Technical data

Using the Rational Method to Calculate Runoff

To calculate the peak discharge using the Rational Method (continued)

Steps

Use

to look up

2 From the Hydrology menu, choose Settings to

display the Hydrology Tools Settings dialog box.

Change the Hydrology

Unit Settings

3 Click the Units button to specify the

measurement units. Click Precision to specify the

required precision settings for your units.

4 From the Hydrology menu, choose

Runoff ➤ Rational to display the Rational Method

dialog box.

Calculate the Peak Runoff

Flow for an Area by Using

the Rational Method

5 Click the IDF button to display the Intensity-

Frequency Factor Editor. Select your IDF curve file.

From the editor, click the Load button to load your

IDF curve file for the project area, and then click OK

to return to the Rational Method dialog box.

Specify the

Rainfall Intensity

6 Select the applicable rainfall frequency from the

popup list.

7 Specify the watershed area.

You can type a value for the area in the edit box,

or, if you created a watershed with the Terrain

Model Explorer, you can select the polyline from

your drawing by clicking Area and selecting the

polyline. You can also draw a new polyline for

selection.

Calculate the Peak

Runoff Flow for an Area

by Using the Rational

Method