Abstract:
Analyzing of river flow events and defining environmental river flow requirements for the
downstream ecosystem have not yet been widely investigated over the world. As the result of
this scarcity of water, on the other hand uncontrolled flood causes a great damage on living
and nonliving things. The simulated stream flow was used to reduce an error that was
developed by the large missing gaps. In the simulation process spatial data DEM, land use
land cover map, soil map and time series data were used to estimate flow at gauging station
which was taken as an outlet. SWAT model was selected as it utilizes various spatial
parameters to simulate runoff at required scale and easy availability. Sensitivity analysis has
shown that the base flow alpha factor (days) and curve number are the most sensitive
parameters that affects the hydrology of the watershed particularly runoff generation. The
model was calibrated using flow data from 2005 to 2010 and validated for the period 2011 to
2013. The model was checked by statistical model performance indicators such as the
coefficient of determination (R
2
) is 0.84 and 0.82 for calibration and Nash-Sutcliffe model
Efficiency (ENS) is 0.82 and 0.75 for validation respectively. The simulated output of
SWAT2012 was used in the process of the selection of fit distribution by easy fit and flow
event was determined. Peak yearly Discharge Prediction for the watershed were determined
by Gen. extreme value for 2,10,20,,50,100.200,500, returned periods to be found
59.17,109.72,132.92,166.73,195.18,226.5,272.88. Finally the river environmental flow
required for downstream was calculated by using Global environmental flow calculator
(GEFC) software. Instream flow allocated to the river of EMC class Largely modified (class
D) was 89.72 MCM (i.e., equivalent to 23.5 % of the natural MAR)
