d. method is used to add starting and

d. Model
Application

 

HEC-HMS Model: The Hydrologic
Engineering Centre- Hydrologic Modelling System (HEC-HMS) is used for
rainfall-runoff simulation over large basins. It consists three main components
explained in detail as follows.

Basin Model Component:
The
purpose of basin model component is to add the data required for computation of
basin characteristics from HEC-HMS. The hydrologic methods like SCS Curve
Number is used for calculation for losses in watershed and SCS Unit Hydrograph
is used for transformation of rainfall into runoff.

 

Meteorological
Model Component: This
model component is used to select method for adding the precipitation data and
used for connecting the gauges with their respective sub-basins. In this study
Specified Hyetograph method was used as it allow to specify exact time-series
to use for hyetograph at sub-basins and also it is useful when only one gauge
precipitation data available is used for entire basin.

 

Control
Specification Component: This method is used to add starting and ending date
and time of the simulation.

 

Calibration and
validation of the model:

The
calibration of the model is made to match the simulated runoff peaks, volumes
and time of peaks with the observed data. The results obtained from the Hasur Watershed
10 events of runoff data selected for calibration and validation.

 

The
data is divided into 5 events for calibration (2000-2004) and 5 events
(2005-2009) for validation. The parameter selected for calibration is Curve
Number value and Optimization Technique value.

 

III. RESULTS AND
DISCUSSIONS

 

Calibration of
the model:

The
simulated results obtained from the HEC-HMS model shows that R2
value and NSE value very minimum hence calibration of the model is required.
Calibration is made by changing the optimization technique value and Curve
Number value. Runoff value, R2 value and NSE value before
calibration found to be 2118.2 m3/s, 0.5148 and -2.655.

The
below Fig: 2 (a) and Fig: 2 (b) shows the comparison graph of simulated runoff
values and observed runoff values after calibration. The Runoff value, R2
value and NSE value after calibration found to be 2125.3 m3/s,
0.9322 and 0.554.

 Validation of the Model:

 Validation of
the model is done by using the 2000-2004 calibrated discharge values with the
next 2005-2009 observed and simulated discharge values. The below Fig: 2 (c)
and Fig: 2 (d) shows the difference between the observed and simulated values
after validation and scattered graph shows the R2 value for the
observed and calculated discharge values and it is found to be 0.825.Therefore
the calibrated and validated HEC-HMS model provided runoff rate for each the
un-gauged sub-basins in the watershed. The simulated results provide
information about maximum, minimum and mean value of discharge for each of the
basin. These predicted flow values can be used for planning and designing of
various watershed management measures like water conservation, flood control,
etcFigure
2. (a) Comparison of Observed and Simulated Discharge after Calibration, (b) Scattered
graph of Observed and Simulated Discharge after Calibration, (c) Comparison of
Observed and Simulated Discharge after Validation, (d)  Scattered graph of Observed and Simulated
Discharge after Validation  IV. CONCLUSIONS In
the present study attempt has been made to simulate the runoff from the HEC-HMS
model for the Hasur Watershed of Malaprabha River sub-basin of Krishna basin,
Karnataka, India.  The HEC-HMS model
required data’s were prepared from Arc Hydro and HEC-Geo HMS. For simulating
runoff in HEC-HMS model SCS Curve Number method and SCS Unit Hydrograph method
were used. The obtained results from the HEC-HMS model shows that calibration
is required to fit with the observed results. After calibration the R2
value and NSE value found to be 0.9322 and 0.554 and after validation R2
value found to be 0.825.

From
the overall consideration, it concludes that HEC-HMS model is suitable for
simulation of rainfall-runoff for large watersheds. It is also suitable for the
area where there is no gauges to measure the runoff.

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