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

Presentation Overview ASFPM Discussion Paper Process Background: The Status Quo Discussion Paper Overview Facilitated Discussion

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 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 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 (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 Major Structural Engineering Analyses –Hydrology –Debris Flow –Sediment –Erosion –Avulsion –Local Runoff –O&M Plan

Paper 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 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) – : Fan Delineation Studies

Paper 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: 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

Paper Overview: Recommendations #2: Recognize That There Are Different Types 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

Paper Overview: Recommendations #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)

Paper Overview: Recommendations #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

Paper Overview: Recommendations #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

Paper Overview: Recommendations #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

Paper Overview: Recommendations #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

Paper Overview: Recommendations #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

Paper Overview: Recommendations #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….

Paper Overview: Recommendations #11: Collect Better Documentation of Fan Floods –Photographs & Accounts –Central Repository #12: Explore Linkages Between Improved Delineation & Management Tools –Link Hazards to Management (RiskMAP) –Link Hazards to Insurance Rates

Where Do We Go From Here? ASFPM Board Approval….Done Consideration by IPT….Scheduled –FEMA, ASFPM, NAFSMA, USACE Action….Future –Study & Analysis? –Committee? –Recommendations?

Questions Jon –Linkedin : Alluvial Fan Floods Group –Future: