Subject:   3 Types of Manholes in SWMM 5 and InfoSWMM

There are three types of interior manholes in SWMM 5 and InfoSWMM as regards water surface elevations above the Node Rim Elevation:

1^st Excess Water leaves the Node as flooded water if the water surface elevation equals the Rim Elevation (Figure 1 and Gravity Mains),

2^nd Excess Water is  stored in the manhole as pressurized depth if the Node Surcharge Depth is used (Figure 2 and Force Mains)

3^rd Excess Water is stored above the Node Rim Elevation (Surface Ponding and Figure 3)

Figure 1.  The default node in SWMM 5 and InfoSWMM has just the Manhole Invert Elevation, the program calculated elevation of the highest connected link and the Node Maximum Depth or Rim Elevation.  If the Water Surface Elevation exceeds the Rim Elevation then any excess flow is lost as flooded flow.

Figure 2.  A force main or pressure in SWMM 5 and InfoSWMM has the Manhole Invert Elevation, the program calculated elevation of the highest connected link, the Node Maximum Depth or Rim Elevation and the Node Surcharge Depth.  If the Water Surface Elevation exceeds the Surcharge Elevation then any excess flow is lost as flooded flow but this allows more the links to have more pressure and hence more flow.

Figure 3.  The flooded Node option in SWMM 5 and InfoSWMM has just the Manhole Invert Elevation, the program calculated elevation of the highest connected link, the Node Maximum Depth or Rim Elevation and Node Ponding.  If the Water Surface Elevation exceeds the Rim Elevation then any excess flow is NOT lost but stored in the ponded area.  The depth of the ponded area is a function of the ponding area and the excess inflow.  If the water surface elevation goes below the Rim Elevation then the ponded volume flows back into the network.