HEC HMS Instructions by KHm9im6

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									9/23/05

                         INTRODUCTION TO HEC-HMS:

          A COMPUTER MODEL FOR RAINFALL-RUNOFF MODELING

Objectives of this class:
   1) To demonstrate rainfall-runoff modeling in HEC-HMS and learn how the land
       components of the hydrologic cycle are represented on a watershed scale.
   2) To learn how to implement HEC-HMS for a simple rainfall-runoff modeling
       exercise for a watershed.

Steps:
   1) Go to the HEC-HMS website at:
   http://www.hec.usace.army.mil/software/hec-hms/hechms-hechms.html

   2) Click on “HEC-HMS” under the “Download” button on your left hand side. This
      will take you to a page where you need to download the HEC-HMS version 2.22
   3) Download hms222single.exe in your local PC. This is a self-extracting setup file
      that will install HEC-HMS once you double click on it.
   4) Install HEC-HMS in your specified folder (say HEC-HMS) and restart.
   5) Now run your HEC-HMS. It will open a window as follows:




   FIGURE 1
   6) The HEC-HMS that you have installed already has the necessary hydrologic and
      watershed data and parameter files to run a rainfall-runoff modeling scenario for a



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   watershed. The watershed is called “Little River” near Tifton, GA. This is a
   research watershed maintained by ARS (Agricultural Research Service) and
   USDA (US Dept. of Agriculture). For more details on the watershed you may
   refer to: http://sacs.cpes.peachnet.edu/sewrl/LittleRiver/littleriver.htm
7) You will now see three different items in each column that define the rainfall-
   runoff modeling for HEC-HMS: a) Under Basin Model, you have ‘Tifton’ – this
   item contains all the necessary hydrologic data of the river basin (such as
   parameters for infiltration, surface runoff, area of watershed, soils type etc.). The
   name “Tifton’ is arbitrary as – for your own specific problem and watershed you
   can have your own name; b) Under “Meteorologic Model”, you have “Tifton
   Hyetograph” – this item contains all the necessary files for meteorologic input to
   the modeling process – mainly the rainfall file; c) Under ‘Control Specifications”
   you have the item that controls how you will simulate the rainfall runoff process,
   mainly your timestep and the total time period for simulation.
8) Now click on “Tifton” under Basin Model. This opens a new window that
   graphically represents the watershed as a landscape unit for simulation of rainfall-
   runoff process.




FIGURE 2
9) Essentially, all the major watershed hydrologic processes are represented by the
   green box, even though you do see the actual watershed delineation with the river


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    network. NOTE: It is only a conceptualization and it DOES NOT mean that the
    processes are physically taking place there. Basically the green box represents the
    ‘average’ watershed processes, whence the ensuing runoff as overland flow is
    ‘routed’ via the river network to the basin outlet. Again, the river network is also
    idealized as a straight pipeline for transporting the generated runoff from rainfall.
    Finally, you have a blue junction symbol at the basin outlet that basically
    indicates. Let’s not worry about what the ‘junction’ actually means at this stage
    other than representing a typical weir type structure to measure observed flow
    draining out of the basin.
10) Now right click on the green box for watershed process and then click ‘edit’. This
    will open a window where you can decide on the specific submodels/techniques
    to solve/represent the hydrologic sub processes (e.g. infiltration, groundwater
    flow, ET, river flow etc.). You also assign the watershed area here (in this case, it
    is 19.27 mile 2)




FIGURE 3

11) The ‘Loss Rate” is used to represent Infiltration; ‘Transform” represents how the
    surface runoff or direct runoff will reach the river network from the upstream hills
    and the “Baseflow” represents the groundwater flow process. You can click on



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    any of these links to modify the parameters or input needed to model the
    processes.
12) Make sure you are still on the “Loss Rate” page and notice carefully how the
    current model setup for Tifton is configured. The infiltration is being modeled by
    a method called SMA (Soil Moisture Accounting). But you can actually change it
    to say, Green and Ampt or the NRCS (in this case, SCS) curve number method. I
    want you to play with these links and connect what you see to what you have
    learned so far in class (focus mainly on Green and Ampt and SCS method for
    infiltration). We shall ignore ‘Base Flow Method” and “Transform” for the time
    being.
13) Running the Model: First you need to click on “Control Specifications” “(Jan 1
    – Jun 30, 1970) to define your timestep and total period of simulation. The default
    configuration is Jan 1- Jun 30, at hourly timestep. Next, click on ‘Simulate” (on
    the window that is generated when you click on the Basin Model (see figure 2).
    Therein, click on ‘Run Configuration’. Select all the items you see – i) Basin
    Model ii) Met Model id and iii) Control id; Give the ‘Run’ any number you want.




FIGURE 4
Now click on ‘Compute Run’ under ‘Simulate’. Your configured HEC HMS model
should run to complete the rainfall runoff simulation from Jan 1 to Jun 30



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14) Viewing/analyzing Model output: Right click on the green box to view results
for the watershed processes (e.g. infiltration pattern in time, baseflow in time etc.).
You can also click on the basin outlet blue box (junction) to view results for the
outflow hydrograph. Please play around a little bit to find out how you can actually
save the output data in text format to do your required analyses.




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