Assessment of River Bank Overtopping Problem (In case of Sedie River, Abbay basin, Ethiopia)
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Date
2020-06
Authors
Journal Title
Journal ISSN
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Publisher
Addis Ababa University
Abstract
Flood forecasting is an important mechanism to prevent and manage the consequences of flood
damage problem on agricultural areas. This study focuses on assessment of Sedie river flooding
problem by preparing flood inundation map for different return periods. Different models
including hydraulic model HEC Ras, hydrological model HEC HMS with integration of ArcGIS,
HEC GEOHMS and Ras Mapper tools used for conducting this study. Primary data, surveyed river
cross section and secondary data’s such as rainfall, stream flow, DEM, Land use / land cover and
Soil type data’s collected and used for the study. Totally around 8 years of observed flow data 5
years (1996-2000) for calibration and 3 years (2001-2003) for validation used. After the analysis
of the data it was found that HEC HMS calibration and validation result was good and the
performance of the model checked with the coefficient of determination and Nash-Sutcliffe with
good result of 0.84 and 0.83 for calibration, 0.74 and 0.73 for validation respectively. Due to the
unavailability of observed water level and rating curves in the study area the HEC RAS model
calibration and validation result compared qualitatively and relatively good result obtained. The
calibrated manning roughness for the left and right bank obtained 0.035 and 0.025 for the main
channel of the river. The flood inundation map prepared by using Ras Mapper tool and different
flood inundation map results for different return periods obtained. The flood inundation map shows
that for especially 50yr and 100yr return periods the flood damages 177.22 ha and 280.78 ha
farming areas respectively. Therefore in order to mitigate this damages structural and nonstructural
measures
recommended
depending
upon the
severe of
damage
at
each
stations.
Description
Keywords
Arc GIS, Economic analysis, Flood mapping, HEC GEOHMS, HEC HMS, HEC RAS, Ras Mapper