BLTN7 partner FIM (depth grids) are incorrect

[RyanSpies-NOAA]

Issue was initially flagged when evaluating very poor alpha test performance metrics at this site. It appears the original HEC-RAS depth grids are incorrect for this location. There is almost no discernable difference in the inundation extent between the minimum stage (<action) and maximum stage (>major). This can be seen in the HEC-RAS depth grid outputs as well as on the published partner FIM maps on NWPS.

BLTN7: Swannanoa River at Biltmore
https://water.noaa.gov/gauges/bltn7

However, when looking at the HEC-RAS derived polygon flood extents, we can see a more realistic pattern in the inundation with action stage largely contained to the channel and then incremental expansion as we increase stage up to the major flood stage.

Here is action stage (1985ft NAVD88) differences:
From HEC-RAS depth raster -->

Aligns with extent shown on NWPS gauge site (exceeds FEMA FIRM 1%):

From HEC-RAS polygon extent -->

Suggested actions:

• Report issue to NWPS
• Add BLTN7 to the alpha test "exclusion" list
• Reprocess the benchmark library using the polygon extents instead of the depth rasters (this would require some dev)