Bernie Engel, Larry Theller, James Hunter 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,

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

LID Hydrologic Analysis - CN Curve number & consequential runoff / NPS is affected by:  Soil Type  Landuse / Site Envelope  Site imperviousness  Vegetation  Disconnection of site imperviousness

LID Hydrologic Analysis - CN Prince George’s County, Department of Environmental Resources Low--Impact Development Hydrologic Analysis, July 1999

TR-55 Hydrologic Analysis – CN % Impervious Hydrologic soil type A B C D

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

Data requirements and components for analysis in L-THIA Soils Land use Curve Number values Daily precipitationLocation Runoff depths NPS pollutants Runoff volumes User supplied information Performed by L-THIA L-THIA Model

L-THIA LID

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

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

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

For more information and a list of tools: –L-THIA –L-THIA LID –Web-GIS tools (Online LTHIA) for Spatial Hydrologic Analysis

Preliminary Evaluation of LID for Pendleton, IN

Using web-based tools to delineate and capture watershed, land use, and soils data for L-THIA input

Current Landuse (from L-THIA) LanduseAcresPercent Agriculture % 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

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

Using L-THIA LID Basic – Reducing Impervious Surface by 10% Reduces runoff by 23%

Using L-THIA LID Lot Level Purdue University is an Equal Opportunity/Equal Access institution. Reduce street width from 26ft. to 18ft. Rain barrels for Residential Green Roofs for Commercial Bioretention/Raingardens Reduces Post-developed runoff by 46%

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 