River flow volumes, as visualized by some guys at Pacific Institute, who explain:
Major rivers of the 48 contiguous United States, scaled by average flow where river symbols are proportional to the “gage-adjusted flow.” The symbols drawn here have widths proportional to the square root of the rivers’ estimated average annual discharge. Only rivers with discharge above 1,000 cfs are shown. Data from NHDPlus v2. Background map by ESRI.