What are the Conditions in Which Bioretention Systems are Required?

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What are the Conditions in Which Bioretention Systems are Required?

March 26, 2019

Bioretention systems are specially landscaped basins. Actually, they're a waste material percolating system that's designed to process large volumes of stormwater. In truth, this naturally planned contaminant screening construct is both of those things. The ground-based depressions use Mother Nature's finest features to treat contaminated run-off. Definition complete, the next question is whether the conditions around a newly interred Bioretention depression favour this solution.

Slowing Down the Run-Off

Less running and more meandering, that's the requirement the system designer is addressing. The stormwater can't just pour into the basin, not without causing a bank-busting glut of dirty water. Like any other natural ground feature, a moderately paced filtering process is essential. To cut fluid velocity, a technical services consultant incorporates several fluid buffering components, including dense strips of grass and soil. Next on the agenda, special nutrients are mixed with that soil to encourage the formation of swathes of vegetative growth. Now the Bioretention basin is surrounded by a coarse ring of prefiltering grass and vegetation, which grows on a perfectly graded bank.

Determining the Inclination Factor

Conventional biofiltering depressions are set up on level land parcels. There could be a slight funnelling effect in place, so the polluted waters flow towards the depression. Otherwise, the landscaping in and around that area will be sparse. It's the same back at a road or parking area, with a slight curvature of land imparted to those artificial surfaces. Slotted curbs stop that managed water flow from causing miniature floods, then a side slope controls the direction of the run-off. By the way, for this polluted content to be properly treated, those slopes cannot be too steep. A poorly graded slope will just cause a nasty biofilter clog.

Assessing the Local Conditions

All of this work takes place before a Bioretention Basin gets the go-ahead. Before the mulch and slope grading, before the soil engineering practices and planting of mature vegetation, the feasibility of utilizing such a biofiltration solution is assessed. Is this one large plot of land? Will a single basin do the job, or are we looking at multiple land depressions? At the end of the day, site hydrology and topography are two fascinating domains, but they can't be properly interpreted without the aid of an engineer.

Land behaves in a certain way because of its topological features and soil type. Add to that the fact that water tables vary at different times of the year, and we see that this is a challenging project. Indeed, it's managed by a series of naturally functional ground basins, but it takes time for biofilters to process pollutants. By knowing the conditions around that basin, and influencing them, we gain a productive floodwater processing aid, one that uses the land's own natural resources.

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