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Flood Hazards
Flood Hazards
My work, in collaboration with USACE staff, HEC, Reclamation staff, and others, focuses on understanding and estimating extreme flood hazards for critical infrastructure such as dams and nuclear reactors. I provide some summary concepts, notes on ongoing efforts, reports, and presentation on this page for several key areas. These include: Hydrologic Hazard Curves; Hydrologic Risk Analysis and Risk-Based Design; Paleofloods; and Extreme Storm Rainfall. See the Bulletin 17C page for some details and ongoing work on flood frequency analysis (focusing on the Expected Moments Algorithm). Eventually, some specific software and data sets may be added here, in addition to those mentioned on the Resources page.
Big Thomson River at mouth of the canyon near Loveland, CO; flood of July 31- August 2, 1976.
Big Thomson River at mouth of the canyon near Loveland, CO; flood of September 12-14, 2013.
To understand extreme floods, it is necessary to examine the largest floods observed or recorded, and conduct field studies and data collection of historic floods, paleofloods, and recent floods. These types of studies, as well as conducting reviews of past flood estimates, help in flood prediction and uncertainty estimation. In the United States, reviews of the largest peak discharges described by England (2004) and Costa and Jarrett (2008) indicate that improvements are needed in: flood process identification; quantifying uncertainty of floods; and use of better hydraulic methods to estimate peak discharge.
West Nueces River near Kickapoo Springs, TX; looking upstream toward the site of the June 14, 1935 record flood estimate (580,000 ft3/s).
Hydrologic Hazard Curve Definition
A Hydrologic Hazard Curve (HHC) is defined as a graph of peak flow and/or volume (for specified duration) versus Annual Exceedance Probability (AEP) (< 1 in 10,000 for Reclamation)
Hydrologic Hazard Curves may also depict Maximum Reservoir Elevation versus AEP
AEP estimates are made for peak flows, runoff volumes and reservoir elevations to cover the range of values needed for risk-based dam safety decision making at a specific facility
HHCs are used to evaluate specific Potential Failure Modes (overtopping, gates, spillway chute, etc.) in a risk-based framework
See the November 2013 Reclamation Flood Overtopping Workshop Hydrologic Hazards presentations - Introduction and Methods/Applications for additional background.
Some Key Hydrologic Hazard Analysis (HHA) Concepts
Hierarchy and Risk Process – Agency Specific
Probability Estimates and Full Distributions needed, with Uncertainty
PMF and Single (Point) Deterministic Flood Estimate No Longer Adequate – more information required
Hydrologic Hazard Curves are the Load Input to Risk
Peak Flow and Volume Frequency Curves
1/1,000 AEP to 1/10,000 AEP (typical for failure probability)
less than 1/10,000 AEP extrapolation!
Hydrographs; Maximum Reservoir Levels
HHA Methods vary; depend on study level
Multiple HHA Methods Used and Combined
Hydrologic Hazard Curve Principles - Reclamation Flood Workshop
Do Not Assign AEP to the PMF
No Single Approach Describing Flood Hazards Over the Range of AEP Needed
Greatest Gains From Incorporating Regional Precipitation, Streamflow, Paleoflood Data
Honestly Represent Uncertainty
Research and Development - Data/Methods
Hydrologic Hazard Curve Principles
Data - focus on past (paleoflood) and present (recent) data
Future climate projections assessed/used project by project – study and decision dependent
Flood Hazards Estimated using Interdisciplinary Teams
Hydrologists/Hydrologic Engineers
Meteorologists
Geomorphologists
Flood Models, Relationships and Tools developed in-house by Reclamation and collaborators
Uncertainty of Estimates is Quantified
Hydrologic Hazard Guidelines
2006 Guidelines Report provides details on the HHA methods and overall framework
Reclamation hydrologic hazard technical reports for specific facilities/dams describe advances in data and methods since the 2006 report; see Hydrologic Hazard Applications
Some recent techniques are described in the Best Practices in Dam and Levee Safety Risk Analysis - Probabilistic Hydrologic Hazard Analysis Chapter
Hydrologic Hazard Guidance and Applications
Some example hydrologic hazard guidance documents and reports that demonstrate applications for dam safety and floodplain management are the following. Most of these studies include the key ingredients: regional precipitation frequency, extreme storm rainfall, historical and paleoflood data with flood frequency, and stochastic rainfall-runoff modeling with reservoir routing. Technical training seminars and short courses describe the concepts.
Hydrologic Hazard Guidance
Smith, H., Bartles, M., and Fleming, M. (2018) Hydrologic Hazard Methodology for Semi-Quantitative Risk Assessments: An Inflow Volume-Based Approach to Estimating Stage-Frequency Curves for Dams, Report RMC-TR-2018-03, U.S. Army Corps of Engineers Risk Management Center, Lakewood, CO, 132 p.
Branard, A. and Stowasser, E. (2018) Data Sources for Estimating Hydrologic Hazards for Semi-Quantitative Risk Assessments, Report RMC-TR-2019-07, U.S. Army Corps of Engineers Risk Management Center, Lakewood, CO, 33 p.
Stochastic Rainfall-Runoff Modeling (HEC-WAT, SEFM, and variants)
Schaefer, M.G. and B.L. Barker (2005) Stochastic Modeling of Extreme Floods on the American River at Folsom Dam Flood-Frequency Curve Extension. MGS Engineering Consultants for U.S. Army Corps of Engineers, Research Document 48, Hydrologic Engineering Center, Davis, CA, September 2005.
Sutley, D.E., Klinger, R.E., Bauer, T.R., and Godaire, J.E. (2009) Trinity Dam Detailed Hydrologic Hazard Analysis Using the Stochastic Event Flood Model, CVP-Shasta/Trinity Project, California, Mid-Pacific, Bureau of Reclamation, Flood Hydrology and Consequences Group, October, 84 p. and appendices.
Tetra Tech, Inc. (2009) Baker River Project Flood-Frequency Curve Extension, FERC Project No. 2150, prepared for Puget Sound Energy, April, 64 p. and appendices.
Novembre, N.J., et al. (2012) Altus Dam Hydrologic Hazard and Reservoir Routing for Corrective Action Study, U.S. Department of the Interior, Bureau of Reclamation, Denver, CO.
Wright, J.M., V. Sankovich, J. Niehaus, N. Novembre, R.J. Caldwell, R. Swain, and J. England (2013) Friant Dam Hydrologic Hazard for Issue Evaluation, Bureau of Reclamation, Flood Hydrology and Consequences Group, September, 225 p.
Smith, C.H., Karlovits, G., Moses, D. and Nelson, A. (2015). Herbert Hoover Dike, Hydrologic Hazard Assessment. Prepared for the US Army Corps of Engineers Jacksonville District, by the US Army Corps of Engineers Risk Management Center.
Tennessee Valley Authority (2017) Chapter 3 Hydrologic Loading, Watts Bar Project, iSQRA, draft report
Smith, C.H., et al. (2018 ) Trinity Basin Dams, Hydrologic Loading Report, Trinity River Basin (Texas), draft report, U.S. Army Corps of Engineers, Risk Management Center.
Simplified Stochastic Rainfall-Runoff with AEP-Neutral Concepts
England, J.F. Jr., Klawon, J.E., Klinger, R.E. and Bauer, T.R. (2006) Flood Hazard Study, Pueblo Dam, Colorado, Final Report, Bureau of Reclamation, Denver, CO, June, 160 p.
Dworak, F., Novembre, N., and Sankoich, V. (2011) Green Mountain Dam, Colorado-Big Thompson Project, Hydrologic Hazard Report. U.S. Department of the Interior, Bureau of Reclamation, Denver, CO
England, J.F. Jr., Dworak, F.J., and Sankovich, V.L. (2012) Hydrologic Hazard Analysis, Anderson Ranch Dam, Idaho, Final Report, Bureau of Reclamation, Denver, CO, June, 140 p.
Smith, H., Sasaki, R., Karlovits, G.S., Hall, B.M., and Parola, A. (2018) Hydrologic Hazard Curve Analysis for Whittier Narrows Dam (CA10027), Rio Hondo and San Gabriel Rivers, California, Report RMC-TR-2018-11, U.S. Army Corps of Engineers Risk Management Center, Lakewood, CO, 145 p.
Duren, A.M., et al. (2018 ) Willamette Basin Dams, Hydrologic Loading Report, Willamette River Basin (Oregon), draft report, U.S. Army Corps of Engineers, Risk Management Center.
Reclamation uses risk analysis in the Dam Safety Program to: evaluate existing structures; design new structures; and prioritize expenditures. Risk analysis is a key input to dam safety decision making. Reclamation's Public Protection Guidelines describe the overall risk framework (see f-N chart). An overview of dam safety processes is in a presentation given at the workshop on Probabilistic Flood Hazards at the Nuclear Regulatory Commission. A reservoir frequency relationship (HHC) is a key input to evaluate hydrologic risk for specific potential failure modes such as dam overtopping (see Gibson Dam), evaluate spillway adequacy, etc.
Reclamation uses HHCs and risk analysis methods to estimate Inflow Design Floods (IDFs) and IDF ranges. These IDFs are based on risk: flood load probabilities; failure probabilities; and consequences. In some situations, there is no single IDF (in contrast to deterministic standards such as the Probable Maximum Flood), because combinations of flood hydrographs, antecedent reservoir levels, and routing assumptions result in reservoir ranges (see reservoir elevation frequency relationship). The IDF selection process is described in Design Standard 14, Chapter 2. The ranges encompass flood load uncertainties, response of the structure, and robustness considerations. Additional Reclamation Design Standards are here.
f-N Chart; Reservoir Elevation Frequency Relationship
Gibson Dam overtopping; Design Standard 14 Chapter 2 IDF Summary
Paleoflood data are crucial in order to estimate hydrologic hazards for dam safety, and are also useful for floodplain management.
Paleoflood Data:
Consists of individual (discrete) floods and non-exceedance information; discharge and age estimates include uncertainty
Extends short or non-existent flood records
Extending record to include the last 1000 years is common, up to and including much of the last 10,000 is not unusual
Addition of any paleoflood data to a frequency analysis has been shown to improve accuracy of the estimate
Places extreme outlier(s) into temporal context
Time interval between events of similar size (if they are recurrent) or the time since the event last occurred can often be determined
Cost effective and robust
Paleoflood data are used extensively by Reclamation in risk analysis. Risk-based design modifications for hydrologic considerations at several facilities such as Folsom Dam (additional spillway capacity), Glendo Dam (additional spillway capacity), and A.R. Bowman Dam (parapet wall) have been based in-part on hydrologic hazard curves with paleoflood data. See the Folsom and Glendo flood hazard reports, as examples.
The USACE is collecting paleoflood data and conducting paleoflood studies in support of risk-informed hydrologic hazards for the dam and levee safety program. Some example projects are for: Ball Mountain Dam in Vermont; Garrison Dam in North Dakota; and Lookout Point Dam in Oregon. Contact Keith Kelson or me for details.
Additional information on paleoflood data can be obtained from: the AGU book Ancient Floods, Modern Hazards: Principles and Applications of Paleoflood Hydrology; presentations by Drs. Ralph Klinger and Jim O'Connor at the NRC workshop on Probabilistic Flood Hazards, and Reclamation's geology and paleoflood staff.
Paleoflood Publications
Some example paleoflood hydrology reports that demonstrate applications for dam safety and floodplain management are the following.
USACE
Contact me
U.S. Army Corps of Engineers (2020) Developing Paleoflood Information for Flood Frequency Analysis. Engineering Technical Letter No. 1100-2-4, U.S. Army Corps of Engineers, Washington, D.C., 34 p.
2019 Paleoflood Geomorphology Training Course - Harpers Ferry, WV, USACE Visiting Scholars
Kelson, K.I., Hall, B.M., Sasaki, R., Leonard, C.M., and Potts, S. (2017) Paleoflood Analysis for Ball Mountain Dam, Report RMC-TR-2017-08, U.S. Army Corps of Engineers Risk Management Center, Lakewood, CO, 74 p.
Pearce, J.T. (2017) Limited Geomorphic Investigation of Paleoflooding for Cherry Creek Dam (CO01280), Report RMC-TR-2017-10, U.S. Army Corps of Engineers Risk Management Center, Lakewood, CO, 26 p.
Margo, D.A. (2017) Flood Hazard Analysis for Cherry Creek Dam (CO01280), Report RMC-TR-2017-11, U.S. Army Corps of Engineers Risk Management Center, Lakewood, CO, 39 p.
Kelson, K.I., Hall, B.M., Walters, G.S., Duren, A.M., and Leonard, C.M. (2018) Paleoflood Analysis for Lookout Point Dam, Report RMC-TR-2018-02, U.S. Army Corps of Engineers Risk Management Center, Lakewood, CO, 80 p.
Kelson, K.I., Pearce, J.T., and Kinder, D.S. (2018) Paleoflood Analysis for Proctor Dam, Report RMC-TR-2018-09, U.S. Army Corps of Engineers Risk Management Center, Lakewood, CO, 36 p.
Bureau of Reclamation
Contact: Seismology and Geomorphology Group, TSC
Bureau of Reclamation (2002) Flood Hazard Analysis - Folsom Dam, Central Valley Project, California. Bureau of Reclamation, Denver, CO, January, 128 p.
Klinger, R.E., and Klawon, J.E. (2002) Development of a paleoflood database for rivers in the western U.S. U.S. Department of Interior, Bureau of Reclamation, Denver, Colo., 38 p.
Levish, D.R., England, J.F. Jr., Klawon, J.E. and O’Connell, D.R.H. (2003) Flood Hazard Analysis for Seminoe and Glendo Dams, Kendrick and North Platte Projects, Wyoming, Final Report, Bureau of Reclamation, Denver, CO, November, 126 p.
England, J.F. Jr., Klawon, J.E., Klinger, R.E. and Bauer, T.R. (2006) Flood Hazard Study, Pueblo Dam, Colorado, Final Report, Bureau of Reclamation, Denver, CO, June, 160 p.
Klinger, R.E., and Bauer, T.R., 2010, Paleoflood study on the South Fork of the Boise River for Anderson Ranch dam, Idaho: U.S. Department of Interior, Bureau of Reclamation, Denver, Colo., 30 p.
Godaire, J.E. and Bauer, T.R., 2011, Paleoflood study of Blue River near Green Mountain dam, Colorado: U.S. Department of Interior, Bureau of Reclamation, Denver, Colo., 60 p.
Godaire, J.E., Bauer, T.R., and Klinger, R.E., 2012, Paleoflood study, San Joaquin River near Friant dam, California: U.S. Department of Interior, Bureau of Reclamation, Denver, Colo., 60 p.
Godaire, J.E., and Bauer, T.R. (2012) Paleoflood study, North Fork Red River basin near Altus dam, Oklahoma: U.S. Department of Interior, Bureau of Reclamation, Denver, Colo., 55 p.
Godaire, J.E., and Bauer, T.R. (2013) Paleoflood study on the Rio Chama near El Vado dam, New Mexico. U.S. Department of Interior, Bureau of Reclamation, Denver, Colo., 58 p.
USGS
Contact: Jeanne Godaire
Harden, T.M., O’Connor, J.E., Driscoll, D.G., and Stamm, J.F., 2011, Flood-frequency analyses from paleoflood investigations for Spring, Rapid, Boxelder, and Elk Creeks, Black Hills, Western South Dakota: U.S. Geological Survey Scientific Investigations Report 2011–5131, 136 p.
O’Connor, J.E., Atwater, B.F., Cohn, T.A., Cronin, T.M., Keith, M.K., Smith, C.G., and Mason, R.R., 2014, Assessing inundation hazards to nuclear powerplant sites using geologically extended histories of riverine floods, tsunamis, and storm surges: U.S. Geological Survey Scientific Investigations Report 2014–5207, 65 p.
Harden, T.M., and O’Connor, J.E., 2017, Prehistoric floods on the Tennessee River—Assessing the use of stratigraphic records of past floods for improved flood-frequency analysis: U.S. Geological Survey Scientific Investigations Report 2017–5052, 15 p.
Paleoflood and non-exceedance data
South Fork American River near Lotus, CA stratigraphy
South Fork American River near Lotus, CA
Photos courtesy of the late Dr. Ralph Klinger (USBR)
Extreme storm rainfall , meteorology, and hydrometeorological analyses are critical components needed to estimate hydrologic hazards. Some recent work in key areas is listed below.
See the various technical reports, journal articles and papers on the publications page for some additional resources on extreme rainfall, radar, precipitation frequency, and PMP, as well as the Extreme Precipitation Events (Panel 3) at the NRC workshop on Probabilistic Flood Hazards.
Regional Precipitation Frequency Analysis
Key reports and references on regional precipitation frequency analysis for dam and levee safety are the following. These are generally in chronological order.
Schaefer, M.G. and B.L. Barker (2005) Stochastic Modeling of Extreme Floods on the American River at Folsom Dam Flood-Frequency Curve Extension. MGS Engineering Consultants for U.S. Army Corps of Engineers, Research Document 48, Hydrologic Engineering Center, Davis, CA, September 2005.
Sutley, D.E., Klinger, R.E., Bauer, T.R., and Godaire, J.E. (2009) Trinity Dam Detailed Hydrologic Hazard Analysis Using the Stochastic Event Flood Model, CVP-Shasta/Trinity Project, California, Mid-Pacific, Bureau of Reclamation, Flood Hydrology and Consequences Group, October, 84 p. and appendices
Novembre, N.J., et al. (2012) Altus Dam Hydrologic Hazard and Reservoir Routing for Corrective Action Study, U.S. Department of the Interior, Bureau of Reclamation, Denver, CO.
Regional precipitation frequency studies for Friant and El Vado Dams included accounting for orographic precipitation with isopercentile techniques, detailed spatial and temporal storm patterns, elements of storm transposition, and basin-average precipitation frequency with uncertainty based on a regional 4-parameter kappa distribution and point-to-area regression.
Wright, J.M., V. Sankovich, J. Niehaus, N. Novembre, R.J. Caldwell, R. Swain, and J. England (2013) Friant Dam Hydrologic Hazard for Issue Evaluation, Bureau of Reclamation, Flood Hydrology and Consequences Group, September, 225 p.
Caldwell, R.J., Bahls, V.S., Swain, R. and J.England, (2014) Volume 2: El Vado Dam Meteorology for Corrective Action Study, Bureau of Reclamation, Flood Hydrology and Consequences Group, November, 111 p.
Karlovits, G.S., Otero, W., and Brown, W.A. (2017) Willamette Basin Regional 72-Hour Wintertime Precipitation Frequency Analysis, Report RMC-TR-2017-09, U.S. Army Corps of Engineers Risk Management Center, Lakewood, CO, 60 p.
Smith, H., Sasaki, R., Karlovits, G.S., Hall, B.M., and Parola, A. (2018) Hydrologic Hazard Curve Analysis for Whittier Narrows Dam (CA10027), Rio Hondo and San Gabriel Rivers, California, Report RMC-TR-2018-11, U.S. Army Corps of Engineers Risk Management Center, Lakewood, CO, 145 p.
Trinity River Watershed above Dallas, Texas (work directed and peer-reviewed by John England)
Crow, B.R., Martin, D.L., Caldwell, R.J., Parzybok, T.W., Wells, B.L., and Ward, K.L. (2017) Trinity River Hydrologic Hazards Project, Task 1 Report - TX-OK Extreme Storms from HMR 51 and Extreme Storms for the Trinity River Basin. MetStat, Inc. for USACE Risk Management Center, 67 p.
Martin, D.L., Caldwell, R.J., Parzybok, T.W., Bahls, V., Crow, B.R., and Gibson, W. (2018) Trinity River Hydrologic Hazards Project, Task 2 Report - Storm Typing for the Trinity River Basin. MetStat, Inc. for USACE Risk Management Center, 39 p.
Martin, D.L., Schaefer, M.G., Parzybok, T.W., Ward, K.L., Bahls, V., and Caldwell, R.J. (2018) Trinity River Hydrologic Hazards Project, Task 3 Report - Regional Extreme Precipitation-Frequency Analysis for the Trinity River Basin. MetStat, Inc. for USACE Risk Management Center, 112 p.
Task 2 Storm Typing and Task 3 Regional Precipitation Frequency Appendices - Directory of Files
Task 1 Storms from HMR 51 can be obtained from the USACE Extreme Storms Database
Skahill, B.E. (2022) Cool Season Extreme Precipitation Estimates for Seven Dam Safety Projects in Oregons Willamette River Basin, RMC-TR-2023-01 U.S. Army Corps of Engineers Risk Management Center, Lakewood, CO, 34 p.
Stochastic Storm Transposition
England, J.F. Jr., Klawon, J.E., Klinger, R.E. and Bauer, T.R. (2006) Flood Hazard Study, Pueblo Dam, Colorado, Final Report, Bureau of Reclamation, Denver, CO, June, 160 p.
England, J.F. Jr., Julien, P.Y., and Velleux, M.L. (2014) Physically-Based Extreme Flood Frequency Analysis using Stochastic Storm Transposition and Paleoflood Data on Large Watersheds, J. Hydrol., 510, https://doi.org/10.1016/j.jhydrol.2013.12.021, pp. 228-245.
Wright, Daniel B., Yu, Guo, and England, John F. (2020) Six decades of rainfall and flood frequency analysis using stochastic storm transposition: Review, progress, and prospects, Journal of Hydrology, Volume 585, 124816, https://doi.org/10.1016/j.jhydrol.2020.124816
Climate Change - Precipitation Frequency and Hydrologic Hazards for Dam Safety
Bahls, V.S. and K. Holman (2014) Climate Change in Hydrologic Hazard Analyses: Friant Dam Pilot Study – Part I: Hydrometeorological Model Inputs, Bureau of Reclamation, Flood Hydrology and Consequences Group, 74 p.
Novembre, N.J., Holman, K., and Bahls, V.S. (2015) Climate Change in Hydrologic Hazard Analyses: Friant Dam Pilot Study – Part II: Using the SEFM with Climate-Adjusted Hydrometeorological Model Inputs, Technical Memorandum 8250-2015-010, Bureau of Reclamation, Flood Hydrology and Meteorology Group, 61 p.
Atmospheric Modeling, Probable Maximum Precipitation (PMP), Extremes, and New Concepts
Sankovich, V., Caldwell, R.J., and Mahoney, K. (2012) Green Mountain Dam Climate Change, Bureau of Reclamation, Dam Safety Technology Development Program Report DSO-12-03, 31 p.
U.S. Army Corps of Engineers (2017) Willamette Basin Dams, Probable Maximum Precipitation Report. Willamette River Basin, Oregon, U.S. Army Corps of Engineers, Portland District
Kavvas, M.L., Iseri, Y., and Toride, K. (2018) Evaluating Atmospheric Modeling to Predict Risk to Dams from Extreme Rainfall Events. Draft Report - Willamette River Basin, University of California, Davis for US Army Corps of Engineers, 154 p.
Kavvas, M.L., Iseri, Y., Hiraga, Y., Toride, K., Duren, A., England, J., Frans, C., and Warner, M. (2023) Atmospheric Modeling to Predict Risks to Dams from Extreme Rainfall Events at Columbia River Basin. University of California, Davis and US Army Corps of Engineers, 154 p.
National Academies of Sciences, Engineering, and Medicine (2024) Modernizing Probable Maximum Precipitation. Washington, DC: The National Academies Press. [In Review] https://www.nationalacademies.org/our-work/modernizing-probable-maximum-precipitation-estimation
Extreme Storm DAD Data and Mass Curves - Historical References
Stodt, R.W. (1995) Manual for automated depth-area duration analysis of storm precipitation. Department of Interior, Bureau of Reclamation, Denver, CO, November, 96 p.
U.S. Weather Bureau (USWB) (1946) Manual for Depth-Area-Duration Analysis of Storm Precipitation. Cooperative Studies Technical Paper No. 1, U.S. Department of Commerce, Weather Bureau, Washington, D.C.
World Meteorological Organization (WMO) (1969) Manual for Depth-Area Duration Analysis of Storm Precipitation. WMO No. 237. TP.129, Geneva, 114 p.
Shands, A.L. and Brancato, G.N. (1946) Applied Meteorology: Mass Curves of Rainfall. Cooperative Studies Technical Paper No. 4, U.S. Department of Commerce, Weather Bureau, Washington, D.C., March 1946, 34 p.
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