Design and application of coastal erosion indicators using satellite and drone data for a regional monitoring program

Abstract

Coastal erosion is a complex issue that affects landforms at various spatio-temporal scales, with concerns rising due to the impending threats of climate change. Given the increasing availability of coastal shoreline data, we identify a gap in present coastal management methods: the need for a simple and cost-effective mechanism to track and compare shoreline trends, to inform high-level reporting, down to local management scales. This study introduces simplified, automated erosion indicators, demonstrated for 20 morphologically diverse beach sites across the temperate coast of Victoria, Australia. The methods utilise coastal drone surveys (2018–2023; 560 surveys) and satellite-derived shorelines (Digital Earth Australia Coastlines, 1988 to 2021). Two tools are introduced: (1) the Erosion Warning Indicator, for high-level reporting, reducing multiple aspects of shoreline change (long-term vs. short-term; widespread vs. hotspot) to a simplified scoring system allowing overall site assessment and comparison across sites; and (2) the Erosion Hotspot Detector, to aid local managers to automatically identify and analyse emerging erosion areas. Results for a 2-year period (2021-22) indicate one site with a high erosion warning level, and four sites with a moderate level. Tracking the indicator over time (2018–2022) identifies two sites with persistently high erosion warning levels (Apollo Bay and Marengo). Importantly, the indicators also highlight areas where recent erosion trends differ from longer-term patterns (e.g., Inverloch), allowing re-evaluation of short-term expenditure on management interventions, without impacting longer-term adaptation pathways. The erosion indicators presented here hold value for coastal managers in many parts of the world. If comparable approaches are introduced and shared at scale, we will collectively be better equipped and informed to respond to future challenges to our coastlines.