Import Cross Section From HECRAS Project File
This program can import the HEC-RAS cross sections of the stream at the approach and at the bridge. At the bridge, the program will also import the bridge deck data.
Both the downstream and upstream bridge data can be imported but only the downstream bridge data is saved and used to model the ABSCOUR bridge section. The upstream bridge section will not be saved but can be used to obtain bridge upstream side low and high chord elevation and also the ground elevation at the specific station. For the upstream bridge section, use the import button on the upstream bridge data card or on the menu of the utilities unit of the program. Follow the same procedure described in the guidance below for the downstream bridge section.
For the downstream bridge section, use the Actual Section card to import the downstream bridge section using the guidance described below.
The User needs to be careful to select the appropriate HEC-RAS plan when using the import function. Before importing the HEC-RAS cross-sections into ABSCOUR Program, we recommend that the user follow the procedure outlined below to make sure that the desired HEC-RAS plan is imported into ABSCOUR:
- Run and save the HEC-RAS Program with the geometry file and the flow file that is to be used in the scour analysis. This file should be considered the current active plan.
- Close the HEC-RAS program. This step establishes the desired plan (geometry and flow files) as the current active plan.
- (Note: An alternative approach to avoid the potential for importing incorrect geometry is to save the desired HEC-RAS model as a Scour Model using File/Save Project, and deleting all plans and geometry files except the plan that scour is to be computed for.)
- Now use the import procedure in ABSCOUR to select the desired project file and the appropriate approach section and bridge section.
- To import the approach section, select the HECRAS project file in the open file dialog. The program will read the current active plan of HECRAS project and generate a list of available cross sections. The user can then choose the cross section of the desired approach section on the list. The imported data includes the station and elevation of the ground points in the cross section and the left bank and right bank point stations.
- For the bridge section, the program will search through the geometry file of the current active plan of HEC-RAS project and find the available bridges. If more than one bridge exists, a list of the bridges will be generated and the user can pick the desired bridge. If only one bridge exists, the program will import the bridge data without asking. The bridge data includes the downstream section (or upstream section for the upstream tool) and the bridge deck high chord and low chord elevations. The left bank and right bank point stations are also obtained. Note, if the left bank and right bank do not match what is used in the scour analysis, the user needs to adjust these two stations as explained below
- The Program uses the left bank and right bank stations of the actual cross-section to calculate the station at center of the channel. The ABSCOUR cross section is then drawn based on this station. If no actual cross section is available, this station will be set to 0. If the channel top width as defined in the HECRAS cross section is the same as in the ABSCOUR cross section, then the ABSCOUR cross-section and the actual HECRAS cross-section should match at the channel banks. If these two channel widths are different, the user can adjust the left and right bank stations to match the ABSCOUR cross-section.
- The program assumes that the orientation of the cross-section is the same in the HEC-RAS Program and the ABSCOUR Program, whether looking downstream or looking upstream. In case they are different, change the ABSCOUR input data to match the HEC-RAS data. This should not normally be a problem since the input data in ABSCOUR is usually obtained from the HEC-RAS output.
- If the user inadvertently imports the wrong approach or bridge section station, the problem can be corrected by repeating the import procedure and selecting the correct station.
- To graphically check the sections, click on Tools/Draw Section/OK.
ACTUAL BRIDGE SECTION MANNING ROUGHNESS
This is the Manning roughness n value of the left overbank, channel or the right overbank of the actual bridge section. These values can be imported from the HECRAS studies where they were used in the discharge distribution calculations. They are not used in the scour computations for the Maryland ABSCOUR method or the NCHRP 24-20 method; however, these "n" values are used in the computation of the contraction scour for the HEC-18 method "Ultimate Contraction Scour for Cohesive Soil.