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What is Bioretention?

what-is-bioretention-soil | norcal ag service

Unchecked, stormwater runoff can be a dangerous contaminate that does more harm than good. But, since we are just talking about water here, the potential for useful repurposing is also enormous.

As concerns over stormwater runoff became increasingly more prevalent, productive solutions are ever more necessary.

That is where bioretention comes into play. A bioretention area can serve as a safe, useful solution to stormwater treatment.

Bioretention is a process that removes contaminants from storm runoff and improves the overall water quality so that it can be put to good use.

There are various means of accomplishing this (a basin or swale just to name two), but almost all of them require special landscaping features, and bioretention soil plays an integral part.

Today we will look at the ends and outs of bioretention management practices.

Bioretention Basin

The bioretention basin is what many people think of when stormwater treatment comes to mind. It’s actually a landscaping feature. A depression that collects storm runoff into a designated area where it is subsequently filtered through the area until it is purified.

The water then slowly collects towards nearby native areas where it can be used to practical effect.

These features are often used in residential areas, and can even look decorative. For example, a bioretention designed parking lot island might be a stormwater basin—where water is collected, utilized, and then subsequently siphoned by a nearby storm drain.

Though these systems sound very simple, they are actually quite nuanced and consist of multiple parts.

Bioretention basins may include a grass buffer strip. The purpose of this feature is to slow the water down, and also to collect surface contaminants so that they aren’t absorbed into the soil.

Additional vegetation may also be present to further serve this purpose.

Then there is also typically a ponding area where the water collects, then several layers of solution for nutrient and contamination absorption.  

Mulch, special soils, and sand beds all filter and percolate storm water to rid it of harmful substances and excessive nutrients while an underdrain system removes the water once it has been treated so that it can be usefully applied to nearby native areas.

You might also hear this system referred to as a rain garden. Essentially it’s like a nature’s water filter. It brings in contaminants and excessive moisture, and can in turn them into something beautiful.

Though this option is generally used for large to medium size parcels of land, the range of application is actually quite large. With tweaks to the design it can be optimized for climates both warm and cold.

Bioretention basins can even be used in high contamination areas like gas stations with the right equipment. However, in these sites elaborate filters may be needed for quality control.

Bioretention Swale (Bioswale)

Similar to the basin, we have the bioretention swale. Or, as it is also known, the bioswale. The bioswale is often seen in urban or suburban settings, and can be a simple, low cost solution to storm runoff mitigation.

This water harvesting system features landscaped depressions that disrupt the flow of water at the bottom of a descending side slope.

They offer lots of real estate for attractive greenscape, but do take up a considerable amount of space making them difficult to use in cooperation with larger sidewalk areas.

In instances of heavy rain, they are invaluable assets. They are also generally safe in the event of accidental pedestrian foot traffic, and additional prevention strategies are also possible to make sure this risk is minimized.

To the layperson the difference between this system and the basin is actually quite minimal. The most substantial distinguishing feature pertains to the quantity of water that either is able to accommodate.

Bioswales are usually made for larger amounts of water, which is why you might see them being applied near a highway or city street where proper water collection is of extreme importance.

The importance of bioswales in urban communities is currently experiencing an increase in awareness. As a result, there are many initiatives across the country to improve their presence in communities that could use them. For more information on this trend visit NACTO.

Bioretention Soil

Last, there is bioretention soil (also called bioretention media). This material isn’t quite as obvious as a big swale or basin, but that is only because it works behind the scenes.
In any serious bioretention project, bioretention soil will be at the heart of the operation.

The name of bioretention soil does well to describe its function. Essentially, it is just soil made with the right draining and purification properties.

The right soil will ensure that a basin or swale is able to drain properly and work to its intended effect. Done wrong and the water will pool uselessly at the surface.

Though simple relative to impressive landscaping feats illustrated above, proper bioretention media is actually harder to find than one might assume. While experts are all in agreement as to what it should do, not everyone is adequately equipped to come up with a mix that performs the intended function.

Ideally, bioretention soil will both drain well, and facilitate vegetation and even tree growth.

This means finding the right mix of draining properties, such as sand, while still creating a nutritionally viable blend.

Right now, conventional wisdom indicates that a proper mix should include 5% clay make up, and 12% fines.

However, in application, different mixes with a higher level of fine presence are also finding success. In other words? Science has yet to find the perfect combination.

Get In Touch With Us

When planning a bioretention strategy it helps to have the right people in your corner. As illustrated above, the right soil remedy can be the difference between success and failure. Finding the right product is integral to success.

Contact us today for a free quote so that you can get your project up and running the right way.

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