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Title: Urbanization and Its Effect on Surface Runoff (A Case Study on Great Akaki River, Addis Ababa, Ethiopia)
???metadata.dc.contributor.*???: Dereje Hailu (PhD)
Misganaw, Nega
Keywords: DEM;TIN;flood modeling;HEC-HMS/RAS;HEC- GeoHMS/RAS
Issue Date: Jun-2016
Publisher: AAU
Abstract: On this study the effect of high urbanization rate of Addis Ababa City in general the study area on the Great Akaki River is assessed. The surface runoff generated from the catchment is estimated based on the rainfall intensity and major characteristics of the catchment area which are the major factors for designing urban storm water drainage facilities and structures. Satellite image for 1989, 2000 and 2010 of the catchment area is taken based on the quality of data and the available resolution. ArcGIS and GIS extension tools are used to extract hydrological characteristics of the catchment; HEC-RAS for hydraulic modeling, and HEC – HEC-HMS to simulate rainfall - runoff process on Great Akaki watershed which is the major watershed located at the center of Addis Ababa. The hydrological and hydraulic modelings are accomplished by dividing the watershed in to different sub-catchments. To compute infiltration loss SCS CN method; converting excess rainfall to runoff model SCS unit hydrograph, and channel flow routing accomplished by using Muskingum routing method of HEC-HMS model. To evaluate the accuracy of the simulation model calibration and validation was conducted. The hydrological modeling classified in to two: the first simulation shows the effect of high urbanization growth on the basin. Accordingly, the peak discharge for 1989, 2000 and 2010 at the Bridge outlet along Addis Ababa Bishoftu Road is 131, 153.4 and 188.1m3/s respectively. To avoid the effect of rain fall variation on the generated peak discharge similar hourly rainfall of 18 July 2010 was used for each respective year. The second simulation uses frequency storm method for 10, 50 and 100 return periods and peak discharge of 403.80, 546.50 and 634.70m3/s for each respective return period was obtained. The result found from HEC-HMS frequency storm method used for hydraulic analysis and flood map hazard generation. Flood inundation maps produced using ArcGIS to visualize flood depth and extent for each return period. Accordingly, maximum flood depth of 7.86, 9.07 and 9.82m for 10, 50, and 100 year return periods respectively was found with flood extent of 82.34 for 10 return period and 100.15 for both 50 and 100 year return periods at the middle of the final reach of the study area.
Appears in Collections:Thesis - Hydraulics Engineering

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