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Chapter 5 Working with Hydrology Commands
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The Start Computations section has four options for specifying the starting
water surface elevation of the beginning or ending cross section:
n
Starting Critical Depth: Appropriate at cross section locations where critical
or near critical conditions are known to exist for the computed range of
discharges.
n
Start with Known Water Surface Elevation: When selected, this check box
lets you enter an appropriate value in the Starting Water Surface Elevation
text box. You can also select a point from the current surface by clicking
Select.
n
Rating Curve: When selected, this check box lets you enter an appropriate
value from an existing rating curve in the Starting Elevation text box
associated with the Rating Curve option. You can also select a point from the
current terrain model surface by clicking Select.
The next line of information associated with the Rating Curve option first lists
the current rating curve file name, which, by default, is None. Three additional
buttons are available when using the Rating Curve option:
Clear: Clears the current rating curve data.
View: Displays a specific rating curve in the Rating Curve Display dialog box.
Select: Lets you select an existing rating curve file.
n
Slope-Area Method: When selected, this check box lets you enter an
appropriate estimated energy grade line slope value in the Est. Energy Slope
text box. You can also select points from the current surface by clicking the
Select button next to the Est. Energy Slope text box.
3 After you establish the flow regime and starting water surface elevation, enter a
starting flowrate value in the Starting Flowrate text box.
NOTE
If you are using the Start with Known Water Surface Elevation or Slope-Area
Method of Start Calculations, you must first enter the Starting Water
Surface Elevation.
4 In the Mannings n box, enter a channel roughness coefficient value.
You can also click Select and choose one from the Channel - Mannings n
dialog box.
5 Select or clear the No Interpolated X-Sections check box:
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Select the No Interpolated X-Sections check box to prevent interpolated cross
sections from being generated as the HEC-2 calculations are made.
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Clear the No Interpolated X-Sections check box, and then type a maximum
change in velocity head value in the Max. Change in Vel Head text box.
Interpolated cross sections are then generated when velocity head changes
occur that match the specified parameters.
6 After you have established the required parameters, click Create File to display
the compiled HEC-2 data in your currently configured ASCII text editor.
NOTE
If you are using Windows 95 and Notepad is your default ASCII text editor,
save the file by selecting Save As. Type quotes around the filename. For
example, if you want to save the file as hydro.dat, choose Save As and
enter the file name as hydro.dat. If you do not do this and choose Save,
Notepad saves the file as <filename>.dat.txt.