Dechatu Catchment (Dire Dawa Town) Flood Study
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Date
2009-04
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Addis Ababa
Abstract
Nowadays, extraordinary floods are common to many parts of Ethiopia every year causing a lot of losses to human lives as well as damage to property. However, the researches and studies related to this problem are not as intensive as the damage.
Historically, Dire Dawa has been vulnerable to flash flooding from rainfall, in particular of the ungaged Dechatu catchment which passes through the centre of the city. The tributary rivers are originating from the southern highlands of Kersa, Lange and Dengego catchments.
Some organizations have tried to estimate the amount of flood and recommended the mitigation measures previously.
Traditional flood design methods are increasingly supplemented or replaced by risk-oriented methods which are based on comprehensive risk analysis. Besides meteorological, hydrological and hydraulic investigations such analyses require the estimation of flood impacts.
Hence, this thesis is to identify peak flood and delineate risk areas that can be affected by extraordinary floods and to recommend mitigation measures.
This thesis tries to consider more options and fills the gaps not covered by others adopting more than seven application softwares like GIS, ArcView, Global Mapper, HEC-HMS, HEC-GeoHMS, HEC-RAS and HEC-GeoRAS. Specially, delineation of the flood area and recommended mitigation measures selection method believed to be the gap not properly covered in the previous Dire Dawa flood studies which I have seen. The data usage for this thesis tried to make very intensive by considering different data options like gridded (DEM and contour), digitized (soil, land use and 1:50,000 scale map) and text (rainfall and discharge) type.
For precipitation modelling, ERA Intensity-frequency-duration curve is used for frequency storm and for the gage weights annual maximum daily rainfall for 24 hours and 6 hours duration storm are used since the concern is flood that uses more than one nearby metrological stations.
For geographic and terrain data, 57m resolution DEM for catchment, 4m contour interval for the town part and 0.5m contour interval for the Dechatu Stream cross section are used.
In this thesis, the flood magnitude estimated, flood area delineated and mitigation measures selection method recommended. The potential vulnerable areas for the 50 years return period flood are Kefira, Gende Gurage, Dechatu Kebele, Coca Cola factory areas, Ashewa Tera, Number one and Half-Cat.
Dire Dawa Administrative Council (DDAC), Organizations, engineers and planners who are involved in the study and management of the Dire-Dawa town flood are the direct beneficiaries. Others who are engaged in similar flood related problems believed to be benefitted from this thesis.
Now on ward, this will contribute to change the traditional trend of flood damage analysis which is found to be the outstanding problem by now.
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Organizations, Engineers