1. A method of assessing a riparian area, comprising: mapping a physical extent of a potential riparian area (PRA) along a stream using first imagery; determining a percent of basic functional groups of vegetation with the PRA using the first imagery; determining a Normalized Difference Vegetation Index (NDVI) for the PRA over multiple years using second imagery; setting an NDVI threshold value for riparian vegetation in the PRA using the NDVI; mathematically relating the percent of basic functional groups with the NDVI threshold value to evaluate and correct the NDVI threshold value; and determining a proper function and condition (PFC) assessment of the PRA using the corrected NDVI threshold value.