A few considerations to think about when you are modeling natural channels or irregular channels in SWMM 5:
1. The Maximum depth is limited to the Transect Highest minus the Lowest Elevation
2. If the Maximum depth is reached during the simulation any excess water from the upstream node is either stored at the upstream node or lost as flooded water
3. If the excess water is stored it means you are using the Surface Ponding option in SWMM 5
4. If you using the Surface Ponding option then the depth at the upstream node will increase based on the Excess Flow / Pond Area
5. The Irregular channel is restricted to full flow but if the HGL at the upstream head rises you can get more flow through the Irregular channel as the flood level rises.
6. The flow is thus sensitive to the ponding area
|Surface Ponding and its Impact on Irregular Channels in SWMM5|