Charlotte-Mecklenburg Flood Risk Assessment & Risk Reduction Plan

1. Charlotte-MecklenburgFlood Risk Assessment & Risk Reduction Plan Timothy J. Trautman, P.E., CFMFlood Mitigation Program ManagerCharlotte-Mecklenburg Storm Water Services Darrin R. Punchard, AICP, CFMSenior Project ManagerAECOM

2. What’s unique about this plan Charlotte-MecklenburgFlood Risk Assessment & Risk Reduction Plan

3. Mecklenburg County,North Carolina Charlotte-MecklenburgFlood Risk Assessment & Risk Reduction Plan • Pop. 919,628 (2010) • 32% increase since 2000 • 330 regulated stream miles • 3,000+ properties in FEMA Floodplain • 4,400+ properties in Community (future) Floodplain

4. Flood History in Charlotte, NC Charlotte-MecklenburgFlood Risk Assessment & Risk Reduction Plan • Nearly 50 major flood events in the past century • 17 known deaths and more than $80 million in property damage   • Heavy impact from tropical systems • Tropical Storm Jerry, 1995 • Tropical Storm Danny, 1997 • Tropical Storm Fay, 2008

5. History of Floodplain Management – 1970s-1990s Named Project Impact Community Joined CRS Became a CTP Joined NFIP 1979 1975 1999 1977 1981 1985 1983 1989 1991 1993 1995 1997 1987 Measurement of potential flood damages to flood-prone structures Updated flood maps Created CMSWS Prepared flood risk analyses & various studies on hazard mitigation alternatives Created Floodplain Management Guidance Document Adopted SWIM Implementation Strategy Charlotte-MecklenburgFlood Risk Assessment & Risk Reduction Plan

6. 2000s - Present First community to show future and existing conditions on flood maps Adopted Multi Hazard Mitigation Plan Updated Multi Hazard Mitigation Plan 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 Updating floodplain maps to show flood hazards Prepared 10 watershed-based preliminary engineering studies Launched Floodplain Buyout (Acquisition) Program Charlotte-MecklenburgFlood Risk Assessment & Risk Reduction Plan

7. Challenges and Plan Need Charlotte-MecklenburgFlood Risk Assessment & Risk Reduction Plan • Current Flood Hazard Mitigation Plan • Over 8 years old • Successfully implemented the acquisition and demolition of 200+ flood-prone structures • Very few properties remain that are deemed cost-effective under FEMA requirements • 3 significant events within 3 years (2008 – 2010) • 50 SRL properties, 1,500 non-compliant buildings remain • Develop next phase of Capital Improvement Projects

8. Flood Risk Assessment & Risk Reduction Charlotte-MecklenburgFlood Risk Assessment & Risk Reduction Plan • Prepared as an update to existing flood mitigation plans • Purpose • To recommend specific flood mitigation techniques at a building or parcel level • To assist in planning, prioritizing, and funding future flood mitigation projects • Use a new, comprehensive and holistic approach to flood risk assessment and reduction • Create a broader and more inclusive risk-based strategy

9. Flood Risk Assessment & Risk Reduction DYNAMIC PLAN Charlotte-MecklenburgFlood Risk Assessment & Risk Reduction Plan • Goals & Objectives • Create an automated planning tool to identify, prioritize and plan future flood mitigation projects • Provide detailed parcel level plan information to the public via internet • Create athat can be continuously updated as new data becomes available • To assist private property owners and local government officials in making informed decisions about flood mitigation strategies

10. Project Phases Charlotte-MecklenburgFlood Risk Assessment & Risk Reduction Plan • Phase I – Develop the framework • Parcel-based scoring methodology (flood risk and mitigation) • Appropriate flood mitigation techniques for Mecklenburg County • Criteria for recommending/applying the techniques • Phase II – Refine, finalize and apply the methods in Phase I • Use an experienced consultant (AECOM) • Run pilot studies to test scoring methodology, etc. • Apply to all flood-prone properties in the county • Develop a tool to continuously update the Plan

11. Concept Overview Charlotte-MecklenburgFlood Risk Assessment & Risk Reduction Plan Three step process

12. Citizen Review Committee Neighborhoods Watersheds Charlotte-MecklenburgFlood Risk Assessment & Risk Reduction Plan • Citizen-based advisory group • “Disgruntled” owners of flood-prone residential properties • Comprised of 12 residents from: • 7 neighborhoods • 3 watersheds • Monthly meetings

13. Citizen Review Committee Charlotte-MecklenburgFlood Risk Assessment & Risk Reduction Plan • Purpose: • Affected residents become part of the solution. • Members realize that they are not alone. • Residents provide input and feedback throughout. • Provides staff with a “user” perspective. • Assist in determining ways to effectively communicate flood risk to the public. • Challenge: • Keeping the group unbiased. • Results: • Gain buy-in and support • Better products

14. Citizen Review Committee Charlotte-MecklenburgFlood Risk Assessment & Risk Reduction Plan AREAS OF INPUT • Flood Risk Score • Flood Impacts • Exterior Property Improvements • Mitigation Recommendations • Mitigation Techniques • Mitigation Score • Property Factors • Communication • How to effectively communicate this information to the public?

15. Pilot Studies • Two areas are being used to manually test and refine proposed scoring methods • 126 properties • Mix of residential/commercial • Results used to identify and address potential issues of concern • Data accuracy (flood models, building inventory, etc.) • Scoring methodology (criteria, values and weighting) • Compare with actual flood event data Charlotte-MecklenburgFlood Risk Assessment & Risk Reduction Plan

16. Flood Risk Score Charlotte-MecklenburgFlood Risk Assessment & Risk Reduction Plan • Impact-based scoring • Determined by assigning probability (return period) to various flood impacts (damage or loss) to property • Location-based scoring • Multiplier to impact-based scores for structures located in known risk zones • Depth-velocity hazard zones • Proximity to storm drainage overflows

17. Impact-based Scoring Charlotte-MecklenburgFlood Risk Assessment & Risk Reduction Plan

18. Impact-based Scoring Charlotte-MecklenburgFlood Risk Assessment & Risk Reduction Plan • Each property independently assessed in GIS using aerial imagery, flood model data, building footprints, elevation certificates and other County data layers • Manual processing used for pilot studies, but will become automated as part of new planning tool

19. Impact-based Scoring Charlotte-MecklenburgFlood Risk Assessment & Risk Reduction Plan

20. Location-based Multiplier Charlotte-MecklenburgFlood Risk Assessment & Risk Reduction Plan • Depth-Velocity Hazard Zones • Created using velocity and flood depth rasters developed from effective HEC-RAS models • Determined using depth-velocity curves tied to safety criteria for people • High danger = Significant hazard to adults • Moderate danger = Significant hazard to children

21. Pilot Study Results Charlotte-MecklenburgFlood Risk Assessment & Risk Reduction Plan • Properties classified according to their relevant risk scores: • High Risk = Top 10% • Moderate Risk = 10%-35% • Low Risk = Below top 35% • Key conclusions • Flood risk scores are driven heavily by flood frequency determinations • Flood risk scores are not being skewed by any specific flood impact criteria (first floor flooding, etc.) • Flood risk scores are not being skewed by location-based multipliers (velocity zones) • Flood risk scoring appears reasonable and is achieving objectives of CMSWS

22. Flood Mitigation Techniques Charlotte-MecklenburgFlood Risk Assessment & Risk Reduction Plan • Mitigation recommendations will be made for each flood prone property • Each mitigation technique will be evaluated and placed into one of four categories:

23. Flood Mitigation Priority Scores • Flood Mitigation Priority Scores • Other Community Benefits • Flood Mitigation Property Score • Use to prioritize properties • Flood Mitigation Project Score • Use to prioritize projects (Neighborhoods) Charlotte-MecklenburgFlood Risk Assessment & Risk Reduction Plan • Used to prioritize mitigation projects • Blends flood risk scores with other community-based factors • Other factors to prioritize and rank projects: • Homeowners with flood insurance • Severe Repetitive Loss • Other public benefits (parks, greenways, wetland restoration, etc.)

24. Next Steps Charlotte-MecklenburgFlood Risk Assessment & Risk Reduction Plan • Finalize recommendations for flood mitigation techniques and apply flood mitigation scoring to pilot study areas • Complete requirements analysis and develop database(s) and tool for implementing and automating the flood risk and mitigation assessment countywide • Communication & Implementation

25. Communicating Plan Results Charlotte-MecklenburgFlood Risk Assessment & Risk Reduction Plan

26. Keys to Success Charlotte-MecklenburgFlood Risk Assessment & Risk Reduction Plan • Quality data • Active involvement and input from stakeholders • Holistic approach to mitigation: • Prioritization based heavily on flood risk, but also mitigation feasibility and other important community factors • Capture opportunities to group properties (vs. piecemeal approach) • Capitalize on multi-objective projects to achieve other public benefits • Effective communication & outreach after plan completion

27. Thank You tim.trautman@mecklenburgcountync.gov darrin.punchard@aecom.com