Discharge results on the floodplain
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To measure the discharge across a series of floodplain grid elements, use a floodplain cross section. The floodplain cross section is set up in the GDS. It records a hydrograph of time vs. discharge for a series of grid elements and a selected flow direction.
Create a floodplain cross section in the GDS by clicking the Tools menu and selecting Create Floodplain Cross Section. Draw the floodplain cross section by using the click and drag method to paint a series of cells. The cells must be contiguous and in a straight line. They can be vertical, horizontal or oblique. Double click to finish the line. The next step is to add a flow direction. Click the cross section and click Edit Floodplain Cross Section. Assign a general flow direction and click OK. Save the FLO-2D files to create a file called FPXSEC.DAT.
When the next simulation is run, the flow across the cross section will be recorded in three files CROSSQ.OUT, CROSSMAX.OUT and HYCROSS.OUT. These data files can be accessed directly with a text editor such as WordPad(TM) or UltraEdit(TM). The results can be viewed graphically in the HYDROG program.
For more information on creating floodplain cross sections and the HYDROG post processor program see the DATA Input Manual (Chapter 4: FPXSEC.DAT tab and Chapter 6: Post Processor Programs: HYDROG.
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Floodplain cross sections are used to determine the discharge across a series of grid elements.
Common uses for this tool
1. Capture flow across an alluvial fan surface.
2. Capture flow across the boundary of one model to use as input into another model.
3. Capture flow from a rainfall event to input as inflow into another model.
4. Capture the total discharge across a series of grid elements including streets and channels.Common question
Q. If the flow direction is south, what happens to the flow moving in other directions southeast and southwest?
A. If the flow direction is south and the entire width of the flow field is captured, the calculated Q will be captured because the other two directions are added into the flow calculation.
Common Mistakes
1. Not capturing the entire flow because the placement of the cross section is too far downstream or not wide enough.
2. Listing a grid element more than once in the FPXSEC.DAT file will result in an incorrect CROSSQ.OUT but the CROSSMAX.OUT and HYCROSS.OUT files will be fine.
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