Effect of Urbanization on Flood Generation (A Case Study on Addis Ababa City)

Abstract

The hydrologic behavior of the Addis Ababa urban watershed was characterized as subtle charter, with the objective of evaluating the hydrologic impacts of the increasing of the impervious area within its watershed and other factors. In order to decide on minimizing the impact of floods and to know the impact of urbanization on flood volumes and peak discharges, an effective flood volume estimation model is required. Towards this end, HEC HMS rainfall run off model has a great potential to quantify the actual increase river flow in urban development over the past 4 decades and including the future land use impact. This study of Addis Ababa will; gather IDF curve precipitation data for the watershed, generate a database using appropriate software, estimate flood volume, show urbanization effect on flood and use the model to simulate potential future effects on the Addis Ababa watershed using HEC­ HMS. Arc GIS, a software mapping tool using land use, soils, and property boundaries, facilitates definition of watershed hydrologic parameters and allows these parameters to be incorporated into HEC-HMS. Finally all the existing information related to the historical floods that have happened in the city during the studied period, as well as the historical evolution of land uses, was compiled and by running the model the result was compared at each junctions of the Addis Ababa city for each land use period. Therefore comparing the results of the model, the author is able to successfully establish the concern for increasing river flows due to urbanization. The results of this study will encourage emergency managers and local planning authorities to consider land use planning as an effective measure for flood risk