Creating Floodplain Estimates using ArcHydro

Hi All,

I am currently undertaking a project where estimating the floodplain of a river would be incredibly useful. I have depth gauge data from the USGS, DEM and flow models from NHD+ dataset. I have been doing research as the best way to estimate the floodplain using ArcHydro and other modeling tools. I came across information on RESonate and FLDPLN from KSU. Are these tools widely available or included in ArcHydro? Or is there an easier way to estimate the floodplain?

Thanks,

Allison