GEOSPATIAL ASSESSEMENT OF SHORELINE CHANGES ALONG THE COASTAL AREA OF ONDO STATE, NIGERIA.

Abstract

.Studies have revealed that poorly monitored changes in shorelines may lead to disastrous effects on human and livelihood. Over four decades, shorelines of Ondo State have been experiencing a consistent landward movement, thereby causing sea incursion in some communities along the coastal areas of the state, which have claimed lives and properties. This study determined; the horizontal changes in the coastal area of Ondo state between 1911 and 2019; the bathymetry characteristics of the coastline between 1986 and 2019; the volume and rate of change of sediment gain and loss; and predicted the future positions of the coast, both horizontally and vertically. The aim of the study was to assess the changes in the shoreline along the coastal area of of Ondo State, Nigeria with a view of providing relevant information that will be of assistance to coastline management in the state. The shorelines at different years were delineated using historic administrative maps covering the study area, which was produced in 1911 and 1978, and from Landsat imageries of 1986, 1999, 2002, 2015, 2016, 2017, 2018 and 2019. Horizontal changes in the coastline over the years were determined using five transect methods. Satellite Derived Bathymetry (SDB) was used to determine depths along the coastal areas, which was used to estimate the volume of sand sedimentation. The results however indicated that there were horizontal changes in the coastal area as accretion occurred mostly in the western flank of the coastline, while coastal erosion occurred majorly in the eastern flank of the coastline. The bathymetric characteristics showed that the depth of the ocean was increasing farther away from the coastline into the Atlantic Ocean. It was deduced that the period between 2015 and 2016 had the highest sediment net loss, while the highest sediment net gain occurred between 2017 and 2018. It was then forecasted that accretion will probably continue to occur in the western flank of the coast, while erosion will probably likely occur in the eastern flank of the coast in the year 2039, based on the historical data of the coastline. The vertical forecast, which is the bathymetric characteristics showed that depths will probably follow the same pattern as the previous years. It was further deduced that majority of the sediment net gain will be deposited towards the western flank of the coast, which is Abala axis in the year 2039.