Transcript LID Presentation for SD PMs

Land Development
Ordinance Changes
Greenville County, SC
PART 2
Clemson University
ICAR Campus
AT&T Auditorium
June 24, 2009
3: Storm Water Utility Credit Program
SECTION 3:
STORM WATER UTILITY
CREDIT PROGRAM
Land Development Ordinance Changes – Greenville County, SC
3: Storm Water Utility Credit Program
Purpose
Applicability
Credit Schedule
County Inspections
Facility and BMP Maintenance
Maintenance Agreement
Facility/ BMP not in Dedicated
Easement
 Disqualifying Provisions
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Land Development Ordinance Changes – Greenville County, SC
3: Storm Water Utility Credit Program
Purpose
 Provide credits against Storm Water
Service Fee for Class 2 properties
(developed non-residential properties)
 Encourage sound technical design
practices and use of applicable storm
water control facilities and water quality
BMPs to reduce impact of development on
drainage system and environment
Land Development Ordinance Changes – Greenville County, SC
3: Storm Water Utility Credit Program
Applicability
 Class 2 property (developed nonresidential
 Approved, on-site, post-construction storm
water control facility or water quality BMP
 Facility/ BMP within a recorded sanitary
sewer/ drainage easement (or equivalent
restrictions to future changes in use)
 Must have applicable permits
Land Development Ordinance Changes – Greenville County, SC
3: Storm Water Utility Credit Program
Applicability
 Constructed in compliance with approved
plans
 Owner responsible for all O & M costs
 Maintained in compliance with County
standards
 County permitted access for inspection
 No significant changes in land use or
impervious service within facility/ BMP
service drainage area
Land Development Ordinance Changes – Greenville County, SC
3: Storm Water Utility Credit Program
Credit Schedule
 Properties can qualify for:
− Water Quantity Credits (up to 25%)
− Water Quality Credits (up to 25%)
 A total maximum of up to 25% credit
against the Storm Water Service Fee
 Credit applied by reducing the number of
billable ERUs
 Adjusted ERU includes credit for both
water quantity and water quality
 Minimum adjusted ERU is one (1)
Land Development Ordinance Changes – Greenville County, SC
3: Storm Water Utility Credit Program
Water Quantity Credits
 Tree Preservation Policy Credit
(up to 10%)
 Upgrade Existing Detention/Retention
Facility Credit (up to 15%)
 Over-Detention Credit (up to 25%)
 Discharge Elimination Credit
(up to 25%)
Total Water Quantity Credit – NOT TO EXCEED 25%
Land Development Ordinance Changes – Greenville County, SC
3: Storm Water Utility Credit Program
Tree Preservation Policy Credits
 Up to 10% credit for going above and
beyond requirements of Greenville County
Tree Ordinance
 Preservation of natural undisturbed areas
of at least 1 contiguous acre
 Must meet standards to qualify for
conservation use per SC Nature
Conservancy guidelines
Land Development Ordinance Changes – Greenville County, SC
3: Storm Water Utility Credit Program
Tree Preservation Policy Credits
 Must be recorded in restrictive covenants
 Impervious surface runoff treated by
stream buffers will also be considered for
credit
 Allow 1% credit for each acre of
contiguous area up to 10%
Land Development Ordinance Changes – Greenville County, SC
3: Storm Water Utility Credit Program
Upgrade Existing Detention/
Retention Facility Credit
 Up to 15% credit for reconstruction of
existing detention/retention basins that
comply with current storm water
regulations
 Engineer’s certification of compliance
required
Land Development Ordinance Changes – Greenville County, SC
3: Storm Water Utility Credit Program
Over-Detention Credit
 Up to 25% credit for detention/ retention of
runoff in excess of current regulations
 Engineer’s certification required
 Maximum credit per storm event allowed as
follows:
−
−
−
−
−
100-year = 1%
50-year = 2%
25-year = 11%
10-year = 6%
2-year = 5%
 Calculations must reflect a pre-development land
use without development and/or prior land
disturbing activities
Land Development Ordinance Changes – Greenville County, SC
3: Storm Water Utility Credit Program
Discharge Elimination Credit
 Up to 25% credit for properties that do
not discharge storm water runoff or
pollutants to the County MS4
 These areas treat, store, dispose,
transpire, evaporate, infiltrate or otherwise
manage runoff from all rainfall events up
to and including 100-year
 Engineer certification required
Land Development Ordinance Changes – Greenville County, SC
3: Storm Water Utility Credit Program
Water Quality Credits
 New Development, New BMPs Credit
(up to 10%)
 Retrofit Existing Facility Credit
(up to 25%)
 Offsite Storm Water Quality Control Credit
(up to 25%)
Total Water Quality Credit – NOT TO EXCEED 25%
Land Development Ordinance Changes – Greenville County, SC
3: Storm Water Utility Credit Program
New Development, New BMPs Credit
New Storm Water Quality Control BMP Credit = %
impervious area of property routed through BMP x
Water Quality Factor % x 0.10
 Up to 10% credit for installing water
quality facilities/ BMPs
 BMPs designed in accordance with
Greenville Co. Storm Water Design Manual
 List of Approved BMPs – Appendix G of
Design Manual
Land Development Ordinance Changes – Greenville County, SC
3: Storm Water Utility Credit Program
New Development, New BMPs Credit
 Water Quality Factors: available for
approved BMPs in Appendix G of Design
Manual
 Innovative solutions encouraged (may require
valid documentation from full scale testing by independent
3rd party for verification of pollutant removal efficiency)
 Engineer’s Certification required
(verifying that
flow from the specified % of impervious area of property is
routed through BMP)
Land Development Ordinance Changes – Greenville County, SC
3: Storm Water Utility Credit Program
New Development, New BMPs Credit
APPROVED BMPS
NON-STRUCTURAL BMPS
Open vegetated conveyance systems
Natural stream buffers
Disconnected rooftop to pervious area
Grass or alternative paving surfaces
Natural Infiltration
Water Quality Factor (%)
20
25
15
15
65
STRUCTURAL BMPS – GENERAL APPLICATION
Dry Detention Basin
Wet Detention Pond
Storm Water Wetlands
Biofilter
Media Filter
Media Filter (Manufactured Devices)
Hydrodynamic Device (Manufactured Devices)
65
80
80
65
65
65
35
STRUCTURAL CONTROLS – LIMITED APPLICATION
Vegetated Filter Strip (L < 150 ft.)
Vegetated Filter Strip (L > 150 ft.)
Vegetated Channels and Swales
20
50
20
Land Development Ordinance Changes – Greenville County, SC
3: Storm Water Utility Credit Program
Retrofit Existing Facility Credit
 Up to 25% credit allowed for retrofit of
existing facilities to meet current
standards
 File credit application and obtain
development permit prior to making
changes
 One credit application per parcel
Land Development Ordinance Changes – Greenville County, SC
3: Storm Water Utility Credit Program
Retrofit Existing Facility Credit
 Site map prepared by SC licensed engineer
or land surveyor showing key site
characteristics
 Storm water design analysis, H & H report,
as-builts by SC licensed PE
 Service fee credit for 5-year term
 Annual report and certification of proper O
&M
Land Development Ordinance Changes – Greenville County, SC
3: Storm Water Utility Credit Program
Offsite Storm Water Quality Control Credit
Offsite Storm Water Quality Control Credit = Offsite
Drainage Area/ Onsite Drainage Area x Water
Quality Factor % x 0.25
 Up to 25% credit allowed if demonstrated that
on-site storm water treatment facility adequately
treats offsite runoff from one or more developed
properties (for which no storm water control
exists at time of application)
 No credit granted for non-point source pollution
control for offsite undeveloped properties
Land Development Ordinance Changes – Greenville County, SC
3: Storm Water Utility Credit Program
Offsite Storm Water Quality Control Credit
 Offsite drainage area contiguous with onsite
drainage area
 No contractual BMP maintenance agreement
between owners (notarized certification from
licensed SC engineer)
 At such time as offsite runoff is treated prior to
draining to onsite BMP or maintenance agreement
is executed between on-site and off-site parties,
credit may be reevaluated for reduction or
cancellation
Land Development Ordinance Changes – Greenville County, SC
3: Storm Water Utility Credit Program
Storm Water Service Fee Credit
Application Form
 Application Form available on Greenville County
website at:
http://www.greenvillecounty.org/land_development/
pdf/sw_fee_credit_app_form.pdf
 Credit application documentation requirements
checklist
 Credit calculation worksheets
 Engineer’s Certification sheets
 Maintenance Agreement
Land Development Ordinance Changes – Greenville County, SC
3: Storm Water Utility Credit Program
County Inspections
 Periodic evaluations of facilities/ BMPs to
ensure proper maintenance and function
 Failure of evaluation will lead to NOV
− Fee credit rescinded if adequate corrections
not made within specified timeframe
− Reapplication is required for reinstatement of
credit (after one year waiting period)
Land Development Ordinance Changes – Greenville County, SC
3: Storm Water Utility Credit Program
Facility and BMP Maintenance
 Prior to submittal of Credit Application:
− Must be constructed in compliance with
approved plans
− Functioning as intended
− Properly maintained
 Inspections by property owner’s engineer
to be done using County provided forms
 Annual report and certification of proper
O&M required to maintain credit
Land Development Ordinance Changes – Greenville County, SC
3: Storm Water Utility Credit Program
Maintenance Agreement
 Master Agreement for all types of storm
water control facility or water quality BMP
 Use for on-site facilities/ BMPs (between
property owner and County)
 Use for off-site facilities/BMPs (between
applicant and facility/ BMP owner)
Land Development Ordinance Changes – Greenville County, SC
3: Storm Water Utility Credit Program
Maintenance Agreement
 Storm Water Facility/ BMP Location Map
 Legal Description of Facilities/ BMPs
 Long Term Maintenance Plan:
− BMP schematics
− Schedule of inspections
− List techniques to inspect and maintain systems
(Use documentation checklists provided by County
on website - available for all approved BMPs)
Land Development Ordinance Changes – Greenville County, SC
3: Storm Water Utility Credit Program
Maintenance Agreement
 Long Term Maintenance Plan (continued):
− Describe where and how trash, sediment, and
other pollutants removed will be disposed
− Identify person(s) responsible for inspection and
maintenance
− Provisions for permanent access and maintenance
easements
Land Development Ordinance Changes – Greenville County, SC
3: Storm Water Utility Credit Program
Facility/BMP not Located in Dedicated
Easement
 May be allowed
 Applicant must enter into a Maintenance
Agreement with County
 Acceptance at discretion of County
 Contact County prior to requesting Credit
Application
Land Development Ordinance Changes – Greenville County, SC
3: Storm Water Utility Credit Program
Disqualifying Provisions
 Development/ construction in floodplain
 Development/ construction on slopes in
excess of 15%
 Siting on porous or erodible soil
 Excessive soil removal and excavation
 Severe topography modifications
Land Development Ordinance Changes – Greenville County, SC
3: Storm Water Utility Credit Program
Disqualifying Provisions
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Channelization
Development in sensitive areas
Clear cutting
Excessive grading
Windborne dust and soils
Transfer of pollution by vehicles and
equipment
Land Development Ordinance Changes – Greenville County, SC
3: Storm Water Utility Credit Program
QUESTIONS ???
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
SECTION 4:
CHANGES TO STORM
WATER DESIGN MANUAL
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
List of Chapters with Major Changes
 Ch.2.2
 Ch.2.3
 Ch.3.1.2
 Ch.3.1.3
 Ch.3.1.4
 Ch.3.3.3
 Ch.3.3.4
Engineer Minimum Plan
Special Pollution Abatement
Permit
Preferred Storm Water
Management Facilities
Fee-in-lieu
Minimum Preliminary Site
Development Plan Requirements
Storm Water Management
Design Standards
Erosion & Sediment Control
Design Standards
(Note: Items in blue discussed elsewhere in presentation.)
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
List of Chapters with Major Changes
 Ch.3.3.5
 Ch.3.3.7
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Ch.3.4
Ch.3.7
Ch.3.9.8
Ch.3.9.9
Ch.4.4
Ch.5.6
Ch.7.2.3
Ch.8.4.8
Single and Multi-Family
Development Regulations
Storm Water Facility Ownership
& Maintenance
Digital submittal requirements
Performance Security
Service Fee Credit Calculations
Approved BMPs
Easement Widths
First Flush Water Quality Volume
Detention Structure Design
Final Stabilization
(Note: Items in blue discussed elsewhere in presentation.)
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
List of Chapters with Major Changes
 Ch.9.4
 Ch.9.5
 Ch.9.10
Water Quality Regulations
First Flush Water Quality Volume
Special Pollution Abatement
Permit
 Ch.10
Low Impact Development
 Ch.12.2.2 Inspections During Construction
 Ch.12.3 Correction Orders
 Ch.12.6 Civil Citations
 Ch.12.7 Consent Process
 Ch.12.8 Criminal Penalties
 App. G
Approved BMPs, Fee Credits
(Note: Items in blue discussed elsewhere in presentation.)
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.2.2 Engineer Minimum Plan
 Small scope projects with design criteria
requiring professional designer due to one
of the following will submit an Engineer
Minimum Plan:
− Quantity control in place as part of large
common plan but quality control may or may
not be in place and EPSC plan is required
− Redevelopment requires post-construction
BMP upgrades and an EPSC plan
− Minor modification or reconstruction of
existing facility/ BMP
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.2.2 Engineer Minimum Plan
 Small scope projects with design criteria
requiring professional designer due to one
of the following will submit an Engineer
Minimum Plan (continued):
− Site drains to 303(d) or TMDL waterbody or
have potential impact requiring BMPs for
correction of violation of grading without
permit
− Project has negative downstream impacts
− Site requires storm drain pipe or alterations to
existing pipe
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.2.2 Engineer Minimum Plan
 Application, permit process same as NonSimplified Plan except for design criteria
and fees
 Minimum design criteria set on case-bycase basis during pre-design meeting
 Fees are same as Simplified Permit
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.2.2 Engineer Minimum Plan
 Plans require oversight by Design
Professional
 CEPSCI inspections and engineer of record
certification may be required
 Plan may be forwarded to SCDHEC for
general permit based on disturbed area
and if part of larger common plan
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.3.1.3 Fee-in-lieu
 Ordinance language additions are
presented in Part 1 of presentation.
(Ordinance Location: Division 1 – Storm Water
Management, Sec. 8-78. Fee-In-Lieu.)
 Additional guidance is provided in Design
Manual:
−
−
−
−
Purpose
Application
Criteria
Procedures
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.3.1.3 Fee-in-lieu
 Purpose: To allow payment of a fee-in-lieu
of providing storm water detention on a
development site:
− At sites where county intends to construct
downstream storm water conveyance
upgrades or regional controls, or
− To encourage use of LID practices
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.3.1.3 Fee-in-lieu
 Application:
− Larger sites:
• Prove no downstream impacts
• Be in specified watersheds where county
intends to construct storm water conveyance
upgrades or regional controls
− Sites with < 1 acre impervious:
• Preferred method
• Fee waived if LID used
− Certain practices required (enhanced
infiltration with permeable pavements, bioswales, bio-retention cells, rain gardens, storm
water harvesting and reuse, green roofs)
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.3.1.3 Fee-in-lieu
 Criteria:
− Modeling shows on-site detention results in
unfavorable downstream impacts (increase in
peak discharge, flooding depth, erosion, water
quality)
− Runoff from area is controlled via regional,
county maintained conveyance system,
storage and water quality enhancements
− Site with one acre or less impervious area, or
with a flow increase of 1 or more cfs
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.3.1.3 Fee-in-lieu
 Criteria (continued):
− MS4 conveyance and natural system provide
adequate capacity and demonstrate no
adverse effects to all upstream, adjacent and
downstream properties in full build out
watershed conditions
− Development adds a minimum of 5,000 square
feet of impervious area (does not apply to
individual residential homes, separately built)
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.3.1.3 Fee-in-lieu
 Criteria (continued):
− Development located in watershed where
model and master plan exists for impact
evaluation purposes (currently:
Gilder/Horsepen Creek, Brushy Creek, Rocky
Creek, and Reedy River)
− Can show site specific controls constitute a
hardship case and fee-in-lieu is only option
− Proposals presented during pre-design
meeting
− Fee paid prior to issuance of land disturbance
or grading permit
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.3.1.3 Fee-in-lieu
 Procedures:
− For requiring and collecting fee-in-lieu of
revenues:
• Submit written request (will be rejected or
approved within 45 days unless additional
engineering studies are required)
• Fee-in-lieu = estimated construction cost
of proposed and approved on-site storm
water storage, including land costs
− County maintained fund for identifying and
controlling all revenues and expenditures
resulting from fee-in-lieu approvals.
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.3.1.3 Fee-in-lieu
 Procedures (continued):
− Revenues received from each watershed to be
deposited in these funds for use within that
watershed
− Revenues may be used to plan, design or
construct upgrade to existing or future storm
water management systems if upgrades are
consistent with a storm water master plan,
floodplain study or storm water system
improvement approved by Director
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.3.1.4 Minimum Preliminary Site
Development Plan
 All Site Development Plan Requirements,
as listed in revised Ordinance Sec. 8-68,
have been added to Design Manual in
Ch.3.1.4.
 The only revisions to Site Development
Plan Requirements in Ordinance are (also
discussed in Part 1 of presentation):
− Plans must meet all other applicable plan
requirements in effect at time of submittal
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.3.1.4 Minimum Preliminary Site
Development Plan
 The only revisions to Site Development Plan
Requirements in the Ordinance are (continued):
− Requires a tree saving and planting plan consistent
with GC Tree Ordinance and Landscape Plan
requirements of Design Manual
− Certification that land clearing, construction,
development and drainage done in accordance
with approved plans
− Approved plans remain valid for 2 or 5 years
(depending on fee paid)
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.3.4 Digital Submittal Requirements
 Submit electronic copy of plans with preliminary
approval per Greenville County’s Electronic
Submission Standards and Procedures posted at:
http://www.greenvillecounty.org/land_developme
nt/Planning.asp
 Will be used only for anonymous inclusion in GC
GIS
 Submit drawings in DWG or DXF format to
County’s ftp site or on approved standard storage
media
 Land disturbance permit will not be issued until
electronic submittal has been received and
approved
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.4.4 Easement Widths
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Total easement width (permanent and
temporary) sufficient to allow contractor
flexibility in construction
No excessive widths requiring needless clearing/
cutting of wooded/ vegetated areas
Provide minimum requirements:
− Adequate access to drainage system and structures
− Sufficient land area for maintenance equipment and
personnel to adequately and efficiently maintain
drainage system and storm water facilities;
− Prohibit all fences and structures that interfere with
access and/or maintenance function
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.7.2.3 Detention Structure Design
 General Design Criteria:
− Criteria to ensure long term function of
structure while minimizing maintenance
responsibilities
− Includes criteria for: basins on slopes; inlet
and outlet locations; inlet design; relationship
to groundwater; scour; access; outlet
protection; minimum buffer/ setback; safety
fence
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.7.2.3 Detention Structure Design
 Surface Detention Design Criteria:
− Includes criteria for: basin side slopes; basin
shape; dry detention bottom slopes;
underdrains, permanent pools; emergency
spillways (location, exit channel grade); Safe
Dams Act; principal spillways (trash racks,
seepage control, anti-flotation)
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.7.2.3 Detention Structure Design
 Subsurface Detention Design Criteria:
− Includes criteria for: emergency spillways;
pretreatment; observation wells; access port
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.7.2.3 Detention Structure Design
 Landscaping Criteria:
− Criteria established to ensure engineering
function is protected
− Criteria included for: types of vegetation;
spacing of plantings; location of plantings;
side slopes; soil types; maintenance
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.9.4 Water Quality Regulations
 Minimum Water Quality Requirements:
− All storm water runoff generated from a site to
be adequately treated before discharge
− Presumed compliance if:
• Preferred method – size water quality device
to trap 85% of TSS based on annual loadings
by particle class (use IDEAL to model)
• Alternative as default criteria – size device to
capture First Flush (first inch of runoff from
site impervious area) and discharge over 24hrs
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.9.4 Water Quality Regulations
 Minimum Water Quality Requirements:
− Appropriate structural storm water controls or
non-structural practices are selected,
designed, constructed or preserved, and
maintained according to the specific criteria in
this manual
− More stringent controls may be required in
environmentally sensitive areas
− All development/ redevelopment projects
disturbing > 1 and resulting in > 1 cfs
increase in peak runoff to meet these
requirements even if no change in land use
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.9.4 Water Quality Regulations
 IDEAL Model:
− The Greenville County IDEAL Model or other
models such as the USEPA SWMM or Overflow
Rate Model may be used to design BMPs to
meet 85% TSS removal requirement
− Updated IDEAL Users Manual available on
Greenville County website describes how to
use the model to design several BMPs to this
standard
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.9.4 Water Quality Regulations
 IDEAL Model:
− Updated IDEAL Users Manual includes:
• Trapping Efficiency Curves for Engineered
Storm Water Quality Devices
• Method for calculating trapping efficiency
for treatment trains (multiple BMPs in
series or in parallel)
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.9.4 Water Quality Regulations
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.9.5 First Flush
 Same as First Flush design requirements
described in Ch.9.4. Water Quality
Regulations, Minimum Water Quality
Requirements
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.10 Low Impact Development
 What is LID?
− An ENGINEERING design approach to
STORMWATER MANAGEMENT focusing on
mimicking natural state hydrologic regime
through infiltration, separation, filtration,
evaporation, retention, and detention.
− Synonymous with USEPA’s Green
Infrastructure or Better Site Design
− LID attempts to offset environmental impacts of
development by copying nature
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.10 Low Impact Development
 What LID is NOT:
LEED (Leadership in Energy and
Environmental Design)
− Smart Growth
− New Urbanism
− Sustainable development
−
… but is a potential element in all of these.
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.10 Low Impact Development
 Basic Principles of LID:
− Minimization of impact
− Conservation of ecological and natural
resources
− Maintain predevelopment runoff patterns
− Source control of runoff and pollution
− Public/property owner education and buy-in
− Economic feasibility
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.10 Low Impact Development
 Common Impacts of Land Development:
− Increased storm water runoff volumes, rates,
and pollutant transport
− Higher pollutant loads (sediment/debris,
fertilizers, SSOs, and leaks)
− Modification of natural streams/floodplains
− Reduced biodiversity
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.10 Low Impact Development
 How Do We Maintain Pre-Development
Conditions?
− Reduce Limits of Clearing and Grading
• Preserve existing trees
• Preserve permeable soils
• Preserve vegetated areas (especially
trees)
− Site Fingerprinting
• Minimize disturbance
• Re-vegetate
− Maintain flow pathways for large events
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.10 Low Impact Development
 Preserve and Maintain Predevelopment
Runoff Volume:
−
−
−
−
−
Reduce impervious surfaces
Disconnect impervious surfaces
Reduce road widths
Use retention and rainwater harvesting
Promote infiltration (e.g., porous pavers)
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
Ch.10 Low Impact Development
 Preserve and Maintain Predevelopment
Runoff Velocity:
−
−
−
−
Use open swales instead of pipe
Increase roughness
Flatten slopes and widen swales
Lengthen flow path
Land Development Ordinance Changes – Greenville County, SC
4: Changes to Storm Water Design Manual
QUESTIONS ???
Land Development Ordinance Changes – Greenville County, SC