Design of Backyard Rain Gardens Gloucester County, New Jersey February 14, 2008
Christopher C. Obropta, Ph.D., P.E. Water Resources Extension Specialist Rutgers Cooperative Extension Phone: 732-932-9800 ext. 6209 E-mail: obropta@envsci.rutgers.edu Gregory Rusciano Program Associate, Water Resources Rutgers Cooperative Extension/ NJ Sea Grant Extension Program Phone: 732-932-9800 ext. 6130 E-mail: greg.rusciano@rutgers.edu http://www.water.rutgers.edu/
Let s start with a scenario Homeowner calls ABC Landscaping Homeowner: Will you install a rain garden? Landscaper: Yes. I need to evaluate your property. Homeowner: How much will it cost? Landscaper: It could cost about $ depending on a few considerations. (we will get to that later)
Talk to the Homeowner Ask the following: Do you have a septic system? Do you have a basement? Do you have a placement preference (front, back or side of the house)? Do you have a deer problem?
Perform a Site Visit Determine possible areas for placement Tools needed Locate existing roof leaders Approximate the roof area and/or driveway area 100 300 tape measure Camera Sketch pad and pencil Approximate the slope Take note of existing large trees and other landscaping next to the house
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. Place a rain garden down-slope to collect overland flow Do not put rain garden in places where the water already ponds or the lawn is always soggy. Place in full or partial sunlight as a first option Select a flat part of the yard for easier digging as a first option. Avoid large tree roots. http://clean-water.uwex.edu/pubs/raingarden/rgmanual.pdf
Placement Options Road, driveway or parking lot runoff (no curb)
Placement options Road, driveway, or parking lot runoff (curb cut)
Placement Options Roof runoff Utilize existing roof leaders Multiple rain gardens are required to manage the entire roof area Combination of roof and driveway (example to follow) Over-land flow of the lot or neighbor s lot
http://clean-water.uwex.edu/pubs/raingarden/rgmanual.pdf Rain Garden Placement
Is the Soil Type Suitable? 1. Percolation test/infiltration test 2. Texture test/soil type test 3. Soil test kit ($15) From your county extension office Texture Analysis Percent sand/silt/clay ($45) Fertilizer recommendations ph
Options If the Perc. Test Fails.. 1. Move on to another house 2. Consider amending the soil for better percolation: Requires digging deeper (at least 6 inches deeper) Replace with sandy loam top soil or mix in sand with rototiller Requires additional discussion with homeowner It will drive up the price Perform the additional tests described previously
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 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 Check: 200 square feet x 0.5 ft deep = 100 cubic feet of storage volume
Rain Garden Sizing Table for NJ s Water Quality Design Storm Area of Impervious Surface to be Treated (ft 2 ) Size of 6 deep Rain Garden (ft 2 ) or [w x d] Size of 12 deep Rain Garden (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 does this 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: 0.9 x 44 = 40 /year = 3.3 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 of these and we have treated and recharged 1,000,000 gallons of water per year!
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. http://clean-water.uwex.edu/pubs/raingarden/rgmanual.pdf
On Installation Day MATERIALS NEEDED Triple-shredded hardwood mulch (no dye) Plants Soil amendments Fertilizer ph adjustment Sand Optional Decorative stone Pipe extensions Grass seed/sod Pavers for path Soil rakes Shovels TOOLS NEEDED Rototiller ($500 - $1,000 investment) Work crew (1 supervisor and 3-4 laborers) Wheelbarrow Leaf rakes (for spreading mulch)
Digging Your Garden (3-8% Slope)
Digging Your Garden (>8% Slope)
Find the Slope of the Lawn Height 100= % Slope Width
Keep Your Rain Garden Level
Plant Selection Native plants Shrubs, grasses, rushes, flowers, trees (in some cases) Facultative wetland (FACW, FACW+, FACW-) Facultative (FAC, FAC+, FAC-) Facultative upland (FACU, FACU+, FACU-) Purchase wholesale and stockpile Use as needed Buy small and transfer to larger pots Purchase as needed Investigate local nurseries for natives Does the homeowner prefer large potted plants or smaller cutting that will grow large over time?
Plant Selection Sun or shade layout Refer to schematics (NPSNJ Manual)
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
Frequently Asked Questions: Q: I have a wet spot behind my house; would this be a good place for a rain garden? A: No, a rain garden is suppose to drain after 24 hours. Q: Can I put plants in my berm? A: Yes. Q: What about deer? A: We recommend purchasing a SUVs (Hybrid of course) and driving very fast on the back roads at night. Or fencing or deer resistant plants or deer retardant sprays.
Frequently Asked Questions: Q: Do I need to fertilize? A: You should fertilize during the initial planting according to the county soil test kit results. Q: Do I need to water? A: Yes. Frequently during the first year. Especially the first few months after planting (particularly if it is in the middle of the summer). Q: What if some plants die? A: Younger plants will be more susceptible to drowning if they are immersed in standing water for too long. As a rule of thumb place the most water tolerant plants near the water s entrance to the garden. Replace the dead plants with larger cuttings or a species that you know have survived.
Frequently Asked Questions: Q: How do I know if my soil is suitable to for a rain garden? A: Do a perc test or an infiltration test. If the infiltration rate is at least one inch per hour, you are good to go! Q: Can I build my rain garden clay soils? A: Yes, but there are some additional measures to take: increase the area and decrease the depth make sure the clay layer is dry (otherwise shovels will seal pores) Add soil amendments (using your rototiller) Replace the first 0.5-2 feet (below the ponding area) with sandy loam soil. You can create your own by obtaining bank run sand from a nursery. DO NOT USE MASON OR BALL FIELD SAND. Mix in 3 inches of compost at the top
Frequently Asked Questions: Q: How do I slow down the speed of water as it enters the garden? A: (1) Attach a perforated plastic diffuser to the end of your roof leader (2) Use river rock at the entrance point (3) Site your rain garden with a 10 15 foot grass buffer between it and the roof leader. Use native grasses and let them grow tall. Q: What to I do with my existing grass before starting the rain garden? A: A two options: (1) Kill the grass with herbicide beforehand or (2) Remove the turf as sod pieces. You can reuse it on your berm or another area of your yard.
Costs
Back to Our Original Scenario Homeowner: How much will it cost? 1. Determine overhead costs Plants Wholesale or retail Homeowner preference Small or large stock Soil amendments Labor (usually requires a half-day of work) Mulch Optional features 2. Determine reasonable profit 3. Inform the homeowner of maintenance costs Some maintenance will have to be done by the homeowner Some may or may not be done by the landscaper
Back to Our Original Scenario Typical Overhead Costs Plants: $200 - $750 Mulch: $20 - $30 per yard Coarse sand: $20 $40 per yard Compost: $20 - $40 per yard Equipment rentals Rototiller Bobcat/small backhoe
Maintenance Landscaper and/or Homeowner
Bioretention Basin: Maintenance Issues Repair mulch 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! (every one to three years recommended)
Maintaining Your Rain Garden Types of Maintenance Measures: Inspections Soil Testing Weeding Pruning Mowing Revegetating as necessary Sediment removal as necessary Notice that FERTILIZING is not listed above. A rain garden sustains itself with the help of organic material in the topsoil.
Measure #1: Inspections What am I inspecting for? Weeds & Invasive Plants Plant Health Excessive Sediment Movement of Sediment within the Garden When? Prior to Season GROWING SEASON After large storm events During weather extremes End of Season
Measure #2: Soil Testing Soil should be tested every 1-3 years ph should be in an acidic range If ph is < 5.2, apply limestone If ph is > 7.0 to 8.0, add iron sulfate and sulfur to reduce ph Soil amendments should only be added when no storms are expected
Measure #3: Weeding Weeding more often will limit the amount of time you will have to spend weeding in the end Watch for overly-competitive species Look to RCE N.J. Weed Gallery for more info NRCS also hosts a PLANTS Database for the entire US Some weeds can be aggressively spreading underground by rhizomes
Measure #4: Pruning Pruning directs growth of plants, improves health, and increases production of flowers and fruits. How does pruning a rain garden differ from my other gardens? In a rain garden, dense shrub growth is encouraged rather than eliminated to provide increased filtering capacity Tattered and discolored plants should be cut back after spring arrives and growth is 4-6 tall Deadheading plants will also lead to succeeding new growths
Types of Pruning THINNING = basically, thinning out. This type of pruning removes entire branches back to main trunk. Or major branches to the ground. Expected result: large, open shrub HEADING = also known as heading back. This type of pruning removes only part of a branch. Expected result: growth of multiple branches in place of single branch, thus a more dense shrub
Pruning & Types of Wood In the case of flowering shrubs, pruning is a function of species and flowering periods. Determine if the shrub blooms on new or old wood NEW = shrub blossoms in late spring or summer on wood that is grown during the current season. This wood may be light green or pinkish in color. Prune during dormant season or just before new growths in early spring. OLD = shrub blossoms in early spring on wood grown during previous season. This wood will be dark in color and can be brittle.
Measure #5: Mowing After the growing season, it will not be necessary to remove stems and seedheads. These can be left for habitat and in some cases, aesthetics. A string trimmer can be used to maintain over-competitive growths. Dead plant materials can also be removed by a string trimmer or mower, if the mowing deck can be raised to cut at 6-8.
Mowing Schedule Mowing should occur two times a year, in your rain garden. Initial mowing can be done after the first few weeks of growth early Spring. Final mowing can be completed after ground nesting birds have hatched the next generation usually near mid-may.
Measure #6: Revegetating After the first season, it may be obvious what plants were successful in this niche and what plants do not work for your rain garden. Over the growing season, was the weather drastically different than the conditions the basin was designed to retain? Did the topsoil limit the holding capacity of the basin or encourage adsorption? Was flow too fast through the basin, damaging health? Is flow being incorrectly diverted from the rain garden? Is sediment covering vegetation? Were some species over-shadowing others? Did pests reduce the success of certain species? Is one area of the rain garden not growing at the same rate as another? Why?
Revegetating & Re-evaluating Questions from the previous slide require some thought as to whether the rain garden is serving the purposes of: a. Trapping Pollutants b. Reducing Runoff and Promoting Infiltration c. Creating Habitat for Birds, Butterflies, & Beneficial Insects d. Adding Beauty to your Yard
Next Steps Collect seeds and cuttings from successful plants in the rain garden and use them for the new season. Plant more of the successful species in the rain garden as necessary. Re-seed the berm if there are areas of exposed soil. Replace rocks that may be diverting flow out of the garden. Alternately, build up areas where more protection is needed.
Measure #7: Sediment Removal Since the rain garden serves the purpose of catchment, sediment will tend to accumulate within the garden. This a sign of success this soil would have been directed straight to the stream, without your efforts! With a flat shovel, remove soil that has accumulated in the basin. Avoid the vegetation. Sediment can be added to a compost pile, but do not use the compost in a vegetable garden. There is no exact schedule for when this should be done. Try to monitor sediment accumulation, especially after all heavy storm events. Be sure that sediment is not churning up from exposed areas of the rain garden. Flow should be dissipated to avoid these situations, which are likely to occur in the early stages of stabilization. Heavy equipment should not be needed for this task
Conclusions Rain gardens (bioretention basins) provide extremely high levels of storm water treatment. These systems design will detain runoff from 1 inch or smaller storms (90% of all storms) for several days. These designs will provide mechanism for stormwater temperature decreases. The plant material (trees and shrubs) within the basins will provide diversity in the landscape and wildlife habitat. New stringent storm water treatment requirements may be satisfied using rain gardens and bioretention basins. They are aesthetically pleasing and easily incorporated into the landscape
MORE ABOUT BIORETENTION LARGER STRUCTRAL BEST MANAGEMENT PRACTICES
Nonstructural Low Impact Development Strategies Minimize impervious cover Minimize disturbance Maximize vegetation, minimize lawns Pollutant Reduction Minimize vegetation that needs fertilizers Trash racks and receptacles
Groundwater Recharge Groundwater Recharge: Infiltrated water that is not evapotranspired Groundwater shall not be recharged in areas with high pollutant loading Waiver available for urban redevelopment Groundwater Criteria: Maintain existing (100%) average annual groundwater recharge OR Infiltrate the increase in runoff volume for the 2-year storm event
Critical Issue Question: How can we develop property without increasing Non-Point Source (NPS) loads while maintaining groundwater recharge? Answers: Advanced Best Management Practices (BMPs)
The Traditional Approach Design Dry Detention Basin that: Treat Water Quality Storm (1.25 rain over 24 hours) Detain for 18 hours (residential) or 36 hours (commercial) Minimum outflow orifice = 3 inches Use Concrete Low Flow Channels to Minimize Erosion
The Traditional Detention Basin
The New Approach Combines settling of detention basin with physical filtering and adsorption processes Provides very high pollutant removal efficiencies More aesthetically pleasing than conventional detention basins Can be incorporated into the landscapes of individual homes
Rain Gardens (Bioretention Basins) Landscaped areas that treat stormwater runoff. Designed to merge two important goals: aesthetics and water quality Can be blended into the landscape and made to look natural. Water is directed into them by pipes, swales, or curb openings.
Rain Gardens (Bioretention Basins)
Rain Gardens (Bioretention Basins)
Rain Gardens/Bioretention Systems NJDEP. 2004. NJ Stormwater BMP Manual.
Absorption to soil particles Removes dissolved metals and soluble phosphorus Plant uptake Removes small amounts of nutrients Microbial processes Removes organics and pathogens Exposure to sunlight and dryness Removes pathogens Infiltration of runoff Pollutant Removal Mechanisms NOTE: 90% of all storm events produce less than 1 inch of rain. Therefore, the key to reducing pollutant loads is to treat the runoff associated with the first 1 inch of rain (Claytor & Schueler, 1996). Provides flood control, groundwater recharge, and nutrient removal Sedimentation and filtration Removes total suspended solids, floating debris, trash, soil-bound phosphorus, some soil-bound pathogens
Cross-Section of Rain Garden - Bioretention Basin BASIN SLOPE NATIVE PLANTINGS 4 IN. MULCH LAYER MIN. 5 FT. DEPTH 2.5 3 FT. PLANTING SOIL BED (MIN. PERMEABILITY 0.5 IN. PER HOUR) 12 IN. SAND BED 12 IN. GRAVEL BED 4 IN. PERF. PVC PIPE FILTER FABRIC
Bioretention Basin Expected Infiltration 0 Hours 12 ponding depth 6 Hours 9 ponding depth 3 infiltration 12 Hours 6 ponding depth 6 infiltration
Bioretention Basin Expected Infiltration 1 Day No Standing Water 2 Days 12 infiltration No Standing Water 24 infiltration 3 Days No Standing Water 36 infiltration
Pollutant Removal Rate Comparison Detention Basin (Detain 1.25 storm for 12 hours) Bioretention Basin - (exfiltrate 1 runoff volume/impervious acre) RAIN GARDEN/ PARAMETER DETENTION BASIN BIORETENTION BASIN PROBABLE RANGE PROBABLE RANGE Suspended Solids 70% to 90% 90% Total Phosphorus 10% to 60% 70% to 83% Total Nitrogen 20% to 60% 68% to 80% BOD 30% to 40% 60% to 80% Lead 20% to 60% 93% to 98% Zinc 40 % to 60% 93% to 98% Hydrocarbons 60% to 77% 90%
Bioretention Basin