1. Low Impact Development
Civil Engineering and Architecture
Unit 3 − Lesson Site Considerations
Low Impact Development
They took all the trees and put them in a tree museum and they charged all the people a dollar and a half just to see 'em. Don't it always seem to go that you don't know what you've got till it's gone? They've paved paradise and put up a parking lot.”
Joni Mitchell
Project Lead The Way, Inc.
Copyright 2010

2. Low Impact Development
Civil Engineering and Architecture
Unit 3 − Lesson Site Considerations
TABLE OF CONTENTS
Development and Storm Water Runoff
Storm Water Pollutants
Low Impact Development (LID)
Goals
Benefits
Common Practices
Project Lead The Way, Inc.
Copyright 2010

3. Development and Storm Water Runoff
Low Impact Development
Civil Engineering and Architecture
Unit 3 − Lesson Site Considerations
Development and Storm Water Runoff
40% evaporation
38% evaporation
10% runoff
20% runoff
25% shallow infiltration
21% shallow infiltration
25% deep
infiltration
21% deep
infiltration
Natural Groundcover
% Cover
35% evaporation
30% evaporation
Most development results in covering the ground with impervious surfaces such as buildings, roads, sidewalks, and parking areas. As the concentration of development increases, the percentage of the ground covered by impervious surfaces increases. Because rain water cannot penetrate impervious surfaces, the amount of storm water runoff from the area increases.
Notice that in a natural setting, only about 10 percent of rain runs off of the ground – the rest infiltrates or is released back into the atmosphere through evapotranspiration. In an urban environment, with 75 to 100 percent impervious cover, runoff increases to 55%.
Excessive storm water runoff disturbs the natural water cycles and can create serious consequences to the environment and human health.
55% runoff
30% runoff
20% shallow infiltration
15% deep
infiltration
10% shallow infiltration
5% deep
infiltration
35 – 50 %l Cover
% Cover
Project Lead The Way, Inc.
Copyright 2010

4. Storm Water Pollutants
Low Impact Development
Civil Engineering and Architecture
Unit 3 − Lesson Site Considerations
Storm Water Pollutants
Not treated – Flows directly to nearest stream
Picks up pollutants
Sediment
Pathogens
Nutrients
Toxic contaminants
Debris/litter
Storm water will follow the natural drainage path or be transported by man-made drainage infrastructure to the nearest water body. Contrary to popular belief, storm water is not transported to a water treatment facility – it flows into our water system without treatment.
As storm water runs across yards and parking lots, storm water picks up a multitude of pollutants.
Sediment is collected on construction sites and bare spots in lawns and gardens or is added to the system when it is washed off of cars or when stream beds are eroded. Sediment can destroy aquatic habitat and cause marine navigational problems.
Pathogens can be introduced to the storm water system from pet waste or malfunctioning septic systems. This can be a serious risk to human health.
Nutrients from fertilizers, grass clippings, and leaves can increase algae production in down-stream water bodies.
Toxic contaminants from car and truck exhaust, debris, oil and gas spills, and pesticides create a serious risk to aquatic life.
Debris and litter (like plastic bags, six-pack rings, cigarettes, etc.) can create risks for human and aquatic life. Such debris is also ugly when deposited along roadsides and in water bodies.
©iStockphoto.com
Project Lead The Way, Inc.
Copyright 2010

5. Low Impact Development (LID)
Civil Engineering and Architecture
Unit 3 − Lesson Site Considerations
Low Impact Development (LID)
A storm water management approach that uses green space, native landscaping, and other techniques to reduce the volume of and improve the quality of storm water runoff.
Low Impact Development is a storm water management system intended to reduce the negative impacts of storm water runoff by reducing the quantity of storm water that runs off of a property. Low Impact Development also strives to improve the quality of the water that exits the property.
Project Lead The Way, Inc.
Copyright 2010

6. Low Impact Development
Civil Engineering and Architecture
Unit 3 − Lesson Site Considerations
Goals of LID
Mimic predevelopment hydrology
Reduce storm water runoff and pollution
Store
Treat
Infiltrate
Water collected on site can be stored. Storage allows evaporation or slow infiltration of the water. It also provides a means to use the water for nonpotable purposes such as irrigation or toilet flushing.
LID improves water treatment of storm water in several ways – physical treatment such as filtration when water passes through plants or soils, chemical treatment such as ion exchange and organic complexing, and biological treatment such as microbial decomposition.
LID provides a means for water to slowly infiltrate and replenish ground water.
This image shows a landscaped area that breaks up impervious surfaces and provides a collection point to temporarily store, treat, and allow the water to infiltrate the ground.
EPA
Project Lead The Way, Inc.
Copyright 2010

7. Low Impact Development
Civil Engineering and Architecture
Unit 3 − Lesson Site Considerations
Benefits
Effective
Economical
Flexible
Adds value
Effective – LID is relatively simple to implement and is effective at reducing storm water runoff and pollutants.
Economical – LID often costs less than conventional storm water management; fewer pipes and below ground infrastructure requirements.
Flexible – LID techniques include a wide variety of opportunities to reduce runoff speed and volume and improve quality. These techniques can be tailored to site-specific conditions.
Adds value – Preserves natural features of the landscape resulting in more aesthetic value of the property. Also provides flood control, conserves wildlife habitat, increases the area of property available for other uses.
Project Lead The Way, Inc.
Copyright 2010

8. Low Impact Development
Civil Engineering and Architecture
Unit 3 − Lesson Site Considerations
Common LID Practices
Rain gardens and bioretention
Rooftop gardens
Vegetated swales, buffers, and strips
Rain barrels and cisterns
Permeable pavers
Permeable pavement
Impervious surface reduction
The best way to reduce the impact of storm water is to keep the water close to the source. LID techniques concentrate on treating, storing, and infiltrating the runoff onsite before it can enter the local storm water system and affect downstream water bodies.
Project Lead The Way, Inc.
Copyright 2010

9. Low Impact Development
Civil Engineering and Architecture
Unit 3 − Lesson Site Considerations
Common LID Practices
Rain gardens and bioretention
A rain garden can collect water from impervious surfaces such as roofs and parking lots.
A rain garden or bioretention area is a shallow depression that is integrated into the landscape that captures runoff and allows the water to evaporate or infiltrate the soil. A rain garden typically has plant life chosen to bind nutrients and other pollutants, to remove water through evapotranspiration, and to promote infiltration through root development.
Image by the Environmental Protection Agency
Project Lead The Way, Inc.
Copyright 2010

10. Low Impact Development
Civil Engineering and Architecture
Unit 3 − Lesson Site Considerations
Common LID Practices
Green roof
A green roof captures rainfall and promotes evaporation. An added bonus is the improved energy efficiency of the building.
Image by the Environmental Protection Agency
Courtesy Eric Fisher
Project Lead The Way, Inc.
Copyright 2010

11. Low Impact Development
Civil Engineering and Architecture
Unit 3 − Lesson Site Considerations
Common LID Practices
Vegetated swales, buffers, and strips
Vegetated swales (left) promote infiltration and can improve the quality of the storm water as it moves through the plant material.
Strips of vegetation and landscaping (right) within impervious surfaces provide opportunities to store, treat, and infiltrate water.
Courtesy Eric Fisher
Image by the Environmental Protection Agency
Project Lead The Way, Inc.
Copyright 2010

12. Low Impact Development
Civil Engineering and Architecture
Unit 3 − Lesson Site Considerations
Common LID Practices
Rain barrels and cisterns
Storm water collected from roof gutters and drains can be stored in rain barrels (like that shown in the picture) or cisterns, which are underground tanks, and can be used to irrigate landscaping or other nonpotable needs such as flushing toilets.
©iStockphoto.com
Project Lead The Way, Inc.
Copyright 2010

13. Low Impact Development
Civil Engineering and Architecture
Unit 3 − Lesson Site Considerations
Common LID Practices
Permeable pavers
Permeable pavers allow the movement of air and water around the paving material so that it may infiltrate the soil below.
Image by the Environmental Protection Agency
Project Lead The Way, Inc.
Copyright 2010

14. Low Impact Development
Civil Engineering and Architecture
Unit 3 − Lesson Site Considerations
Common LID Practices
Permeable pavement
Permeable pavement is different from permeable pavers in that the paving material is porous and allows water to drain through to a gravel bed below. From there the water can infiltrate into the soil. Permeable pavement typically looks like asphalt or concrete but is made without fine material creating voids in the pavement.
Image by the Environmental Protection Agency
Project Lead The Way, Inc.
Copyright 2010

15. Low Impact Development
Civil Engineering and Architecture
Unit 3 − Lesson Site Considerations
Common LID Practices
Impervious surface reduction
Another way to reduce runoff is to reduce the area of impervious pavement. Concrete and asphalt should not be used more than absolutely necessary, and alternative materials, such as gravel for walkways, should be used when possible.
Some municipalities have revised regulations to allow fewer parking spaces or shared parking, smaller parking space sizes, and/or narrower streets under certain circumstances.
©iStockphoto.com
Project Lead The Way, Inc.
Copyright 2010

16. Conventional Versus LID Site Design
Low Impact Development
Civil Engineering and Architecture
Unit 3 − Lesson Site Considerations
Conventional Versus LID Site Design
Many of you may live in homes with conventional landscaping consisting mostly of turf. An alternative LID design is shown in the plan on the right in which existing natural vegetation in the woods are to be preserved and includes less turf, a bioretention area, and a vegetated swale. Also note the reduced road width that is sometimes allowed by municipal regulations.
Conventional
Site Design
Low Impact Development
Site Design
Project Lead The Way, Inc.
Copyright 2010

17. Low Impact Development
Civil Engineering and Architecture
Unit 3 − Lesson Site Considerations
LID Commercial Design
The site design for the EPA headquarters incorporates several LID techniques including a bioretention cell (or area), a cistern, permeable concrete pavement, and permeable block pavers.
Image by the Environmental Protection Agency
Project Lead The Way, Inc.
Copyright 2010

18. Low Impact Development
Civil Engineering and Architecture
Unit 3 − Lesson Site Considerations
LID Commercial Design
Image by the Environmental Protection Agency
The rendering shows a perspective view of the EPA courtyard. The photograph in the bottom right is a photograph of the finished project. The courtyard is adjacent to a parking area and is designed to capture runoff from the impervious surface.
Image by the Environmental Protection Agency
Project Lead The Way, Inc.
Copyright 2010

19. Low Impact Development
Civil Engineering and Architecture
Unit 3 − Lesson Site Considerations
TABLE OF CONTENTS
Development and Storm Water Runoff
Storm Water Pollutants
Low Impact Development (LID)
Goals
Benefits
Common Practices
Project Lead The Way, Inc.
Copyright 2010

20. Low Impact Development
Civil Engineering and Architecture
Unit 3 − Lesson Site Considerations
Resources
Bioretention.com: An online reference for designers. (n.d). Retrieved Dec. 15,2009 from Department of Environmental Resources of Prince George’s County, Maryland. (1999). Low-Impact Development Design Strategies –An Integrated Design Approach. Retrieved December 15, 2009, from Environmental Protection Agency. (n.d). Stormwater management best practices. Retrieved December 15, 2009, from meablepavers Low Impact Development Center, Inc. (n.d.). Urban design tools. Retrieved December 15, 2009, from
Project Lead The Way, Inc.
Copyright 2010

21. Low Impact Development
Civil Engineering and Architecture
Unit 3 − Lesson Site Considerations
Low Impact Development
Project Lead The Way, Inc.
Copyright 2010