How to model a bridge scupper

Product(s): SewerGEMS, CivilStorm, StormCAD
Version(s): CONNECT Edition, V8i
Area: Modeling


How do I model a bridge scupper with a vertical drain pipe connected to the bottom of a catch basin, to ensure that it has more capacity than the inlet?


Conduits are assumed to be horizontal, so connecting a near-vertical conduit downstream of the catch basin may not work well. A good option to consider is to estimate this using the orifice or weir equation (Depending on the depth of flow inside the catch basin vault), using the size of the hole.

In the CivilStorm/SewerGEMS/StormCAD model, you can simply connect the catch basin node directly to an outfall via a short conduit (with the assumption that the inlet opening is the restricting factor and the vertical pipe will have as much or greater capacity to drain the water that the inlet opening captures)


With the above approach, the invert of the catch basin (inlet) would not matter, since the hydraulics downstream of the inlet opening do not matter (because the assumption is that you will design it so that the vertical pipe has adequate capacity). You could set the catch basin invert an arbitrary distance below ground elevation such as 5 feet, or if reasonable and if you need to see it in profile view, you could set it equal to the bottom of the scupper where the water drains out. Similarly, the conduit and outfall inverts would not matter much, though you may want to set them such that they start at the catch basin invert and have a small slope down to the outfall, so as not to clutter your User Notifications with messages about extreme slopes. If you utilize the "Notes" property, you could make note of your assumption there for future reference. Be sure that the hydraulic gradient line at the upstream end of pipe doesn't go higher than the bridge deck.

Note: if you're using StormCAD (or the GVF Rational solver in SewerGEMS or CivilStorm), you could omit the conduit and outfall seen in the above screenshot. For more on this, see the "Inlet-Only Hydraulic Calculations" section in this technote: What's new in StormCAD V8i SELECTseries 4?

If you know the rating curve you want to use for an inlet, you can apply it using the inlet catalog.

1.Go to: Components > Catalog > Inlet Catalog

2.Select the New icon.

3.Set Inlet Type to "Gutter Depth vs. Captured Flow" or "Flow to Inlet vs. Flow Captured".

See Also

Forum Thread: bridge drainage outlet velocity calculation in close vertical drainage system

"Intake shape and boundary-related considerations in the operation and design of storm-sewer drop structures" by A. Auckland, I. Nistor, R. Townsend. Canadian Journal of Civil Engineering, 2009, 36(11): 1825-1834,

[Enhancement Request: 931035]

Modeling Custom Inlets Using a Gutter Depth vs. Captured Flow Curve