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Low
Impact Development |
What is Low Impact Development?
Web Resources &
Fact Sheets
Low Impact Development or LID is the practice of
taking steps during development design to minimize changes to the
hydrologic cycle (runoff and infiltration after a storm). LID strategies
integrate green space, native landscaping, natural hydrologic functions,
and various other techniques to generate less runoff from developed
land (NRDC,
Stormwater Strategies 2001 Report).
Many innovative site designs and stormwater management
practices are grouped together under the heading of LID. Examples
of these strategies include open space planning, constructed stormwater
wetlands, and filter strips.
Have
you played LID Play? Download this interactive game ...
Incorporating vegetation and
pervious surfaces into a
hardened landscape provides infiltration areas for stormwater.
Why consider LID?
LID has many practical and economical
benefits for communities looking to improve the quality of their
stormwater runoff. According to the EPA report Low
Impact Development, A Literature Review, October 2000 "In
general LID measures are more cost effective and lower in maintenance
than conventional, structural stormwater controls. Not all sites
are suitable for LID. Considerations such as soil permeablility,
depth of water table and slope must be considered, in addition to
other factors. Further, the use of LID may not completely replace
the need for conventional stormwater controls."
The following information is taken
from Low
Impact Development, A Literature Review
LID Pollutant Removal
Several studies have been conducted
to analyze the effectiveness of various LID practices based on hydrology
and pollutant removal capabilities. Bioretention areas, grass swales,
permeable pavements and vegetated roof tops were the most common
practices studied.
In general bioretention areas were found to be
effective in reducing runoff volume and in treating the first flush
(first ½ inch) of stormwater. Results from three different
studies indicate that removal efficiencies were quite good for both
metals and nutrients. Removal rates for metals were more consistent
than for nutrients. Removal rates for metals ranged from 70–97%
for lead, 43–97% for copper and 64–98% for zinc. Nutrient
removal was more variable and ranged from 0–87% for phosphorus,
37–80% for Total Kjeldahl Nitrogen, <0–92% for ammonium
and for nitrate <0–26%. Effluent volumes were lower than
influent volumes.
The effectiveness of grass swales was also quite
good for both pollutant removal and runoff volume reduction. In
general, performance of swales is dependant on not only channel
length, but also longitudinal slope and the use of check dams to
slow flows and allow for greater infiltration. Further, the removal
of metals was found to be directly related to the removal rate of
total suspended solids, and the removal rate of metals was greater
than removal of nutrients.
Reduction of impervious surfaces can greatly reduce the volume of
runoff generated by rainfall. Several methods can be employed to
reduce total impervious surface area. Permeable pavements
and vegetated rooftops are two methods to accomplish
this goal. Vegetated rooftops have been used extensively in Germany
for more than 25 years and results show up to 50% reduction in annual
runoff in temperate climates.
Permeable pavements can also reduce impervious
surfaces. However, they are more expensive to construct than traditional
asphalt pavements. Costs of these systems may be off set by the
reduction of traditional curb and gutter systems to convey stormwater.
Benefits of these alternate pavement types include better infiltration,
ground water recharge, reduction in runoff volume and treatment
of stormwater for pollutants.
Maintenance Issues
Maintenance issues for LID can be more
complicated than for conventional stormwater controls if the LID
measures reside on private property. Generally, bioretention facilities
require replacement of dead or diseased vegetation, remulching as
needed, and replacement of soils after 5–10 years. Grass swales
require periodic mowing and removal of sediments. Maintenance of
permeable pavements requires annual high-powered vacuuming or scouring
of the area to remove sediments.
Who is doing LID?
Many communities are turning to LID
to assist with stormwater management. Conventional solutions to
handling stormwater runoff are not always compatible with community
interests, or local, state, and federal water quality regulations.
Prince
George's County, Maryland has pioneered many stormwater management
practices and protective policies. The Puget
Sound Action Team has taken a leading role in promoting LID
in the Pacific Northwest
The benefits of LID can be large while
the accompanying costs may be lower than expected. Many studies
and reports have been completed that show benefits of LID along
with reasonable costs. A few examples are listed below - more information
may be found in the Web Resources
& Fact Sheets section.
Environmentally
Sensitive Low Impact Development
Low
Impact Development Strategies for Rural Communities
ToolBase
Services - The Home Building Industry's Technical Information Resource
LID in Action ...
Auburn University Building Science, Sherman Concrete and the
Alabama Concrete Industry partnered on several demonstration
projects.
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Contact John Sorrell, Director of Engineering, Alabama
Concrete Industries Association for more information on pervious
concrete in Alabama.
(800) 732-9118
Website: www.alconcrete.org
LID Resources
LID
Play!
Download the different scenarios and use the LID Flash Cards to
come up with solutions to development scenarios ... should be used
in group role plays.
LID Flash Cards (PowerPoint)
Set 1
Set 2
Set 3
LID Play Scenarios (Microsoft
Word)
Scenario 1 - Residential Development
(role play)
Scenario 1 -
11x17 Activity Sheet
Scenario 2 - Commercial
Development (role play)
Scenario 2 -
11x17 Activity Sheet
Scenario 3 - Park Renovation
(role play)
Scenario 3 - 11x17 Activity
Sheet
Learn more about ....
Green
Roofs
Rain Gardens
Rain Barrels
Permeable Pavement, NCSU BAE
Download North Donahue Parcel A (pdf)
North Donahue Parcel B (pdf)
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