Hec Hms Lab Report

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 challen ge and is extremely important for the people living in the world. Failure F ailure to manage the water sources in an a n 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 Hydrological modeling is a commonly used tool to estimate the basin’s hydrological response due to precipitation. Various types of h ydrological 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 h ydrologic analysis procedures such as event infiltration, unit hydrographs, and h ydrologic routing. HEC-HMS also includes procedures necessary for continuous simulation including evapo-transpiration, snowmelt, and soil moisture accounting. The 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 bound ary 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 1

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

Initial

2

Area(km )

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

3

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 5

Computed Results

Observed Results

Peak Discharge(m /s)

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

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(m /s)

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

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. S an 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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