Designing for exceedance

Step-by-step:

InfoDrainage includes the ability to route flood water across the catchment surface. The direction and speed of flood water is determined by the surface data.

In addition to simulating a very large storm, you can artificially induce flooding by reducing the size of one of the upstream pipes. But before you do, best practice is to copy a design phase so that you can perform the exceedance calculations without altering the data.

To create a new design phase:

  1. In the Tree View, right-click the phase Optimised SuDS design, and select Duplicate.
  2. Name the new phase “Exceedance Assessment”.
  3. Exclude the Optimised SuDS design phase from analysis and turn OFF its visibility.
    A portion of the Tree View in InfoDrainage, showing only the Exceedance Assessment phase on and running, with a callout to the other phases not in use showing a red stop sign.

To artificially induce flooding:

  1. In the model, select pipe 1.003.
    The InfoDrainage Plan View, with a callout pointing to the pipe to be changed that will artificially induce flooding in the model.
  1. In the Connections dialog box, change the Diameter / Base Width of pipe 1.003 to 3mm.
    The Connections dialog box, with the pipe ID and diameter value change highlighted.
  1. Save the file.
  2. On the ribbon, Analysis tab, Analysis panel, click Validate to validate the model.
  3. Click OK to close the Validate dialog box.

Be aware that, in InfoDrainage, 2D assessments are conducted for one storm at a time, as the concept of critical duration does not really apply to flooding across a catchment surface. Therefore, the first task is to determine which storm or storms should be used in the 2D analysis.

To create the flooding simulation:

  1. On the ribbon, Rainfall/Pollutants tab, Rainfall panel, click Rainfall Manager.
  2. In the Rainfall Manager, right-click the SPR Wizard FSR storm and select Duplicate.
  3. Name the new study “Exceedance Storms”.
  4. Click the Return Periods tab.
  5. Set the Return period to 100 years.
  6. Set the Increase Rainfall value to 40%.
    The Rainfall Manager, showing that the Exceedance Storms event is set current, the Return Periods tab as active, and the return periods have been configured.
  1. From the Rainfall Manager toolbar, click Save to save the rainfall event.
  2. Name it “100 year plus 40”.
  3. On the ribbon, Analysis tab, Criteria panel, click Analysis Criteria.
  4. Change the rainfall event. Enable the Exceedance Storms Disable all others.
    The Plan View in the background with the Analysis Criteria dialog box in the foreground, with the Exceedance Storms event being turned on, and the others already off.
  1. Click the Analysis tab on the ribbon again, and then click Validate.
  2. On the ribbon, click Go.
  3. Once the program has finished the calculations, in the Stormwater Controls Summary, click Critical Storm.

The results show that only the Cellular Storage floods. The critical duration event for it was the 360-minute winter event. You will therefore carry this event forward to 2D analysis. In reality, you may want to look at which junctions flood and possibly run a series of simulations.

  1. On the ribbon, click the 1D - 2D Analysis button.
    The top-right corner of the InfoDrainage interface, with a callout pointing to the 1D – 2D Analysis button in the ribbon, Analysis tab.
  2. In the 2D Analysis Criteria dialog box, keep Manning’s n set to Urban.
  3. Enter 10 for the Min Element Area.
  4. In the Select Rainfall group box, select the Exceedance Storms rainfall from the drop-down.
  5. In the Select Storm drop-down, select the 100 years: +40%: 360 mins: Winter storm.
  6. Click OK.
    The 2D Analysis Criteria dialog box, with the settings configured and the rare, 100-year storm selected for analysis.
  7. After the calculations are complete, review the results in the Stormwater Controls Summary.
  8. The results have changed little in comparison with the 1D simulation. Close the Stormwater Controls Summary.
  9. In the Tree View, for the 2D analysis, toggle ON Depth and Legend.
  10. From the bottom-left corner of the screen, run a replay to see flooding across the catchment surface.
    The Tree View and Plan View, with the replay button being clicked to see the flooding across the catchment surface. In the bottom of the Tree View, you can see that both Depth and Legend have been turned on, and the cursor has clicked the Play button.
  1. In the Tree View, right-click the 2D analysis and select Display Settings.
  2. In the Display Settings dialog, enable the Depth layer to turn it ON.
  3. Leave Contours and Flow Direction OFF.
  4. Set the Edit Maximum value to 0.5.
  5. Set the Edit Minimum value to 0.1.
  6. Expand the Ramp drop-down and choose a color scheme.
  7. Notice how the surface appears with the Show Continuous surface option ON.
    The InfoDrainage interface, with the flooded surface showing in the background in the Plan View behind the Display Settings dialog. The Show Continuous Surface option is on, and the image of the flooding appears fuzzy.
  8. Turn Show Continuous Surface Now, the deluge appears clearly as triangles.
    The InfoDrainage interface, with the flooded surface showing in the background in the Plan View behind the Display Settings dialog. The Show Continuous Surface option is off, and the image of the flooding appears crisp, with clearly defined triangles.