Sizing pipes for no surcharge criteria

Video quiz

In a profile view, what does it mean if you see that pipes are laid along the top of the catchment surface, and not in the ground?

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Step-by-step:

Once you have defined the Network Design criteria, as has been done in this example, you then simply need to run the Network Design Wizard to apply that criteria.

First, load the rainfall study if it is not already:

  1. On the ribbon, Rainfall Pollutants tab, Rainfall panel, click Rainfall Manager.
  2. In the Rainfall Manager toolbar, click Open.
  3. Browse to and open the file design rainfall.idrx.
  4. Click OK to close the Rainfall Manager.
  5. In the Tree View, expand Flow Paths.
  6. Right-click Flow1 and select Show Profile.

In the Profile – Flow1 dialog box, notice that the pipes are currently laid along the top of the catchment surface.

  • The InfoDrainage interface, with the Profile – Flow1 dialog box open, showing the profile view of the flow path named, ‘Flow1’. The pipes show as just lines, since they have no sizes or depth assigned to them yet.

To specify the flow path and assign a depth to the pipes:

  1. On the ribbon, Preliminary Sizing tab, Network Design panel, click Network Design Wizard.
  2. In the Network Design Wizard, Select Flow Path page, expand the Select Flow Path drop-down and select Flow1.
    The Network Design Wizard, Select Flow Path page. The Flow1 flow path is being selected, and the pipes are all listed below in the table.
  3. Click Next.
  4. On the Enter Flow Criteria page, check that the Peak Flow Calculation is set to (UK) Modified Rational Method.
    The Network Design Wizard, Enter Flow Criteria page. The Peak Flow Calculation is being selected and called out.
  5. Enable From Library.
  6. Expand the drop-down and select Rain 1.
    The Network Design Wizard.
  7. Click Next.
  8. On the Enter Design Options page, review the design options. In this case, these were configured previously, so you should not need to change anything.
    The Network Design Wizard.
  9. Click Next.
  10. Once the calculations are complete, you can review the Summary of Changes. If you are satisfied with them, click Finish.
    The Network Design Wizard,
  11. In the Network Design Report dialog box, review and compare the Capacity vs. the Flow of each pipe in the network.

For the first catchment area, the capacity of 24.08 liters per second far exceeds the flow of 9.88 liters per second, so this pipe is sized plenty big enough. If additional structures are to be built within that first area, it is likely that the pipe will be able to accommodate the increased flow.

Now look at the Pipe (2) values. Here, the flow is closer to the capacity, in which case, for those same additional structures in the first catchment area, this pipe may not be big enough to accommodate the greater flow.

After that, there is a big jump in the capacity of the next couple of pipes, likely from a greater size pipe.

  • The Network Design Report,
  1. To see the new pipe sizes, right-click Flow1 and select Show Profile.
  2. Note the sizes and placement of the pipes in the profile.

The pipes have been laid much deeper in the ground upslope than downslope. This is because the design had to meet either the slope criteria or the velocity criteria that was specified.