A THESIS SUBMITTED TO ARBA MINCH UNIVERSITY IN PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THE DEGREE OF MASTERS OF SCIENCE IN HYDROLOGY AND WATER RESOURCES MANAGEMENT

Abstract

The August, 2006 flood event was one of the most significant and damaging natural disasters ever hit Diredawa. The total damages to public and private property were estimated 94,327,416.21Birr, 256 people died,244 people missing, crops on 256.7 ha of land were destroyed, rural water supply schemes were damaged in 17 rural kebeles, irrigation schemes were damaged and thousands of people evacuated and sheltered in temporary camps and fed for months there. This emphasizes the need for more reliable predictions of floods and their causes. This study focuses on the investigation of the cause and magnitude of flood in Diredawa area. Hydro-meteorological, topographic, land use and soil data of the study area have been used for the study. Various time scale rainfall data (monthly, daily or less than daily) have been examined to establish the causes of the flood. The aerial coverage, duration and intensity of the rainfall data were used. Accordingly the result revealed that the extreme daily rainfall which occurred on August 6, 2006 was found to be the cause of the flooding. Rational method was used to calculate peak discharge. This flood has produced /sec which flooded the densely settled suburb of Diredawa town. The destruction caused by this flood reveals the high cost imposed upon life and property by floods, and thus highlights the importance of preparing for such occurrences. It is possible to predict and contain a flood to a reasonable extent. The paper discuses some of the details of the flood, the precipitation event caused the flood and the mitigation measures. The rational method predicts peak runoff rates from data on rainfall intensity and drainage basin characteristics. In application of the rational method, design values of time of concentration and runoff coefficient was estimated. IDF curve was developed to find the intensity used in the rational formula .The predicted frequensy is determined by finding the intersection of the lines defined by the measured intensity and storm duration .The basic data used for intensity- duration-frequensy analysis of point rainfall consists of the largest events of each year. The point rainfall 3 an estimated discharge of 642.32m v estimate obtained from IDF curves were adjusted for large areas because the point estimates represent extreme values.