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
Nonpoint source pollutant loads based on landuse based event mean concentrations (EMC) and runoff 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
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 rainfall to runoff ratio for different surfaces Direct Runoff Rainfall (in) Purdue University is an Equal Opportunity/Equal Access institution.
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) Low-Impact Development (LID) 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
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 Purdue University is an Equal Opportunity/Equal Access institution.
BMPs at Lot Level Each land use has a set of controls for LID practices. In this tutorial we have one postdeveloped land use, High Density Residential and two clusters of tools because there are two soil types. Land use Soil Group B Soil Group C
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
LD Residential 615 lbs Conclusion this HUC 12 is a poor choice for urban BMPs Crops 45100 lbs
Nearby, East Findlay HUC 12, much better choice for urban BMPs LD Residential 1485 lbs Crops 6300 lbs
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 nonpoint 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
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