The Steady Flow Calibration command is used to perform HEC-RAS steady flow model calibration using observed water surface elevations. Using this command, the user can adjust the cross section Manning’s roughness to match an existing flood event so that the HEC-RAS model accurately predicts future floods.
Follow the steps below to use the Steady Flow Calibration command:
- From the Analysis ribbon menu, select the Steady Flow Calibration command.
- The Steady Flow Calibration dialog box will be displayed.
The following sections describe the Steady Flow Calibration command and how to interact with the above dialog box.
Selecting River Reach
For an HEC‑RAS model with multiple river reaches, the user can select the desired river reach to perform the steady flow model calibration. The River name and Reach name dropdown combo boxes display a listing of the river and corresponding reaches contained within the model. The user can select the preferred river reach using these dropdown combo boxes.
Alternatively, click the [Pick] button adjacent to the Reach name entry to directly select a river reach from the Map View. On clicking the [Pick] button, the Steady Flow Calibration dialog box will temporarily disappear. The software will then prompt the user to select the river reach from the Map View. After selecting a river reach, the user will be returned to the dialog box with the river reach selected.
The Profile dropdown combo box displays a listing of all the computed water surface profiles contained within the selected model. The user can select the profile for which the HEC-RAS steady flow model calibration is to be performed.
Selecting Manning’s Roughness Data
The Manning’s Roughness Data dropdown combo box allows the user to select the cross section subareas on which the Manning’s adjustments are to be applied. The following options are provided in the dropdown combo box.
Based on the selected subareas, the data table will be updated and will show only those values that correspond to the selected subarea.
The data table in the Steady Flow Calibration dialog box lists the observed and computed water surface elevations and the roughness coefficients corresponding to the respective cross sections.
The data table displays the following data:
- River station
This column lists all of the river stations contained in the selected river reach.
This column defines the river station type. The river stations can be one of the following types:
- Cross Section
- Inline Structure
- Lateral Structure
- Roadway Crossing/Bridge and Culvert
Note that this column defines the river station types that are other than cross-section. If the river station is a type of cross-section, the column will be empty.
- Observed WSEL
This column allows the user to define the observed water surface elevations for each cross section (including bridges and inline structures) within each profile.
- Downstream Distance
This column allows the user to define a distance downstream of the specified river station, to further define the actual location of the observed water surface data. Click the […] button to measure the downstream distance from the river station to the observed water surface elevation from the Map View.
- Interpolated WSEL
This column lists the interpolated water surface elevation for each cross section. It is determined by interpolating the computed water surface elevation at the defined offset by looking at the water surface elevation at the two bounding cross sections and then using similar triangles to interpolate the elevation.
- Computed WSEL
This column lists the computed water surface elevation for each river station.
- WSEL Change
This column lists the differences between the Computed WSEL and Observed WSEL for each cross section.
- Roughness Coefficients
The n1, n2,…, and n7 columns allow the user to define Manning’s roughness coefficients.
In addition, the data contained in the table can be copied to the clipboard or exported as a Microsoft Excel or PDF document. To do this, right-click on the table and select the Copy Table to Clipboard, Export Table to Excel, or Export Table to PDF command from the displayed context menu.
Selected Cells Group Editing
This section allows the user to select the type of adjustment to be performed on the selected river reach(es) and cross section subareas. The user can select the desired cells from the data table and then edit the cell’s coefficient either individually or in a batch.
The user can edit the coefficients using:
- Add Constant: This option adds a constant value to the selected cell’s value.
- Multiply By Factor: This option multiplies the selected cell’s value by a user-defined number.
- Apply Value: This option replaces the selected cell’s value with the user-specified value.
To edit the cell’s coefficient, select the cell by clicking on it while pressing the [Ctrl] or [Shift] key; choose the desired cell-editing option; enter the change coefficient, and then click the [Apply Change] button. Note that the [Apply Change] button is only available when the group editing option other than the No Change option is selected and at least one cell is selected.
When all the options have been defined, click the [Analyze] button to perform the HEC-RAS steady flow model calibration. While the analysis is running, the button changes to [Cancel] so that the user can cancel the analysis if desired. When finished, the computed values will be shown in the Steady Flow Calibration data table. Click the [Close] button to close the dialog box.