FLOOD INUNDATION MAPPING AND HAZARD ASSESSMENT:A CASE OF WERA RIVER FLOOD PLAIN OF BOYO CATCHMENT, ETHIOPIA

Abstract

Floods are one of the most common hazards in the world and cause loss of lives, livelihood, and property destruction. The objective of this research is to carry out flood inundation mapping and hazard assessment in the Wera River flood plain of Boyo catchment. The flooded areas along the Wera River flood plain of Boyo catchment have been mapped based on using the HEC-RAS (5.0.7) model, GIS (10.4.1) for spatial data processing, and HEC-GeoRAS (10.3) for interfacing between HEC-RAS and GIS. From this study peak floods was estimated statistical frequency analysis was carried out by log persons three distribution function based on the procedure frequency analysis for 5, 10, 25, 50, 100, 200, 500 years return periods were 61.03, 159.82, 239.71, 344.84, 421.22, 493.50, 560.96, 642.16m3/s for Alaba kulito ,55.18, 147.42, 218.82, 307.52, 368.01, 422.07, 469.61, 522.93m3/s for Wera and 12.23, 24.82, 37.74, 61.27, 85.57, 117.23, 158.30, 231.46m3/s for Batena respectively for respective return period, inundation map in study area was delineated for 5, 10, 25, 50,100, 200, and 500 years return period were 112.31,112.97, 113.56, 113.85, 114.25, 114.43, 114.73 and 114.77 Km² respectively. Flood hazard maps were prepared by reclassifying the depth grid and its area bounding polygon. Also, the area inundated at very severe, severe, high, moderate, and low flood hazards around 90%, 2%, 2% 2.33%, and 4%, respectively for all return periods. Due to the topographic setup, most of the tributaries of Lake Boyo start their courses from relatively higher elevations, so heavy floods during the rainy season at very flatlands of the area, especially flood plains in shashogo Woreda which is susceptible to flooding every year during the rainy season. Consequence waters remain stagnant for about one to two weeks over the flood plain of the Woreda. A flood hazard map was developed, to reduce economic and environmental losses, crop failure, loose life, and property study area. This study results recommended that Government and other concerned bodies should make a motivation program policy for planting endemic vegetation on flooded areas and change those flooded areas into green areas