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Table Of Contents
Time of Concentration and Time of Travel
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To calculate the peak runoff flow for a watershed subarea using the rational
method
1 From the Hydrology menu, choose Runoff รค Rational Method to display the
Rational Method dialog box.
You can also click Load at the bottom of the dialog box and select a rational file
that you have previously saved.
2 In the Description box, type a general description for the area.
3 Select the Rainfall Frequency. The Rainfall Frequency values are obtained from
an intensity-duration frequency file (.idf file). Autodesk Civil Design does not
automatically load an .idf file, however sample files are provided that you can
load. You can obtain an .idf file from your local NRCS office and use the
following steps to load it into the Rational Method dialog box.
In this calculator, each row represents a different drainage area. Peak flows are
listed separately for each drainage area.
4 From the lower part of the dialog box, click the IDF button to display the
Intensity-Duration Frequency Editor dialog box.
5 Click the Load button to display the Intensity-Duration File Selection dialog
box. The Files of Type list displays *.idf as the file type.
6 Use the navigation tools to open the c:\Program Files\Land Desktop
R2\Data\hd folder.
7 Select a sample .idf file, or select a file you have supplied for your local region,
and click Open. The Intensity-Duration Frequency Editor dialog box is re-
displayed, and now contains the intensity and duration values from the sample
file.
There are a variety of viewing and editing tools you can use to examine and
adjust the intensity-duration values.