This is the first in a series of CHECK-RAS exercises in which we will examine some of the program's features and problems. This exercise will examine how CHECK-RAS flags erroneous values for hydraulic parameters, and parameters that appear to be outside of the typical range. The parameters that will be examined are the Manning's "n" value and the contraction and expansion coefficients. For those of you who have previously used CHECK-RAS for more complex problems, you should still complete this exercise as we will be using the files and building on the problem in the future.
Before we begin, we will make a copy of the sample data that we will be using. Create a folder under your CHECK-RAS directory called "tutorial 1".
For this tutorial, we will use the set of sample data provided with HEC-RAS called "Bogue Chitto, MS - Example 13" (the file name is bogchit.prj). Run HEC-RAS and open the data set, which should be under your HEC-RAS directory in the folder called "data". Click on File Save project as and save it in the "tutorial1" folder that you created previously. Name it "tutorial1.prj".
We will examine the program's response to "n" values that are too low. We will assign an "n" value for concrete (+/- 0.015) as the channel "n" value. At Station 52.29, this data set also contains a cross section for which the contraction coefficients are 0.3 and 0.5. This cross section is not immediately downstream of the bridge, so CHECK-RAS will flag it.
Follow these steps:
- Click on the "Edit/Enter geometric data button" on the main HEC-RAS interface
- Click on the "Cross section' button
- Select River Station 55.40 from the pull down menu
- For the channel "n" value, enter 0.015 and click on the "Apply Data" button
- Return to the main HEC-RAS interface, and click on the "Save Data button"
- Click on the "Run flow simulation" button
- Click on "Compute" to run the simulation
- Close the DOS window once the simulation is complete
Now we will run CHECK-RAS to find the error:
- Run CHECK-RAS
- Click on the "Open" button, and open "tutorial prj" in the tutorial1 folder
- Click on the "Extract" button
- CHECK-RAS will state that you have not generated a report for the project
- Click on OK
- CHECK-RAS will bring you back to HEC-RAS to generate the report file
- Click on File Generate Report
- Click on "Generate Report" to create the report file.
- Close the window when finished
- Return to CHECK-RAS and click on "Extract"
- A "Select Profile" window will appear
- Select the top "100-year profile" (not the multiple profile one) radio button and click on #100-yr in the list
- Click OK
- Click on the NT button
- Under Report in the menu bar, select NT report
At the end of the report, a summary of the errors will be given as follows:
Roughness Coefficient CheckRS: 55.4 NT RC 03 Channel n value is equal to or less than 0.025 The n value of the channel is usually larger than 0.025. The n value should be reevaluated it if is not representing a concrete lined channel.
Transition Loss Coefficient CheckRS: 52.29 NT TL 02 Contraction and expansion loss coefficients are 0.3 and 0.5 respectively. However, this cross section is not at the structure. They should be equal to 0.1 and 0.3.
Note that the Roughness Coefficient check may produce this message if you are evaluating a channel that is concrete lined on the bottom with grassy slopes and overbanks.
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Last Modified: Friday, 15-Jun-2007 11:57:20 EDT