Post-Construction Storm
Water Program Updates
Presented to:
2013 Surveyors Workshop
December 3, 2013
Don Ceccarelli
don.ceccarelli@mecklenburgcountync.gov
Post Construction Program
1. Post Construction Overview
2. Changes in BMP Design Manual
3. Changes in Administrative Manual
4. Buffers Everywhere
Storm Water Trivia
Annual rainfall in Charlotte =
43 inches
Annual rainfall in Mt. Waialeale = 39 feet
Mt. Waialeale in Kauai, HI
Post-Construction Ordinance
Goals
1. Achieve compliance with Storm Water
Permit requirements.
2. Satisfactorily address the pollution control
criteria recommended by Wildlife agencies.
3. Satisfactorily address the causes of water
quality impairment.
4. Satisfactorily address detention measures
for the control of flooding.
WARNING
There are 8 postconstruction
ordinances within
Mecklenburg
County.
NO two
ordinances
are the same.
Post-Construction Ordinance
Standards
1. Structural BMPs
2. Buffers
3. Detention
4. Open Space
Requirements for Post-Construction Ordinance
Watershed Districts
Yadkin District
CENTRAL CATAWBA
WESTERN CATAWBA
BMPs CATAWBA
>10% BUA @ 85% TSS
YADKIN-SOUTHEAST
& 70%TP removal
GOOSE CREEK
HUNTERSVILLE
* >12% in Mint Hill
Western Catawba District
BMPs
N
LAKE
>12% BUA @ 85%
NORMAN
TSS & 70%TP
removal
* >24% in Cornelius
UPPER
MTN
ISLAND
Buffers
Same as Central
Catawba District
Detention
Same as Central
Catawba District LOWER
Open
Space
Same as Central
Catawba District
CLARKE
McDOWELL
MALLARD
LONG
Huntersville
BMPs
>24% BUA @
85% TSS
BEAVERDAM
removal
Buffers
S.W.I.M. + 30 ft on int.
streams
Detention
LAKE
WYLIE
V = post 1-yr, 24-hr
storm;
P = 10-yr & 25-yr, 6-hr
Open
Space
<24% BUA = 25%;
>24% BUA = 17.5%;
>50 BUA = 10%
<50 ac.= 50 ft.;
>50 ac. = 100 ft
Detention
Same as Central
Catawba District
Open
Space
Same as Central
Catawba District
BACK
>12% BUA @ 85% TSS
McKEE
IRWIN & LID BMPs REEDY
BMPs
CALDWELL
* >6% in MI Critical Area
PAW
Central Catawba District
BMPs
LOWER
CLARKE
Buffers
GAR
MTN
ISLAND
CATAWBA
ROCKY
RIVER
Buffers
UPPER BRIAR
LITTLE
Same as Central
SUGAR
Catawba District
Goose Creek District
CLEAR Buffers
SUGAR
Detention
STEELE
GOOSE
V = pre–post 1-yr, or 2-yr
McALPINE
24-hr based on zoning
McMULLEN
Detention
LOWER P (> 12% BUA) = 2-yr &
LITTLE 10-yr, 24-hr
CROOKED
FOUR MILE
SUGAR
Open Space
None
TWELVE MILE
Open
Space
SIX MILE
CLEM
5
5
Exceeds current
State0requirements
10 Miles
Any BUA @ 85% TSS
(pre-post, 1-yr, 24-hr)
S.W.I.M +
100-ft on streams;
200-ft on streams
w/floodplain
V = pre–post 1-yr, 24-hr
P = 10-yr & 25-yr, 6-hr
<20% BUA = 0%;
>20% BUA = 15%;
>50 BUA = 10%
Key Factors for Post Construction
Ordinance Applicability:
•
•
•
•
•
•
Date of Activity – some “grandfathering” of activities
based upon submittal date (not approval date)
Vested Right – some activities exempt if vested rights
established
Conditional Zoning District – some activities deferred
from complying
Type of Development –
Industrial/Commercial/Residential, new development
or redevelopment
Size of Disturbance – some exemptions based upon
the amount of disturbed area
Increase of BUA – some exemptions allowed if no net
increase in BUA and no decrease in storm water
control
Post-Construction Requirement
Applicability:
•
BUFFERS – Except in Goose Creek, post-construction
buffers only apply if the post-construction ordinance
applies
•
WQ BMPs– Except in Goose Creek, BMPs are required
if BUA percentage is greater than Threshold Amount
•
DETENTION – Detention is required if BUA percentage
is greater than Threshold Amount (or if detention
policy applies)
•
UNDISTURBED OPEN SPACE– Required for
development only, not redevelopment
BMP Design Manual Updates
http://charmeck.org/stormwater/regulations/Pages/BMPStandardsManual.aspx
BMP Design Manual Updates (July 2013)
•
•
•
•
•
•
•
•
3.0 Hydrology
Alternative methodology for 5% volume remaining
Water balance calculations modified to account for
rainfall discharged through outlet structures
4.1 Bioretention
New sizing criteria similar to NCDWQ
Allowance for IWS and infiltration
Allowance for sodded bioretention
Requirement for watertight seal of pipe to outlet
structure
BMP Design Manual Updates (July 2013)
•
•
•
•
•
•
•
•
4.2 Wet Ponds
Minimum drainage area increased to 25 acres with
addition requirements (permeability tests, etc.)
Allowance for use of floating islands and irrigation.
Requirement for watertight seals of pipes and
outlet structures.
Forebay embankment detail updated to include riprap armoring.
4.3 Wetlands
Requirement for watertight seals of pipes and
outlet structures.
Require the permanent pool near the water table.
BMP Design Manual Updates (July 2013)
•
•
•
•
•
•
•
•
•
•
4.4 Enhanced Swales
Allowance for IWS and infiltration.
4.6 Infiltration Trench
Allowance for infiltration in hydraulic calculations.
4.8 Sand Filters
Allowance for IWS, void space, and infiltration.
Allowance of sod or stone surface cover.
Provided a design standard for optional oversized
basin for additional storage.
4.9 Dry Detention
Added standards for underground detention
structures
BMP Design Manual Updates (July 2013)
•
•
•
•
•
•
•
•
4.10 Permeable Pavement
Allowance for BUA credit similar to NCDWQ with
the exception of Watershed caps. (May require
ordinance changes to implement).
4.10 Green Roofs
Revised minimum depth of media from 5 to 4
inches.
4.10 Storm Water Harvesting
Allowance for storm water harvesting systems.
5.5 Outlet Pipes / Level Spreaders
Added language and design standards to define
“diffuse flow” to prevent erosion within buffers.
2013 Administrative Manual Updates
http://charmeck.org/stormwater/regulations/Pages/PostConstructionAdminManualCountyTowns.aspx
Administrative Manual Updates (2013)
•
•
•
•
•
•
BMP Maintenance Covenant & Plan
Combined Covenant and Maintenance Plan into
one document.
Same Covenant for Owner and HOA.
Escrow accumulation periods changed.
Maintenance Cost Estimation spreadsheet revised.
Post-Construction Certification
•
Design Engineer required to certify that
construction, as-built surveys, recorded plats, and
field conditions are in compliance with the
approved designs, plans, and the PostConstruction ordinance
Administrative Manual Updates (2013)
•
Detention and Peak Control
•
Section 2.5.3 was revised to clarify interaction of
detention ordinance with Post-Construction
ordinance.
•
Mint Hill eliminated detention requirements for
non-Post-Construction projects.
•
Matthews changed Detention Ordinance
grandfathering date to July 10, 2000.
•
Significant Changes to Grandfathered Plans
•
Language added to clarify changes to previously
grandfathered developments that could trigger
post-construction applicability.
Administrative Manual Updates (2013)
•
•
Recorded Plats
•
Built-upon area maximums are required to be listed
for each lot subject to the Post-Construction
ordinance.
Ordinance Changes
•
Town of Cornelius changed high density BUA
threshold from 12% to 24% BUA.
•
Town of Huntersville changed high density BUA
threshold from 6% to 15% BUA, adds LID
mitigation options, and allows “qualified
professionals” to perform annual BMP inspections.
Water Quality Buffers
ftp://ftp1.co.mecklenburg.nc.us/WaterQuality/WQ%20Buffer
s/WaterQualityBufferImplementationGuidelines.pdf
How are Buffers Measured
Types
OfOfWater
QualityBuffers
Buffers
Types
Water Quality
1. Water Supply Watershed Buffer: 1995
through 1998.
2. Surface Water Improvement &
Management (SWIM Buffer): 1999
through 2000
3. Catawba River Buffer Rules: 2001
4. Post-Construction Buffer: 2007 through
2008
5. Goose Creek Buffers – February 2009
Buffer Ordinances
• Watershed
– Lake Norman
1. Davidson
2. Cornelius
3. Huntersville
– MI Lake
4. Cornelius
5. Char-Meck
6. Huntersville
– Lake Wylie
7. Char-Meck – Upper
8. Char-Meck - Lower
• SWIM
9.
10.
11.
12.
13.
14.
15.
16.
Charlotte
Cornelius
Davidson
Huntersville
Matthews
Mecklenburg County
Mint Hill
Pineville
Buffer Ordinances
• Post-Construction
17. Charlotte
18. Cornelius
19. Davidson
20. Huntersville
21. Matthews
22. Mecklenburg County
23. Mint Hill
24. Pineville
• Catawba River
25. NCDWQ Riparian
How To Determine The Buffer
That Applies
• Review the applicability sections of the
ordinances.
• If more than one buffer applies to the
same parcel, the more stringent will
govern.
Information to Gather
•
•
•
•
•
•
Buffer Types
Existing location of buildings
Existing condition of buffers
Date the lot was platted
Date the building was constructed
Future Plans of Owner…. Expansion?
Clearing?....Pool?.....Gazebo?
• SWIM Buffers
Quick Tips
– Existing platted lots are not subject
– Contains multiple “zones” within buffer with different
restrictions for each zone.
• Watershed Buffers
– Existing Lots are generally subject
– Existing Development are generally not subject
• Post-Construction Buffers
– Buffers apply if the post-construction ordinance applies
(which is typically if greater than 0.5 acres is disturbed)
– Contains multiple “zones” within buffer with different
restrictions for each zone
– Six Mile Creek and Goose Creek buffers apply as of 2009
• All planned additions, expansions, and grading must be
evaluated individually and cumulatively
Case Study
Case Study
Case Study
Planned Expansion:
-0.6 acre site
-disturbs 5,000 ft2
- Adds 4,000 ft2
Case Study
Planned Expansion:
-0.6 acre site
-disturbs 5,000 ft2
- Adds 4,000 ft2
Questions?