Chapter 4 Integrating Site Design and Stormwater Management

1. Chapter 4Integrating Site Design and Stormwater Management Frank X. Browne, Ph.D., P.E. F. X. Browne, Inc. www.fxbrowne.com

2. Presentation • Overview of Low Impact Development Concepts • Discussion of Chapter 4 • Case Studies

3. Low Impact Development An innovative, ecosystem-based approach to land development and stormwater management

4. Why We Need Low Impact Development • Protect and Improve • Water Quality • Watershed Hydrology • Fish and Wildlife • Reduce Infrastructure Costs • Make Communities More Attractive

5. Low Impact Development Mimic PredevelopmentSite Hydrology Using Site Design Techniques that Store, Infiltrate, Evaporate and Detain Stormwater Runoff

6. “The difficulty lies not in the new ideas, but in escaping from the old ones.” John Maynard Keynes, 1936

7. Conventional

8. Low Impact Development Objectives • Reduce Effective Impervious Area • Infiltrate Stormwater • Maximize Evapotranspiration

9. Low Impact Development Planning Concepts • Maintain/Improve Site Hydrology • Think Small • Control Stormwater at the Source • Use Natural , Nonstructural Methods • Create Multifunctional Environment Modified from Prince George County, Maryland

12. Chapter 4 Integrating Site Design and Stormwater Management

14. SITE ANALYSIS • Background Site Factors • Site Factors Inventory • Site Factors Analysis

15. Background Site FactorsDescribe hydrologic context and other natural elements • Chapter 93 stream use designation • Special Protection Waters (EV, HQ) • Fishery/Aquatic Life Use (WWF, CWF, TSF) • Chapter 303d/impaired streams • Aquatic biota sampling • Sensitive downstream areas (water supply source) • Location of any know downstream flooding • Any Special Areas?

16. Special Areas • Previously Mined AMD/AML areas • Brownfields • Source Water Protection areas • Urban Areas • Carbonate/Limestone • Other

17. Site Factors Inventory • Describe the existing developed features of the site, if any • Describe important natural features of site

18. Describe the size and shape of the site • Special constraints/opportunities • Special site border conditions and adjacent uses

19. Describe the existing developed features of the site, if any • Existing structures/structures to be preserved • Existing cover/uses • Existing impervious areas • Existing public sewer and water • Existing storm drainage systems • Existing on-site water and wastewater

20. Describe important natural features of site • Existing hydrology (drainage swales, intermittent, perennial) • Existing topography, contours, subbasins • Soils on site – potential for infiltration • Areas of vegetation (trees, scrub, etc) • Special Value Areas • Sensitive Areas • PNDI areas or species

21. Special Value Areas • Wetlands, hydric soils • Floodplains/alluvial soils • High quality woodlands, other woodlands and vegetation • Riparian buffers • Naturally vegetated swales/drainageways

22. Sensitive Areas • Steep slopes • Special geologic conditions (limestone) • Shallow bedrock (less than 2ft) • High water table (less than 2ft)

23. Site Factors Analysis • Characterize site constraints • Wetlands • Bog turtle habitat • Streams and ponds • Characterize site opportunities\ • Good soils • Woodlands • Riparian buffers

24. Constraints and Opportunities • Avoid development on or near special and sensitive natural features • Place impervious areas on poor soils • Protect good soils – use for infiltration

25. Using the site opportunities • Has a Potential Development Area been defined? • Does the proposed layout fit the constraints and opportunities of the site?

27. MUNICIPAL INPUTS • Township Comprehensive Plan and Zoning guidance • Township SLDO guidance and options • Township SLDO/stormwater requirements • Is useful interaction at sketch plan or even pre-sketch plan phases occurring?

28. Township ComprehensivePlan and Zoning guidance • Guidance in Comprehensive Plan? • Existing Zoning District? • Total number of units allowed? • Type of units? • Density of units? • Any allowable options?

29. Township SLDOguidance and options • Performance standards for neo-traditional, village, hamlet planning? • Reduce building setbacks? • Curbs required? • Street width, parking requirements, other impervious requirements? • Cut requirements? • Grading requirements? • Landscaping requirements?

30. Township SLDO/stormwater requirements • Peak rate and design storms • Total runoff volume • Water quality provisions • Methodology requirements • Maintenance requirements

32. SITE DESIGN:NON-STRUCTURAL BMPs • Lot Concentration and Clustering • Minimum Disturbance • Impervious Coverage Reduction • Disconnect/Distribute/Decentralize • Source Control

33. Lot Concentration and Clustering • Reduce individual lot size • Concentrate/cluster lots • Configure lots to incorporate natural site characteristics • Orient structures to fit natural topography • Minimize site disturbance

34. Minimum Disturbance • Define disturbance zones for site • Protect good soils • Protect sensitive and special areas • Minimize total site compaction • Maximize zones of open space and greenways • Consider re-forestation and re-vegetation opportunities

35. Impervious Coverage Reduction • Reduce road widths and lengths • Use Cul-de-sacs with vegetated islands • Reduce driveway length and width • Reduce parking ratios and sizes • Evaluate shared parking • Use porous surfaces where applicable • Design single-side sidewalks

36. Disconnect/Distribute/Decentralize • Rooftop disconnection • Existing yard areas • Existing vegetated areas/woods • Disconnection from storm sewers/street gutters • Front/side yard opportunities • Vegetated swales, rain gardens, etc.

38. SITE DESIGN:STRUCTURAL BMPs • Volume/Peak Rate Using Infiltration • Volume/Peak Rate Reduction Using Other Methods • Runoff Quality/Peak Rate Reduction • Site Restoration • Testing Protocols

39. Volume/Peak Rate Through Infiltration • Porous Pavement with Infiltration Beds • Infiltration Basins • Infiltration Trenches • Rain Garden/Bioretention • Dry Wells/Seepage Pits • Vegetated Swales • Vegetated Filter Strips • Infiltration Berm/Retentive Grading

40. Volume/Peak Rate Reduction – Other Methods • Vegetated Rooftops (Green Roofs) • Capture & Reuse • Cisterns • Rain Barrels

41. Runoff Quality/Peak Rate Reduction • Constructed wetland • Wet pond/retention basin • Dry extended detention basin (Naturalized Basin) • Water quality filters: Constructed and Other • Sand and sand/peat filters • Multi-chamber catch basins and inlets

42. Site Restoration for Stormwater • Riparian Buffer Restoration • Landscape Restoration • Soil Amendment/Restoration • Streambank Restoration

43. Testing Protocols • Soil Testing • Site Infiltration

44. STORMWATER METHODOLOGYAND CALCULATIONS • Iterative Process Occurring Throughout Planning and Design to Maximize Non-Structural Practices • Strive to Minimize Stormwater Runoff • Strive to Achieve Standards of Comprehensive Stormwater Management

45. DEVELOP COMPREHENSIVE STORMWATER MANAGEMENT PLAN • Has There Been Thorough Approach To Use of Both Non-Structural and Structural BMPs? • If not, what non-structurals and structurals might be used? • Should the building program be modified? • What Related Benefits Are Being Achieved Through The Use of BMPs?

46. Case StudyStony Creek Farms Age Qualified Residential DevelopmentHomsher Hill, LLC Worcester Township, Pennsylvania

47. Proposed Development • Age-Qualified Community • 209 Townhouses • Clubhouse • Day Spa

48. Site Conditions • Forested • C and D Soils • Mild Slopes • Intermittent Stream • Natural Stream Buffer

49. Goals • Control 2-Year Storm • Peak runoff rates • Runoff volume • Water quality • Larger Storms • Control peak runoff rates

50. Objectives • Reduce effective impervious area • Maintain natural conditions • Treat at source • Minimize storm sewers • Infiltrate and evaporate stormwater