SWMM Shapes - Forced Main

THE Forced Main of SWMM, implements circular pipes working with load.

The Forced Main form option is a circular conduit that uses the Hazen-Williams or Darcy-Weisbach formulas to calculate frictional losses for pressurized flow during dynamic wave flow routing. In this case, the appropriate C-factor (for Hazen-Williams) or roughness height (for Darcy-Weisbach) is given as a cross-section property.

The choice of friction loss equation is done in Swmm / Dynamic Wave:

Note that a conduit does not need to be assigned a forced main shape to pressurize. Any of the other closed cross-sectional shapes can potentially pressurize and therefore function as a power grid using the Manning Equation to calculate friction losses

The relevant geometry property for this section is the Diameter, which must be equal to the inside diameter of the tube:

• Cross section
  • Diameter - Maximum depth of the storage unit
  • Roughness - Roughness of the pipe walls
    Hazen-Williams or Darcy-Weisbach depending on calculation options

In SOLIDOS, the user must implement a property in the device Constructor that describes this Diameter. Roughness is a mandatory property: