Hey
Possibly, by using a FEMA flood map and/or soil map (hydrologic soil group or drainage class), approximate locations for floodplains can be determined. In order to use the soil map, you have to get the data from NRCS or statsgo soils and join tables for chorizon. Chorizon will have the hydrologic soil groups and drainage classes. These are very similar so it is up to you to decide. These are a vector so you need to convert the vector into a raster. Once the soil raster is created, you use the combine tool in arcToolbox to combine the soil raster and the DEM. Using the attribute table, you have to see which values indicate the areas of interest corresponding to your floodplain. Hydrologic soil groups C and D indicate soils that are poorly drained to moderately drained. These classes respond to areas on floodplains and creek terraces.
James