Flood Hazard and Risk Assessment in Fogera Woreda using GIS & Remote Sensing

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Addis Ababa Universty


Flood is a natural disaster. However human activities in many circumstances change flood behavior. Activities in the catchment such as land clearing for agriculture may increase the magnitude of flood which increases the damage to the properties and life. Fogera Woreda is one of the most severally flood affected areas in Northwest Ethiopia in general and Ribb- Gumara Catchment in particular. It is situated in the downstream part of Ribb and Gumara Rivers. Relatively dense population and different landuses are found in this area, which are vulnerable to flood hazard. Intensive agricultural activities on steep slope areas of the catchment and its expansion decrease the abstraction of rain water and there by changed quickly to flood water. The high magnitude of water that enters in to Ribb and Gumara rivers overflows these rivers. For a number of reasons the most frequent choice should be protection from the flooding by revilagizing the people to the safe ground, but there is also a need for a broader and comprehensive program for managing flood hazard in the study area. Flood protection has been helpful and must be continued. Side by side other preventive tools like effective landuse planning, creation of a computerized GIS database for the flood prone areas and a detailed flood risk assessment and mapping are required to minimize the harmful effects of flood hazard. Therefore, an attempt has been made to apply modern techniques like GIS and Remote Sensing for the assessment of flood hazard and flood risk in Fogera Woreda. The flood causative factors were developed in the GIS and Remote Sensing environment and weighted and overplayed in the principle of pair wise comparison and MCE technique in order to arrive at flood hazard and flood risk mapping. Landuse/landcover change detection was done for the catchment using the 1985 and 1999 Landsat images and shrub lands, grass lands and open wood lands were found to be decreased in areal extent while agricultural lands and swamps were increased. Comparison between long year (1974-2006) annual maximum daily rainfall and annual maximum daily gauge levels (1971-2005) data of Ribb and Gumara rivers showed that rainfall slightly decreases while gauge level increases, and this can be attributed to landcover removal especially in the upper catchment. Flood frequency analysis was done using Ribb and Gumara rivers annual daily maximum gauge levels and the likely flood levels in different return periods were found. DEM and the 100 year return period base flood were combined in the GIS environment in order to produce flood inundation maps. Results from the overlay analysis and from the flood frequency analysis soundly agree to each other. The major findings of the study revealed that most of the PAs in the down stream part of the catchment and the different landuses in these areas are within high to very high flood hazard and flood risk level. The presence of risk assessment mapping will help the concerned authorities to formulate their development strategies according to the available risk to the area. Key words: Flood, Hazard, Risk, GIS, Remote Sensing, MCE, Flood Frequency Analysis, Landuse/Landcover Dynamics, Fogera Woreda, Ribb-Gumara Catchment.



Flood, Hazard, Risk, GIS, Remote Sensing, MCE, Flood Frequency Analysis, Landuse/Landcover Dynamics, Fogera Woreda, Ribb-Gumara Catchment