Monitoring Coastal Dune Changes with Geospatial Technology

Author: Marcio DaSilva

DaSilva, Marcio, 2024 Monitoring Coastal Dune Changes with Geospatial Technology, Flinders University, College of Science and Engineering

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Coastal dunes develop across the globe on sandy coasts. Their dynamism and range reflect the world’s variability in climate, sea or water levels, sediment supply, vegetation types and land uses. Their evolution through time is dependent on many inter-related, and often inseparable natural and anthropogenic variables. Shifts in environmental conditions and disturbances can trigger shifts in their form, stability and alter their evolutionary trajectory. They are managed in many places as they provide an immense protective and ecological value to human and non-human communities, but they exist as natural wild environments across most of the world.

This thesis is focused on disturbances, their evolution and the responses of remote unmanaged coastal dune systems in South Australia. These semi-vegetated and stabilised dunefields are located in temperate climates within National Parks on the Southern Ocean. The disturbances studied as part of this thesis are fire and prolonged shoreline erosion, both of which are expected to be more common, severe, and widespread in the future. These disturbances are associated with potential initiation mechanisms or catalysts for transgressive dune phases.

The thesis is comprised of three main chapters formatted as journal articles and includes additional appendices. The chapters incorporate and develop geospatial and remote sensing methods at different spatial resolutions, including in-situ drone surveys, high-resolution aerial imagery and multi-spectral time-series satellite analyses. The contribution of this thesis adds to the contemporary understanding of the way dunefields are studied in the following main areas: (1) fire severity from space focused on the burnt dunefields of Kangaroo Island, (2) the ecogeomorphic response of those burnt coastal dunefields following the fire, and (3) the geomorphic evolution of rapidly eroding, translating and transgressing coastal dunefields on the Younghusband Peninsula in South Australia.

Chapter 2 of this thesis explores how the predominant method of measuring fire severity from space is heavily influenced by soil brightness and canopy density leading to systematic under-assessment of fire severity of coastal dunefields. In this chapter I introduce a new application of a disturbance index, which improves the fire severity from space as derived from a multi-spectral index of satellite imagery.

Chapter 3 examines the response of burnt coastal dunefields using 3D datasets to describe their post-fire trajectory and applies the satellite index from chapter 2. This work contributes to contemporary knowledge of coastal dunes responses to fire and shows that there is a lack of evidence for fire as an initiation mechanism for coastal dune instability and transgression, within this study and across the coastal dune literature.

Chapter 4 investigates the landscape evolution of a rapidly eroding coastal dunefield and describes its short- to medium-term response to prolonged shoreline erosion. 3D and 2D datasets are used to explore the relationship between sediment loss and its landward translation as aeolian cannibalisation drives dunefield transgression.

Overall, the components of this thesis demonstrate the resiliency and responses of these studied temperate coastal dune systems and how these dynamic landscapes respond to severe and prolonged disturbances. The application of geospatial and remote sensing methods to transgressive coastal dunes offers a dynamic approach to studying, monitoring, and understanding their evolution at the various spatial, spectral and temporal scales.

Keywords: Remote sensing, coastal dunes, transgressive dunefields, fire severity, shoreline erosion, multi-spectral satellite indices, drones, UAVs, NDVI, NBR, Kangaroo Island, Younghusband Penninsula, Black Summer fires, Geospatial, geomedians

Subject: Environmental management thesis

Thesis type: Doctor of Philosophy
Completed: 2024
School: College of Science and Engineering
Supervisor: Graziela Miot da Silva