Step-by-step:

Once your drainage design has met the no-surcharge criteria, it must be tested against the no-flood criteria. In this example, the pipes have been sized adequately for no-surcharge; the no-flood design criteria have been set for an 18-storm sample size; and the validation tool has been run to check for missing data errors. At this point, the analysis can be run.

On the ribbon, Analysis tab, Analysis panel, click Go.

InfoDrainage quickly processes the calculations and displays in the Progress dialog box. In this case, the model has only one line of pipes that runs downhill. When it finishes, the Connections Summary dialog box appears, reporting the results for each pipe for one of the eighteen storms.

Expand the Connections Summary dialog box to see the entire table better.

Notice the Maximum Flow column. These values are within acceptable levels for this model. Of more importance is the Status column, which, in this case, reports that the pipes are either OK or Surcharged. If they are showing as surcharged, that is acceptable for this higher return period storm. What you do not want to see is a pipe showing as Flooded. In this example, none of the pipes are flooded.

You can also see that some of these pipes are showing as red and in bold. This indicates that these pipes are under capacity. The surcharged pipes that are showing as normal text may only be surcharged as a result of backing up from slower drainage downstream during this larger storm.

Below the Plan View right in the bottom of the screen, in the Select Event drop-down, is the storm that has created these results. This storm is a 30-year storm that lasted 15 minutes in the summer.

Expand the Select Event drop-down to select any one storm to access the results it produces.
To know whether any of the 18 storms caused flooding, at the top of the Connections Summary dialog box, click Critical Storm.

The results in the table change to show the worst storm of the 18 that were in this study. In this case, it is a 30-year, 15-minute winter storm, as indicated in the Storm Event column. Also, in the Status column, you can see that more pipes are now reported as being surcharged. This is typical of drainage systems such as this model. More complicated systems that have catchments and water storage features will show a variety of pipe statuses for many different types of storms.

Click Critical Storms again to deactivate it.
Expand the Select Event drop-down and select the 30-year, 15-minute.
Drag the dialog box aside, and you can see that the highlighted, bold surcharged pipes in the table are also highlighted in the model.

To look at the graphical information for an individual pipe:

On the ribbon, Results tab, Item Results panel, expand the Connections drop-down, and select Pipe (4).
In the Results Pipe (4) dialog box, click the Graphs tab.

As you can see from the key, the green line represents the rainfall, and the red line represents the flow within Pipe (4). The rainfall graph is representative of a typical dynamic rainfall graph in that it is symmetrical, it starts at zero, builds up to a maximum across a centerline, and then dissipates back down to zero, and in this case, it ends at the 15-minute mark.

The flow graph is very similar in shape. You can see that it lags behind the rainfall in time, and that it builds much more gradually up to the apex, has a nice arc at the top, then comes back down gradually. This smooth increase and decrease in flow provides confidence in the results. If you see rapid oscillations in the flow, it could be a genuine effect, or it could be a sign of an instability. Instabilities occur when the simulation calculations falter and will invalidate the results. So, if you see something that does not make sense, you know it may require further investigation and refinement of the model.

Click the Tables tab.
Review the results.
Close the dialog box.
In the ribbon, Results tab, expand the Junctions drop-down and select Manhole (4).
In the Results: Manhole (4) dialog box, review the graphs.
Close the dialog box.
In the Tree View, right-click Flow1 and select Show Profile.
In the bottom left, click Play to play the simulation through and see the pipes fill up and then drain away.
Rewind it to about halfway through and pause it. Notice that the pipes are full, and Manhole (4) is halfway full.
Zoom into the profile view.

The pipes are full, and Manhole (4) is almost halfway full. So, even though the pipes are surcharged, there is still a great deal of room in the manhole. It is nowhere near flooding, nor is it even within the 300-millimeter threshold that would constitute flood risk. The pink line that is even with the top water level indicates the maximum head of water for the manholes.

Close the profile view.

At this point, these pipes have passed the tests for both the no-surcharge and no-flood states.

Save the model.

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