Brian Friedlich, PE. Jeremiah Bergstrom, LLA

Transcription

1 Engineering Concepts for Bioretention Facilities: From Rain Gardens to Basins NJASLA 2011 Annual Meeting & Expo February 1, 2011 Brian Friedlich, PE Senior Engineer Jeremiah Bergstrom, LLA Senior Project Manager Rutgers Cooperative Extension

2 Overview of Presentation Innovative Stormwater Management - LID The Bioretention ti Concept Applications Basins Rain Gardens Village School Bioretention/Rain Garden Case Study Questions

3 The Urban Water Cycle Figure taken from

4 Conventional Stormwater Design Figure taken from

5 LID Stormwater Design Figure taken from

6 Conventional vs. LID Conventional Concrete-Lined Channel Bioretention Swale in LID Design

7 Conventional vs. LID Conventional Detention Basin Bioretention Basin in LID Design

8 Conventional vs. LID Conventional On-Lot Stormwater Management Rain Garden (Small Bioretention Cell)

9 Other Bioretention Applications Formal Planting Beds Parking Lot Medians Low-Traffic Streetscapes High-Traffic Streetscapes

10 Hydrologic Benefits of Bioretention Reduce peak flows Reduce runoff volume Reduce flooding Convey stormwater to downstream receiving waters Miti Maintain pre-development groundwater recharge Mimic pre-development hydrology

11 Treatment Processes of Bioretention Settling/Filtration Stokes Law Added benefit of dense vegetation and check dams Sorption Bioretention Media Absorption Adsorption Precipitation Transformation ii i Bioretention Treatment Efficiencies: Bioremediation Phytoremediation Pollutant % Removal Suspended Solids 90% Total Phosphorus 70% to 83% Total Nitrogen 68% to 80% BOD 60% to 80% Lead 93% to 98% Zinc 93% to 98% Hydrocarbons 90%

12 Bioretention Basins vs. Rain Gardens While used interchangeably, terms have different connotations: Bioretention Basins Rain Gardens Engineered, larger-scale systems Traditional outlets with hydraulic controls Specialized bioretention media for planting soil Gravel underdrain layer when used on poorly drained soils Smaller-scale systems, frequently used on residential lots Simple overland outlets/overflows Soil amendments for planting bed Shallower ponding depths on poorly drained soils

13 Design of Bioretention Basins

14 The Bioretention Basin Concept NJDEP NJ Stormwater BMP Manual.

15 NJ Stormwater Management Reg s Runoff Quantity Peak flows must not exceed 50, 75, and 80% of the existing peak flows in the 2-, 10-, and 100-year storm events, unless the proposed hydrograph is less than the existing hydrograph at all times during storm events. Runoff Quality Stormwater BMPs must be designed to treat 80% of the annual total suspended solids (TSS) loads. Recharge Existing recharge must be maintained or exceeded for the proposed p site. Nonstructural Strategies (LID) Nonstructural strategies, such as cluster development and vegetative conveyance, g p g y must be used to the maximum extent practicable.

16 General Design Considerations Pretreatment Groundwater Seasonal High Water Table Perched Water Table Native Soils Permeability Karst Formations Existing Topography and Ecological Function Steep Slopes Existing Mature Trees Wetlands

17 NJDEP BMP Manual Design Details

18 Typical Bioretention Outlet Detail OVERFLOW WEIR ~ 1 ft. LOW-FLOW OUTLET, CAPPED BASIN BOTTOM PRECAST CONCRETE STORMWATER OUTLET STRUCTURE PERFORATED PVC UNDERDRAIN SYSTEM

19 Infiltration Through Bioretention Media 0 Hours (Assuming Infiltration Rate of 4.0 inch/hour) 12 ponding depth 2 Hours 4 ponding depth 4 Hours No Standing Water 20 Saturated (40% void) Fully Saturated

20 Routing Bioretention Systems Surface Pond Bioretention Media Stone Layer and Underdrain Outlet Structure/Weir

21 Hydrologic Design Steps 1. Site Investigation/Soil Testing Establish SHWT & Native Soil Permeability 2. Use engineering judgment to decide if underdrain is needed depends on design goals and native soil permeability (<1 in/hr, use underdrain). 3. Setup hydrologic models of pre-development and post-development conditions (i.e. NRCS TR-55 methodology). Segregate contributory area to basin as separate subarea. 4. Setup hydraulic routing of bioretention basin, including surface pond, subsurface media/underdrain, and outlet structure. 5. Use hydraulic routing to size the basin and design the outlet structure. i. Design Goal 1 - Entire water quality event (1.25 over 2 hours in NJ) passes through bioretention media and is treated. ii. iii. Design Goal 2 The lowest orifice on outlet structure should be <12 above the basin bottom. Design Goal l3 Design outlet structure orifices and grate size/elevation i to achieve peak flow reduction or match pre-development hydrograph.

22 Planting Media Specification 1996: 2002: 2009: Clay: 10 to 25% Silt: 30 to 55% Sand: 35 to 60% Clay: < 15% Silt: < 30% Sand: > 65% Clay: 2 to 5% Silt + Clay: <15% Sand: 85 to 95% 3-7% Organics Target infiltration rate is 8.0 inches/hour (4.0 inches/hour used in design). If too slow, then more likely to clog. If too fast, less likely to treat pollutants as efficiently. Basin must drain completely within 72 hours.

23 Bioretention Basin Vegetation Simulated terrestrial forested community Tall Grasses Shrubs Herbaceous Species Trees Native vegetation Diverse species Salt tolerant Flood adaptable

24 Construction Considerations Compaction Bioretention media Underlying soils Light earthmoving equipment Clogging of Bioretention Media Stabilize drainage area prior to installation 2-foot rule when using basin for sedimentation during construction Post-Construction Infiltration Testing

25 Maintenance Considerations Routine Inspections Structures Vegetation Hydrology Vegetation Maintenance Weeding Cutting Grasses Sediment & Trash Removal Inlet and Outlet Structures Pipes in Drainage System

26 Bioretention Basin Case Study Tenacre Bioretention Basin Princeton, New Jersey

27 Bioretention Basin Design Plan

28 Bioretention Basin Design Details

29 Bioretention Basin Construction

30 Bioretention Basin Construction

31 Bioretention Basin Construction

32 Bioretention Basin Construction

33 Bioretention Basin Construction

34 Bioretention Basin Construction

35 Bioretention Basin Construction

36 Bioretention Basin Construction

37 Bioretention Basin Construction

38 Bioretention Basin Construction

39 Design of Rain Gardens

40 What is a Rain Garden? A rain garden is a landscaped, shallow depression that is designed to intercept, treat, and infiltrate stormwater at the source before it becomes runoff. The plants used in the rain garden are native to the region and help retain pollutants that could otherwise harm nearby waterways.

41 Rain Garden Schematic

42 Rain Garden Placement The rain garden should be at least 10 feet from the house so infiltrating water doesn t seep into the foundation. Do not place the rain garden directly over a septic system. Do not put rain garden in places where water already ponds. Place in full or partial sunlight. Select a flat part of the yard for easier digging.

43 Rain Garden Placement

44 Rain Garden Ponding Depth Between four and eight inches deep Depth depends upon lawn slope If the slope is less than 4%, it is easiest to build a 3 to 5-inch deep rain garden. If the slope is between 5 and 7%, it is easiest to build one 6 to 7 inches deep. If the slope is between 8 and 12%, it is easiest to build one about 8 inches deep.

45 Other Considerations Is the soil type suitable? percolation test/infiltration t/i ti testt texture test/soil type test Is the rain garden able to handle the drainage area? if not, consider multiple rain gardens

46 Size of the Rain Garden The size of the rain garden is a function of volume of runoff to be treated and recharged. Typically, a rain garden is sized to handle the water quality design storm: 1.25 inches of rain over two hours. A typical residential rain A typical residential rain garden ranges from 100 to 300 square feet.

47 Example in Sizing Problem: How big does a rain garden need to be to treat the stormwater runoff from my driveway?

48 25 50 Driveway House Driveway Area 50' x 15' = 750 square feet 25' x 10' = 250 square feet Total Area = 1,000 square feet 15 One-Quarter of the Roof 25' x 12.5' = square feet

49 Example in Sizing Drainage Area = 1,000 square feet 1.25 inches of rain = 0.1 feet of rain 1,000 sq. ft. x 0.1 ft. = 100 cubic feet of water for the design storm Let s design a rain garden that is 6 inches deep Answer: 10 ft wide x 20 ft long = 200 square feet

50 Rain Garden Sizing Table for NJ s Water Quality Design Storm Area of Impervious Size of 6 deep Rain Size of 12 deep Rain Surface to be Treated Garden Garden (ft 2 ) (ft 2 ) or [w x d] (ft 2 ) or [w x d] or 10 x10 50 or 10 x or 15 x10 75 or 10 x7½ 1, or 20 x or 10 x10 1, or 30 x or 15 x10 2, or 20 x or 20 x10

51 How much water can we treat? 90% of rainfall events are less than 1.25 New Jersey has approx. 44 of rain per year The rain garden will treat and recharge: 09x =40 /year = 3.33 ft/year The rain garden receives runoff from 1,000 sq.ft. Total volume treated and recharged by the rain garden is 1,000 sq. ft. x 3.3 ft. = 3,300 cubic feet, which is 25,000 gallons per year Build 40 rain gardens and we have treated t and recharged 1,000,000 gallons of water per year!

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53 Rain Garden: Maintenance Issues Repair planting soil bed if erosion occurs. Core aerate or cultivate unvegetated areas annually if surface becomes clogged with fine sediments. Apply mulch twice per year until groundcover establishes. Replace dead or diseased plant material. Inspect/remove any sediment buildup/trash/leaves at inflow and outflow devices on monthly basis. Do NOT fertilize unless you do a soil test!

54 Rain Gardens in NJ? Gardens should be designed to capture 1.25 of rain. Maximum water depth should range from 6 to 12 Size should be 3 to 10% of contributing watershed (e.g., a 1,250 sq. ft. house footprint 125 sq. ft. garden that has a maximum water depth of 1 ft.) Install an underdrain system where soils are not suitable for infiltration Double shredded hardwood mulch 4 thick

55 Rain Garden Plantings Swamp Milkweed Bee Balm Soft Rush Photos by Linda Brazaitis

56 Rain Garden Plantings Blue Flag Iris Cardinal Flower Bald Cypress Shasta Daisy

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59 Rain Garden Case Study Lawrence Nature Center Rain Garden Demonstration Lawrence, New Jersey

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75 Village School Courtyard Rain Gardens Holmdel, New Jersey

76 Village School Site Originally planned as a small educational rain garden project as part of Ramanessin Brook 319(h) grant. After walking the school property, p scope expanded to a more involved courtyard design project. Project Goals: Reduce runoff volumes leaving the site through infiltration in rain gardens. Improve stormwater treatment with filtration through soil. Decrease flows and erosion downstream. Provide science/nature educational setting.

77 Village School - Aerial Courtyard Rain Gardens Project Area

78 Village School Site

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86 Educational Program

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93 Questions Brian Friedlich, PE Senior Engineer Omni Environmental, LLC com Jeremiah Bergstrom, LLA, ASLA Senior Project Manager Rutgers Cooperative Extension Water Resources Program