U.S. Department of Agriculture, National Resources Conservation Service (NRCS). National Engineering Handbook. Part 630, Hydrology, 1969-2001. Originally published as the National Engineering Handbook, Section 4: Hydrology. Available from the NRCS online at http://www.nrcs.usda gov/.
U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Weather Service, Hydrometeorological Design Studies Center. 2004-2006, Precipitation-Frequency Atlas of the United States, Atlas 14, Volume 2. Version 3.0, Silver Spring, Maryland. Internet address http://hdsc.nws.noaa.gov/hdsc/pfds/.