1. L-THIA Online and LID in a watershed investigation
Larry Theller
Agricultural and Biological Engineering,
Purdue University
Great Lakes Sedimentation Workshop
Ann Arbor Mi.

2. 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

3. 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

4. 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

5. Databases provide input
Weather data (30 years of real rainfall)
Soil data SSURGO
NLCD 2006 Landuse
Elevation data = NHD+ V2 30m (for contributing area)

6. Curve Number Analysis rainfall to runoff ratio for different surfaces
Direct
Runoff
Rainfall (in)
Purdue University is an Equal Opportunity/Equal Access institution.

7. EMC Table Averaged mass of NPS contaminant from each landuse
Purdue University is an Equal Opportunity/Equal Access institution.

8. 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

9. Purdue University is an Equal Opportunity/Equal Access institution.
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.

10. 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

11. 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
hh)

12. 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.

13. 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.
Land use
Soil Group B
Soil Group C

14. 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.
This section reports “Curve Number by Land use” which reports curve numbers for each land use. This includes the adjustments added by the LID practices. In this table the user will note (at the dark arrow) that 1/8 acre density residential land use on C soil has a CN of 90 but with some LID practices applied, it is adjusted to an effective CN of 89 which will reduce runoff and pollutant loads.

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

16. Tabulates area (soil, landuse)

17. Impervious surface estimate

18. L-THIA Calculates Runoff and NPS
for each landuse

19. LD Residential 615 lbs
Conclusion – this HUC 12 is a poor choice for urban BMPs
Crops lbs

20. Nearby, East Findlay HUC 12, much better choice for urban BMPs
LD Residential 1485 lbs
Crops 6300 lbs

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

23. Cuyahoga River Project

26. Sediment traps
Lake Rockwell

27. TSS (Tons) Urban TSS (Tons) Crops P Urban (Tons) P Cropland HUC 8 3872
1203
50.7
20.8
East Branch Reservoir-East Branch Cuyahoga River 3 65
0.1
1.1
West Branch Cuyahoga River 19 66
0.3
Tare Creek-Cuyahoga River 37 91
0.5
1.6
Ladue Reservoir-Bridge Creek 94
Black Brook 4 50
0.9
Sawyer Brook-Cuyahoga River
104
1.8
Lake Rockwell-Cuyahoga River 40
160
0.6
2.8

28. Urban runoff = 600 acre feet ( of 4700)
Lake Rockwell

29. Urban vs Cropland TSS = 40 vs 160 tons per year
Lake Rockwell

30. L-THIA Low Impact Development

31. Reduce Low Density Residential zoning from 25 to 20 % impervious

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

34. 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…

37. The End