Analyze the calculated pipe network design criteria for the no-flood status.
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.
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.
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.
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.
To look at the graphical information for an individual pipe:
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.
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.
At this point, these pipes have passed the tests for both the no-surcharge and no-flood states.
