The Stormwater Blog 

Contech Stormwater experts discussing Low Impact Development, Onsite Water Management, Rainwater Harvesting and all things Stormwater.


Biofiltration


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Leave the Bio in BioFilter...Plants Do Matter
Plants provide fresh oxygen to breathe and beautiful aesthetics that can take our breath away, but many people don’t think about the role plants can play in stormwater treatment. The principal notion of Low Impact Development (LID) is founded upon mimicking pre-development conditions. Part of mimicking pre-development conditions includes not just matching pre-development peak flow rates, but also matching the pollutant load discharging from the drainage area.
Rain Gardens Not Permitted?

Current stormwater design guidance typically recommends starting with preservation of the natural landscape and hydrology wherever feasible. But, even with preservation, new stormwater management facilities are likely to be required to capture and clean runoff from pollution generating surfaces. These new stormwater facilities are likely to include imported soil or soil amendments that add permeability and/or optimize soil structure for vegetative growth. For many years, the industry has characterized media in vegetated facilities generically as soil, sand, compost, etc.

Bioretention Part One: Lessons Being Learned

As bioretention becomes more popular, many types of designs are being deployed throughout the U.S.  Though relatively simple in concept, many are finding that the devil is in the details with respect to maintenance and performance.  These issues are driving newer designs and improving criteria for use. Over my next few posts, I will be sharing some of the experiences and lessons learned with bioretention design. 

 

Phosphorus Leaching from Bioretention and Green Roofs: The “Dirty Little Secret”

Bioretention and green roofs have become the centerpieces of Low Impact Development (LID) initiatives throughout North America. The well-publicized benefits of these two types of stormwater management practices focus on runoff reduction, stormwater quality treatment, and landscape aesthetics. Promotional literature provided by various regulatory agencies and environmental organizations typically highlights the processes and mechanisms within bioretention and green roofs that provide desirable outcomes. Normally, one finds mention of evapotranspiration, filtering, and adsorption characteristics of the vegetation and soil mix as beneficial mechanisms for the purposes of runoff reduction, particulate and hydrocarbon removal, and dissolved pollutant capture, respectively.

When Conventional Bioretention is Not Feasible, Consider Tree Box Filters
Perhaps the most recognized Low Impact Development technique, bioretention, incorporates landscaped features to slowly percolate stormwater runoff through plants and engineered soil prior to infiltrating that water into native soils.
Leaves, Trees, and Stormwater BMPs: Designing with Maintenance in Mind
Preserving large trees as runoff interceptors is an integral part of low impact development as well as incorporating trees and vegetation in filtration beds, rain gardens, and bioretention systems. These systems are extremely beneficial and provide essential functions of the natural landscape: infiltration, evaporation, transpiration, interception, and shading.
Structural Considerations for Stormwater Control Measures
As the need for effective stormwater treatment and volume control grows, so does the number of available stormwater control measures (SCMs) such as filtration systems, hydrodynamic separators, bio-retention  systems, green roofs and pervious pavement. As part of their due diligence, engineers go through an evaluation process to determine if the proposed system will meet some basic criteria, one of which is structural considerations. Below are some of the structural considerations.  The engineer should not assume that because a SCM is approved and/or detailed in a manual that all of the structural issues have been addressed. 
What’s Happening Inside My Tree Box Filter?
An appropriately designed and manufactured tree box filter combines the benefits of natural biofiltration with the reliable and predictable performance of an engineered system. Each tree box filter utilizes a multifaceted approach including physical, chemical and biological processes to capture, immobilize and treat harmful pollutants, while also encouraging low impact development practices by treating smaller drainage areas at the source.
Choosing the Right LID Solution – A Hierarchical Approach
With LID, not all solutions are created equal. There is a hierarchy in the regulations for what is the preferred technology. So it’s not so much is it approved or not approved… there are certain preferred technologies that must be considered first, and if that doesn’t work, you consider the next option in preference. This is a huge difference in conventional stormwater regulations, which says technologies must be approved by state of local jurisdictions – and then everything is on a level playing field. 
Four Ways to Keep Your Biofiltration Box Working Properly
Inspection and maintenance are key factors for making sure that your biofiltration box is performing as designed and achieving the required water quality standards.  Here are a few things to keep in mind.

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