needs to update probable maximum precipitation for ... · probable maximum precipitation for...

US Army Corps of EngineersBUILDING STRONG®

US Army Corps of Engineers

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Needs to UpdateProbable Maximum Precipitation for Determining Hydrologic Loading on Dams

USSD 2017 Annual Conference Anaheim, CA

April 5, 2017

Chandra S. Pathak, PhD, PE, F.ASCEEngineering and Construction BranchHQ - U.S. Army Corps of Engineers

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Background Probable Maximum Precipitation (PMP) is

used in computing the Probable Maximum Flood (PMF).

PMF is used as a design criteria for several critical infrastructure projects including: Dams/Reservoirs Nuclear Power Plants others

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Motivation Dam Safety Program: Assessing hazards

under hydrologic loading conditions Previously computed PMP and PMF are

many decades old. Need to update PMP and PMF to

determine revised hydrologic loading for several dams/reservoirs

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PMP DefinedProbable Maximum Precipitation (as defined in HMR 55A):

Theoretically the greatest depth of precipitation for a given duration that is physically possible over a given size storm area at a particular geographic location at a certain time of the year.

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Extreme Precipitation Recorded

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Key PMP Manuals (1986-2009)

Manual on Estimation of Probable Maximum Precipitation (WMO/2009)

Current NOAA/NWS PMP Documents and Related Studieswww.nws.noaa.gov/oh/hdsc/studies/pmp.html

PMP Standards Have Existed For YearsMethods and Assumptions in Need of Revision

http://www.nws.noaa.gov/oh/hdsc/studies/pmp.html

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PMP Estimation Process

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Missing Extreme Storms in HMRsHMR Year

49 197051 197255A 197857 199159 1991

Some HMRs include zero storms from the past 45 years !!

Critical need to update the extreme storm database

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May 2010 – Nashville, TN

Recent Extreme Storms not in HMRsMarch 1997 – Ohio ValleyLate December 1996

Late December 2005

New Insights - Extremes

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Extreme Storm Database

USACE Extreme Storm Database

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Use of New Tool: HEC-MetVueObserved Rainfall Design Storm

Calculation of Basin Averages (PMP)

• Should be user friendly• Can quickly compare recent storms to PMP• Should reduce time needed for site-specific PMP• Should help in performing meteorological analysis for transpositioning

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Challenges in Estimating PMP

1. Professional Judgmenta. Several steps need decisions that would require

professional judgmentb. Need to have good understanding of atmospheric

processesc. HMRs are dated and need recent additional storms

Hayes, B. et al. (2015). Site Specific Probable Maximum Precipitation Estimates and Professional Judgment. American Geophysical Union Fall Meeting, December 18, 2015, San Francisco, CA

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Professional JudgmentHayes, B. et al. (2015). Site Specific Probable Maximum Precipitation Estimates and Professional Judgment. American Geophysical Union Fall Meeting, December 18, 2015, San Francisco, CA

Session H51P: Advances in Hydro-meteorological Extremes Forecasting: Estimation, Integrated Risk Analysis, and Applications I (Paper: H51P-02)

“

….……………….………………………………………………………………”

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Professional Judgment…..

Identify steps in estimating PMP that require professional judgment

For those steps, develop detailed guidance - i.e., sub-steps for a variety of conditions along with appropriate methodology

Spell out assumptions used in the above methodology.

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2. Site Specific PMP Studiesa. Need to include more recent stormsb. Need to remove generalization c. Need detail analysis for each basin

𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆 𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆 𝑃𝑃𝑃𝑃𝑃𝑃

= 𝑆𝑆 𝑎𝑎𝑎𝑎𝑆𝑆𝑎𝑎,𝑑𝑑𝑑𝑑𝑎𝑎𝑆𝑆𝑎𝑎𝑆𝑆𝑑𝑑𝑑𝑑, 𝑠𝑠𝑆𝑆𝑑𝑑𝑎𝑎𝑠𝑠 𝑆𝑆𝑡𝑡𝑆𝑆𝑆𝑆,𝑎𝑎𝑆𝑆𝑆𝑆𝑑𝑑𝑎𝑎𝑑𝑑 𝑆𝑆𝑆𝑆𝑎𝑎𝑆𝑆𝑑𝑑𝑑𝑑, …

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3. Estimating PMP Uncertainties a. Single point PMP estimate – is it enough?b. Qualitative estimation (sensitivity analysis)c. Quantitative estimation (simulation)

PMP Estimate

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3. Estimating PMP Uncertainties a. Single point PMP estimate – is it enough?b. Qualitative estimation (sensitivity analysis)c. Quantitative estimation (simulation)

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New Method - Numerical Modeling

Explore utility of high-resolution, event-based modeling in Complex Terrainwith the Weather Research and Forecasting (WRF) model

Moisture Maximization proof of concept, Colorado (Sankovich et al, 2012)

Can we use knowledge of past events + high resolution numerical model simulations to better estimate (current and future) PMP?

Control RH 1.5x RH 100%

72-h total precipitation (mm)

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New Task Committee on “Use of Atmospheric Numerical Models for Estimating Probable Maximum Precipitation” –Sept/Oct 2014

EWRI/ASCE Surface Water Hydrology Technical Committee Committee has 15 members from Consulting, Academia,

Research, and Federal agencies Committee has three year-term For details please contact: Dr. Chandra S. Pathak, chair [email protected] Dr. Li-Chuan Chen, vice-chair [email protected] Prof. Levent Kavvas, vice-chair [email protected]

ASCE/EWRI - Task Committee

mailto:[email protected]



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Over-estimation from generalization = waste of taxpayer $$ Under-estimation from less severe storms = lives at risk Need site-specific PMP estimates

► Use Corps (in-house) developed methodology/SOP► Include recent extreme storm data from database► Consistency in PMP Estimates► Estimate uncertainties in PMP estimation

Summary/Conclusion

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Questions/Comments

Chandra S. Pathak, Ph.D., P.E., F.ASCEHydrology, Hydraulics and Coastal Community of Practice (CECW-CE)US Army Corps of Engineers – HeadquartersWashington DC 20314Email: [email protected]: 202-761-4668 /Blackberry: 202-699-2771


Subcommittee On HydrologyPurposeImprove the availability and reliability of surface-water quantity information needed for hazard mitigation, water supply and demand management, and environmental protection.ActivitiesQuarterly Meetings, Workgroups, Workgroup Meetings, Announcements, Conferences.Websitehttp://acwi.gov/hydrology/index.html

SOH Quarterly Meeting 26Feb 23, 2017

Presenter

Presentation Notes

[Slide 4 – SOH Purpose] SOH Member organizations, workgroup, its members, and guests work together to improve tha availability and reliability of surface water data for various needs of the country.

SOH Workgroups

SOH Quarterly Meeting 27

• Hydrologic Frequency Analysis Work Group (HFAWG)

• Extreme Storm Events Work Group (ESEWG)• Hydrologic Modeling Work Group (HMWG)• Satellite Telemetry Interagency Work Group (STIWG)• Proposed Streamflow Information Collaborative• Proposed workgroup on filling “data gaps”

Feb 23, 2017

Presenter

Presentation Notes

[Slide 5 – SOH Workgroups] As chair and vice-chair, we have taken an active engagement with SOH’s four active workgroups, not only in guiding the direction but also actively participating, working , and contributing along with the member agency volunteers in carrying out the workgroups tasks and promoting the exchange of information

SOH Extreme Storm Events Workgroup (ESEWG)

ACWI Meeting 28

Thomas J. Nicholson, Chair U.S. Nuclear Regulatory Commission (USNRC) William Otero, Vice-Chair U.S. Army Corps of Engineers (USACE)

Purpose and Goals: Coordinate studies and databases for reviewing and improving

methodologies and data collection techniques used to develop design precipitation estimates of large storm events up to and including the Probable Maximum Precipitation (PMP). Develop a detailed scope of work/plan of study, and Determine the necessary funding requirements to update the Catalog

of Extreme Storms and Hydrometeorological Reports (HMR) for estimating PMP.

Feb 23, 2017

Presenter

Presentation Notes

[Slide 19 – SOH ESEWG] I am providing this slide as a reference to inform you of the purpose and the charge for the Extreme Storms Event Workgroup. ESEWG is about coordinating studies and data related to design precipitation estimates of large storms included the Probable Maximum Precipitation Besides the sharing and exchanging information, a fundamental component of ACWI, ESEWG is working to detailed scope of work/plan of study and necessary funding requirements to update Extreme Storms Catalog and the HMRs.

ACWI Meeting 29

Recommendations from Workshops and Meetings with Stakeholders

1. Coordinate Studies and DatabaseMaintain and post active list of Extreme Storms Studies (such as PMP studies) Develop central repository for precipitation data collected by Workgroup

organizations and foster data agreement with respective agencies.

2. Develop a detailed scope of work/plan of studyWork with the ESEWG Proposal Writing Team (PWT) to complete detailed scope

of work/plan of study

3. Determine necessary funding requirements to pursue rainfall product needsNext step is to present proposal with funding needs to SOH and then onto ACWI Focus should be on highest priority needs to include guidance and shared

databases for regional and site-specific PMP estimates; and for Probabilistic Flood Hazard Assessments.

Feb 23, 2017

Presenter

Presentation Notes

[Slide 20– SOH ESEWG] Development of a detailed strategy for identifying extreme storm data needs: Update HRMs throughout the U.S. to support Dam safety analyses and Nuclear Power Plant flood assessments Develop Storm Catalogues for the U.S. using both historical data and new gauge/radar data Develop consensus standard for reviewing PMP studies by private and governmental contractors to State and Federal agencies Provide a home for the Storm Catalogue and data such as the National Center for Environmental Information of NOAA Coordinate technical reviews of PMP studies and share lessons learned