long-term hydrologic impact assessment

1. Web-based Low Impact Development Decision Support and Planning Tool Overview: Basic Curve Number Analysis The L-THIA LID Model What is Low Impact Development Specific LID Practices long-term hydrologic impact assessment

2. Purdue University is an Equal Opportunity/Equal Access institution. Tutorial Outcomes • User will employ L-THIA LID model to estimate environmental benefits for various LID practices • User will be able to estimate costs of potential “Lot Level” LID practices

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

4. Pre-development Post-development Impact on Hydrology Purdue University is an Equal Opportunity/Equal Access institution.

5. Impact on Hydrology • Eventually, “increase” in • Peak flow • Direct runoff • after urbanization Urbanized Area Direct Runoff (Volume) Detention basin Natural Time Purdue University is an Equal Opportunity/Equal Access institution.

6. Basic 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 Purdue University is an Equal Opportunity/Equal Access institution.

7. Assumptions • Water flows across the surface to form watershed • no storm drains • No routing of runoff • Average antecedent moisture • soil is not saturated or frozen • Rainfall is evenly spread in local area Purdue University is an Equal Opportunity/Equal Access institution.

8. Curve Number to Compute Runoff • The Curve Number (CN) relationship was originally described in the Soil Conservation Service publication “TR-55” (NRCS, 1986) and several modifications have since been proposed. • The relationship between rainfall, runoff and CN value is non-linear, meaning that small changes in land use or rainfall can produce large changes in runoff. • The use of the CN equation in L-THIA LID is a simple alternative to more complicated hydrological models that require extensive data inputs which are often not readily available for most areas, or too complex. Purdue University is an Equal Opportunity/Equal Access institution.

9. Nonpoint Source Calculations • The coefficients or Event Mean Concentration (EMC) data used for the nonpoint source (NPS) water quality calculations was compiled by the Texas Natural Resource Conservation Commission (Baird and Jennings, 1996) from numerous literature and existing water quality data. • NPS pollutant masses are computed by multiplying runoff depth for a land use by the area of that land use and the appropriate EMC value and converting units. • A complete list of the EMC values used in the L-THIA LID model is available in Appendix B1. Purdue University is an Equal Opportunity/Equal Access institution.

10. Nonpoint Source Calculations • The land uses originally proposed by Baird and Jennings have been modified for the Midwest, and consist of the following: L-THIA LID Land Uses: • Commercial • Industrial • High Density Residential (1/4, 1/8 acre lots) • Low Density Residential (1/2, 1, and 2 acre lots) • Water / wetlands • Grass pasture • Agricultural • Forest Purdue University is an Equal Opportunity/Equal Access institution.

11. Nonpoint Source Calculations • EMC values for calculation of average concentration of NPS contaminants from each landuse Purdue University is an Equal Opportunity/Equal Access institution.

12. Nonpoint Source Pollution L-THIA LID produces Average Annual Pollutant Results for sediment, nutrients, a series of metals, and bacterial indicators. (e.g. lbs of Nitrogen per year) Purdue University is an Equal Opportunity/Equal Access institution.

13. Basic Model Concepts • Model is easy to run • Always gives an output… • Important to understand assumptions and limitations Purdue University is an Equal Opportunity/Equal Access institution.

14. How good is L-THIA L-THIA estimates match measured direct runoff separated from USGS daily stream flow VERY WELL Purdue University is an Equal Opportunity/Equal Access institution.

15. L-THIA LID • Based on the rainfall – land cover – runoff analysis method already used in many communities • Input: Land Use Pattern(s) + Soils Pattern • Process: Daily Runoff and Pollutant Loading Calculations (30 years) • Microscale CN Adjustment • Output: Average Annual Runoff and • NPS loads Purdue University is an Equal Opportunity/Equal Access institution.

16. Model Interface Purdue University is an Equal Opportunity/Equal Access institution.

17. Model Interface Purdue University is an Equal Opportunity/Equal Access institution.

18. Model Interface Purdue University is an Equal Opportunity/Equal Access institution.

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

20. LID Benefits Ecologically Sensible Provides Added Values / Ecosystem Services Economically Sustainable Lower Costs (Construction, Maintenance & Operation) vs. Conventional Multifunctional Practices Ideal for Urban Retrofit Purdue University is an Equal Opportunity/Equal Access institution.

21. LID Major Components Conservation (Watershed and Site Level) Minimization (Watershed and Site Level) Integrated Management Practices (Site Level) • Conservation • Forest/Woods • Infiltrable Soils • Storage, Detention & Filtration • Rain gardens • Drainage swales • Green roofs • Porous Pavement • Minimization • Reduce imperviousness • Soil Compaction Purdue University is an Equal Opportunity/Equal Access institution.

22. L-THIA LID Basic Screening 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 Purdue University is an Equal Opportunity/Equal Access institution.

23. 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 –soil conditions Purdue University is an Equal Opportunity/Equal Access institution.

24. LID Estimated Costs Cost estimates (2008) for BMP construction. Purdue University is an Equal Opportunity/Equal Access institution.

25. Next: Review of LID Practices Information sources. Details about estimating costs of specific practices. Design information in Appendix B3. Purdue University is an Equal Opportunity/Equal Access institution.

26. Purdue University is an Equal Opportunity/Equal Access institution. Porous or permeable pavement, sidewalks, driveways are surfaces that infiltrate, constructed from a range of materials.

27. Porous Pavement –Lot Level Specify width of streets and sidewalks, Disconnection from stormwater system; The % impervious of the parking lot pavement Purdue University is an Equal Opportunity/Equal Access institution.

28. Pavement Cost Estimate This land use is 1/8 acre lot, high density residential. The default assumption is 871 ft2of pavement per driveway per lot. To cost the porous pavement option, user assumes 8 lots this size per acre. Cost table has range of $2 to $12 per ft2 of pavement. Estimate could be $10.00 times 8 lots times 871 ft2= $ 69680 / acre Purdue University is an Equal Opportunity/Equal Access institution.

29. http://en.wikipedia.org/wiki/Faroe_Islands.JPG Purdue University is an Equal Opportunity/Equal Access institution.

30. City Hall’s Green Roof, Chicago http://en.wikipedia.org/wiki/Chicago_City_Hall_Green_Roof.jpg Purdue University is an Equal Opportunity/Equal Access institution.

31. Green Roof Wide variation in cost and complexity Low estimate $ 8.50 per square foot High estimate $ 48.50 per square foot. Next slide is an example with 28 commercial acres with 25% roof, or 7 acres of roof. That creates 43560 * 7 = 304920 ft2 feet of roof. And this proposal is that 50% of the roof will have LID practice: Mid-range cost of $ 29.00 ft2 times 0.50 % of 304920 ft2 is $ 4.4 million. Purdue University is an Equal Opportunity/Equal Access institution.

32. Green Roof Percent of roof treated with BMP Total area of this landuse Percent of area which is roof Purdue University is an Equal Opportunity/Equal Access institution.

33. Rain Barrels Installation of rain barrels and cisterns in residential subdivisions allows harvest of rainfall water for potential reuse. In many countries with water scarcity problems, especially in developing countries, the use of vertical storage systems, tanks, and underground storage structures is a common practice and serves as good water supply reservoirs. The value of runoff CN used to represent rain barrels is 94 and cisterns is 85 for the 4 HSGs (Sample et al., 2001). Purdue University is an Equal Opportunity/Equal Access institution.

34. L-THIA LID: Lot Level Screening Tool For a median price barrel assume $200 each; The model assumes one per homeowner. High density residential 1/8 acre lot land use would require 8 barrels per acre if practice is 100%; 4 barrels /ac at 50%. $ 1600 per acre of 1/8 acre lot residential landuse at 100% LID. Rain Barrels may be installed by volunteers or professionals, so costs vary. Purdue University is an Equal Opportunity/Equal Access institution.

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

36. Design of bioretention systems is very site-specific. The L-THIA LID practice is applied as a benefit (to the curve number) for the entire area. The LID size is generalized and assumed to be adequate. A typical size (for cost estimates) for a residential lot could be 100 ft2. Purdue University is an Equal Opportunity/Equal Access institution.

37. 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.

38. 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 • https://engineering.purdue.edu/~lthia/ Purdue University is an Equal Opportunity/Equal Access institution.

39. At the completion of this tutorial, the user should be able to design a similar scenario, enter the needed input data in L-THIA LID, run the model, and create output tables and graphs to address development questions. Walkthrough Digital WatershedHigh Impact targetinglong-term hydrologic impact assessment Purdue University is an Equal Opportunity/Equal Access institution.

40. Walkthrough Task: Use L-THIA LID to explore a 1000+ unit housing proposal for the Milan or Saline area. We will start with the assumption of 1/8 acre lot sizes on 155 acres of land. The model will produce predictions for runoff volume and NPS sediment changes in various configurations of housing unit density including LID vs. non-LID results. While local political focus is on several NPS chemistries, this tutorial’s main focus is on sediment and runoff volume. Purdue University is an Equal Opportunity/Equal Access institution.

41. Walkthrough https://engineering.purdue.edu/~lthia/LID The 5 part process is this: Select a state and county, which determines the rainfall data for the 30 year period. Enter land use and soil data for existing conditions. Enter changed land use, reflecting a proposed development. Select the proportion of the area that will receive LID practices, and may chose to select some parameters for LID practices. The model runs and produces a table of outputs for examination. Purdue University is an Equal Opportunity/Equal Access institution.

42. Hydrologic Soil Groups Hydrologic soil Groups Purdue University is an Equal Opportunity/Equal Access institution.

43. Hydrologic Soil Groups Estimate HSG based on surface texture Purdue University is an Equal Opportunity/Equal Access institution.

44. Select State and county Select Michigan then Washtenaw County. Purdue University is an Equal Opportunity/Equal Access institution.

45. Select Units Select acres as units- Note the tool tips and pop-ups over? Purdue University is an Equal Opportunity/Equal Access institution.

46. Pre-Developed land use and soil Agricultural – B Soil – 35 Acres Agricultural – C Soil – 120 Acres Purdue University is an Equal Opportunity/Equal Access institution.

47. Post-Developed land use In this scenario of a single large development, build High Density Residential 1/8 acre lot – on all the land that is being developed. Purdue University is an Equal Opportunity/Equal Access institution.

48. Apply LID Percentages Apply LID practices to 100 % of the development Purdue University is an Equal Opportunity/Equal Access institution.

49. Select LID Screening Level In this scenario we will do a Lot Level Screening of a single large development, with High Density Residential 1/8 acre lot – on all the land that is being developed. Purdue University is an Equal Opportunity/Equal Access institution.

50. 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