Raingardens for Stormwater Treatment

[lindbls]

My County department has been asked to consider allowing the use of Raingardens as primary treament for stormwater runoff. We expect we are receiving this interest because they can be seen as a more attractive alternative than swales or wetponds (currently allowed per our Drainage manual).
Have others used Raingardens with any success? Any brief pros/cons about the use of these?

 

[bltseattle]

Rain Gardens are also known as bioretention cells. Prince George's county Maryland has refined this approach, and through the County website you can access the Bioretention Manual. This manual is pages of relevant design & construction information.

Also check out the Low-Impact Development Center website and

http://www.stormwatercenter.net

for info/links regarding performance.

Some Pros:
Make use of landscape islands to meet water quality treatment requirements; provide landscape amenity, including opportunity for shade trees in parking/streetscapes, provides some level of flow control in addition to water quality treatment
Some Cons:
Must fit in with landscape plan for site, more expensive than grass swales, may reduce buildable area in comparison to underground SWM facilities, landscape element may require design by non-civil engineering professionals - more complicated design process, extra coordination, plant establishment plan required.

 

[Rookie2]

The soils are critical in the bioretention cells. The municipality I mostly work in is currently testing these. According to their tests, the soil needs to be 80% sand in order to achieve the infiltration rates required. This makes them cost prohibitive in my region, as the soil would need to be hauled to the site. Also there is maintenance. The soil will probably eventually become clogged (preventing infiltration) and have to be removed and replaced.