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.
