Need For Updating Alluvial Fan Floodplain Delineation Guidelines: An ASFPM Discussion Paper ASFPM National Conference Louisville, Kentucky May 19, 2011

Need For Updating Alluvial Need For Updating Alluvial Fan Floodplain Delineation Fan Floodplain Delineation

Guidelines: Guidelines:

An ASFPM Discussion PaperAn ASFPM Discussion Paper

ASFPM National ConferenceASFPM National ConferenceLouisville, KentuckyLouisville, Kentucky

May 19, 2011May 19, 2011

Presentation OverviewPresentation Overview

• ASFPM Discussion Paper Process

• Background: The Status Quo

• Discussion Paper Overview

• Facilitated Discussion

What is a Discussion Paper?What is a Discussion Paper?• It is:

– (The Paper Formerly Known as White)– A Policy Document– An Overview– A Summary– A First Step

• It is NOT:– A Research Project– A Technical Paper– A Detailed Methodology– A Fully Implemented Plan

ASFPM Discussion Paper ProcessASFPM Discussion Paper Process

• ASFPM Arid Regions Committee – Initiate & Write Draft Paper

• ASFPM Committee Group • State Chapters • ASFPM Board

– Approval?– Implementation as Policy– Recommended Actions

• Action by FEMA?• Implementation by Communities?

You are here

Background: Status QuoBackground: Status Quo

• FEMA Appendix G: (Guidelines)– Three Stage Methodology

• Stage 1: Landform• Stage 2: Active v. Inactive• Stage 3: Floodplain Delineation

– Table G1: Delineation Tools• “Not all methods are appropriate for all situations”

• 44 CFR Part 65.13 (Regulations)– Rules for LOMRs

p. G-12

FAN: - Fluvial Fans (not Debris Flow)

Hydraulic Models: - Uncertainty can be set aside - Urbanized areas, stable channel

Geomorphic Methods: - Little Urbanization - Approximate Method

Composite Methods: - Integrate results

NFIP Part 65.13NFIP Part 65.13• Major Structural

• Engineering Analyses– Hydrology– Debris Flow– Sediment– Erosion– Avulsion– Local Runoff– O&M Plan

Paper OverviewPaper Overview

• Alluvial Fan Flooding is Important– Large Percentage of Undeveloped Land– Unique Flood Hazards– Fans Delineation is Unique

• Goal: Improve Tools for Delineating & Managing Alluvial Fan Floodplains

Paper OverviewPaper Overview

• A History of Successes– 1970’s: Alluvial Fan Floods in So. California

• FEMA FAN Model

– 1980’s: Fan Delineation Studies in Southwest– 1990’s: NRC Alluvial Fan Committee

• Evaluation of Methodology• Recommended Improvements (1996)• Appendix G Revision (2002)

– 1996-2010: Fan Delineation Studies

Paper OverviewPaper Overview• Methodology Update Needed

– Lessons Learned from 15 Years of Application• Trial & Error• Identify Shortcomings & Opportunities

– New Tools & Technologies Available• Software• Hardware• Understanding of Physical Systems

– NFIP Reauthorization – RiskMAP Priorities

Paper Overview: RecommendationsPaper Overview: Recommendations

#1: Recognize Fundamental Principles

– Account for Flow Path Uncertainty– Account for Changing Conditions on Fans

• Aggradation, Avulsion, Etc.• Engineering Time Scales

– Account for Differences Between Fans • One Size Does Not Fit All


#2: Recognize That There Are DifferentTypes of Active Alluvial Fans

– Debris Flow Fans vs. Fluvial Fans• Well-Documented in Literature• Different Processes & Hazards

– Channelized Flow vs. Sheet Flooding• Different Degree of Hazard• May Occur on Same Landform

Lesson: One Size Does Not Fit All


#3: The Methodology Should Distinguish High & Low Hazard Portions of Active Fans– Flow Path Uncertainty– Debris Flow Risk– Avulsion Risk– High Flow Depths & Velocities– Shallow Sheet Flooding Areas– Deposition & Scour– (Inactive Areas)


#4: Clarify Appendix G Terminology

– Active Alluvial Fan…Active Alluvial Fan Flooding• Ultrahazardous … Sheet Flooding?• Uncertainty Cannot Be Set Aside?• Active = Flooded During 10,000 years? 1,000 yrs?• Active = Deposition, Erosion & Unstable Flow Paths• Active = Ultrahazardous


#5: Improve Technical Guidance

– Better Documentation of Method Needed• Compare to Riverine Guidance• Fans are More Complicated, Need More Help

– Better Description of Composite Method– Better Description of Geomorphic Data– More Detailed Examples


#6: Recognize Key Processes on Active Fans

– Flow Path Uncertainty• Mechanisms of Avulsion & Movement• Quantify Risk of Avulsion in Engineering Time Scale

– Infiltration• Recharge

– Peak Flow Attenuation • Apex to Toe• Impact of Development on Storage & Losses


#6: Recognize Key Processes on Active Fans

– Avulsion• Definition• Analysis Techniques

– Sheet Flooding• Dominant Flow Type in Central Arizona• Shallow, Low Velocity, Broad Distribution

– Sediment Transport– Debris Flow


#7: Conduct Training– Recognizing Active Alluvial Fans– Identifying Debris Flow Risk– Application of Analytical Tools

#8: Improve Review Process– Assure Fans are Identified– Areas Downstream of Active Fans – Active Fans Have Been Missed in Delineations


#9: Investigate Avulsion Frequency– Identify Methods to Quantify Frequency– Update Methodologies to Reflect Actual Risk

#10: Investigate Other Methods to Quantify Flow Path Uncertainty– USACE Risk Analysis– Monte Carlo Simulations– Other….


#11: Collect Better Documentation of Fan Floods– Photographs & Accounts– Central Repository

#12: Explore Linkages Between ImprovedDelineation & Management Tools

– Link Hazards to Management (RiskMAP)– Link Hazards to Insurance Rates

Where Do We Go From Here?Where Do We Go From Here?

• ASFPM Board Approval….Done

• Consideration by IPT….Scheduled– FEMA, ASFPM, NAFSMA, USACE

• Action….Future– Study & Analysis?– Committee?– Recommendations?

QuestionsQuestions

• Jon Fuller [email protected]– Linkedin : Alluvial Fan Floods Group– Twitter: @alluvialfans – Future: www.alluvialfanflooding.com

Documents

Need For Updating Alluvial Fan Floodplain Delineation Guidelines: An ASFPM Discussion Paper ASFPM National Conference Louisville, Kentucky May 19, 2011