Problem

How does the clogging factor work with catalog inlets?

Solution

The clogging factor comes from the HEC-22 documentation and can be used on any catalog catch basin or inlet. Once you select "Catalog Inlet" for the Inlet Type, a field for Clogging Factor is displayed.

Clogging Factor produces different types of results depending on the inlet location selected in the catch basin properties but generally reduces the effective area of the grate or curb.

For "On Grade" catch basins, the clogging factor can impact the flow downstream of the catch basin. This is because not all capture efficiency will be decreased, resulting in changes in the flow for the downstream conduit and any gutter flow that may be present.

If you use "In Sag", the catch basin is assumed to capture 100% of the flow. For that reason, the clogging factor will not impact the downstream flow. Since all flow is captured, the flow will be same regardless of the value used for the clogging factor. However, the gutter depth reported at the catch basin will be different.

In the image above, you have two different gutter depths being reported. On the right is a case where the clogging factor is 0%. On the left, the clogging factor is 80%. While the downstream flow is the same for both cases, the gutter depth is higher for higher values for the clogging factor. This is because more head is required to push 100% of the water through the inlet grate (since "In Sag" catch basins are assumed to be full capture).

See Also

How do catalog inlets handle clogging at low depths?