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

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

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

Assumptions Water flows across the surface to flowshed no storm drains Water equally spread across landscape No routing Average antecedent moisture soil is not saturated or frozen Rainfall is evenly spread in local area

Limitations Accuracy of landuse and soil data Big limitation Accuracy of runoff curve number Hydrological impacts are understated LID not reflected Accuracy of published NPS relationship Lead in runoff based on 1990’s models

Curve Number Basics: rainfall to runoff ratio for different surfaces Direct Runoff Rainfall http://www.ecn.purdue.edu/runoff/documentation/scs.htm

Averaged mass of NPS contaminant from each landuse EMC Table

Take-Home points DEM is only used to calculate flowshed DEM is not used for erosion – or runoff Runoff is based on surface type – not slope won’t account for frozen ground 30 year average rainfall Chemistry is based on landuse averages

Databases provide input Weather data (30 years of real rainfall) Soil data (SSURGO ) or STATSGO Elevation data 30m or 10m DEM (for contributing area)

L-THIA LID

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

Purdue University is an Equal Opportunity/Equal Access institution. LTHIA-Web with Online Watershed Delineation Region 5 States, visible on Google Maps ™. Flowshed is calculated from pour point then landuse and soil characteristics are loaded into model. https://engineering.purdue.edu/~lthia/ Purdue University is an Equal Opportunity/Equal Access institution.

Purdue University is an Equal Opportunity/Equal Access institution.

One Product of MSDSS partnership

Purdue University is an Equal Opportunity/Equal Access institution.

Purdue University is an Equal Opportunity/Equal Access institution.

Purdue University is an Equal Opportunity/Equal Access institution. Landuse and BMP Editor. Draw polygon by clicking corners, then right-click inside it to select landuse or BMP. Purdue University is an Equal Opportunity/Equal Access institution.

Purdue University is an Equal Opportunity/Equal Access institution. Landuse and Soil are automatically entered into spreadsheet Purdue University is an Equal Opportunity/Equal Access institution.

Tabular and Graphic results Purdue University is an Equal Opportunity/Equal Access institution.

Low-Impact Development (LID) An approach to land development to mimic the pre-development site hydrology to: Reduce volume of runoff Decentralize runoff, diffusing flows into smaller retention/detention areas Improve water quality Encourage groundwater infiltration Reduce runoff = managing stormwater volume and quality, reduce flooding

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

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

1. Conservation (Watershed and Site Level) LID Major Components 1. Conservation (Watershed and Site Level) 2. Minimization (Watershed and Site Level) 3. Integrated Management Practices (Site Level) Storage, Detention & Filtration Rain gardens Drainage swales Green roofs Porous Pavement Conservation Forest/Woods Infiltrable Soils Minimization Reduce imperviousness Soil Compaction http://cobweb.ecn.purdue.edu/runoff/lthianew/lidIntro.htm

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 Hydrologic soil type % Impervious A B C D Standard table from TR-55 assumes a certain % impervious cover. Engineers typically choose the CN corresponding to the lot size or urban type without calculating actual impervious %. If different % is different from the assumed value, TR-55 gives the option of using Figure 2-3. Must chose one pervious CN corresponding to one land cover and soil type.

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

Reduce volume of runoff Decentralize runoff, diffusing flows into smaller retention/detention areas Improve water quality

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: http://cobweb.ecn.purdue.edu/~watergen/ 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) Acres Percent Agriculture 1278 73% Forest 70 4% Grass/Pasture 105 6% Commercial 53 3% Industrial 17 1% HD-Residential 87 5% LD-Residential 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 Reduce street width from 26ft. to 18ft. Rain barrels for Residential Green Roofs for Commercial Bioretention/Raingardens Reduces Post-developed runoff by 46% Purdue University is an Equal Opportunity/Equal Access institution.

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/