Flood Mapping Case study: on Bantyeketu River in Addis Ababa

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Addis Ababa University


Floods represent a natural risk with a very high frequency, which yearly produce important material and human losses. Therefore, developing some detailed maps regarding flood imposes for the accuracy of representation, these must be done at high scales. This study assesses the potential impact of flood on extreme hydrological events in Bantyeketu River in Addis Ababa. ARC-GIS 10 modeling software is used to delineate catchment for different river system in Akaki catchment and helps to obtain hydrological and physical parameters and spatial information of the Akaki catchment. Road Networks, houses and buildings as well as vegetation cover of Akaki catchment is digitized and corresponding areas is calculated. A hydrological model, HEC-HMS was utilized to simulate Runoff in Akaki Catchment. The performance of the model was assessed through calibration process and resulted R2=0.7. Optimal calibration parameters were developed for Akaki Catchment and these parameters was used as an input for HEC-HMS for estimation of peak discharge in the study. The peak discharge for Bantyeketu River for the coming ten years, Twenty five years and fifty years was found to be 13.1 m3/s, 14.7 m3/s and 16 m3/s respectively. Bantyeketu river carrying capacity was estimated using river cross section and HEC-RAS hydrological modeling software. Major problematic areas due to flooding were identified. The cross section around the distance of 1.2 km, 1.5 km, 2.8 km and 3.5 km from Finfina Bridge show low carrying capacity less than 13.1 m 3/s or 10 years estimated probable flood. 50 years return period flood of Bantyeketu River is used for the design of flood protection structure and river bed improvement work. Different flood protection structures and river bed improvement works were recommended depending on the flood depth and condition of river bank. Masonry flood wall and dyke were recommended and designed for areas around ECA ,Hay hulet , and up stream of Bantyeketu confluence with Kebena River. River bed improvement works were also recommended for Bambisse Area



stream of Bantyeketu confluence