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/