An Assessment of Urban Encroachment on Greater-Port Harcourt Watershed Using GIS and Remote Sensing Techniques
AbstractDeveloping countries have been rapidly urbanizing over the last decades, resulting in major environmental impacts and increased vulnerability to natural disasters. The main aim of this study is to critically examine the effects of urban spread along the headwaters of bonny river in Port-Harcourt metrolopolis. Methodologically, various aspects of data acquisition systems such as the use of unmanned aerial vehicle and remotely sensed data were applied. The output was further used to map flood hazards, flood zones and damage potential of the study area. Priority areas and infrastructure at risk were identified by means of their location in flood zones and exposure to floods with high damage potential. In terms of the extent of change, this study revealed that urbanization and loss of agricultural land had been the dominant and intensive land use change along the headwaters of bonny river. Again, the study found that as much as about 20 km2 of urban land lie under low risk. A number of districts selected for analysis indicated that there are more floodplain dwellers in the high-risk zone 1 area than medium risk zone 2 areas. Zoning is more effective in bare areas, and may be less effective where there are existing structures. It is projected to have a considerable impact on peak flow in a number of watersheds, which could have severe implications for flash flooding in some areas. Therefore to reduce flood risk where there are existing structures, this study suggests the need for the integration of structural and non-structural measures as well as relocation of flood channel dwellers to safer areas could also help reduce flood risk. The research was able to produce the flow extent map using elevation model. The research produced the flow direction of the study area which shows the channel direction of flow. It was observed that flood water flows from higher region to a lower region. This study was able to identify areas vulnerable to flooding using multi criteria approach.The study concludes that although the impact of urbanization is projected to be insignificant at the watershed scale. Priority infrastructures and areas of high flood risk within the study area is approximately 15.85 km2 and 19.61 km of road networks are at greater risk of flooding by means of their exposure to floods with the highest damage potential. Urbanization increased flood risk due to greater exposure of elements at risk in the flood plains to damaging floods which includes residential and commercial buildings, roads, schools, clinics and farmlands.Key words: Urbanization, Headwaters, Flooding, Unmanned-Aerial-Vehicle
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