SSA junction flooding

[Anonymous]

I'm working on a storm sewer model and trying to verify that the 100-yr HGL stays below the rim elevation of the structures. The far upstream end of the system consists of a headwall and 36" storm which is collecting runoff from an offsite detention pond. The headwall then connects to multiple junctions with inlets connected to them as you work downstream. I'm modeling the headwall as a storage node and applying a user defined external inflow that I created using the time series results discharged from the pond.

The system results seem to make sense at most of the junctions with a couple surcharging by 1-3 inches; however, the second junction downstream of the storage node is surcharging roughly 25 ft. above the max. rim and much higher than any other junction up- or downstream of it. The total inflow to the junctions is relatively consistent but the head jumps considerably and occurs at or near the peak from the external inflow.

I'm not surprised there's some surcharging but I'm really stumped with the 25 ft. jump at the one junction. Any thoughts or suggestions?

Thanks,

Derek

[Anonymous]

Have you tried decreasing your routing time step?  When I get suspicious hydraulic results I can usually smooth them out by refining the time steps.

Joe

[Anonymous]

Can you post a picture of the profile of the 36" pipe with junctions and HGL displayed?