OBJECTIVE
The objective of the lab session was to model a watershed using the software HEC-HMS and generate the
outflow hydrograph at the outlet. And also to calibrate the model using the river gauge data provided
getting an output of the peak flow, time to peak and the peak shift with the observed streamflow data.
INTRODUCTION
Sustainable management of limited fresh water sources is a major challenge and is extremely important
for the people living in the world. Failure to manage the water sources in an effective manner will
adversely affect the society and the economy of the country. Management of water resources in a basin
essentially requires understanding of dynamics of basin water and assessment of basin water availability
for development use. Hydrological modeling is a commonly used tool to estimate the basin’s hydrological
response due to precipitation. Various types of hydrological models from black box models which require
less basin data to physically based models which require large amount of basin data have been developed.
The Hydrologic Modeling System (HEC-HMS) is designed to simulate the complete hydrologic processes
of dendritic watershed systems. The software includes many traditional hydrologic analysis procedures
such as event infiltration, unit hydrographs, and hydrologic routing. HEC-HMS also includes procedures
necessary for continuous simulation including evapo-transpiration, snowmelt, and soil moisture
accounting. The software features a completely integrated work environment including a database, data
entry utilities, computation engine, and results reporting tools. A graphical user interface allows the user
seamless movement between the different parts of the software.
HEC-HMS needs three input components such as:

The basin model

The meteorological model,

The control specifications.
The basin model is the representation of real-world objects with parameters describing their behavior. The
basin model elements are sub basin, reach, junction, source, reservoir, reach, point of intersection of river
reaches, input flow point to basin system, outlet of the basin system, reservoir, and diversion for a reach,
respectively.
The metrological model is responsible for preparing the boundary conditions that act on the watershed
during a simulation. Meteorological data analysis is performed by the meteorological and includes
shortwave radiation, precipitation, evapo-transpiration, and snowmelt. Not all of these components are
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required for all simulations. Simple event simulations require only precipitation, while continuous
simulation additionally requires evapo-transpiration.
The time span of a simulation is controlled by control specifications and control specification is used to
describe the time period and time step for simulation. Control specifications include a starting date and
time, ending date and time, and a time interval.
METHODOLOGY
From the data provided the catchment was modelled on the software
Figure 1: Catchment Model- Watershed AB01
The below figure shows the model of the watershed AB01 in HEC-HMS software.
Figure 2: Model of Watershed AB01
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RESULTS
The following table shows the input parameters.
There are 4 parameters which need to be provided to run the model

Basin Models

Meteorological Models

Control Specifications

Time-series Data
Table 1: Sub-catchment parameters
Sub-catchment
ID
Area(km2)
Initial
abstraction(mm)
Soil Group
Lag Time (min)
SB1
34.41
1.7
A
78
SB2
25.2
1.4
A
25
SB3
29.63
2.3
C
42
SB4
24.2
1.8
D
48
Table 2: Model Control Specifications
Loss method
SS Curve number method
Transform Method
SCS unit hydrograph method
Catchment cover status
Grass cover < 50%
Muskingum k
1.5 (Hours)
Muskingum x
0.15
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Figure 3: Hydrograph
CALIBRATION OF THE COMPUTED RESULTS
Table 3: Sub catchment parameters
Sub-catchment ID
Initial abstraction
Curve number
Lag Time (min)
(mm)
SB1
2.5
68
120
SB2
2.8
84
85
SB3
1.2
89
110
SB4
1.0
39
40
Table 4: Model Control Specifications
Reach
Muskingum k (hours)
Muskingum x
Reach1
1.0
0.5
Reach 2
1.4
0.45
Reach 3
2.7
0.5
Reach 4
1.0
0.4
4
Reach 5
1.3
0.5
Reach 6
2.0
0.5
Reach 7
0.1
0.5
RESULTS AFTER CALIBRATION
Figure 4: Adjusted Hydrograph
Figure 5: Obtained values
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Computed Results
Observed Results
3.5
3.5
Volume (m )
0.67
0.67
Date/Time of Peak(hr)
01 Apr 2016 / 15:00
01 Apr 2016 / 15:00
Peak Discharge(m3/s)
3
Table 5: Global Summary Table
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DISCUSSION
HEC-HMS software helps us easily calculate and analyze the precipitation rates and the software helps us
prepare hyetographs and hydrographs which helps us to predict the future precipitation rates. A total of six
hydrologic routing methods are included for simulating flow in open channels. Routing with no
attenuation can be modeled with the lag method. The traditional Muskingum method is included for
simple approximations of attenuation. Most parameters for methods included in sub basin and reach
elements can be estimated automatically using optimization trials. Observed discharge must be available
for at least one element before optimization can begin. Parameters at any element upstream of the
observed flow location can be estimated.
Rainfall is the only source of water and there are no trans basin diversions into or out of the basin. The soil
moisture accounting loss method uses five layers to represent the dynamics of water movement above and
in the soil. Layers include canopy interception, surface depression storage, upper groundwater, and lower
ground water.
During this lab session, I had to go through 26 trial runs to get the both computed results and the
computed results similar.
Computed Results
Observed Results
Peak Discharge(m3/s)
3.5
3.5
Volume (m3)
0.67
0.67
Date/Time of Peak(hr)
01 Apr 2016 / 15:00
01 Apr 2016 / 15:00
The adjustable parameters are the:

Muskingum X

Muskingum k

Initial abstraction

SCS Curve Numbers
When changing the Muskingum X I could observe a change in both graphs and also the volume changes
slightly. When altering the SCS curve number the graph had a huge change as well as the volume changed
a drastically. The land surface elevation can vary dramatically from headwaters to outlet. Soil properties
change from one place to another place. Land use also changes with location but also changes over time.
Each of the hydrologic processes can be modeled at varying levels of detail. . All of these issues jointly
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produce uncertainty in the simulated watershed response. The uncertainty analysis allows parameters to be
represented with a probability distribution function.
Previously when the Muskingum k and Muskingum x was:
Muskingum k
1.5 (Hours)
Muskingum x
0.15
I obtained the results shows below
And when the values were calibrated to the values shown in Table 4, I observed certain changes in the
volume and peak discharge. (Figure 5).We can observe that the peak discharge of the computed values
between both cases had varied by 0.3
and the mean Abs error reduced by 0.1
.
A simulation run is created by combining a basin model, meteorological model, and control specifications.
Run options include a precipitation or flow ratio, capability to save all basin state information at a point in
time, and ability to begin a simulation run from previously saved state information. Most parameters for
methods included in sub basin and reach elements can be estimated automatically using optimization
trials. Observed discharge must be available for at least one element before optimization can begin.
Parameters at any element upstream of the observed flow location can be estimated.
There are few limitations in the software when analyzing the results. Every simulation system has
limitations due to the choices made in the design and development of software. Limitations that arise in
this program are due to two aspects of the design: simplified model formulation, and simplified flow
representation. Simplifying the model formulation allows the program to complete programs very quickly
while producing accurate and precise results. Simplifying the flow representation aids in keeping the
compute process efficient and reduces duplication.
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CONCLUSION
The watershed AB01 was modeled using the software HEC-HMS which helps us to determine the effect
of increasing urbanization on peak flood runoff over future periods. The software was used to get the final
output of peak discharge, volume, date and time of peak. The models created can be used to test the
impacts of land use changes, rainfall predictions, and channel modifications.
REFERENCE



Gabrecht, J., Martz, L.W., 1999. Digital elevation model issues in water resources modeling. In:
Proceedings of the 19th ESRI international user conference. San Diego, California, p254–257.
HEC, 2010c. HEC-RAS User’s Manual Version 4.1. Hydrologic Engineering Center.
Combs, J.L., Perry, A.C., 2003. The 1903 and 1993 Floods in Kansas – The Effects of Changing
Times and Technology.
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