4/2/2012. What s a rain garden?

Transcription

1 What s a rain garden? 1

2 Back up what is a watershed? An area of land, delineated by topography, where all water drains to the same place A community 2

3 Stormwater Water that runs off of impervious surfaces like roads, parking lots, and rooftops 3

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8 Managing stormwater on-site 8

9 Multi-functional Lawn Infiltration: 1 inch per hour Prairie Infiltration: inches per hour Water Quality Benefits Rain gardens can remove: percent of total suspended solids 60 percent total phosphorous percent total nitrogen (source: Mich LID manual) 9

10 Drawbacks Need lots of space can be poorly suited for ultra urban areas. Don t work as well during the winter. Don t work well in contaminated soils. De-icing salt Semcog.org /lowimpactdevelopment reference.aspx 10

11 Choose your goal I want my rain garden to soak in some runoff, provide habitat, and look nice. capture runoff from the first half inch of rain that falls. capture all the runoff from a we-only-get-arainstorm-like-this-one-every-two-years-or-so storm. Site planning 11

12 Source: Michigan LID manual 12

13 Do-it-yourself Rain Garden Cheap Handles runoff from a house or driveway Trial-and-error might be okay Engineered Bioinfiltration Expensive Handles runoff from large buildings, parking lots, etc. Needs detailed calculations for volume and infiltration rates Simple basin, maybe with a pipe for emergency overflow Standpipe for overflow, additional cistern or storage beds underground, connected to storm sewer system Will this soil work? It s easier to install a rain garden at a site with sandier soils. If you have heavy clay, you might need to. build an extra-large garden to allow for slow infiltration through clay amend the soil with sand and compost (or make a gravel storage bed underneath) rely on something other than a rain garden to catch your stormwater. Simple home recommendation for soil testing: Dig an 18 hole, fill with water, and let it drain. Refill it, and keep track of how long it takes to drain the second time. If it takes more than 24 hours, hire a landscaper or contractor. (Washtenaw County, ewashtenaw.org) extension.missouri.edu 13

14 Will this spot work? Easier if a construction project is built with a rain garden already in mind (e.g. grading a parking lot) If you already built does the runoff flow here? If not, can I manipulate it to flow here? Fishbeck, Thompson, Carr, and Huber Inc. Inlets Lots of options French drain along roof dripline Rain barrel Curb cut Downspout extension tube (remember ten feet from building) Low spot in your lawn where water already flows during rain Ways to prevent erosion at inlet Flared end section Erosion control matting Grassy filter strip Rocks Homebuilderwholesale.com 14

15 Overflow considerations Lots of options: At inlet Below ground (underdrain, french drain, etc.) Domed riser/standpipe Prevents clogging (alt.=dig out to decrease elevation around drain) Depth The basin Shallowest ~ 3. Normally 6-12, max 18. Do not exceed 18. (and you need different plants for deeper gardens) AREA Rule of thumb: 5:1 Impervious drainage area:rain garden area For larger, engineered areas 15

16 Soil amendments Don t usually need them in sandy soils Add sand to increase infiltration. You can use the heavier soil you replaced as a berm around the basin Compost works well as a sponge Native plants don t usually need the nutrients. Go native! Plant Materials Density: 1 plant per square foot for a full garden Don t forget grasses and sedges Resources: LID Manual, Appendix C 16

17 Plant Materials Go Native 17

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25 5 year plan Maintenance Little to no watering after plants are established No fertilizer Low-maintenance, not No-maintenance. Critical for first 1-2 years Periodic checking and maintenance afterwards Plants can take around 5 years to fill out and mature. 25

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28 Education and outreach potential 28

29 Maintenance Example projects 29

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