1. A Unique Approach to Integrating
Local Municipal Needs
with
Floodplain Mapping Updates
Robert Billings, PE, PH, CFM
Project Manager
Charlotte-Mecklenburg Storm Water Services (County)
Danee McGee, PE, CFM
Project Manager
Charlotte-Mecklenburg Storm Water Services (City)
City of Charlotte, Mecklenburg County, North Carolina
2. Charlotte-Mecklenburg
“The Team”
Mecklenburg County
Tim Trautman, Flood Mitigation Program Manager
Bill Tingle, Floodplain Administrator
Robert Billings, Project Manager- Remapping
City of Charlotte
Tim Richards, Assistant City Engineer
Jennifer G. Smith, Storm Water Division Manager
Danee McGee, Project Manager- ETA Lead
3. Charlotte-Mecklenburg
Background and History
Mecklenburg County includes:
The City of Charlotte
The Towns of Cornelius, Davidson, Huntersville, Matthews,
Mint Hill, and Pineville (8 NFIP Communities)
Land Area: 549 square miles
5. Charlotte-Mecklenburg
Background and History
Local Flood Plain Mapping
Current maps are result of County-
wide FIS completed in February 4,
2004 at a cost of $2,000,000
350 miles of detailed study streams
32 watersheds
FEMA and Community flood fringe and
floodway
Data reproduced in state-wide format
effective March 2, 2009
182 panels, paper and digital forms
Remapping began in 2007 on two
basins , expanded in 2008 to include
the majority of the remainder of the
county
6. Charlotte-Mecklenburg
Background and History
Flood Map Overview
•Land Use and Topographic Data
1997
•Future Build-out District Plans
1999
•Adopted (Local – Regulatory)
5/22/00
•Effective (FEMA - Flood Insurance)
2/4/04
•Map Maintenance Strategy/Planning
2005-2006
•Map Maintenance Implementation
2007 - present
14. Charlotte-Mecklenburg
Local Government
Mecklenburg County
Budget - $1.1 Billion
9 County Commissioners
SWAC – Storm Water Advisory Committee
City of Charlotte
Budget - $1.39 Billion
11 City Council Members
SWAC is a 9 member appointed board
SWAC is a “bridge” between City and
County Stormwater Programs
SWAC’s charge is:
To maintain consistent policy
To identify possible duplication of
services
15. Charlotte-Mecklenburg
Working Together
Mecklenburg County
Floodplains and Floodways
County Manager
Charlotte-Mecklenburg Storm Water Services
City of Charlotte
Capital Projects
City Manager
City Storm Water
County Storm Water
CDOT
Planning Department (Commission)
Consulting Engineers
Citizen Task Force
SWAC
16. Charlotte-Mecklenburg
Working Together
Reasons for Needing a “Standards Document”
Difficult to compare the results of the City and County/FEMA Analyses
Difficult to assess the downstream impacts from upstream
improvements outside of FEMA system
City and County wish to improve the interoperability of two
systems/approaches
Provide consistent base and clear direction on future modeling of
other watersheds
Incorporate lessons learned from sensitivity analysis in the
development of document
17. Charlotte-Mecklenburg
Working Together
Reasons for Differences in City and
County Analysis Techniques
City maintains “minor” system (<1 sq.
mi.)
City drainage improvement projects often
are upstream of, but end at the
County/FEMA floodplain
In recent years, City has included
consideration of impacts on FEMA
streams from CIPs
18. Charlotte-Mecklenburg
Working Together
Comparison of Differing Analysis Techniques
Parameter City County/FEMA
Project Size 200-500 acres (<1 sq. mi.) 1 - 40 sq. mi.
Project Focus
Planning, Design, and
Constructions of
Drainage
Improvements
Develop floodplain/floodway, and
regulate constructions activities
within SFHA (Flood lands Permit).
Reference
Document
Charlotte-Mecklenburg
Storm Water Design
Manual FEMA Guidelines and Specifications
Survey
Detailed survey of storm
water features
Countywide GIS with survey at
structure crossings and sporadic
channel areas
19. Charlotte-Mecklenburg
Working Together
Comparison of Differing Analysis Techniques
Parameter City County/FEMA
Hydrologic Model
HEC-1/HMS/SWMM or
others HEC-1/HMS
Storm Pattern /
Rainfall Depth
6-hour storm using
Charlotte IDF depths SCS 24-hr Type II
Subbasins 15 - 30 acres Average 150 acres
Loss
Methodology SCS Curve Number SCS Curve Number
Hydrograph
Transform/Lag
Time
Typically SCS Unit
Hydrograph Using TR-55
Lag Time Method
SCS Unit Hydrograph Using TR-55
Lag Time Method
Routing Normal Depth, Level Pool Modified Puls
Calibration Typically none Limited Calibration
20. The Need for “Task Force Meetings”
Process Assessment
Identify Stakeholders and Define Objectives
“With recommendations from the City Council and Board of County
Commissioners, County staff will select stakeholders who have
property ownership or interests within the watershed. Each
stakeholder group will reflect neighborhood representatives,
engineers, real estate professionals, environmental advocates,
developers and other interested parties.
Invitations for theTask Force
Charlotte-Mecklenburg
Working Together
21. Charlotte-Mecklenburg
Working Together
Goal of The Stakeholders Task Force:
“To provide input on specific land related information that will be
used in the remapping effort and to make recommendations
regarding the specific land related information”
Their Task:
Review adopted District Plans for their applicability to floodplain
mapping.
Provide input on unique watershed features that may impact flood
levels.
22. Charlotte-Mecklenburg
Working Together
Estimates “existing”
impervious area
Utilized: Rezonings,
Planning Department ‘s
Land use maps and
existing aerials
No straight adoption of
the Planning
Department’s land use
Aerial photography to
verify current
development
Existing Conditions Land Use
23. Charlotte-Mecklenburg
Working Together
Estimating full build
out conditions
Planning Department’s
Land Use plans as starting
point
80 Future Land Use
Categories
Translate to 12 categories
impervious area categories
for floodplain mapping
Comparison –
Existing to Future
Future Conditions Land Use
24. Charlotte-Mecklenburg
Working Together
Example Comment and Response
Comment: “greenway”
Response: Recommend changing designation to Open Space.
Information:
Existing conditions land cover
0.25 to 0.50 Ac Residential
0.50 to 2.0 Ac Residential
Future conditions land cover
> 2.0 Ac Residential/Open Current percent impervious
Percent Impervious Assumption
0.25 to 0.50 Ac Residential - 28%
0.50 to 2.0 Ac Residential - 20%
Open Space – 12%
This area is a greenway and should be Open Space in
existing and future land cover.
25. Charlotte-Mecklenburg
Working Together
Plan on multiple meetings to reach consensus
Meetings should have planned agendas, goals,
and documentation of decisions (i.e. Minutes)
Be prepared to share about “Floodplains 101”
Be prepared to answer, “Why do we need new
floodplain maps”.
Things to Keep in Mind….
26. Charlotte-Mecklenburg
Working Together
Finish Briar Creek
approvals
Concurrent Task Force
Meetings for multiple
watersheds
Start the process over
again once the new maps
are approved by FEMA in
2012
Next Steps
28. Charlotte-Mecklenburg
Future of Map Maintenance
Communicate Risk
Floodzone web application
Merge map data with other data to
better communicate risk
Mitigate Risk
Implement elements in Mitigation Plans
Acquisitions
Elevations
Charlotte-Mecklenburg Comprehensive Approach
29. Closing Thoughts…
Take ownership of managing Flood Risks
Various levels of stewardship in mitigation
Don’t need to do it all yourself (partnerships)
Think holistically
Maps, Regulations, Mitigation Plans, Mitigation
Projects, Communication
Live in the present AND future
Communicate Existing Risk
Communicate and Regulate Future Risk
Determine what type of “Future” mapping is
appropriate
