HEC-RAS Online Help - Entering Cross Section Data

HEC-RAS Online Help

Entering Cross Section Data

The next step is to enter the cross section data. This is accomplished by pressing the Cross Section button on the Geometric Data window (Figure 4.3). Once this button is pressed, the Cross Section Data editor will appear as shown in Figure 4.4 (except yours should be blank). To enter cross section data do the following:

Select a River and a Reach to work with. For this example start with the Fall River, Upper Reach.

Go to the Options menu and select Add a new Cross Section. An input box will appear to prompt you to enter a river station identifier for the new cross section. The identifier does not have to be the actual river station, but it must be a numeric value. The numeric value describes where this cross section is located in reference to all the other cross sections within the reach. Cross sections are located from upstream (highest river station) to downstream (lowest river station). For this cross section enter a value of 10.0.

Figure 4.4 Cross Section Data Editor with example data

Enter all of the data for this cross section as it is shown in Figure 4.4.

Once all the data are entered press the Apply Data button. This button is used to tell the interface that you want the data to be accepted into memory. This button does not save the data to your hard disk, which can only be accomplished from the File menu on the Geometric Data window.

Plot the cross section to visually inspect the data. This is accomplished by pressing the Plot Cross Section option under the Plot menu on the Cross Section Data Editor. The cross section should look the same as that shown in Figure 4.5.

In general, the five steps listed would be repeated for every cross section that is entered. In order to reduce the amount of data entry for this example, the current cross section will be copied and adjusted to represent other cross sections within the river system.

Figure 4.5 Cross Section Plot for river mile 10.0 of Fall Creek

The following steps should be followed to copy the current cross section:

Go to the Options menu on the Cross Section Data Editor and select Copy Current Cross Section. An input box will appear to prompt you to select a river and a reach, and then enter a river station for the new cross section. For this example, keep the river and reach as Fall River and Upper Reach, then enter a new river station of 9.9. Press the OK button and the new cross section will appear in the editor.

Change the cross section description to "River Mile 9.9 of Fall River."

Adjust all the elevations of the cross section by -0.5 feet. This is accomplished by selecting the Adjust Elevations feature from the Options menu on the Cross Section Data Editor.

Adjust the cross section stationing to reduce the overbanks by 10%. This is accomplished by selecting the Adjust Stations feature from the Options menu on the Cross Section Data Editor, then select Multiply by a Factor. When the input box appears for this option, three data entry fields will be available to adjust the stationing of the left overbank, channel, and the right overbank separately. Enter values of 0.90 for the right and left overbanks, but leave the main channel field blank. This will reduce the stationing of both overbanks by 10%, but the main channel will not be changed.

Downstream reach lengths remain the same for this cross section.

Press the Apply Data button.

Plot the cross section to visually inspect it.

These seven steps should be repeated to enter all the data for Fall River (Upper and Lower Reach). The necessary adjustments are listed in Table 4.1. Perform the cross section duplications in the order that they are listed in the table. Make sure to change the description of each cross section, and also press the Apply Data button after making the adjustments for each cross section.

This completes all the cross section data for Fall River (upper and Lower reach). Now let's work on entering the data for the Butte Creek tributary. To enter the first cross section in the Butte Creek tributary do the following:

Go to the River text box on the Cross Section Data Editor and select the Butte Cr. river. The Reach of "Tributary" will automatically be selected since it is the only reach in Butte Creek.

Select Add a new Cross Section from the Options menu. When the popup box appears to prompt you to enter a new river station, enter a value of 0.2.

Enter all the data for this cross section as shown in Figure 4.6.

Once all the data are entered for this section, press the Apply Data button.

Plot the cross section to inspect the data.

Figure 4.6 Cross Section Editor with river mile 0.2 of Butte Creek

There are two other cross sections that need to be developed for the Butte Creek tributary. These two cross sections will be developed by duplicating the cross section that you just entered, and then adjusting the elevations and stationing. The necessary adjustments are listed in Table 4.2. Perform the cross section adjustments in the order that they are listed in the table. Make sure to change the description of each cross section and press the Apply Data button after editing is complete.

Now that all of the cross section data are entered, save the data to a file before continuing. Saving the data to a file is accomplished by selecting the "Save Geometry Data As" option from the File menu on the Geometric Data window. After selecting this option you will be prompted to enter a Title for the geometric data. Enter "Base Geometry Data" for this example, then press the OK button. A file name is automatically assigned to the geometry data based on what you entered for the project filename.