USACE Guidance

EM 1110-2-1415 (USACE, 1993)
USACE. 1993. Hydrologic Frequency Analysis. EM 1110-2-1415, 5 March 1993. U.S. Army Corps of Engineers, Washington, DC. Available from USACE Engineer Manuals.

EM 1110-2-1417 (USACE, 1994)
USACE. 1994. Flood-Runoff Analysis. EM 1110-2-1417, 31 August 1994. U.S. Army Corps of Engineers, Washington, DC. Available from USACE Engineer Manuals.

EM 1110-2-1619 (USACE, 2025)
USACE. 2025. Risk Assessment for Flood Risk Management and Coastal Storm Risk Management Studies. EM 1110-2-1619, 29 September 2025. U.S. Army Corps of Engineers, Washington, DC. Chapter 3 describes how uncertainty in a discharge-frequency function is characterized, including effective record length. Available from USACE Engineer Manuals.

ER 1110-2-1450 (USACE, 1994)
USACE. 1994. Hydrologic Frequency Estimates. ER 1110-2-1450, 31 August 1994. U.S. Army Corps of Engineers, Washington, DC. Available from USACE Engineer Regulations.

ECB 2026-1 (USACE, 2026)
USACE. 2026. Incorporating Resilience to Nonstationary Hydrometeorological Conditions in USACE Civil Works Studies, Designs, and Projects. Engineering and Construction Bulletin 2026-1, issued 9 January 2026, expires 9 January 2028. U.S. Army Corps of Engineers, Washington, DC. Available from the Whole Building Design Guide.

Federal and Technical Guidance

Bulletin 17C (England et al., 2019)
England, J.F., Jr., Cohn, T.A., Faber, B.A., Stedinger, J.R., Thomas, W.O., Jr., Veilleux, A.G., Kiang, J.E., and Mason, R.R., Jr. 2019. Guidelines for Determining Flood Flow Frequency — Bulletin 17C (version 1.1, May 2019). U.S. Geological Survey Techniques and Methods, book 4, chapter B5. https://doi.org/10.3133/tm4B5. Supersedes Bulletin 17B and is implemented in HEC-SSP.

Bulletin 17B (IACWD, 1982)
Interagency Advisory Committee on Water Data (IACWD). 1982. Guidelines for Determining Flood Flow Frequency, Bulletin 17B. Reston, VA, U.S. Geological Survey. Superseded by Bulletin 17C (England et al., 2019); cited in this chapter because EM 1110-2-1415 (USACE, 1993) follows its procedures.

NOAA Atlas 14 (NOAA)
National Oceanic and Atmospheric Administration. Precipitation-Frequency Atlas of the United States, NOAA Atlas 14, Volumes 1 through 12. National Weather Service, Silver Spring, MD. The volumes are: 1 Semiarid Southwest; 2 Ohio River Basin and Surrounding States; 3 Puerto Rico and the U.S. Virgin Islands; 4 Hawaiian Islands; 5 Selected Pacific Islands; 6 California; 7 Alaska; 8 Midwestern States; 9 Southeastern States; 10 Northeastern States; 11 Texas; and 12 Interior Northwest. Estimates are published through the NOAA Precipitation Frequency Data Server.

NOAA Atlas 15 (NOAA, in development)
National Oceanic and Atmospheric Administration. NOAA Atlas 15. Office of Water Prediction. Volume 1 will provide estimates that account for observed temporal trends and will replace NOAA Atlas 14 as the national standard. Volume 2 will provide model-based estimates projected through 2100. For the contiguous United States, preliminary estimates for peer review are expected in September 2026 and published estimates in 2027. Available from the NOAA Atlas 15 information page.

NOAA Atlas 2 (NOAA, 1973)
National Oceanic and Atmospheric Administration, 1973. Precipitation-Frequency Atlas of the Western United States, NOAA Atlas 2, Volumes 1-2, 5, and 9-10 (Idaho, Montana, Oregon, Washington, Wyoming). National Weather Service, Silver Spring, MD. Remains the current source for areas not yet covered by NOAA Atlas 14.

TP-40 (NOAA, 1961)
Hershfield, D.M., 1961. Rainfall Frequency Atlas of the United States for Durations from 30 Minutes to 24 Hours and Return Periods from 1 to 100 Years, TP 40. Originally written for the Weather Bureau, U.S. Department of Commerce, Washington, DC. Available now from the National Weather Service, National Oceanic and Atmospheric Administration, Silver Spring, MD. HEC-HMS still offers annual-partial conversion factors and area-reduction curves derived from this publication.

TP-49 (NOAA, 1964)
Miller, J.F., 1964. Two- to Ten-day Precipitation for Return Periods of 2 to 100 Years in the Contiguous United States, TP 49. Originally written for the Weather Bureau, U.S. Department of Commerce, Washington, DC. Available now from the National Weather Service, National Oceanic and Atmospheric Administration, Silver Spring, MD. HEC-HMS still offers area-reduction curves derived from this publication.

HYDRO-35 (NOAA, 1977)
Frederick, R.H., Myers, V.A., and Auciello, E.P., 1977. Five- to 60-minute Precipitation Frequency for the Eastern and Central United States, HYDRO-35. National Weather Service, National Oceanic and Atmospheric Administration, Silver Spring, MD.

Jennings (1994)
Jennings, M.E., W.O. Thomas, Jr., and H.C. Riggs, 1994. Nationwide Summary of U.S. Geological Survey Regional Regression Equations for Estimating Magnitude and Frequency of Floods for Ungaged Sites, USGS Water Resources Investigations Report 94-4002, Reston, VA. Current regional regression equations are delivered through the USGS StreamStats application.

Sauer (1983)
Sauer, V.B., W.O. Thomas, V.A. Stricker, and K.V. Wilson, 1983. Flood Characteristics of Urban Watersheds in the United States, USGS Water Supply Paper 2207, Reston, VA.

Waananen (1977)
Waananen, A.O. and J.R. Crippen, 1977. Magnitude and Frequency of Floods in California. Water-Resources Investigation 77-21. U.S. Geological Survey, Washington, D.C.

Pilgrim (1975)
Pilgrim, D.H., and Cordery, I., 1975. Rainfall Temporal Patterns for Design Floods. Journal of the Hydraulics Division, ASCE, 101(HY1), 81-85.

TD-11 (HEC, 1980)
U.S. Army Corps of Engineers, Hydrologic Engineering Center. 1980. Adoption of Flood Flow Frequency Estimates at Ungaged Locations, TD-11. Hydrologic Engineering Center, Davis, CA.

HEC Software Documentation

📖 User's Manual

How to build and run the HEC-HMS components used in this chapter.

  • Precipitation — the Frequency Storm and Hypothetical Storm methods and their settings
  • Frequency Analyses — assembling a flow- or stage-frequency curve from a set of frequency events
  • Uncertainty Analyses — sampling model inputs to evaluate their effect on computed flows

📐 Technical Reference Manual

Theory behind the methods used in this chapter.

🛠️ Tutorials & Guides

Hands-on worked examples with downloadable project files.

📈 HEC-SSP

Statistical analysis of gaged data. Current versions apply Bulletin 17C. The link above is the current HEC-SSP User's Manual (version 2.3, June 2023).

CPD-86 (HEC, 2010)
HEC. 2010. HEC-SSP Statistical Software Package, User's Manual, Version 2.0. CPD-86, October 2010. Hydrologic Engineering Center, Davis, CA. Cited for the historical comparison in this chapter's case study.

📊 HEC-FDA

Expected annual damage computations that use the flow-frequency curves developed in this chapter, as described in the Flood Risk Management (FRM) Studies.