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Table Of Contents
Calculating the Runoff from Watershed Areas
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Choosing an Editor
To choose a text editor
1 In the Editor Settings dialog box, click Browse to display the Select Text Editor
dialog box.
2 Choose the text editor you want to use. For example, to choose the Windows
Notepad editor, use the Look in list to open the Windows folder, then pick
NOTEPAD.EXE from the list of files.
3 Click Open to return to the Editor Settings dialog box.
4 Click OK to return to the previous dialog box.
Returning the Hydrology Settings to the Default
Prototype Settings
You can reset the hydrology settings back to the settings that are in the project
prototype by using the Reset option.
NOTE
If you do not want to permanently lose your current settings, save them
before proceeding with the following steps.
To clear the current hydrology settings and return to the default settings
1 From the Hydrology menu, choose Settings to display the Hydrology Tools
Settings dialog box.
2 Click Reset to display the Clear Hydro Data dialog box.
3 Click Yes to confirm that you want to clear the settings.
4 Click OK to exit the dialog box.
Calculating the Runoff from Watershed Areas
Runoff is the amount of water that flows out of a watershed subarea as a result
of a storm event. This value is equal to the amount of rainfall that occurs on the
area, minus the amount of rainfall that is infiltrated by the ground, is
intercepted by foliage, or is held in small depressions.
Runoff is calculated by examining rainfall intensity, duration, and distribution;
soil conditions; antecedent moisture conditions (how much moisture is already
present in the soil before the storm occurs), and land use. Sometimes a runoff
volume amount within a specified time period is adequate for design purposes,
but most likely a peak flow rate and even a hydrograph are needed.
Autodesk Civil Design provides the following methods for calculating peak
runoff flow rates from watershed areas:
n
Rational
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TR-55 Graphical Peak Discharge
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TR-55 Tabular Hydrograph
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TR-20
The graphical peak discharge and tabular hydrograph methods are based on
Technical Release 55 (TR-55), Urban Hydrology for Small Watersheds. TR-55 was