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
What’s unique about this plan
Determine Individualized Flood
Risk
Communicate Relative Risk
Develop Public & Private Risk
Reduction Actions
Implement a Risk Based Capital
Improvement Program
Charlotte-Mecklenburg
Flood Risk Assessment & Risk Reduction Plan
May 19, 2011
Page 2
Mecklenburg County,
North Carolina
• 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
Charlotte-Mecklenburg
Flood Risk Assessment & Risk Reduction Plan
May 19, 2011
Page 3
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
Charlotte-Mecklenburg
Flood Risk Assessment & Risk Reduction Plan
May 19, 2011
Page 4
History of Floodplain Management –
1970s-1990s
Joined CRS
Joined
NFIP
1975
1977
1979
1981
1983
1985
1987
Measurement of potential
flood damages to floodprone structures
1989
1991
1993
1995
Created CMSWS
Prepared flood risk analyses
& various studies on hazard
mitigation alternatives
Charlotte-Mecklenburg
Flood Risk Assessment & Risk Reduction Plan
Became a CTP
Created Floodplain
Management
Guidance Document
May 19, 2011
Named Project
Impact Community
1997
1999
Updated
flood
maps
Adopted SWIM
Implementation
Strategy
Page 5
2000s - Present
First community to
show future and
existing conditions
on flood maps
2000
2001
Adopted Multi Hazard
Mitigation Plan
2002
2003
2004
2005
2006
2007
Updated Multi Hazard
Mitigation Plan
2008
2009
2010
Updating floodplain maps
to show flood hazards
Prepared 10 watershed-based
preliminary engineering studies
Launched Floodplain Buyout
(Acquisition) Program
Charlotte-Mecklenburg
Flood Risk Assessment & Risk Reduction Plan
May 19, 2011
Page 6
Challenges and Plan Need
• 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
Charlotte-Mecklenburg
Flood Risk Assessment & Risk Reduction Plan
May 19, 2011
Page 7
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
Charlotte-Mecklenburg
Flood Risk Assessment & Risk Reduction Plan
May 19, 2011
Page 8
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 DYNAMIC PLAN
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
Charlotte-Mecklenburg
Flood Risk Assessment & Risk Reduction Plan
May 19, 2011
Page 9
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
Charlotte-Mecklenburg
Flood Risk Assessment & Risk Reduction Plan
May 19, 2011
Page 10
Concept Overview
• Three step process
STEP #1
Flood Risk
Assessment
• Flood Risk Score
• Flood Impacts
• Storm
Frequency
(Probability)
• Structure
Location
Charlotte-Mecklenburg
Flood Risk Assessment & Risk Reduction Plan
STEP #2
Risk Reduction
Recommendations
• Evaluate all
mitigation
techniques
• Four
recommendation
categories
May 19, 2011
STEP #3
Mitigation Priority
Score
• Based on Risk
Score
• Factor in other
community
benefits
• Use to prioritize:
• Properties
• Projects
(neighborhoods)
Page 11
Citizen Review Committee
Neighborhoods
Watersheds
• Citizen-based advisory
group
– “Disgruntled” owners of
flood-prone residential
properties
• Comprised of 12
residents from:
– 7 neighborhoods
– 3 watersheds
• Monthly meetings
Charlotte-Mecklenburg
Flood Risk Assessment & Risk Reduction Plan
May 19, 2011
Page 12
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
Charlotte-Mecklenburg
Flood Risk Assessment & Risk Reduction Plan
May 19, 2011
Page 13
Citizen Review Committee
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?
Charlotte-Mecklenburg
Flood Risk Assessment & Risk Reduction Plan
May 19, 2011
Page 14
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-Mecklenburg
Flood Risk Assessment & Risk Reduction Plan
May 19, 2011
Page 15
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
Flood
Impact
+
Probability
Charlotte-Mecklenburg
Flood Risk Assessment & Risk Reduction Plan
Location
Multiplier
May 19, 2011
Flood
Risk
Score
Page 16
Impact-based Scoring
Criteria
Property Flood Impacts
A
Flooding above the lowest finished floor of a building
F
Structure is completely surrounded by flood water AND is a Critical Facility
H
G
G#
Flood water is touching a portion of the building AND has structural damage (subsidence,
shifting, cracking) as a result of cumulative flooding
Structure is completely surrounded by flood water AND is multi-family residential (additional
people, vehicles)
Number of units in building
B
Flooding of electrical and/or mechanical equipment
D
Property 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)
E
Structure is completely surrounded by flood water (ingress/egress to building)
J
I1*
I2*
K
Flooding around area where single-family residential vehicles are typically parked (see separate
guidelines)
Flooding of SIGNIFIGANT exterior property improvements which are deemed functional
necessities to reasonable use of single family residential property (see separate guidelines)
Flooding of MODERATE exterior property improvements which are deemed functional
necessities to reasonable use of single family residential property (see separate guidelines)
Flooding of any yard (any portion of parcel)
Charlotte-Mecklenburg
Flood Risk Assessment & Risk Reduction Plan
May 19, 2011
Page 17
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
Charlotte-Mecklenburg
Flood Risk Assessment & Risk Reduction Plan
May 19, 2011
Page 18
Impact-based Scoring
Charlotte-Mecklenburg
Flood Risk Assessment & Risk Reduction Plan
May 19, 2011
Page 19
Location-based Multiplier
• Depth-Velocity Hazard Zones
– Created using velocity and flood depth
rasters developed from effective HECRAS models
– Determined using depth-velocity curves
tied to safety criteria for people
• High danger = Significant hazard to adults
• Moderate danger = Significant hazard to children
Multiplier
Location Risk Factor
1.5
Building located in high danger depth-velocity zone
1.3
Building located in moderate danger depth-velocity zone
1.3
Building located near area impacted by storm drainage overflows
1.1
Building located in Community Encroachment Area
Charlotte-Mecklenburg
Flood Risk Assessment & Risk Reduction Plan
May 19, 2011
Page 20
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
Charlotte-Mecklenburg
Flood Risk Assessment & Risk Reduction Plan
May 19, 2011
Page 21
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:
Highly Effective
Moderately Effective
Not Recommended
Further Evaluation Needed
Charlotte-Mecklenburg
Flood Risk Assessment & Risk Reduction Plan
May 19, 2011
Page 22
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.)
Flood
Mitigation
Priority
Scores
Other Community
Benefits
Charlotte-Mecklenburg
Flood Risk Assessment & Risk Reduction Plan
• Flood Mitigation Property Score
– Use to prioritize properties
• Flood Mitigation Project Score
– Use to prioritize projects (Neighborhoods)
May 19, 2011
Page 23
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
Charlotte-Mecklenburg
Flood Risk Assessment & Risk Reduction Plan
May 19, 2011
Page 24
Communicating Plan Results
Charlotte-Mecklenburg
Flood Risk Assessment & Risk Reduction Plan
May 19, 2011
Page 25
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
Charlotte-Mecklenburg
Flood Risk Assessment & Risk Reduction Plan
May 19, 2011
Page 26
Thank You
tim.trautman@mecklenburgcountync.gov
darrin.punchard@aecom.com