Flood hazard and risk asseesment using gis and remote sensing techniques in gambella region; a case study makuey woreda

Abstract

Floods can be explained as excess flows exceeding the transporting capacity of river channel, lakes, ponds, reservoirs, drainage system, dam, mountain torrents and any other water bodies, whereby water inundates outside water bodies areas. Human activities such as: land degradation; deforestation of catchment areas; sprawl and increased population density along riverbanks, poor land use planning, zoning and control of flood plain development, changing the natural drainage systems; inadequate drainage, poor infrastructures particular in cities, and inadequate management of discharges from river reservoirs can significantly increase the risk of flood damage. In the Horn of Africa (HOA), composed of Djibouti, Eritrea, Ethiopia, Kenya, and Somalia are suffers from the frequent of flood. In Gambella People's Regional State (GPRS) the Gilo, Baro and Akobo Rivers started to overflow in June due to continuous heavy rains in the central highlands of Ethiopia. The Makuey Woreda and Wanthoa Wored which situated between Baro River and Alwero river or Makuey River were mostly affected by flood hazard in to various degrees at various times during flood. The impartial of the study has been identify the areas which are chronically suffering from flood hazard, analyze the flood probabilities, magnitudes and the vulnerability of people living in floodplain and estimation the flood risk on resident, environmental, agriculture & infrastructure. The methodology was consisted of data collection and data basing required for flood hazard and risk assessment. The multiple Categories of Hydrology modeling Tools, GIS and RS Technologies software and Geo-Statistical data analysis tools where applied. The warning level and danger level of floodplain areas was calculated using the maximum instantaneous discharge data. Flood Hazard Water Depth was calculate to illustrate the total area under the water depth by identify the more than normal levels for consideration of the increase of flood magnitudes. The Flood frequency analysis was done using the Gumbel‟s Method for predication of flood peaks, maximum rainfall and to calculate the peak discharge. In additional proposed methods , the several steps has been involved for analyzing the influences of physical parameters approaches specially Rainfall, slope/elevation, drainages density, stream flow, geological and land used data. The Flood vulnerabilities, floodplain map, flood inundate map and flood hazard maps was developed to carry out the final flood risk maps in study area. The study indicated that the extreme and land use change, which involved intensification of agricultural activities, increased the overflow magnitude that caused high flood hazard in downstream part of the river basins. Based on the flood hazard study in the woreda the very low, low, moderate, high, and very high flood hazards zones were estimated the Agricultural, Crop Vegetation, Building up , Grass land and forest Land areas are classify as 5, 4, 3, 3, and 1 respectively. The interpretation on assessment of the flood hazard and risk indicated that a large percentage of cultivation area lies under high hazard. Areas of high hazard need immediate attention, hence appropriate flood protection measures should be taken earlier and the onset of the flooding used to be more predictable and allowed farmers to plan for sowing crops at the optimal time