US Geological Survey (USGS)
Estimates of streamflow statistics are used for a variety of water-resources and emergency planning, management, and regulatory purposes, and for design of structures such as bridges and culverts. These estimates are often needed at ungaged sites where no observed flow data are available.
To provide simple methods of estimating streamflow statistics, the U.S. Geological Survey (USGS) has developed and published regression equations estimating the magnitude and frequency of floods for every State, the Commonwealth of Puerto Rico, and a number of metropolitan areas in the United States, and regression equations for estimating other streamflow statistics are available for many states. These equations have been compiled into the National Streamflow Statistics (NSS) Program.