Southeast Michigan LID Techniques

What is an LID Technique?

Low Impact Development (LID) is an innovative stormwater management approach with a basic principle to manage rainfall at the source using uniformly distributed, decentralized small-scale controls. LID's goal is to mimic a site's predevelopment hydrology by using design techniques that infiltrate, filter, store, evaporate, and detain runoff close to its source. Techniques are based on the premise that stormwater management should not be stormwater disposal. Instead of conveying and managing / treating stormwater in large, costly, end-of-pipe facilities located at the bottom of drainage areas, LID addresses stormwater through small, cost-effective landscape features located at the lot level. Southeast Michigan Council of Governments and other member governments are active participants in LID and together formed the Southeast Michigan LID team, which provides a venue for implementing LID. The LID Techniques are versatile in treating urban redevelopments, new developments and also transportation corridors. LID has numerous benefits and advantages over conventional stormwater management approaches. It is a more environmentally and economically sustainable technology in addressing the adverse impacts of urbanization.

The benefits of LID include:

1. Improvement of community livability
2. Restoration of urban fisheries
3. Protecting sensitive habitats
4. Meeting regulatory obligations
5. Integrating local greenways initiative

Source: http://www.semcog.org/LowImpactDevelopment.aspx

Rain Gardens

Bioretention areas (often called rain gardens) are shallow surface depressions planted with specially selected native vegetation to capture and treat stormwater runoff from rooftops, streets, and parking lots. Bioretention is a method of managing stormwater by pooling water within a planting area and allowing the water to infiltrate the garden. In addition to managing runoff volume and reducing peak discharge rates, this process filters suspended solids and related pollutants from stormwater runoff. (Low Impact Development Manual for Michigan 2008)

Variations in design include:

• Subsurface storage/ infiltration
• Use of underdrain
• The use of impervious linear

Key design features include:

• Flexible in size and infiltration
• Ponding depths 6-18 inches for drawdown within 48 hours
• Provide positive overflow for extreme storm events
• Amend soil is needed
• Native Plants

Green Roofs

Vegetated roofs, or green roofs, are conventional rooftops that include a thin covering of vegetation allowing the roof to function more like a vegetated surface. The overall thickness of the vegetated roof may range from 2 to 6 inches, typically containing multiple layers consisting of waterproofing, synthetic insulation, non-soil engineered growth media, fabrics, synthetic components, and foliage. (Low Impact Development Manual for Michigan 2008)

Variations in design include:

• Intensive vegetated roofs utilize a wide variety of plant species that may include trees and shrubs, require deeper substrate layers (usually > four inches), are generally limited to flat roofs, require 'intense' maintenance, and are often park-like areas accessible to the general public.
• Extensive vegetated roofs are limited to herbs, grasses, mosses, and drought tolerant succulents such as sedum, can be sustained in a shallow substrate layer (< four inches), require minimal maintenance once established, and are generally not designed for access by the public. These vegetated roofs are typically intended to achieve a specific environmental benefit, such as rainfall runoff mitigation. Extensive roofs are well suited to rooftops with little load bearing capacity and sites which are not meant to be used as roof gardens. The mineral substrate layer, containing little nutrients, is not very deep but suitable for less demanding and low-growing plant communities.
• Semi-intensive vegetated roofs fall between intensive and extensive vegetated roof systems. More maintenance, higher costs and more weight are the characteristics for this intermediate system compared to that of the extensive vegetated roof.

Additional Links:

http://www.ltu.edu/stormwater/greenroof.asp
http://www.greenroofs.org/
http://www.epa.gov/hiri/strategies/greenroofs.html
http://www.hrt.msu.edu/greenroof/
http://www.bae.ncsu.edu/greenroofs/

Porous Pavements

A porous pavement system consists of a permeable surface underlain by a storage reservoir to facilitate stormwater capture and infiltration. The permeable surface can consist of porous asphalt, porous concrete, concrete paver blocks, or reinforced turf. The storage reservoir may consist of a stone bed of uniformly graded and clean-washed course aggregate, 1-1/2 to 2-1/2 inches in size, with a void space of at least 40% or other pre-manufactured structural storage units.

Naturalized Areas

Naturalized Areas is a general term for actively incorporating or restoring sustainable landscaping practices that mimic natural conditions including a reduced dependence on watering and fertilization. These can be incorporated into existing stormwater BMPs, such as naturalized detention basins, but are more commonly found in the context of a riparian (or other specially protected) buffer areas. Native or naturalized areas includes the restoration of forest (i.e. reforestation), savanna, and/or meadow and the conversion of turf to meadow.

LEED Projects

The Leadership in Energy and Environmental Design (LEED) certification encourages and accelerates global adoption of sustainable green building and development practices by creating and implementing widely understood and accepted tools and performance criteria. LEED has developed rating systems for a myriad of development scenarios, including new construction, existing buildings, commercial interiors, core and shell, schools, retail, healthcare, homes, and neighborhood development. As with Smart Growth, there are significant connections between LID and LEED certification. In fact, LID practices are integrated into each of the LEED rating systems.

(Low Impact Development Manual for Michigan 2008)

BioSwales

A vegetated swale (or bioswale) is a shallow stormwater channel that is densely planted with a variety of grasses, shrubs, and/or trees designed to slow, filter, and infiltrate stormwater runoff. Check dams can be used to improve performance and maximize infiltration, especially in steeper areas. (Low Impact Development Manual for Michigan 2008)

Variations in design include:

• Vegetated swales with infiltration trenches
• Linear wetland swale
• Grass Swale

Key design features include:

• Handles the 10-year storm event with some freeboard
• Two-year storm flows do not cause erosion
• Maximum size is five acres
• Bottom width of two to eight feet
• Side slopes from 3:1 (H:V) to 5:1
• Longitudinal slope from one to six percent
• Check dams can provide additional storage and infiltration.

Riparian Projects:

A riparian buffer is the area of land that exists between low, aquatic areas such as rivers, streams, lakes, and wetlands, and higher, dry upland areas such as forests, farms, cities, and suburbs. Unaltered riparian buffers may exist as various types of floodplain forest or wetland ecosystems. The Michigan Natural Features Inventory (MNFI) has identified multiple types of distinct natural communities which may occur in Michigan's riparian areas, such as southern floodplain forest, southern wet meadow, emergent marsh, and hardwood conifer swamp.

(Low Impact Development Manual for Michigan 2008)

Key design features consist of three distinct codes:

• Zone 1: Streamside zone extends a minimum distance of 25 feet.
• Zone 2: Middle zone extends immediately from the outer edge of Zone 1 for a minimum distance of 55 feet.
• Zone 3: Outer zone extends a minimum of 20 feet immediately from outer edge of Zone 2.