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Table Of Contents
Chapter 5 Working with Hydrology Commands
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Selecting the Rainfall Frequency for a County
Use the Define Rainfall-Frequency dialog box to select the rainfall depth for a
particular storm frequency in a selected county.
To select the rainfall frequency for a county
1 In the Define Rainfall-Frequency dialog box, click Select to display the County
Selection dialog box.
2 Select the county, and then click OK.
The Define Rainfall-Frequency dialog box is displayed, and the county that you
selected displays in the County text box.
3 From the Rainfall Frequency list, select a rainfall frequency. For example, for a
10-year storm event, select 10 years.
When you select the rainfall frequency, the Rainfall label shows the amount of
rainfall for a 24-hour event of the frequency type you selected. For example, if
you selected 10 years in the Rainfall Frequency list, then the Rainfall labels
displays the amount of rain you could expect for that location in 24 hours in a
10-year storm event.
4 Use the Apply Rainfall list to apply the rainfall amount that is shown in the
Rainfall label to the watershed(s) in the TR-55 Tabular Hydrograph Method
dialog box. From the Apply Rainfall list, select All to apply the rainfall amount
to all watershed subareas, or select Single to apply the rainfall amount to the
single subarea.
NOTE
When you click OK, the rainfall value is added to the 24-hrs Rainfall In.
column in the TR-55 Tabular Hydrograph Method dialog box. If you specify
Single, then the value is added to the column of the row in which your
cursor was located when you selected the Rainfall button. If you specify All,
then the value is added to all of the columns of data.
NOTE
You can access the Rainfall-Frequency Editor dialog box to edit and define
new values by clicking the Edit button.
5 Click OK to return to the TR-55 Tabular Hydrograph Method dialog box.
Customizing the Rainfall Distribution File
Autodesk Civil Design provides data files for the following rainfall distributions:
Type I, IA, II, III, and IV. The Type II distribution is the most widely applicable.
While other distribution tables are in use, most have been developed to more
closely map the rainfall in a specific area. Although Autodesk Civil Design
cannot support all these methods, you can either edit the existing file to include
the data for your area, or replace the file.
If you decide to edit the file, please keep the following cautions in mind:
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If the file is edited, Autodesk Civil Design is not responsible for erroneous
data that may be entered and subsequently used.
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The file must be in the same format as the existing data files that store the
rainfall distribution information.