Problem:

As SWMM5 is a link node network, the area of a Storage Node is both the area of the Wet Well and typically ½ the surface area of the connecting links. There is no surface area for the Pump(s) downstream of the Wet Well (Storage) but the area of the upstream links will add to the surface area of the Wet Well. One Answer: You can eliminate this issue by adding a in a Dummy link to connect the upstream Gravity Main links to the Wet Well. The Dummy link has no surface area and sets the Outflow of the link to the Total Inflow of the Upstream Node to the Dummy link. The Wet Well will then only have the surface area of the Wet Well.

In SWMM5's link-node network structure, storage node areas currently incorporate both the wet well area and approximately half the surface area of connecting links. This creates two key issues:

The model excludes downstream pump surface areas
Upstream link areas incorrectly contribute to wet well calculations

The Impact on Infrastructure Planning

This modeling limitation affects the accuracy of critical infrastructure calculations. When city planners rely on these models for flood prediction and sewage capacity planning, the discrepancy between modeled and actual system behavior can lead to infrastructure vulnerabilities.

The Solution: Implementing a Dummy Link

To address this limitation, we can introduce a dummy link between the upstream gravity main links and the wet well. This dummy link:

Has zero surface area

Sets outflow equal to the total inflow from the upstream node
Effectively isolates the wet well's true surface area

This modification ensures the storage node accurately represents only the wet well area, providing more precise modeling results for infrastructure planning and system analysis.