Browsing by Author "Ezenwa, Kenneth Onyemauche"

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    Geospatial analysis of shoreline dynamics in Ondo State Nigeria
    (Geography,Obafemi Awolowo University, 2015) Ezenwa, Kenneth Onyemauche
    The study identified the shoreline positions from satellite imageries during different periods and determined the sections of the shoreline affected by erosion and accretion. It also determined the shoreline migration rate during the study period and analysed the shifts of the shoreline during the study period from 1969 to 2013. This was with the view to evaluate the changes in the shoreline positions along Ondo State shoreline between 1969 and 2013. Primary and secondary data were used for the study. Multi-temporal satellite images of 1986 and 1999 Landsat Thematic Mapper (TM), 2005 and 2013 Enhanced Thematic Mapper Plus (ETM+) were utilized for the study. A topographic map of 1969 was used to derive digital map data for the study. A maximum likelihood supervised classification method and nearest neighbor resampling technique were adopted in processing the satellite images and topographic map in ILWIS environment. All exported data from ILWIS were incorporated into ArcGIS 10.1 and analyzed with various modules including 3D Analyst, Spatial Analyst and Spatial Statistics tools. The Digital Shoreline Analysis System (DSAS) was used to analyze and predict rate of shoreline displacement. The linear regression results enumerated changes which are likely to take place along the shoreline. The results of the study showed a preponderance of erosion over accretion during the study period. During the period between 1969 and 1986, 4,081,916.66 m2 of land was lost to erosion while 3,104,099.88 m2 of land was accreted. The period from 1986 to 1999 witnessed 5,573,979.52 m2 of land being lost to the ocean from erosion while 1,498,052.52 m2 of land was gained due to accretion. Erosion of the shoreline between 1999 and 2005 accounted for 3,337,573.18 m2 of land loss to the ocean while accretion within the same period accounted for 1,961,082.53 m2 of land gained from the ocean. In the period 2005 to 2013, erosion of the shoreline accounted for 3,066,233.23 m2 of geospatial change due to erosion while accretion of the shoreline within the same period accounted for 3,396,440.8 m2 of land gained from the ocean. Out of the sixty four (64) settlements located within 1000 m of the 1969 shoreline, thirteen were seen to have been washed away by erosion. This figure represents 20.3% of the settlements overtaken by the ocean within the last 45 years. The Digital Shoreline Analysis System (DSAS) was used to compute shoreline rate of change statistics. Approximately 93 transect profiles at 600m spacing were cast at right angles to the shoreline. The results showed that Ondo State shoreline was a very dynamic feature with an average rate of erosion and accretion estimated to be about -4.23 m/yr and +3.42 m/yr, respectively. Individual rates of erosion and accretion along some transects were as high as -10.42 m/yr and +8.052 m/yr, respectively. With the aid of Linear Regression analysis, future positions of the shoreline were predicted for the years 2023, 2033 and 2043. The study recommend that erosion control be erected, proper monitoring and mapping of coastal zones should be implanted to reduce the shoreline accretion and erosion. The study concluded that the shoreline dynamics evaluation (coastal zone management and monitoring) can be carried out using remote sensing and GIS techniques.