Abstract:
Understanding the relationship between catchment characteristics and the resulting
flow is a fundamental problem for water resource planning, operation and
management.In this paper, an attempt has been made to evaluate the effect ofphysical
catchment characteristics on reaction of river flowof watersheds from Gidabo, Gelana
and Bilate catchments in central rift valley basin using statistical method and
hydrological model. This allowed to be seen the most influential watershed
characteristics that govern the runoff generation and hopes to offer useful tips for
decision makersin efficient management and planning of water resources in the study
area.Statistical analysis using statistical package for social science (SPSS)was used in
nine watersheds and recognizedrelationships among the watershed variables, among the
hydrological variables, as well as between the watershed and hydrological
variables.Runoff coefficient, average annual rainfall and average slope of a watershed
were themost important variables to forma good regression model to explain the
response variable (mean annual stream flow) in the sub basin.Furthermore, Soil and
water assessment tool (SWAT) was used todistinguish the watershedvariables that
causes runoff variation inthe two comparableand neighboring watersheds; Gidabo near
Miesso and Gelana near Tore.Watershed characteristics that differs significantly in the
two watersheds (Rainfall, temperature, land use and Soil) were tested and evaluated in
the calibrated and validated SWAT model one at a timeby assumingthat Gidabo have
similar in rainfall, temperature,land use and soil as Gelana.Rainfall, temperature and
land use/land cover of Gelana would have resulted in decrement of the long term
annual mean flow of concurrent period at Gidabo witha magnitude of 55%, 12.6% and
10.8% respectively while replacing Gelana’s soil for Gidabo resultsa 5.4% increment of
flow at Gidabo.As resulted from statistical analysis and SWAT model rainfall was the
highly significance watershed variable and a direct source of water. However, it losses
in terms of surface runoff in watersheds where shrubs and forest cover were
substantially low and in intensively cultivated watersheds.
