Rain Gardens

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Rain Gardens

There are numerous websites describing how to design and construct a rain garden. Search the web and find two good sites to use as resources for the assignment this week.

What is a Rain Garden?

A rain garden is a garden designed to intercept runoff from roofs, downspouts, driveways, patios, and other impervious areas. A rain garden is designed to allow some of the runoff to soak into the ground, and to slow down flows and remove some pollutants. A rain garden captures runoff water that would otherwise enter streets and storm drains and thus helps reduce stormwater flooding and improves water quality.

Designing and installing a rain garden

  1. A rain garden needs to go where the water flows – it should be downhill from the water source.
  2. It should be at least 10 feet away from the foundation of the house, wells, or septic systems.
  3. A rain garden should not be installed where soils are shallow, or the water table is high (within 4ft of the surface).
  4. It should be located where water soaks into the ground (Evaluate the soil type and do a percolation test to evaluate the site prior to construction. Dig a hole to the depth of the proposed rain garden and fill with the hole with water. Water should drain away within 2-4 hours).
  5. In areas with high risk of sink-holes the garden can be lined. This will prevent infiltration but the garden will still provide water capture and use by evapotranspiration.
  6. Size the rain garden to capture the desired storm event. The Pa stormwater bmp manual provides guidance on sizing rain gardens for PA. http://www.depweb.state.pa.us/watershedmgmt/cwp/view.asp?a=1437&q=529063&watershedmgmtNavPage=|
  7. Call Pa one call before starting any digging
  8. Lay out the garden and remove the turf.
  9. Cut and fill to create a berm on the downslope side – make sure the bottom of the depression is level
  10. Refill the depression (if necessary) with amended soil
  11. Provide an outlet for large rain events. An inlet may be needed to dissipate energy if the flow is from a downspout.
  12. Plant species adapted to intermittent wet and dry conditions and appropriate for the light conditions of the site.


Read the article below:


This Old House article on rain gardens - Click on the screen shot to see the article.



Exercise: 

Follow the link below to the rain garden design assignment and turn in your submissions to the drop box in the Week 11 Canvas module

Raingarden design assignment



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