Geometric Data File

1. On the main window of HEC-RAS, Click on Edit-->Geometric Data

2. On ‘Geometric Data’ Window, Click on ‘River Reach’

After the click, your mouse cursor will become a pencil.

3. Click on any place on the white area of ‘Geometric Data’ Window. This is a rough sketch of your river reach you are about to model. In our case, this is an 800 m long channel with straight length. You can just double click somewhere on the screen to show the end of the reach. A line will be shown similar to the figure below.

4. Write the river and the reach names
River: New Canal
Reach: Constricted
And Click ‘Ok’

Now you have to edit river cross section data. Click on Cross Section tab  , It is 2nd from the top on the left side of the window.

Before you have to do some rough work on paper or on AutoCAD to help you during this activity
This rough work includes following steps.

 i. Draw a rough plan view on paper and mark all important locations of this channel. Important means
           a. Start and end points, and locations where cross –section changes, as shown in the figure below.

           b. Make a longitudinal profile (see the figure below)
           c. Make a datum line (any distance below the lowest point of the channel can be chosen). Here, in this exercise we have chosen datum line below 9m from the lowest point.
           d. Use this datum line, channel slope, and cross section shape to calculate the coordinates of the cross section. (Please note that cross-sections are entered as coordinates of cross section in way that the left most point of the cross section is 0 in the horizontal plan)

 ii. See which points are important as far as channel geometry is concerned
          a. HEC-RAS requires cross section details at start and end of the reach
          b. It also requires points where cross section geometry changes
          c. You should notice that there are four river stations where the channel needs to be entered in the cross section editor of HEC-RAS.
          d. Since downstream RS (river station) no. is lowest in HEC-RAS. Name these 4 RSs from 1.0 to 4.0 from downstream RS to most upstream RS.

iii. Take any arbitrary benchmark (sea level) and assume that channel invert (lowest point of the channel) of the most downstream cross section is at 2.4m above it. Now you already have the slope, so you need to calculate the channel invert at RS. 4.0 (most upstream RS). HEC-RAS will calculate the channel invert at RS. 2.0 and 3.0 during the process of interpolation.

iv. Now with the help of this rough work you should be able to draw the cross sections of RS 1.0 and RS 4.0 as it is required in HEC-RAS. Since the cross section geometry is rectangular. You will require 4 points to define a cross section.

5. On Geometric Data window on ‘Cross Section’ icon.
i. On Cross section data window click on Options-->Add a new cross section
ii. Name RS as 1.0 on prompted window.

iii. Enter Station and Elevation values as shown below and click on ‘Apply Data
Click on ‘Apply Data’
Enter Manning values which is 0.012,
LOB is 0 and ROB is 5

iv. Repeat step ‘a’, ‘b’ and ’c’ for RS 4.0, that is
On Cross section data window click on Options-->Add a new cross section Name RS as 4.0 on prompted window.
Enter Station and Elevation values
LOB is 7 and ROB is 15
Downstream reach length is 800m


v. Close cross section editor. Now the main geometric window should show RS 4.0 at upstream and RS 1.0 at downstream as shown in the figure.

6. Now you have to make use of interpolation process to introduce cross section at 200m from RS4.0
On ‘Geometric Data’ Window Click on Tools-->XS Interpolation -->Between 2 XS’s

7. On new window select option ‘Set Location (m)’, and enter 200 in distance

8. Click on ‘Interpolate New XS’s’
This will make a new interpolated XS at 200 m with name 3.2500*.
See the 3D view of the channel (XYZ Plot  HEC-RAS-->View-->X-Y-Z Prospective Plot) you will notice that this is not the desired shape of channel cross section. Because Channel has to be prismatic between RS 4.0 and RS 3.25*

9. Again go to the Cross section editor and
a. Open RS 3.2500* and Change name of cross section from 3.2500* to 3.0. On ‘cross section data’ window click on Option-->Rename River Station

b. Make station values same as these are in RS 4.0, Do not change elevation values. Also, change LOB and ROB of interpolated cross section. Click “Apply Data” and close the window.
c. Close Cross section editor

10. Now you have to again interpolate to place a cross section at point D. which is 20 m ahead of RS 3.0.
Repeat steps from 11 to step 14 to create RS 2.0. Therefore now enter distance as 20 m from RS 3.0
On ‘Geometric Data’ Window Click on Tools--> XS Interpolation --> Between 2 XS’s
Select upper river station as 3.0
On new window select option ‘Set Location (m)’, and enter 20 in distance

11. Again go to the Cross section editor and
a. Open RS 2.9333* and make station values same as these are in RS 1.0, Do not change elevation values. Also change LOB and ROB of interpolated cross section (same as in RS 1.0)
b. Rename 2.9333* to 2.0

 c. Change the RS 2.0 “Station values” as these are in RS 1.0. Change LOB and ROB. Apply data and close the "Cross Section Date" window.

Since we are interested to know water surface profile of this channel, therefore, we are interested in having sufficient number of River Stations. Thus, we will now interpolate cross sections at every 6m in the whole reach
12. On ‘Geometric Data’ Window Click on Tools-->XS Interpolation -->Within a reach

a. Set “maximum distance between XS’s” as 6
b. Click on “Interpolate XS’s” and close the window

c. Geometric Data window will now look something like this

13. On ‘Geometric Data’ window click on File -->Save Geometry Data. If will have prompted, give a proper file name for geometric data.

a.       Close Geometric Data Window

⬅Starting HEC-RAS                                                                                   Steady Flow Data File➡