STORMWATER MANAGEMENT ORDINANCE IMPLEMENTATION Presented by: Butler County Planning Commission
STORMWATER MANAGEMENT
ORDINANCE IMPLEMENTATION
Presented by:
Butler County Planning Commission
AGENDA
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Introduction and Review
The Model Ordinance
Brief Discussion of SWM Report Technical Criteria
Easements
Miscellaneous Requirements
Test
IMPORTANCE OF STORMWATER MANAGEMENT
Pre-developed
ConditionDeveloped
Condition
IMPORTANCE OF STORMWATER MANAGEMENT
FloodingCosts Associated with Storm Events
County
10-year Event 100-year Event
Buildings Damaged
Tons of Debris
Economic Loss
Buildings Damaged
Tons of Debris
Economic Loss
Crawford 374 25,153 $237.78 495 36,898 $306.15
Erie 110 8,007 $57.52 169 12,502 $72.31
Venango 154 13,211 $60.73 360 28,542 $112.75
Warren 262 19,916 $92.98 470 34,487 $148.92
total 900 66,287 $449.01 1,494 112,429 $640.13
TRADITIONAL SWM STANDARDS
• Collection & Conveyance
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• Rate Control
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Traditional design standards addressed:
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The problem with traditional standards:
• Application of Theory
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• Technical Shortcomings
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Post-Development with SWM
Post-Development with no SWM
Existing
TRADITIONAL SWM STANDARDS
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The problem with traditional standards:
• Content (cont.)
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Total hydrograph at confluence A-B
Watershed B
Watershed A
tpA Tp tpB
“Controlled” Total hydrograph
“Controlled” Watershed A
Watershed APre-Development
TRADITIONAL SWM STANDARDS: UNDER ACT 167
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3 Technical Components:
• Volume Control
• Rate Control
• Water Quality Treatment BIO-RETENTION [RAIN GARDENS] CAN PROVIDE ALL
THREE COMPONENTS
BIO-RETENTION [RAIN GARDENS] CAN PROVIDE ALL
THREE COMPONENTS
CURRENT SWM STANDARDS: UNDER ACT 167
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Focus is on volume control
Why?
• The majority of rainfall occurs
during small storms
• Provides benefits during all
storms (Tech Components)
• Increases groundwater
recharge
• Assumed to meet WQ
standardsDistribution of precipitation by storm magnitude ( Or ig in a l D a te fr o m Pe n n S t a te C l i m a t o l og ic a l O f f ic e, 1 9 2 6- 2 0 0 3 )
2-year, 24-hour design storm = 2.50 inches2-year, 24-hour design storm = 2.50 inches
CURRENT SWM STANDARDS: UNDER ACT 167
Focus on volume control:
How do we remove volume?
• LID / Green Infrastructure
• Non-Structural BMPs
• Structural BMPs
What are the physical processes
employed ?
• Infiltration
• Evapotranspiration
• Capture and Reuse
CURRENT SWM STANDARDS : UNDER ACT 167
LID / GREEN INFRASTRUCTURE
What is Low Impact Development (LID)?
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S o u r c e: L I D T e c hn i c a l G u i d an c e M an u a l f o r P u g e t S o un d ( 2 0 0 5 )
Core Design Principals of LID:
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Uses Best Management
Practices (BMPs). What are
they?
• Non-Structural
• Structural
���� Prevention
���� Mitigation
Reduce Impervious Area Disconnect Downspouts
Vegetated SwaleRain Garden
Non-Structural BMPs
Structural BMPs
LID / GREEN INFRASTRUCTURE
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INTEGRATING SWM W/DESIGN - Residential
BUTLER COUNTY ACT 167 PLAN and Model Ordinance
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Sizing Criteria Description of Stormwater Sizing Criteria
Volume Control –Using Design Storm
(CG1)
Regulation of the 2-year storm event:
• No Increase in the post development total runoff
• Applicable for any size of regulated activity
• No increase in total runoff volume for the 2-yr/24-yr event
• Consider existing non-forest pervious area as meadow
• 20% of existing impervious area considered as meadow
Volume Control -
Using SimplifiedMethod
(CG2)
Regulation of stormwater runoff from new impervious:
• capture of first 2” of runoff
• 1” of captured runoff shall be permanently removed
• ½” of captured runoff shall be infiltrated
Peak Rate Controls No Increase in the post development total runoff rate
Water Quality
Calculations
BMP Control of 90% of Disturbed Area
Specific BMP’s for Pollution Prevention
Pollutant Load Estimates
Pollutant Load Reduction for BMP’s
Nitrate (N), Total Suspended Solids (TSS), and Total Phosphate(TP) Requirements
MODEL ORDINANCE – Control Standards
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MODEL ORDINANCE – Release Rates
MODEL ORDINANCE – Exemptions
New Impervious Area1, 2
(square footage)Applicant Must Provide
0 – 2,500 No Submission is required
2,500 – 5,000 Documentation of Impervious surfaces3
> 5,000Rate Controls, Volume Controls & SWM Site
Plan
NOTES:
1 New Impervious Area since the date of Adoption of this Ordinance.
2 Gravel in existing condition shall be considered pervious and gravel inproposed condition shall be considered impervious.
3 The Small Project Stormwater Management Application included inAppendix E shall be used to document new impervious surfaces.
MODEL ORDINANCE – Exemptions
1. Comply with Sections 301.G,
MODEL ORDINANCE – Exemptions
2. Comply with Sections 302.A,
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MODEL ORDINANCE – Exemptions
2. Comply with Sections 302.B,
MODEL ORDINANCE – Exemptions
2. Comply with Sections 302.C,
MODEL ORDINANCE – Exemptions
MODEL ORDINANCE– Small Project Application
• Simple Process using Application.
• 5,000 SF threshold for Volume Control.
• Can be integrated into the building permit process.
MODEL ORDINANCE– Small Project Example
+75’
MODEL ORDINANCE– Small Project Example
0.65 acre lot
New garage
Paved Driveway
MODEL ORDINANCE– Bigger Project Example
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MODEL ORDINANCE – Waivers
Must meet the provisions of Section
303.G and 303.H.
Cannot issue waivers if conditions
prevent -
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The Technical/Construction
Standards are at discretion of the
municipality
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MODEL ORDINANCE – Waivers
Section 303.G (Municipality may
impose reasonable conditions to
substantially meet objectives of the
requirements that are to be
modified.)
Example:
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MODEL ORDINANCE – Waivers
Section 303.H (Lists items that will
guide Municipalities in granting
waivers.)
Example:
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MODEL ORDINANCE – Technical Criteria
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MODEL ORDINANCE – Easements
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Maintenance
Inspections of Facilities
Enforcement Options
Fees
MODEL ORDINANCE – Miscellaneous
Questions