Bernie EngelPurdue 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

• Ecologically Sensible• Provides Added Values / Ecosystem Services• Economically Sustainable• Lower Costs (Construction, Maintenance &

Operation) vs. Conventional• Multifunctional Practices• Ideal for Urban Retrofit

Minimization– Reduce imperviousness

– Soil Compaction

Storage, Detention & Filtration Rain gardens Drainage swales Green roofs Porous Pavement

Conservation Forest/Woods

Infiltrable Soils

http://cobweb.ecn.purdue.edu/runoff/lthianew/lidIntro.htm

LID Major Components LID Major Components

1. Conservation 1. Conservation (Watershed and Site Level) (Watershed and Site Level)

2. Minimization 2. Minimization (Watershed and Site Level) (Watershed and Site Level)

3. Integrated Management Practices 3. Integrated Management Practices (Site Level)(Site Level)

L-THIA ModelL-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• 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

ResultsWithout 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%

SummaryL-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/