Transcript Document

Bernie Engel
Purdue University
Low-Impact Development (LID)
An approach to land development to mimic
the pre-development site hydrology to:
1) Reduce volume of runoff
2) Decentralize runoff, diffusing flows into
smaller retention/detention areas
3) Improve water quality
4) Encourage groundwater infiltration
Adapted from Prince George's County, MD, LID IMP Guidance Document, 2002. www.lid-stormwater.net
LID Benefits
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Ecologically Sensible
Provides Added Values / Ecosystem Services
Economically Sustainable
Lower Costs (Construction, Maintenance &
Operation) vs. Conventional
• Multifunctional Practices
• Ideal for Urban Retrofit
LID Major Components
1. Conservation (Watershed and Site Level)
2. Minimization (Watershed and Site Level)
3. Integrated Management Practices (Site Level)
 Conservation
 Storage, Detention & Filtration
 Forest/Woods
 Rain gardens
 Infiltrable Soils
 Drainage swales
 Green roofs
 Minimization
 Porous Pavement
– Reduce imperviousness
– Soil Compaction
http://cobweb.ecn.purdue.edu/runoff/lthianew/lidIntro.htm
L-THIA Model
• Long-Term Hydrologic Impact Assessment
– Average annual runoff
– NPS pollution
• An overview / screening model
• User friendly tool
• Does not require detailed data input
• Identifies need for more detailed modeling
• Provides "What-If" alternatives evaluation
scenarios
Inputs to Model
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Lot – High density residential, ¼ acre lot
Soil Type B
Impervious land area - 0.047 Acres
LID implementations
– Rain Barrel
– Bio-retention / rain gardens – 0.007 acres
• Impervious land area – 0.047 Acres
– House – 1650 sq. ft
– Driveway – 384 sq. ft
Results
Without LID
With LID
% reduction
Runoff depth (in)
2.82
2.59
14.9%
Runoff Volume
1.4
1.19
15%
Non Point Source pollution
-Nitrogen (lb)
0.054
0.0.046
14.8%
-Phosphorous (lb)
0.017
0.014
17.7%
- BOD (lb)
0.764
0.065
15%
-Oil & Grease
(lbs)
.043
.05
14%
Summary
L-THIA LID is a screening tool to evaluate the
benefits of LID practices
L-THIA LID provides an easy to use interface
Will enable decision makers to formulate
watershed management plans to meet goals
Along with other tools, allows stakeholders to
understand impacts of water quantity and
quality resulting from land use change
http://cobweb.ecn.purdue.edu/~watergen/