Web-based Low Impact Development Decision Support and Planning Tool

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Web-based Low Impact Development Decision Support
and Planning Tool
Bernie Engel, Larry Theller, James Hunter Purdue
University
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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

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Adapted from Prince George's County, MD, LID IMP
Guidance Document, 2002. www.lid-stormwater.net
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Adapted from Prince George's County, MD, LID IMP
Guidance Document, 2002. www.lid-stormwater.net
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LID Benefits

• Ecologically Sensible
• Provides Added Values / Ecosystem Services
• Economically Sustainable
• Lower Costs (Construction, Maintenance
  Operation) vs. Conventional
• Multifunctional Practices
• Ideal for Urban Retrofit

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LID Major Components
1. Conservation (Watershed
and Site Level) 2. Minimization (Watershed and
Site Level) 3. Integrated Management Practices
(Site Level)

• Minimization
• Reduce imperviousness
• Soil Compaction

https//engineering.purdue.edu/mapserve/LTHIA7/lth
ianew/lidIntro.htm
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LID Hydrologic Analysis - CN

• Curve number consequential runoff / NPS is
  affected by
• Soil Type
• Landuse / Site Envelope
• Site imperviousness
• Vegetation
• Disconnection of site imperviousness

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LID Hydrologic Analysis - CN
Prince Georges County, Department of
Environmental Resources Low--Impact Development
Hydrologic Analysis, July 1999
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TR-55 Hydrologic Analysis CN
Hydrologic soil type
Impervious
A B C D
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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

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L-THIA Model
Data requirements and components for analysis in
L-THIA
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L-THIA LID
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Calculating a Custom LID CN

1. Determine the land use combination and soil type
2. Calculate composite CN without considering
   disconnection of imperviousness (Watershed and
   site level)
3. Where impervious area is lt 30 of site, adjust CN
   for disconnected impervious area (Site level)

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L-THIA LID Basic

• Application Target preliminary goals at the
  
• watershed and site level
• Reduce imperviousness
• Conserve infiltratable soils
• Conserve functional / sensitive landscape
• Minimize land disturbances
• Anticipate need for other LID practices to reduce
  NPS and stormwater volume

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https//engineering.purdue.edu/mapserve/LTHIA7/lth
ianew/lidIntro.htm
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L-THIA LID Lot Level Screening Tool

• Application Target preliminary goals by
  adjusting lot level features
• Site Design Development preparation
• Narrowing impervious areas (sidewalks, driveways,
  roads)
• Natural resource preservation
• Heavy equipment use ? compaction
• Permeable paving materials
• Vegetative roof systems
• Bioretention cells
• Vegetated swales /Filter strips
• Rain barrels
• Disconnect impervious areas

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For more information and a list of tools

• https//engineering.purdue.edu/lthia/
• L-THIA
• L-THIA LID
• Web-GIS tools (Online LTHIA) for Spatial
  Hydrologic Analysis

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Preliminary Evaluation of LID for Pendleton, IN
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Using web-based tools to delineate and capture
watershed, land use, and soils data for L-THIA
input
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Current Landuse (from L-THIA)
Landuse Acres Percent
Agriculture 1278 73
Forest 70 4
Grass/Pasture 105 6
Commercial 53 3
Industrial 17 1
HD-Residential 87 5
LD-Residential 105 6
Water 35 2
Current Curve Number 77
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Assumption For Max. Development Scenario

• 983 Acres Commercial / Mixed Residential
• Most Agriculture 55 B Soils, 45 C Soils
• Current CN 78
• Post Developed w/o LID CN 84
• Post Developed w/ LID CN ? 76-82

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Using L-THIA LID Basic Reducing Impervious
Surface by 10
Reduces runoff by 23
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Using L-THIA LID Lot Level

• Reduce street width from 26ft. to 18ft.
• Rain barrels for Residential
• Green Roofs for Commercial
• Bioretention/Raingardens

Reduces Post-developed runoff by 46
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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
• https//engineering.purdue.edu/lthia/