Metro Boston Stormwater / Low Impact Development Capacity Building Project

Lexington & Wakefield

1 st Workshop - February 7, 2007 Wakefield Town Hall Slide show prepared by: Metropolitan Area Planning Council With funding provided by Massachusetts Office of Coastal Zone Management

Reasons for Stormwater Management:

IMPACT OF DEVELOPMENT

Typical pre-development conditions: Runoff = 10% Infiltration = 50%

Reasons for Stormwater Management:

IMPACT OF DEVELOPMENT

Typical post-development conditions: Runoff = 55% Infiltration = 15%

Reasons for Stormwater Management:

• Stormwater quality • Stormwater quantity – flooding • Groundwater – recharge • National Pollution Discharge Elimination System (NPDES) requirements

STORMWATER MANAGEMENT POLICY

• Clean Water Act (CWA) – Phase II • National Pollution Discharge Elimination System (NPDES) - Phase II Objectives

STORMWATER MANAGEMENT PROGRAM

(Phase II):

1. Public Education & Outreach 2. Public Involvement 3. Illicit Discharge Detection & Elimination 4. Construction Site Stormwater Runoff Control 5. Post Construction Stormwater Management For New Development and Redevelopment 6. Pollution Prevention / Good Housekeeping For Municipal Operations

STORMWATER MANAGEMENT PROGRAM

(Phase II):

• Zoning, subdivision, site plan review, and other existing permitting processes • Stormwater bylaws / ordinances and regulations • Inspection and enforcement activities • System inventory / mapping • Operations and maintenance • Capital projects • Project administration • Funding (e.g. Stormwater Utility)

What is

Low Impact Development?

• • • • Comprehensive, landscape-based approach to sustainable development Set of strategies to maintain existing natural systems, hydrology, ecology Cost-effective, flexible approach based on a toolkit of simple techniques Collection of practices that have been implemented nationwide

What is

Low Impact Development?

• • • • • NOT rocket science NOT formulaic NOT the answer to every challenge NOT yet finished evolving NOT common in Massachusetts

WHY DO WE NEED LOW IMPACT DEVELOPMENT?

C

onventional strategies aren’t working

• • • • • Increased runoff & decreased recharge Loss of vegetation and wildlife habitat Loss of community character Polluted waterways Cost of development

LID PRINCIPLES

1.

Work with the existing landscape 2.

Focus on prevention 3.

Practice micromanagement 4.

Emphasize simplicity 5.

Practice multi-tasking 6.

Maintain and sustain

• • • •

LID PRINCIPLES 1. Use existing natural systems as the integrating framework for site planning

Land use planning and watershed planning Identify environmentally sensitive resources: wetlands, mature trees, slopes, drainageways, permeable soils, waterway buffers Assess existing hydrology Define a development envelope

LID PRINCIPLES 2. Focus on prevention

• • • • • • Minimize clearing and grading Cluster buildings and reduce building footprints Reduce road widths, use shared driveways, reduce parking area Align roads to minimize impact Use green rooftops Use permeable paving

LID PRINCIPLES 3. Treat stormwater close to the source

• • • • Create subwatersheds and “micromanage” runoff in a treatment train of small structures Flatten slopes, lengthen flow paths, maximize sheet flow Maintain natural flow paths, use open drainage Use LID techniques to manage frequent, low-intensity storms

• • • • • • •

LID PRINCIPLES 4. Emphasize simple, nonstructural, low-tech, low-cost methods

Open drainage systems and filter strips Disconnection of roof runoff Rain barrels Street sweeping Public education Reduce construction disturbance Minimize lawn area

LID PRINCIPLES 5. Create a multifunctional landscape

• • • • • Use stormwater management components that provide filtration, treatment, and infiltration. Provide open space and wildlife habitat.

Store water for landscape use Reduce heat island effect Enhance site aesthetics

LID PRINCIPLES 6. Maintain and sustain

• • • • Reduce use of pesticides and fertilizers. Use drought-resistant plants.

Maintain rain gardens and bioretention areas.

Provide adequate funding for public works departments

LID STRATEGIES

• • • • • • • Low impact site design • • Stormwater Management Buildings and Roadways Roadways and Parking Areas Permeable paving Bioretention Vegetated Swales Rain Barrels and Cisterns Green Roof Systems

LID STRATEGIES Low Impact Site Design Conservation Typical Subdivision

• • • • • Conservation of natural hydrology, trees, vegetation Stream & wetland buffers Minimize impervious surfaces Stormwater micromanagement Ecological landscaping

LID STRATEGIES

Low Impact Site Design

Stormwater Management

• • • • Minimize directly connected impervious area Create multiple sub-watersheds Increase time of concentration Use a “treatment train” of LID techniques to deal with frequent, low-intensity storms.

LID STRATEGIES

Low Impact Site Design

Buildings and Roadways

• • • • • Cluster buildings within the development envelope Design buildings with smaller footprints Roadways should follow existing grades.

Use parking structures Separate parking areas

LID STRATEGIES Roadways and Parking Areas Road Profile

• • • • Narrower roadways (18-24 feet) Permeable parking lanes Open section roadways Alternative curb designs

LID STRATEGIES Roadways and Parking Areas Alternative Turnarounds

• • • • Smaller cul-de-sacs Bioretention islands One-way-loops Hammerhead turnarounds

LID STRATEGIES Roadways and Parking Areas Parking Lots

• • • • • Create multiple small lots Allow shared parking Reduce requirements near transit Require compact spaces Set parking maximums

LID STRATEGIES

Permeable Paving

Applications

• • • • Parking stalls Overflow parking Driveways Walkways and plazas

LID STRATEGIES

Bioretention

Treatment, retention, infiltration, landscaping

• • • • Excavation filled with engineered soil mix Herbaceous perennials, shrubs, trees Ponded water infiltrates within 72 hours Overflow outlet and optional underdrain

LID STRATEGIES Bioretention Applications

• • • Parking lot islands Median strips Rooftop runoff

LID STRATEGIES Vegetated Swales Conveyance, treatment, infiltration

• • • • Roadside swales “country drainage” Parking lots Low-angle slopes only Opportunity for snow storage

LID STRATEGIES Vegetated Swales Conveyance, treatment, infiltration

LID STRATEGIES Rain Barrels and Cisterns Runoff Reduction and Water Conservation

• • • • Downspouts directed to tanks or barrels 50 – 50,000 gallons Excess diverted to drywell or rain garden Landscaping, car washing, other nonpotable uses

LID STRATEGIES Rain Barrels and Cisterns Runoff Reduction and Water Conservation

LID STRATEGIES Green Roof Systems Runoff Reduction, Reduce Heating/Cooling Costs

• • • • Rainwater stored in a lightweight engineered soil medium Hardy, drought resistant vegetation Reduce runoff by 50% Not for use in stressed basins

LID STRATEGIES Green Roof Systems Applications