AN ASSESSMENT OF URBAN ENCROACHMENT ON OGUN RIVER BANK PROTECTION ZONE IN ABEOKUTA CITY, NIGERIA
An assessment of urban sprawl in Abeokuta city, Nigeria from 1964 to 2008 was conducted. The study investigated the rate of encroachment of buildings on the Ogun River bank using Geographical Information Systems and remote sensing techniques. Topographic map of the city was scanned, imported into GIS, and digitized. Series of multi-date remote sensing satellite imageries were also acquired, processed, classified (where necessary) and vectorized to enable full assessment of the spread of built up area into the River bank Protection zone (RBPZ). A recent, high resolution satellite (Ikonos) image was utilized to assess the situation at present. Results of the assessment revealed progressive spatial expansion in the city and progressive encroachment on Ogun river right of way. Particularly, gross encroachments were pronounced in the aboriginal part of the city. A total of 34.1ha of built up area are completely within the protection zone as at 1964, this increased to 50ha in 1974, 77 ha in 1984 and 90 ha in 1994. In the year 2008, the encroachment was almost four times (123 ha) what it was in 1964. The study demonstrated that use of remote sensing and GIS is very useful and effective for the monitoring of urban sprawl. It provides a tool of the quantitative measurement that is needed for rapidly growing regions in identifying internal variations and temporal change of urban sprawl patterns in different periods.
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