129-45 Effects of Vegetation Colonization on Shoreline Retreat Following a Channel Avulsion in the Caraulun River Delta, Timor-Leste

Abstract:

River channels deliver sediment to delta shorelines, where deposition promotes land building and shoreline advance. However, channel avulsion can redirect sediment delivery to different parts of the shoreline, leaving the abandoned shoreline vulnerable to inundation and erosion. Vegetation colonization may stabilize abandoned shorelines by trapping and reinforcing sediment, but the influence of vegetation colonization on post-avulsion shoreline retreat remains poorly constrained. To address this gap, we investigated the relationship between vegetation colonization and shoreline change in the Caraulun River Delta, located in southern Timor-Leste, following a channel avulsion that occurred in the mid-to-late 2000s. We obtained Landsat imagery for a 30 year period spanning pre-, syn-, and post-avulsion conditions and generated seasonal composite imagery for each year of the study period. We used these composites to identify shoreline positions throughout the observational record and calculate shoreline retreat rates for the pre-, syn-, and post-avulsion phases. We then used post-avulsion composite images to calculate the normalized difference vegetation index (NDVI) within the abandoned shoreline region and assessed the relationship between vegetation colonization and shoreline retreat during the post-avulsion period. Preliminary results indicate that shoreline retreat rates decrease as vegetation cover increases, but further analyses are required to determine the strength and significance of this apparent relationship. This study will improve understanding of the role of vegetation in regulating delta shoreline response following channel avulsion. 

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