriate. Instead, two main evolutionary pathways are proposed, with the sequence of development being principally controlled by the nature of the cheniers’ longer-term sediment budgets.