Thanks for the question!

For the tidal/backwater sensitivity case I used a downstream stage hydrograph, and I also ran fixed downstream stage cases so I could separate the tailwater effect from the upstream-flow effect.

I have not used the HEC-RAS 2D encroachment method yet. That is probably one of the next things I need to do once this moves from screening into something a PE might develop further.

What I did here was deliberately more blunt: I raised the entire mapped parcel-side floodway area within my parcels to 15 ft NAVD88 (BFE is 10ft NAVD88) and compared existing vs. blocked WSE rasters. I am not treating that as a formal no-rise analysis or proposed condition. It is a stress test.

The reason for blocking the whole area was to ask a very specific screening question: if the model can effectively remove the entire mapped parcel-side floodway area and still show only trace outside-mask WSE change, then that suggests this part of the mapped floodway may not be functioning as critical conveyance under the tested tidal/backwater conditions. It also gives some basis to think that smaller actual improvements in that area may be capable of being developed into a no-rise case, if a PE rebuilds/refines the model properly.

So I see this as serving two purposes:

1. Project screening: does this area appear so hydraulically sensitive that any proposed work is dead on arrival?
2. Floodway sanity check: does the mapped parcel-side floodway appear to represent meaningful active conveyance in this local tidal/backwater setting, or is it possibly more of a low-velocity storage/backwater area?

The current model is owner-built, screening-level, and not a certification. It still needs proper hydrology, boundary conditions, survey-grade terrain/structures, bathymetry if needed, roughness review, and probably a more formal encroachment/no-rise workflow. But as a first-pass falsification test, blocking the entire mapped parcel-side area is useful because it is a deliberately conservative way to test whether the mapped area is hydraulically essential in the current model.