Bioretention 1

[bank]

We are contemplating installation of bioretention within the limits of detention ponds, which might be as much as four feet deep. However, the implementation of bioretention as a Storm Water Quality BMP is very new in this area, and there are many unknowns. For instance, the literature I have been reading generally specify a maximum ponding depth of six inches in the bioretention areas. Is there any reason why it is limited to six inches, other than to prevent the suspension and removal of mulch? Can bioretention even work in a detention pond setting?

 

[jartgo]

The major issue is the mortality of the plants. In my experience frequent heavy flooding (a foot or more) of the plants makes it very difficult to keep the plants alive, which is the whole premise of the treatment provided by a bioretention area. The regulatory requirement for bioretention in my area is maximum of 10 inches of ponding and using a planting soil with minimum infiltration rate of 1/2 inch per hour. My designs now include a maximum ponding of 8 inches and an infiltration rate of a least an inch per hour. Bioretention works great, but you have to have the right conditions for it. Maintenance is very important.

Similar planting in the vicinity of a pond is not uncommon and provides some nutrient uptake, but I would make sure the water can get out quick once it's a foot above the planting elevation. I would recommend consulting a landscaping specialist in your area familiar with this type of work. I usually speak with the local nurserys.

 

[newnickname]

Maryland was one of the first to implement Bioretention BMP's.

You can download their Stormwater manual at

http://www.mde.state.md.us/Programs/WaterPrograms/SedimentandStormwater/stormwater_design/index.asp

 

[francesca]

Another issue is getting enough water often enough to keep it wet. In this area, I believe that a minimum of 20 acres is required to get credit for bioretention in a detention basin.