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Charlotte-Mecklenburg Flood Risk Assessment & Risk Reduction Plan Timothy J. Trautman, P.E., CFM Flood Mitigation Program Manager Charlotte-Mecklenburg.

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Presentation on theme: "Charlotte-Mecklenburg Flood Risk Assessment & Risk Reduction Plan Timothy J. Trautman, P.E., CFM Flood Mitigation Program Manager Charlotte-Mecklenburg."— Presentation transcript:

1 Charlotte-Mecklenburg Flood Risk Assessment & Risk Reduction Plan Timothy J. Trautman, P.E., CFM Flood Mitigation Program Manager Charlotte-Mecklenburg Storm Water Services Darrin R. Punchard, AICP, CFM Senior Project Manager AECOM

2 What’s unique about this plan May 19, 2011 Charlotte-Mecklenburg Flood Risk Assessment & Risk Reduction PlanPage 2 Determine Individualized Flood Risk Communicate Relative Risk Develop Public & Private Risk Reduction Actions Implement a Risk Based Capital Improvement Program

3 Pop. 919,628 (2010) –32% increase since regulated stream miles 3,000+ properties in FEMA Floodplain 4,400+ properties in Community (future) Floodplain Mecklenburg County, North Carolina May 19, 2011 Charlotte-Mecklenburg Flood Risk Assessment & Risk Reduction PlanPage 3

4 Flood History in Charlotte, NC 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 May 19, 2011 Charlotte-Mecklenburg Flood Risk Assessment & Risk Reduction PlanPage 4

5 History of Floodplain Management – 1970s-1990s Joined NFIP Joined CRSBecame a CTP Named Project Impact Community Created Floodplain Management Guidance Document Measurement of potential flood damages to flood- prone structures Prepared flood risk analyses & various studies on hazard mitigation alternatives Created CMSWS Updated flood maps Adopted SWIM Implementation Strategy May 19, 2011 Charlotte-Mecklenburg Flood Risk Assessment & Risk Reduction PlanPage 5

6 2000s - Present First community to show future and existing conditions on flood maps Adopted Multi Hazard Mitigation Plan 2003 Prepared 10 watershed-based preliminary engineering studies Updating floodplain maps to show flood hazards Launched Floodplain Buyout (Acquisition) Program May 19, 2011 Charlotte-Mecklenburg Flood Risk Assessment & Risk Reduction PlanPage 6 Updated Multi Hazard Mitigation Plan

7 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 Challenges and Plan Need May 19, 2011 Charlotte-Mecklenburg Flood Risk Assessment & Risk Reduction PlanPage 7

8 Flood Risk Assessment & Risk Reduction 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 May 19, 2011 Charlotte-Mecklenburg Flood Risk Assessment & Risk Reduction PlanPage 8

9 Flood Risk Assessment & Risk Reduction 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 a that 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 May 19, 2011 Charlotte-Mecklenburg Flood Risk Assessment & Risk Reduction PlanPage 9 DYNAMIC PLAN

10 Project Phases 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 May 19, 2011 Charlotte-Mecklenburg Flood Risk Assessment & Risk Reduction PlanPage 10

11 Three step process Concept Overview STEP #1 Flood Risk Assessment Flood Risk Score Flood Impacts Storm Frequency (Probability) Structure Location STEP #2 Risk Reduction Recommendations Evaluate all mitigation techniques Four recommendation categories STEP #3 Mitigation Priority Score Based on Risk Score Factor in other community benefits Use to prioritize: Properties Projects (neighborhoods) May 19, 2011 Charlotte-Mecklenburg Flood Risk Assessment & Risk Reduction PlanPage 11

12 Citizen-based advisory group –“Disgruntled” owners of flood-prone residential properties Comprised of 12 residents from: –7 neighborhoods –3 watersheds Monthly meetings Citizen Review Committee Neighborhoods Watersheds May 19, 2011 Charlotte-Mecklenburg Flood Risk Assessment & Risk Reduction PlanPage 12

13 Citizen Review Committee 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 May 19, 2011 Charlotte-Mecklenburg Flood Risk Assessment & Risk Reduction PlanPage 13

14 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? Citizen Review Committee May 19, 2011 Charlotte-Mecklenburg Flood Risk Assessment & Risk Reduction PlanPage 14

15 Pilot Studies May 19, 2011 Charlotte-Mecklenburg Flood Risk Assessment & Risk Reduction PlanPage 15 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

16 Flood Risk Score 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 May 19, 2011 Charlotte-Mecklenburg Flood Risk Assessment & Risk Reduction PlanPage 16 Flood Impact + Probability Location Multiplier Flood Risk Score

17 Impact-based Scoring May 19, 2011 Charlotte-Mecklenburg Flood Risk Assessment & Risk Reduction PlanPage 17 CriteriaProperty Flood Impacts AFlooding above the lowest finished floor of a building FStructure is completely surrounded by flood water AND is a Critical Facility H Flood water is touching a portion of the building AND has structural damage (subsidence, shifting, cracking) as a result of cumulative flooding G Structure is completely surrounded by flood water AND is multi-family residential (additional people, vehicles) G#Number of units in building BFlooding of electrical and/or mechanical equipment DProperty is completely surrounded by flood water (ingress/egress to flooded property) C Flood water is touching a portion of the building (likely crawlspace or unfinished basement being impacted) EStructure is completely surrounded by flood water (ingress/egress to building) J Flooding around area where single-family residential vehicles are typically parked (see separate guidelines) I1* Flooding of SIGNIFIGANT exterior property improvements which are deemed functional necessities to reasonable use of single family residential property (see separate guidelines) I2* Flooding of MODERATE exterior property improvements which are deemed functional necessities to reasonable use of single family residential property (see separate guidelines) KFlooding of any yard (any portion of parcel)

18 Impact-based Scoring 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 May 19, 2011 Charlotte-Mecklenburg Flood Risk Assessment & Risk Reduction PlanPage 18

19 Impact-based Scoring May 19, 2011 Charlotte-Mecklenburg Flood Risk Assessment & Risk Reduction PlanPage 19

20 Location-based Multiplier 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 May 19, 2011 Charlotte-Mecklenburg Flood Risk Assessment & Risk Reduction PlanPage 20 MultiplierLocation Risk Factor 1.5Building located in high danger depth-velocity zone 1.3Building located in moderate danger depth-velocity zone 1.3Building located near area impacted by storm drainage overflows 1.1Building located in Community Encroachment Area

21 Pilot Study Results –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 May 19, 2011 Charlotte-Mecklenburg Flood Risk Assessment & Risk Reduction PlanPage 21

22 Flood Mitigation Techniques Mitigation recommendations will be made for each flood prone property Each mitigation technique will be evaluated and placed into one of four categories: May 19, 2011 Charlotte-Mecklenburg Flood Risk Assessment & Risk Reduction PlanPage 22 Highly Effective Moderately Effective Not Recommended Further Evaluation Needed

23 Flood Mitigation Priority Scores 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.) May 19, 2011 Charlotte-Mecklenburg Flood Risk Assessment & Risk Reduction PlanPage 23 Flood Mitigation Priority Scores Other Community Benefits Flood Mitigation Property Score –Use to prioritize properties Flood Mitigation Project Score –Use to prioritize projects (Neighborhoods)

24 Next Steps 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 May 19, 2011 Charlotte-Mecklenburg Flood Risk Assessment & Risk Reduction PlanPage 24

25 Communicating Plan Results May 19, 2011 Charlotte-Mecklenburg Flood Risk Assessment & Risk Reduction PlanPage 25

26 Keys to Success 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 May 19, 2011 Charlotte-Mecklenburg Flood Risk Assessment & Risk Reduction PlanPage 26

27 Thank You


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