[13pt] Low-head dams causing HAND issues

[CarsonPruitt-NOAA]

Low-head dams often cause FIM overprediction upstream of the dam, even in Stage-based CatFIM. One strategy suggested by @RyanSpies-NOAA is to force a catchment break at these locations. This image of AMCK1 shows 2 houses in the 500-yr floodplain which are inundated at our minor category.

The following is a map with a national inventory of low-head dams. However, I have not yet determined its completeness.
https://sarp.maps.arcgis.com/apps/webappviewer/index.html?id=1cab6b600069461da86a416173a585b2

[CarsonPruitt-NOAA]

So the more that I look at this, the more it looks like it's only a Stage-based CatFIM issue. Flow-based and NRP FIM seem slightly affected, but not as much. Below this dam, Flow- and Stage-based have fairly good agreement at Action.

However, above the dam, Stage-based well over-extends Flow-based at Action even getting closer to Minor.

There's actually another dam close to the upper end of this site that exacerbates the issue even further where the Stage-based Action exceeds the Flow-based Record.