Spatio-Temporal Analysis of Shoreline Changes in Bonny Island, Nigeria

Abstract

The study examined the shoreline changes over time in Bonny Island of Rivers State, Nigeria. Satellite images comprising of Landsat TM of 30m by 30m of 1986, 2001, 2003 and 2006; and Nigersat image of 30m by 30m of 2004 were used as the sources of data. The satellite images underwent series of geo-processing. The bands (red, blue and green) of each image were combined using Erdas Imagine 9.0. The images were imported to ArcGIS 9.2 whereby the shoreline from each image was digitized as polylines. The shoreline of 1986 was overlaid on that of 2001, shoreline of 2001 was overlaid on 2003, 2003 on 2004 and that of 2004 on 2006. Thereafter, overlaid maps were converted to polygons using Features to  Polygon module of ArcGIS 9.2. The polygons were grouped to advanced (land gained) or retreat (land lost) with which spatial query was done. The result revealed that Bonny Island lost about 1793.24 km² of land while 419.31 km² was gained between 1986 and 2001 whereas between 2001 and 2003; 1246.46 km² was lost while 1200.43 km² of land was gained. During the period between 2003 and 2004, the analysis showed that 858.47 km² was gained while 3408.68 km2 was lost whereas between 2004 and 2006, the 2460.30 km² of land advanced seaward while 2450.03 km2 of land was lost. The percentage change was highest between 1986 and 2001 with 76.62% of land loss. The study recommended periodic monitoring of the coastal area on monthly and yearly bases.

Keywords: Shoreline, GIS, Remote sensing, Bonny Island, Water transport, ArcGIS 9.2, Erdas Imagine