Assessing The Impact of Sea Encroachment in Ilaje, Ondo State, Using Optical Satellite Imagery Analysis and Shuttle Radar Topography Mission

Abstract

This study assessed the impacts of sea encroachment in Ilaje Local Government Area of Ondo State, Nigeria, using multi-temporal optical satellite imagery and the Shuttle Radar Topography Mission (SRTM) Digital Elevation Model (DEM). This study analyzed past and recent shoreline change trends, simulated elevation-based vulnerability to flooding, and predicted the potential effects of sea-level rise. Landsat images from 1995, 2000, 2005, 2010, 2015, 2020, and 2025 were analyzed to identify the shoreline, and shoreline changes were calculated using the End Point Rate (EPR) and Linear Regression Rate (LRR) in the Digital Shoreline Analysis System (DSAS). Elevation-based vulnerability maps were modeled using the SRTM DEM, and future inundation was projected using sea-level rise data. Results showed that erosion was more severe along the Ilaje coastline, with over 70 percent of the shoreline retreating at different rates, while only small sections experienced accretion. The inundation model, assuming a conservative rise of 0.269 m, indicated that more than 555 km$^2$ of land could be submerged, and a 1m rise could flood over 650 km$^2$ by the year 2150, an event that would affect settlements such as Ayetoro, Ogogoro, and Gbeke Eke. These findings emphasize why Ilaje communities are at risk of land loss, displacement, and livelihood impacts. The analysis concludes that sea intrusion poses a significant threat to the coastal ecosystem in Ilaje. This study recommends integrating the coastal zone into planning efforts, restoring mangroves as natural barriers, adopting stricter measures to prevent unsustainable human activities, and maintaining ongoing geospatial monitoring as part of a sustainable strategy for change.