QUANTIFICATIONS OF DAM-INDUCED HYDROLOGICAL ALTERATION IN GILGEL GIBE I WATERSHED

Abstract

Flow alteration due to the climate variation/ change and Antropogenic activities are common. In this, we investigate the impact of climate variation and human activity particularly Gilgel Gibe dam I construction on total flow of Gilgle Gibe I watershed for pre and post dam construction period. Man-kendall trend test used to analyze climate variation, Sihymd model were identify the effect of climate variation and human activity by comparing simulate and observed flow statistically and also lan use and land cover change of two distnict period classification were analyzed by Ar-GIS for the pre and post dam period. The Indicators of Hydrological alteration soft ware were used to quantify the total flow of Gilgle Gibe I watersh ed at dam site. And we get the significant effect of climatic variability for pre-dam construction in this study area the data such precipitation, temperature and evapotranspiration were used to analyze the trend over the range of 1988–2010 at annual timescale. Change to rainfall trends of the Asendabo and Limmu station shows the decreasing trend where the temperature and Evaporation of the two stations shown the increasing trend which contributed to decrease the stream flow change in watershed but this was statistically insignificant. We also simulate and calibrate the Simhyd conceptual model for pre and post dam construction and the result show the were the significant anthropogenic impact on the streamflow during the post dam. LULC change was examined for two distinct periods of the 2000 and 2010 using Arc GIS10.1. This trend was not reflected in climatologically drivers such as rainfall, evaporation and temperature (which shows a positive trend), but rather is attributed to the substantial changes in land use and land cover in the watershed. The significant shift from forest and woodland to grassland, cropland and water body results in a decrease of actual evaporation and subsequent increase in (dry season) runoff. We used the ‘Range of Variability Approach’ to quantify hydrological alteration at Gigle gibeI Dam site. The analysis shows that the five groups of hydrological characteristics natural flow regime using the IHA (magnitude, timing, duration, frequency and variability), only those related to magnitude were found to show significant trends, with the main trend being the increase of flow during the dry season.