*Article* **Spatiotemporal Trends of Bora Bora's Shoreline Classification and Movement Using High-Resolution Imagery from 1955 to 2019**

**Emma Gairin 1,2,3,\*, Antoine Collin 1,4, Dorothée James 1, Tehani Maueau 5, Yoann Roncin 6, Lucas Lefort 6, Franck Dolique 7, Matthieu Jeanson 8,9 and David Lecchini 4,10**

	- Okinawa 904-0495, Japan

**Abstract:** Coastal urbanisation is a widespread phenomenon throughout the world and is often linked to increased erosion. Small Pacific islands are not spared from this issue, which is of great importance in the context of climate change. The French Polynesian island of Bora Bora was used as a case study to investigate the historical evolution of its coastline classification and position from 1955 to 2019. A time series of very high-resolution aerial imagery was processed to highlight the changes of the island's coastline. The overall length of natural shores, including beaches, decreased by 46% from 1955 to 2019 while human-made shores such as seawalls increased by 476%, and as of 2019 represented 61% of the coastline. This evolution alters sedimentary processes: the time series of aerial images highlights increased erosion in the vicinity of seawalls and embankments, leading to the incremental need to construct additional walls. In addition, the gradual removal of natural shoreline types modifies landscapes and may negatively impact marine biodiversity. Through documenting coastal changes to Bora Bora over time, this study highlights the impacts of humanmade structures on erosional processes and underscores the need for sustainable coastal management plans in French Polynesia.

**Keywords:** coast; erosion; urbanisation; airborne imagery; spaceborne imagery; French Polynesia
