Over the years the perennial flooding has not abated. Vanguard Newspaper of Nigeria of Monday 27th June 2005 reported that, "about 3,500 families in Owerri municipality and its adjoining villages were at the weekend sacked by flood, which resulted from a heavy rainstorm that lasted for two days." The Newspaper put the cost of the material loss at N200 Million. (2010) reporting for the United Nations Office for the Coordination of Humanitarian Affairs, Regional Office for West and Central Africa (UNOCHA/ ROWCA) writes, "Since 2007, the flood situation in West Africa is becoming more and more recurrent and the impact on the population and infrastructures is becoming more severe.” Owerri, capital city of Imo State, South East Nigeria has also had many cases of flooding in the past quarter of a century, along with a good number of other Nigerian cities. As atmospheric temperatures nudge higher, the scientific world is responding with efforts at learning more of the way the morphology of sub-catchments reacts with rain storm runoffs. Introduction Runoff prediction and control are gaining global attention due to increasing flooding resulting from more tempestuous climate events owing to global warming. Characteristics of the sub-catchments including the average slope, the longest flow distance, the area and the centroid coordinates required for input in the Storm Water Management Model of the Environmental Protection Agency of U.S.A. All cells that contribute into each stream were dissolved into a single unit of sub-catchment polygon and delineated. The DEM was processed through a number of steps in GIS to determine drainage routes with a minimum accumulation threshold. The DEM was validated using Global Navigational Satellite Systems (GNSS) surveys. In this study, Geographic Information Systems (GIS) were used to create a Digital Elevation Model (DEM) of Owerri, South East Nigeria. The delineation and characterization of sub-catchments would provide some basic data required for flood prediction, drainage design, water quality studies, erosion data, and sediment transport among others. All surface water flow systems occur in units of sub-catchments, the basic unit of landscape that drains its runoff through the same outlet to contribute to the main stream of the overall catchment. Catchment delineation and characterization are gaining increasing global attention as scientists seek better understanding of how runoff interacts with the landscape in the face of increasing flood devastations across the globe.
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