Brian Friedlich, PE. Jeremiah Bergstrom, LLA

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

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

The Urban Water Cycle Figure taken from http://www.manukauwater.co.nz

Conventional Stormwater Design Figure taken from http://www.michiganlakeinfo.com

LID Stormwater Design Figure taken from http://www.michiganlakeinfo.com

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

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

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

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

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

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%

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

Design of Bioretention Basins

The Bioretention Basin Concept NJDEP. 2004. NJ Stormwater BMP Manual.

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.

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

NJDEP BMP Manual Design Details

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

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

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

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.

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.

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

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

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

Bioretention Basin Case Study Tenacre Bioretention Basin Princeton, New Jersey

Bioretention Basin Design Plan

Bioretention Basin Design Details

Bioretention Basin Construction

Design of Rain Gardens

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.

Rain Garden Schematic

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.

Rain Garden Placement http://clean-water.uwex.edu/pubs/raingarden/rgmanual.pdf

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.

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

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.

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

25 50 Driveway House 25 50 10 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' = 312.5 square feet

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

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] 500 100 or 10 x10 50 or 10 x5 750 150 or 15 x10 75 or 10 x7½ 1,000 200 or 20 x10 100 or 10 x10 1,500 300 or 30 x10 150 or 15 x10 2,000 400 or 20 x20 200 or 20 x10

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: 09x44 0.9 =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!

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!

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

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

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

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

Village School Courtyard Rain Gardens Holmdel, New Jersey

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.

Village School - Aerial Courtyard Rain Gardens Project Area

Village School Site

Educational Program

Questions Brian Friedlich, PE Senior Engineer Omni Environmental, LLC bfriedlich@omni-env.comenv com Jeremiah Bergstrom, LLA, ASLA Senior Project Manager Rutgers Cooperative Extension Water Resources Program jbergstrom@envsci.rutgers.edu