[5pt] Use the 1% FEMA NFHL as the boundary for floodplain adjustment

[CarsonPruitt-NOAA]

There are a few areas that FIM v6 is inundating well outside of the channel due to the floodplain adjustment. In Phoenix, the FEMA 0.2% NFHL is very expansive, which I think is the main cause. Let's try switching to the 1% boundary and also halve the buffer in areas without NFHL coverage to 1.5 km.

This is in HUC 15070102.

[mluck]

The FEMA NFHL availability data look bad in this area. None of the Phoenix area is covered by the availability layer (gray shade), even in areas where there is 100- and 500-year NFHL coverage (solid blue and red hatched, respectively). Another thing of note is that the 500-year data cover nearly the entire area.