L-THIA Online and LID in a watershed investigation

Larry Theller Agricultural and Biological Engineering,

Purdue University

Great Lakes Sedimentation Workshop Ann Arbor Mi.

L-THIA On-line watershed delineation and CN analysis

• Online map tool with delineation and landuse editing

• Exports to online spreadsheet with LID urban BMP evaluation

• Exports to Purdue’s web version of STEPL

L-THIA is CN Based analysis • Long-Term Hydrologic Impact

Assessment (L-THIA) – Average annual runoff – NPS pollution

• User friendly overview / screening model • Does not require detailed data input • Identifies need for more detailed modeling • Provides "What-If" alternatives evaluation

scenarios

L-THIA Science Curve Number (CN) runoff estimation DEM is only used to calculate watershed boundary

Daily Runoff is based on surface type – not slope for 30 year average rainfall

Nonpoint source pollutant loads based on landuse based event mean concentrations (EMC) and runoff

Databases provide input • Weather data (30 years of real

rainfall)

• Soil data SSURGO • NLCD 2006 Landuse

• Elevation data = NHD+ V2 30m (for contributing area)

Curve Number Analysis

•

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rainfall to runoff ratio for different surfaces

Direct Runoff

Rainfall (in)

Averaged mass of NPS contaminant from each landuse

EMC Table Purdue University is an Equal Opportunity/Equal Access institution.

Assumptions • Water flows across the surface to form

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

Disadvantages • No wetlands treatment option ( in CN

analysis wetlands don’t remove P…) • No routing • No erosion • Landuse pixel size defines analysis • We offer no information management

system 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:

1) Reduce volume of runoff 2) Decentralize runoff, diffusing flows into

smaller retention/detention areas 3) Improve water quality 4) Encourage groundwater infiltration

hh • hh)

• Microscale CN Adjustment • Based on the rainfall – land cover – runoff analysis

method already used in many communities • Input: Land Use Pattern(s) + Soils Pattern and

desired type and extent of BMP • Process: Daily Runoff and Pollutant Loading

Calculations (30 years) • Output: Average Annual Runoff and

NPS loads

Low-Impact Development (LID)

L-THIA LID Available Practices • porous pavement (narrow or pervious) • permeable or disconnected patios/sidewalks • rain barrel/cistern • green (vegetative) roof • bioretention/rain garden • grass swale • open wooded space –varying soil conditions

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BMPs at Lot Level

Each land use has a set of controls for LID practices. In this tutorial we have one post-developed land use, “High Density Residential” and two clusters of tools – because there are two soil types.

Soil Group B

Soil Group C

Land use

Outputs

This section reports “Curve Number by Land use” and includes the adjustments added by the LID practices. The Average Annual Runoff Depth will be reported for each landuse.

What areas within a given watershed are contributing the most sediment and nutrient loadings?

Tabulates area (soil, landuse)

Impervious surface estimate

L-THIA Calculates Runoff and NPS for each landuse

Crops 45100 lbs

LD Residential 615 lbs

Conclusion – this HUC 12 is a poor choice for urban BMPs

Crops 6300 lbs

LD Residential 1485 lbs

Nearby, East Findlay HUC 12, much better choice for urban BMPs

What measures would be most effective in addressing these loadings and where should they be placed?

Cuyahoga River Project

Lake Rockwell

Sediment traps

TSS (Tons) Urban

TSS (Tons) Crops

P Urban (Tons)

P Cropla

nd HUC 8 3872 1203 50.7 20.8

East Branch Reservoir-East Branch Cuyahoga River 41100020101 3 65 0.1 1.1

West Branch Cuyahoga River 41100020102 19 66 0.3 1.1

Tare Creek-Cuyahoga River 41100020103 37 91 0.5 1.6 Ladue Reservoir-Bridge Creek 41100020104 19 94 0.3 1.6

Black Brook 41100020105 4 50 0.1 0.9 Sawyer Brook-Cuyahoga River 41100020106 3 104 0.1 1.8 Lake Rockwell-Cuyahoga River 41100020203 40 160 0.6 2.8

Urban runoff = 600 acre feet ( of 4700)

Lake Rockwell

Urban vs Cropland TSS = 40 vs 160 tons per year

Lake Rockwell

L-THIA Low Impact Development

Reduce Low Density Residential zoning from 25 to 20 % impervious

How can I rank proposals based on their effectiveness in reducing non-point source loadings?

Ranking Answers

• What are metrics, how measured? • Where am I judged? Edge of a field or in a Stream? • What kind of problem in HUC12- Run Load

Duration Curve • Distribution of point-sources. –Examine USA

Permitted Point Source Water Pollution Map • Distribution of Impaired Waterways – EPA Waters

Map • Consider the big picture…

The End

L-THIA Online and LID�in a watershed investigationL-THIA On-line watershed delineation and CN analysisL-THIA is CN Based analysisSlide Number 4Databases provide inputCurve Number AnalysisSlide Number 7AssumptionsDisadvantagesLow-Impact Development (LID)hhL-THIA LID Available PracticesBMPs at Lot Level OutputsWhat areas within a given watershed are contributing the most sediment and nutrient loadings?�Slide Number 16Slide Number 17Slide Number 18Slide Number 19Slide Number 20What measures would be most effective in addressing these loadings and where should they be placed?Slide Number 22Cuyahoga River ProjectSlide Number 24Slide Number 25Slide Number 26Slide Number 27Urban runoff = 600 acre feet ( of 4700)Urban vs Cropland TSS = 40 vs 160 tons per yearL-THIA Low Impact DevelopmentSlide Number 31Slide Number 32How can I rank proposals based on their effectiveness in reducing non-point source loadings?Ranking Answers Slide Number 35Slide Number 36The End