Foredune Blowout Sediment Transport: Event Scale Dynamics and Meso-Scale Geomorphic Change.

Abstract

Blowouts are dune landforms associated with high relative levels of aeolian sediment transport. Conceptual models of coastal morphodynamics explain system behavior, through cross-shore transfers of energy and materials (Short and Hesp, 1982). Further, the seminal model of evolution, (Psuty, 1988) denotes beach-foredune sediment exchanges to be of paramount importance to meso-scale change. Therefore, foredune blowouts, recognised for heightened sediment transport activity, and located in a critical cross-shore position, may be landforms of particular significance. Whilst in a period of prolonged sea level rise, as coastal dunes act as a natural buffer against storms and flooding, this thesis addresses the need for better understanding of foredune blowout transport events, and their implications to longer term evolution.

The research examines event scale airflow and transport dynamics at a foredune blowout location. Synchronous, high frequency airflow and instantaneous sediment transport were measured using ultra-sonic anemometry, and laser particle counters respectively. Meso-scale geomorphic change was assessed along a transgressive coastline which is characterised by frequent foredune blowouts, using a LiDAR time-series of an unprecedented duration (19 years).

Longshore transport across the foredune was identified as a principle pathway for sediment delivery to the blowout. At the landform scale, wind approach angle relative to foredune orientation, governed airflow enhancements within the blowout, which were a primary control on transport. The spatial clustering of trough sensors demonstrated an inverse relationship between wind speed and transport intensity. Sediment input from the far field and directional divergence of airflow and transport vectors exerted strong control on event dynamics. Novel analytical techniques are introduced which offer improvements to conventional methods.

At the meso-scale, foredune blowouts were confirmed to enhance the rates and magnitude of geomorphic change. Blowouts, formed and maintained by visitor pressure, made significant direct contributions to coastline recession and indirectly augment trends of retreat.

Date of Award	10 Nov 2021
Original language	English
Awarding Institution	Edge Hill University
Supervisor	IRENE DELGADO-FERNANDEZ (Director of Studies), PAUL APLIN (Supervisor) & JOAQUIN ALBERTO CORTES CARRILLO (Supervisor)