1. Implementing Low Impact Development in Utah - An Engineer’s Perspective PRESENTED BY: CRAIG BAGLEY, P.E., CFM BOWEN, COLLINS & ASSOCIATES

2. What is Low Impact Development?  A comprehensive, landscape-based approach to sustainable development  A management strategy to maintain pre-development natural systems, hydrology and ecology  A cost-effective, flexible approach based on a set of simple techniques  A collection of practices that have been implemented nationwide

3. What is Low Impact Development?  NOT rocket science  NOT formulaic  NOT the answer to every storm water challenge  NOT yet finished evolving  NOT very common in Utah

4. Typical pre-development conditions: Runoff = 10% Infiltration = 50%

5. Typical post-development conditions: Runoff = 55% Infiltration = 15%

6. LID Principles  Work with the landscape and natural systems  Focus on prevention (flood, erosion, pollution, etc.)  Micromanage stormwater – treat near source  Keep it simple  Design multi-functional features (filter, treat, infiltrate)  Maintain and sustain

7. 1.Use existing natural systems as the integrating framework for site planning Land use planning and watershed planning Identify environmentally sensitive resources: wetlands, mature trees, slopes, drainageways, permeable soils, waterway buffers Mimic pre-development hydrology

8. 2.Focus on prevention Minimize clearing and grading Cluster buildings and reduce building footprints Reduce road widths, use shared driveways, reduce parking area Align roads to minimize impact Use green rooftops Use permeable paving

9. Create subwatersheds and “micromanage” runoff in a treatment train of small structures Flatten slopes, lengthen flow paths, maximize sheet flow Maintain natural flow paths, use open drainage Use LID techniques to manage frequent, low-intensity storms 3.Treat stormwater close to the source

10. Open drainage systems and filter strips Disconnection of roof runoff Rain barrels Street sweeping Reduce construction disturbance 4. Emphasize simple, nonstructural, low-tech, low-cost methods

11. Use stormwater management components that provide filtration, treatment, and infiltration. Provide open space and wildlife habitat. Store water for landscape use Reduce heat island effect Enhance site aesthetics 5.Create a multifunctional landscape

12. Reduce use of pesticides and fertilizers. Use drought-resistant plants. Maintain rain gardens and bioretention areas. Provide adequate funding for public works departments 6.Maintain and sustain

13. Key LID Strategies  Conserve natural hydrology, trees and vegetation  Preserve stream and wetland buffers  Minimize impervious surfaces (DCIA)  Micromanage stormwater  Plant ecological landscaping

14. LID Advantages over Conventional Means  Reduces need for large detention facilities and flood control structures  Reduces pollutant loading to receiving waters  Reduces stream bank erosion associated with peak flow and volume  Provides visual amenity  Costs less to construct (less pipe, less pavement, smaller facilities)

15. Conventional LID BMPs/Integrated Management Practices  Bioretention  Dry wells  Filter/buffer strips  Vegetated swales  Rainwater harvesting  Infiltration trenches  Reducing roads and parking areas  Permeable pavement

16. LID Design Process  Develop site plan  Perform hydrologic analysis  Evaluate/select BMPs/Integrated management practices  Develop erosion and sediment control measures

17. LID Site Planning  Define development envelope  Reduce/minimize total impervious area on site  Disconnect impervious areas  Modify/increase flow paths

18. LID Hydrologic Analysis  Delineate drainage basin and sub-basin areas  Define the design storm characteristics  Select modeling techniques  Estimate runoff from pre-development conditions (baseline)  Estimate runoff from propsed new development without BMPs  Evaluate alternative BMPs to mitigate impacts of development on stormwater

19. Select LID BMPs/Integrated Management Practices  Define needed hydrologic controls to mitigate  Evaluate site constraints  Screen potential BMPs  Evaluate impacts of implementing BMPs on post-developed model  Select BMPs to implement  Incorporate additional controls if necessary

20. Select Erosion & Sediment Control Methods  Plan and phase construction  Select appropriate erosion control measures  Select sediment control measures  Identify needed maintenance activities

21. LID Planning/Design Considerations  Space requirements  Soil characteristics  Slopes (hillside, channel, etc.)  Depth to water table or bedrock  Proximity to building foundations & wells  Maximum depth AND Maintenance costs

22. Low Impact Site Design Example Conservation of natural hydrology, trees, vegetation Stream & wetland buffers Minimize impervious surfaces Stormwater micromanagement Ecological landscaping Typical Subdivision Conservation

23. Low Impact Site Design Example Open Space Residential Design 1. Identify Conservation Areas

24. Low Impact Site Design Example Open Space Residential Design 1. Identify Conservation Areas 2. Locate House Sites

25. Low Impact Site Design Example Open Space Residential Design 1. Identify Conservation Areas 2. Locate House Sites 3. Align Roads & Trails

26. 1. Identify Conservation Areas 2. Locate House Sites 3. Align Roads & Trails 4. Draw the Lot Lines Open Space Residential Design Low Impact Site Design Example

27. Buildings and Roadways Low Impact Site Design Example Cluster buildings within the development envelope Design buildings with smaller footprints Roadways should follow existing grades. Use parking structures Separate parking areas

28. Buildings and Roadways Low Impact Site Design Example Cluster buildings within the development envelope Design buildings with smaller footprints Roadways should follow existing grades. Use parking structures Separate parking areas

29. Stormwater Management Low Impact Site Design Example Minimize directly connected impervious area Create multiple sub-basins Increase time of concentration Use a “treatment train” of LID techniques to deal with frequent, low-intensity storms.

30. Stormwater Management Low Impact Site Design Example Minimize directly connected impervious area Create multiple sub-basins Increase time of concentration Use a “treatment train” of LID techniques to deal with frequent, low-intensity storms.

31. Low Impact Site Design Examples

32. Roadways and Parking Areas Road Profile Narrower roadways (18- 24 feet) Permeable parking lanes Open section roadways Alternative curb designs

33. Roadways and Parking Areas Alternative Turnarounds Smaller cul-de-sacs Bioretention islands One-way-loops Hammerhead turnarounds

34. Roadways and Parking Areas Parking Lots Create multiple small lots Allow shared parking Reduce requirements near transit Require compact spaces Set parking maximums

35. Roadways and Parking Areas Parking Lots Create multiple small lots Allow shared parking Reduce requirements near transit Require compact spaces Set parking maximums

36. Permeable Paving Grass pavers Paving stones Porous asphalt Pervious concrete Runoff reduction

37. Permeable Paving Parking stalls Overflow parking Driveways Walkways and plazas Applications

38. Bioretention Excavation filled with engineered soil mix Herbaceous perennials, shrubs, trees Ponded water infiltrates within 72 hours Overflow outlet and optional underdrain Treatment, retention, infiltration, landscaping

39. Bioretention Parking lot islands Median strips Rooftop runoff Applications

40. Bioretention Applications Urban retrofits High-density areas

41. Vegetated Swales Roadside swales “country drainage” Parking lots Low-angle slopes only Opportunity for snow storage Conveyance, treatment, infiltration

42. Vegetated Swales Conveyance, treatment, infiltration

43. Grassed Filter Strips Pretreatment and Attenuation Low-angle vegetated slopes Adjacent to parking lots and roadways Opportunity for snow storage

44. Grassed Filter Strips

45. Infiltration Trenches / Dry Wells Infiltration and Volume Reduction Runoff stored in void space; slowly percolates into the ground Excellent for rooftop runoff Pretreatment is critical for surface runoff

46. Infiltration and Volume Reduction Infiltration Trenches / Dry Wells

47. Runoff Reduction and Water Conservation Rain Barrels and Cisterns Downspouts directed to tanks or barrels UT – up to 2500 gal/lot Excess diverted to drywell or rain garden Landscaping, car washing, other nonpotable uses

48. Runoff Reduction and Water Conservation Rain Barrels and Cisterns

49. Runoff Reduction, Treatment, Attenuation Stormwater Planters “Bioretention in a Box” Vegetative uptake of stormwater pollutants Pretreatment for suspended solids Aesthetically pleasing Reduction of peak discharge rate

50. Stormwater Planters

51. LID BENEFITS Lower Peak Discharge Rates Reduced Runoff Volume 0 4 8 12 16

52. LID BENEFITS Improved Water Quality Increased Aquifer Recharge

53. ConventionalLow Impact Grading/Roads $569,698$426,575 Storm Drains $225,721$132,558 SWM Pond/Fees $260,858$ 10,530 Bioretention/Micro —$175,000 Total$1,086,277$744,663 Unit Cost$14,679$9,193 Lot Yield7481 Lower Construction Costs Higher Lot Yield

54. Important Design Considerations Selection of pretreatment prior to infiltration Wellhead protection Emergency access Snow removal issues Overflow/bypass controls Mosquito issues and concerns

55. Important Design Considerations Select appropriate cold climate techniques Ensure adequate emergency access Prioritize pedestrian safety Define ownership: public, private, mix? Develop monitoring and inspection plan Assign maintenance responsibilities

56. QUESTIONS?

57. LID IMPLEMENTATION Long-Term Maintenance All stormwater systems require maintenance LID maintenance often simple, low cost Ensure adequate funding for PW Depts Homeowner/landscaper education Consider requiring permanent sureties

58. LID IMPLEMENTATION Review of Local Codes Zoning Bylaw and Site Plan Review Subdivision Rules and Regulations Board of Health Regulations Wetland Regulations Building Codes

59. LID IMPLEMENTATION Stormwater/LID Bylaw Replace the “patchwork” of stormwater codes with a single set of local standards Establish Stormwater Permitting Authority to review all projects over a certain size Specify performance standards Utilize expert review when necessary Permit/promote the use of LID techniques Require a maintenance plan

60. LID IMPLEMENTATION Collaboration is Critical! Local boards Public works officials Fire department and emergency response Developers and builders Consultants and engineers Business interests and property owners Environmental advocates