1. Low Impact Development Training Design Examples Presented by: The Low Impact Development Center, Inc. A non-profit water resources and sustainable design organization www.lowimpactdevelopment.org

2. Copyright 2009 Low Impact Development Center, Inc. Objectives Planning and site design approach Site Analysis tools and information Site Analysis techniques (Hydrology and Hydraulics) Demonstration of Process (NRCS, SWMM, EISA, other)

3. The HydrologIic Goals and Design Approach Copyright 2009 Low Impact Development Center, Inc.

4. Hydromodification Alteration of flow characteristics through a landscape which has the capacity to result in degradation of water resources

5. Copyright 2009 Low Impact Development Center, Inc. 1. Conservation 2. Minimization 3. Strategic timing 4. Best management practices retain / detain / filter / recharge / evaporate / use 5. Pollution prevention LID Design Approach

6. Copyright 2009 Low Impact Development Center, Inc. 1. Conservation 2. Minimization 3. Strategic timing 4. IMP’s 5. Pollution Prevention LID Design Approach Perform Site Evaluation Develop LID Strategies Prepare LID Concept Design Target O & M Strategy Critical Elements Iterative Process LID Planning Steps

7. Copyright 2009 Low Impact Development Center, Inc. 1. Conservation Plans/Regulations Local watershed and conservation plans Forest (contiguous and interior habitat) Streams (corridors) Wetlands Habitats Step slopes Buffers Critical areas Parks Scenic areas Trails Shorelines Difficult soils Ag lands Minerals

8. Copyright 2009 Low Impact Development Center, Inc. 2. Minimize Impacts Minimize clearing Minimize grading Save A and B soils Limit lot disturbance Reforestation Reduce impervious surfaces replace

9. Copyright 2009 Low Impact Development Center, Inc. Q T Developed condition, with reduced or disconnected impervious areas Pre-developed Reduced runoff volume Developed - no controls Reduced peak flow Reduce the Runoff Generated by Source Areas

10. Copyright 2009 Low Impact Development Center, Inc. 3. Strategic Timing Maintain natural flow paths Maximize sheet flow Reduce pipes, curb & gutter Open drainage Use green space Flatten slopes Disperse drainage Save headwater areas Vegetative swales

11. Copyright 2009 Low Impact Development Center, Inc. 4. Storage, Detention & Filtration “LID BMP’s” Uniform distribution at the source Open drainage swales Rain gardens / bioretention Permeable pavement Infiltration trenches Green roofs Blue roofs Rainwater reuse Soil amendments

12. Copyright 2009 Low Impact Development Center, Inc. 5. Pollution Prevention Maintenance Proper use, handling, and disposal –Individuals vehicles / hazardous wastes / reporting / recycling –Navy facilities Good house keeping / proper disposal / reuse / spills Joint Service Pollution Prevention and Sustainability Technical Library A Website Supported by the Joint Services, the Defense Logistics Agency, and the U.S. Coast Guard http://205.153.241.230/p2_documents/navy.html Regional Municipal and Joint Services Resources

13. LID Analysis Tools

14. Copyright 2009 Low Impact Development Center, Inc. Design Storm Approaches Single Event vs. Continuous Simulation - peak flows / - volume / hydromodification flooding - water quality

15. Copyright 2009 Low Impact Development Center, Inc. Hydrologic Analysis National Resources Conservation Service (NRCS) methods –curve numbers (0-100) –storm type (I, IA, II, III) –time of concentration Curve Numbers for Hydrologic Soil Group Cover TypeABCD Woods (Good Condition)30486573 Paved Areas98 Computed process simulations –ex. Hydrologic simulation program – FORTRAN (HSPF)

16. Copyright 2009 Low Impact Development Center, Inc. Models and Tools Stormwater Models EPA Stormwater Management Model (EPA SWMM) Source Loading and Management Model (SLAMM) LID Sizing Tools National LID manual technique 438 Guidance

17. Copyright 2009 Low Impact Development Center, Inc. EPA SWMM DeveloperUS EPA; Oregon State U.; Camp, Dresser and McKee (CDM) Rainfall ModeledSingle Event and Continuous Watershed Size1 to 100+ Acre Drainage Areas Primary UseFlooding, Quantity, and Quality Land Use & Source Area User defined land uses and source areas Application to LIDCan be adapted to simulate LID controls, models storage and infiltration processes

18. SWMM 5 LID Templates Copyright 2009 Low Impact Development Center, Inc.

19. SLAMM DeveloperDr. Robert Pitt, U of Alabama; John Voorhees RainfallContinuous Watershed Size10 to 100+ acre Drainage Areas Land UsesResidential, Commercial, Industrial, Highway, Institutional, and other Urban Source AreasRoofs, Sidewalks, Parking, Landscaped, Streets, Driveways, Alleys, etc. Primary UseRunoff Quantity and Quality Application to LIDInfiltration, Wet Ponds, Porous Pavement, Street Sweeping, Biofiltration, Vegetated Swales, Other Urban Control Device

20. Copyright 2009 Low Impact Development Center, Inc.

21. National LID Manual Technique DeveloperUS EPA; Prince George’s County RainfallSingle Event Watershed Size Small Sites Primary UseEstimates retention and detention requirement to meet quantity and peak flow goals Application to LID Applies to any BMP with retention storage: bioretention, infiltration, porous pavement, swales, and planters

22. Copyright 2009 Low Impact Development Center, Inc. Case Studies Used to Demonstrate Models Hypothetical DoD Housing Design –National method (PG County, MD method) –438 Norfolk

23. Copyright 2009 Low Impact Development Center, Inc. National LID Manual Techniques Based on NRCS methods Uses peak storm event Nomographs that reflect graphical peak discharge method

24. Example New Development: Hypothetical DoD New Housing Design (Site A) From LID UFC 2004 Version 6.5 acres of woods Avg. slopes of 2% Soils are Type B –moderate infiltration –typically silt loam or loam Drains to small channel & wetland Copyright 2009 Low Impact Development Center, Inc.

25. Proposed Conventional Design Clustered housing, classified as “Townhouse Residential District” Stormwater system is curb and gutter and closed drainage to stormwater pond

26. Proposed LID Site Copyright 2009 Low Impact Development Center, Inc.

27. Conventional

28. Copyright 2009 Low Impact Development Center, Inc. LID

29. Copyright 2009 Low Impact Development Center, Inc. Conventional

30. Copyright 2009 Low Impact Development Center, Inc. LID

31. Copyright 2009 Low Impact Development Center, Inc. Conventional

32. Copyright 2009 Low Impact Development Center, Inc. LID

33. Copyright 2009 Low Impact Development Center, Inc. Site A Project Objectives Integrate LID practices into a medium density residential housing area Hydrology goals: –Maintain the 2-year 24-hour and 10-year 24-hour peak runoff rate –Provide water quality treatment

34. Calculate a Composite Curve Number (CN) for Pre-Developed and Developed Conditions Weighted CN = Sum of Products ÷ Drainage Area Copyright 2009 Low Impact Development Center, Inc.

35. CN Pre-Developed, Proposed, & LID Composite Conditions Condition10yr Runoff (in) Existing (CN = 63)1.5 Proposed (CN = 80)2.9 LID Composite CN (CN=73)2.3

36. Copyright 2009 Low Impact Development Center, Inc. ConditionCNTcTc Peak Discharge (CFS) Runoff depth (in.) 2-yr (3” depth) 10-yr (5” depth) 2-yr10-yr Existing Condition 630.242100.41.5 Proposed Condition – conventional CN 800.229231.32.9 Proposed Condition using LID site design 730.246170.92.3 Summary of Graphical Peak Discharge Results Conventional vs. LID

37. Copyright 2009 Low Impact Development Center, Inc. Conventional vs. LID

38. Copyright 2009 Low Impact Development Center, Inc. Design Storm Conventional Site Design LID Site Design Depth, in Volume, ac-ft Depth, in Volume, ac-ft 2-yr 24-hr0.520.28 0.15 10-yr 24-hr0.850.460.530.29 Post-Development Storage Volumes Conventional vs. LID

39. Copyright 2009 Low Impact Development Center, Inc. Conventional vs. LID

40. Copyright 2009 Low Impact Development Center, Inc. Conventional vs. LID Post-Development Storage Volumes –Use National Method to determine volume of retention and detention needed on site Assumes –Landuse is homogenous –Practices are evenly distributed

41. Flowchart similar to TR-55 Method Copyright 2009 Low Impact Development Center, Inc.

42. VS/VR

43. Copyright 2009 Low Impact Development Center, Inc. Runoff Equation Solution

44. Copyright 2009 Low Impact Development Center, Inc. Existing CN: 63 Proposed CN: 73 Required Retention Storage Volume = (0.30in)(1ft/12in) (6.5 ac) = 4.5 ac-ft Maintaining Pre-Development Runoff Volume

45. Copyright 2009 Low Impact Development Center, Inc. Existing CN: 63 Proposed CN: 73 Required Retention Storage Volume =(0.50in)(1ft/12in) (6.5 ac) = 0.27 ac-ft Maintaining Pre-Development Runoff Volume

46. Copyright 2009 Low Impact Development Center, Inc. LID Techniques and Objectives Choosing LID Practice techniques

47. Copyright 2009 Low Impact Development Center, Inc. Base Storage Capacity Base & subbase materials No. 57 crushed stone base or similar 1.5 - 1/8 in. (38 – 3 mm) No. 2 crushed stone subbase or similar 2½ in. – ¾ in. (65 mm – 20 mm) ~ 30% to 40% void space Quarry or lab provides % of voids - ASTM C 29 3 in. (75 mm) base stores ~1 in. (25 mm) water Design for 24 - 48 hour storage Base Subbase Base Subbase

48. Infiltration Infiltration, detention & filtering Impermeable Liner Option for filtering Permeable Paver Water Management Options Copyright 2009 Low Impact Development Center, Inc.

49. Soil Infiltration Establish suitability Soil maps NRCS soil classification (ABCD) USCS soil classification Bracket infiltration, CBR (R-value) range Conduct on-site infiltration tests Use lowest (conservative) values for preliminary “desk top” design

50. Copyright 2009 Low Impact Development Center, Inc. Subgrade Infiltration Determining soil infiltration rates Dig holes on the site Approx. top-of-subgrade depth Double ring infiltrometer test Use lowest infiltration rate Test areaMultiple test holes

51. Copyright 2009 Low Impact Development Center, Inc. Soil Design Strength Design assumptions Subgrade strength for vehicular traffic: –Min. 96-hour soaked CBR = 5% –(Min. R-value = 11) What if < 5%CBR? Capping layer of geotextile and aggregate base –Stabilize soil with cement – PCA guidelines –Use no exfiltration design

52. Copyright 2009 Low Impact Development Center, Inc. Base Sizing Steps 1 – Assess soil infiltration conditions, design storm depth, determine exfiltration option 2 – Compute increased runoff depth from area contributing to the PICP (if any), add rainfall depth falling directly on PICP 3 – Compute the depth of the base for storage: rule-of-thumb…1 in. (25 mm) rainfall storage requires 3 in. (75 mm) of base/subbase depth 4 – Compute the maximum base depth for drainage in 24 – 48 hours given conservative soil infiltration rate (safety factor = 2) 5 – If needed, revise base depth to accommodate storage and site area limitations 6 – Design perforated pipes at base to drain non-infiltrated water 7 – Design overflow for rainfalls exceeding the design storm

53. Copyright 2009 Low Impact Development Center, Inc. Base Sizing Steps (cont’d) 8 – Determine the base/subbase thickness for traffic using Figure 18 (see next slide) 9 – Compare required traffic base/subbase thickness water storage thickness: always use thicker one 10 – Check clearance from bottom of subbase to seasonal high water table (> 2 ft) 11 – Check geotextile filter criteria

54. Copyright 2009 Low Impact Development Center, Inc. Step 8 – Check the structural base thickness Fig. 18 - Base thickness guidance

55. Copyright 2009 Low Impact Development Center, Inc. ICPI Permeable Design Pro Software

56. Copyright 2009 Low Impact Development Center, Inc. EISA Section 438 Guidance 95th Percentile Storm Event NRCS* Continuous Simulation (SWMM/HSPF) NRCS/MDE Modeling Infiltration w/TR-20 -1983

57. Copyright 2009 Low Impact Development Center, Inc. Section 438 Case Study 95 th Percentile Storm Event Method Conditions

58. Copyright 2009 Low Impact Development Center, Inc. Parameters and Results Bioretention and Permeable Pavements only options due to operational requirements. Considers high water table and poor soils 30% of site available for “permeability” 2,000 sf of bioretention and 7,500 sf of permeable pavement 75% storm event managed