Classification by Discharge and Area for Regions
Regional curves relating a certain class of Stream discharge to watershed drainage area classify Streams based on their hydrologic, physiographic, land use, climatic or geologic region. Often, these curves present the Bankfull Discharge, and in this graph the mean annual Stream flow was also plotted.
Classification based on regional curves can help to categorize new FGM data regarding Bankfull flows from ungauged Streams. To generate the curves, the Streams in one region are sampled at various upslope watershed drainage areas, and the Bankfull flow is determined from USGS gaging records and/or detailed field surveys of cross sectional area, slope, and roughness. Lines connecting the gathered data points for that region are then graphed using a logarithmic scale, which avoids the lines becoming curves. The mechanistic reason for having different lines for different regions are not well understood.
Image courtesy of FISRWG