Time-lapse Analysis of the Effects of Oil and Gas Exploitation Using Remote Sensing and GPS in Parts of the Niger Delta, Nigeria

Changes due oil exploration and production have occurred within Cawthorne Channel area from 1986 to 2003. Three satellite image datasets consisting of Landat TM acquired On 19th of December 1986; SPOT 4 of 16th December 1998 and Landsat ETM of 8th January 2003 were used for the study. The satellite image datasets were processed using ISOclass unsupervised classification to generate the various landcover classes. Baseline information was extracted from Natural Colour Composites, LandCover Classification and Normalized Difference Vegetation Index (NDVI) composites, for the three epochs. The statistics of the various classes were then generated for each processed dataset. These statistics were further analyzed to identify the change patterns. Change analysis also involved processing and graphically identifying various landcover types and the changes that have occurred over the years. Normalized Difference Vegetation Index was performed using NDVI processing algorithm for the three epochs to adduce the possible reasons for such changes. From the analysis carried out, it is evident that the landcover classes changed across the three epochs. The water class covered an area of 80.12 km2 in 1986: 85.05 km2 in 1999 and 76.64 km2 in 2003. High mangrove covered an area of about 32.64 km2 in 1986, 77.72 km2 in 1998 and 110.41 km2 in 2003. This could be due to the decrease in low mangrove. Low mangrove covered an area of about 146.96 km2 in 1986, 100.66 km2 in 1998 and 75.41 km2 in 2003. Wet mangrove covered an area of about 25.46 km2 in 1986, 18.57 km2 in 1998 and 19.71 km2 in 2003. The increase in 2003 could be due to the presence of water within the mangrove. Settlements, sand and cloudcover covered an area of about 1.85 km2 in 1986, 5.03 km2 in 1998 and 4.86 km2 in 2003. The decrease in 2003 after the increase in 1998 might be attributed to sand reduction and vegetation growth. Also, orthometric elevation changes are carried out using Global Positioning System (GPS) to ascertain areas where elevation changes (land subsidence) have occurred. The rate of elevation changes (land subsidence) in the study area is at each location of levelling. It varies from 66.67 mm yr-1 to 200.00 mmyr-1, and an average of 86.00 mmyr-1. The elevation changes in this Field are localized only where the measurements are located, and are mainly in river and drenched channels and slopes caused by erosion. This conclusion regarding minimal impacts of hydrocarbon production on elevation changes is based only on orthometric height difference, and not on the reservoir stress changes. Knowledge of the present distribution and area of landcover, elevation changes, as well as information on their changing proportions, is needed by legislators, planners, and State and local governmental officials to determine better land use policy, to project transportation and utility demand, to identify future development pressure points and areas, and to implement effective plans for regional development.