For more information on the USGS-the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment-visit https://www.usgs.gov or call 1-888-ASK-USGS.For an overview of USGS information products, including maps, imagery, and publications, visit https://store.usgs.gov/.Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government.Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.Suggested citation: 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., 2018, Guidelines for determining flood flow frequency-Bulletin 17C: U.S. Geological Survey Techniques and Methods, book 4, chap. B5, 148 p., https://doi.org/10.3133/tm4B5. PrefaceThis series of manuals on Techniques and Methods (TM) describes approved scientific and data-collection procedures and standard methods for planning and executing studies and laboratory analyses. The material is grouped under major subject headings called "books" and further subdivided into sections and chapters. Book 4 is on hydrologic analysis and interpretation and section B is on surface water.The unit of publication, the chapter, is limited to a narrow field of subject matter. These publications are subject to revision because of experience in use or because of advancement in knowledge, techniques, or equipment, and this format permits flexibility in revision and publication as the need arises. Chapter B5 of book 4 (TM 4-B5) deals with flood flow frequency analysis at gaged sites using the Expected Moments Algorithm. The use of extreme flood data represented by interval and censored data types, including historical, paleoflood, botanical evidence, is emphasized.This revision is adopted with the knowledge and understanding that review of these procedures will be ongoing. Updated methods will be adopted when warranted by experience and by examination and testing of new techniques. AcknowledgmentsThese revised Guidelines were written by a team assembled from the Hydrologic Frequency Analysis Workgroup (HFAWG), under the auspices of the Subcommittee on Hydrology (SOH) of the Advisory Committee on Water Information (ACWI). Input from other members of HFAWG and of the SOH is gratefully acknowledged. HFAWG and SOH Work Group Members and participants in this revision are listed in appendix 2. The authors would also like to acknowledge the contributions of the U.S. Geological Survey (USGS) colleague reviewers, whose comments and suggestions materially improved this report. We also appreciate the technical advice and assistance from Dr. William H. Asquith (USGS).Lastly, our colleague and friend, Dr. Timothy A. Cohn, authored or coauthored many of the papers that form the foundation of this update to the flood ...

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Climate warming is likely to challenge many current conceptions and regulatory policies, particularly for water management. A warmer climate is likely to hinder flood operations in California's Sacramento Valley by decreasing snowpack storage and increasing the rain fraction of major storms. This work examines how a warmer climate would change flood peaks and volumes for nine major historical floods entering Shasta, Oroville, and New Bullards Bar reservoirs, using current flood flow forecast models and current flood operating rules. Shasta and Oroville have dynamic flood operation curves that accommodate many climate-warming scenarios. New Bullards Bar's more static operating rule performs poorly for these conditions. Revisiting flood operating rules is an important adaptation for climate warming.

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