Modeling an obstruction, clog or excessive sediment in a conduit or outlet structure

  Product(s): SewerCAD, StormCAD, SewerGEMS, CivilStorm
  Version(s): V8i, CONNECT Edition
  Area: Layout and Data Input


How can I model an obstruction or clog in a conduit (pipe) or outlet structure? (orifice, weir, culvert, etc) For example excessive silt or sediment in a pipe, or build-up of leaves, branches and trash for an outlet structure.

Solution - Conduit (pipe)

Here are some possible options for modeling a conduit with an obstruction:

1) If using the Explicit (SWMM) numerical solver in SewerGEMS or CivilStorm, use the "fill depth" property.

2) Make the conduit size / diameter smaller

2) Adjust the roughness coefficient number to increase friction/resistance

3) Use one of the other section shapes to approximate it. For example irregular closed section, arch-pipe, etc.

4) Insert a node at the location of the obstruction and model it as a structure loss. For example a manhole with a bolted cover and structure loss method selected.

5) Specify a conduit start or stop control structure and model it as an orifice (to use the orifice equation to model the restriction)

Solution - Outlet Structure

For a clogged outlet structure, the solution would depend on the outlet structure type.

For an orifice, you could adjust the orifice diameter such that it has 50% of the capacity of the actual diameter.

If you want to assume the clogging / debris is stuck at the bottom of a culvert, weir or vertically-oriented orifice, you could use the "Elevation (On)" field in the composite outlet structure for that particular outlet component. Set this to the elevation that the clogging rises up to. For example of a weir invert is at 100 ft but it is clogged up to an elevation of 102 feet, set the "Elevation (On)" to 102 ft and there will be no flow through the weir until 102 ft.

See Also