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Turn Your Attention to Bioretention

What is a bioswale? How does bioretention work?

A bioswale is a low-lying, linear depression that directs the flow of water while letting it percolate into the soil.  This process is known as bioretention: using biology to retain, or slow, water.

How do bioswales, streetscapes and rain gardens work?

Bioswales, streetscapes, and rain gardens apply the same strategy in different formations: they use soil and plants to manage stormwater and reduce erosion in cost effective, environmentally-friendly manners. The plants and soil – or bioretention media – serve as natural filters that remove silt and pollution from runoff water.

How do bioswales remove pollutants?

Bioswales behave like mini constructed wetlands. After a rain, water flowing off of surfaces – typically roofs or roadway – gets diverted into beds of hardy grasses and other plants. Then, the following occurs as illustrated in the photo:

  1. Soil in the bioswale catches contaminants in the runoff.
  2. Oil and metal contaminants are broken down by soil microbes. This changes their chemical structure so they are no longer toxic.
  3. Contaminant-eating microbes need oxygen to work. Wetland plants bring oxygen into the soil.

Water leaving the bioswale is cleaner than when it came in.

 

What are other ways bioretention soils help reduce pollution?

  • They slow the flow. Water that falls to the earth during rain events has a chance to get absorbed by the earth and return to the groundwater table, as opposed to getting whisked away by sewers and drains.
  • They filter out pollutants. Ideally water that reaches surrounding lakes, streams and bodies of water does not have debris or pollutants.

What elements of rain gardens should I look for in a rain garden, streetscape, or bioswale?

A cross section reveals four different layers:

  • Dry – The top where floodwaters never reach. Drainage here is good because it’s at the top of a slope.
  • Mesic – This level, just below the dry zone, experiences occasional, brief winter flooding and summer drought.
  • Moist –  The zone approaching the bottom that experiences frequent winter flooding. The number of plants that can grow here without summer water is limited.
  • Wet – The bottom of the swale will be saturated for a large portion of the year; water plants can be grown here if supplemental water is given in the winter. Without summer irrigation, fewer plants can grow here.

A small rain garden can capture driveway runoff in elegant fashion.How do I build a rain garden or bioswale in on my property?

A rain garden is a planted depression where run-off from roofs, driveways and other surfaces is directed so that it can soak back into the soil naturally rather than run into storm drains. The soil and plants in these areas filter out some impurities before the water drains into sewers, groundwater, rivers and streams.

  • Choose a location: Choose a spot where water can be easily directed through the landscape or from downspouts. Make sure to leave at least 6 feet from your house, and allow for overflow away from foundations and other structures.
  • Prepare the site and soil: Amend the soil so the mix is roughly 50% native soil, 30% soil amendment or compost-based product, and 20% pumice.
  • Mulch: Two kinds of mulch are important in a rain garden. A mulch of pea gravel or river rocks at the point where water enters will help prevent erosion; this mulch should be thick enough that no soil shows through. The rest of the rain garden should have a high-quality soil amendment or compost-based product 1-3” deep added once a year as spring rains taper off. This will help suppress weeds and maintain moisture levels during dry periods.
  • Water during the first couple years: All plants (even drought-tolerant ones) will need supplemental watering the first 1-2 years until they are well established.
  • Avoid fertilizers and pesticides: These should both be avoided in your rain garden whenever possible; part of the goal is to help keep these synthetic chemicals out of local waterways. If necessary, use granular, low phosphorous, organic fertilizer, and the least toxic pesticide available. Plant selection is critical; consult with the nursery specialist for plants that will thrive in this environment.

How does compost fit in to bioretention?

Specially formulated soils rich in organic matter help provide both short-term and long-term positive impacts on soil structure. With compost, the soils resist compaction in finer soils and provide greater drought resistance and water holding capacity in coarse, sandy soils. Soil porosity is key in soil structure and the coarse organic texture of compost creates an environment for better root development. Compost increases Cation Exchange Capacity (CEC) which is the ability for soils to retain micro nutrients for the plant to utilize and lowers nutrient leaching. Compost supplies many beneficial micro-organisms and nutrients to soils and growing media as well as bind and degrade specific pollutants – a strong characteristic in bioretention soil use.

The benefits of using compost for plants, the environment and completing the recycling loop in our communities are tremendous. As a plant organic and nutrient source compost works with soil biology naturally to increase soil organism activity. This relationship between planting soils and compost derived from green waste can support a wide variety of soil amendment needs for growing plants, stormwater management and soil erosion.

Where can I get bioretention media?

Harvest offers custom blends in almost all of its markets. Our soil specialists can help meet your needs. Minimum quantities apply.

Supplying Soil for Stormwater Management Success

When people think of stormwater management, they might immediately jump to thinking about the health of rivers and streams. But a key ingredient in improving water quality that many people often overlook is soil.

Harvest routinely provides custom soils blended for bioretention and rain gardens. We were especially honored to provide the soil for three stormwater management containers – two at-grade precast concrete bio-retention planters and one above grade planter, all supplied by Olcastle Precast-Chesapeake Region – at the U.S. Coast Guard Yard in Baltimore, Maryland.

Specially formulated soil, rich in organic matter, will help achieve two ideal outcomes:

  1. It will slow the flow. Ideally water that falls to the earth has a chance to get absorbed by the earth and return to the groundwater table, as opposed to getting whisked away by sewers and drains.
  2. It will filter out pollutants. Ideally water that reaches surrounding lakes, streams and bodies of water does not have debris or pollutants. Healthy soil can act as a natural filter for water.

These ingredients – thoughtful engineering and healthy soil – will help make the world greener and the water cleaner.  Contact us today for your bioretention/stormwater/rain garden/bioswale/soil needs.

Making the Most of Rainwater: Commercial Applications

The Issue: Stormwater

Bioretention_DDOT_DDOEIn an increasingly paved world, stormwater management is the name of the game for municipalities and businesses looking to reduce costs, improve water quality, and enhance performance of their existing infrastructure.

Stormwater is the rush of water that occurs during a rain event, especially during the initial stages. Imagine rain falling in two different scenes: a gigantic forest and a paved city.  In a forest, streams and rivers rise, lower spots in the ground fill with puddles, and the earth gets saturated for a period of time as the water slowly percolates back down into the groundwater.  In a city, gutters gush, basements flood, highways get slick, and drainage systems discharge water into rivers and bodies of water. This article highlights a key tool – green infrastructure – that helps paved cities behave more like spongy forests, thereby decreasing the negative impacts of stormwater.

Green Infrastructure and Its Impacts

Bioretention_Montgomery_CountyGreen infrastructure refers to many tools and products – soils, filters, plants, pervious surfaces, green roofs, bioswales, and retention ponds to name a few – that help typically paved environments absorb more water. Green infrastructure serves two bioretention purposes:

  1. It slows down the first flush of runoff by increasing the amount of surface area where water can get absorbed.
  2. It increases the quality of runoff by intercepting pollutants closer to the source.

Key Components

When embarking on a stormwater management project, a few key factors can influence the outcome. Entire courses and forums are devoted to this topic.  A quick overview includes:

  • Size: Evaluate the catchment area. A gutter that gets disconnected from the downspouts will have different needs than a parking lot.
  • Medium: Identify the ideal characteristics of the planting medium.  If it’s a green roof, you’ll need a lightweight, engineered blend. For example, if it’s a backyard bioswale, you’ll likely want a mixture of soil with a high organic content (compost) and strong filtration properties (sand).
  • Plants: What conditions will the plants need to endure?  Conditions will vary depending on the depth of the depression and typical weather patterns.
  • Flow: Identify the slope and where the flow will need to be managed or controlled.

custom_designed_blendsAt Harvest, specifically Harvest RGI, we have qualified experts that help guide and shape soil selection.  Commercial contractors depend on us to meet their engineered soil specifications for erosion and stormwater control. Residential customers also get involved: several homeowners may work together in a community effort to manage rainwater on their properties, benefiting from the economies of scale associated with purchasing a 15-20-cubic yard truckload of soil together.

A Rain Garden for Driveway Runoff

Are you ready to take storm water management on your property to the next level, but not quite sure what to tackle? Here’s a simple idea for how to divert water flowing on your property – in this case your driveway – into a rain garden to slowly absorb the water into the groundwater table (as opposed to into the municipal treatment or storm water system).

A small rain garden can capture driveway runoff in elegant fashion.

The best way to position your mini rain garden properly is to go outside the next time it rains and see where your water is flowing. We found this article super helpful in describing how to identify the best spot for a rain garden. Good job on taking steps to manage stormwater on your property!

From Rooftop to Runoff: What the High Line teaches us about green roofs

With the Grey to Green Conference coming up (June 1-2, 2015 in Montreal), all eyes will be on green infrastructure.

High Line - unique green roof with walking paths on either sideIn early April we took a cruise down the High Line in Manhattan. It’s a unique experience: it’s an abandoned elevated rail platform that’s been renovated into a narrow walking park. You get to experience the Big Apple two stories up from the streets, noise, traffic, and hustle and bustle.

Some people get drawn into the unique architecture (for example, they revived the train aesthetic and the park has glimpses of whimsical industrial-chic old rail ties, with lounge chairs overlooking the Hudson, and angular benches) and cool concrete forms. We were drawn in by the vegetation: The High Line is basically a gigantic green roof.

A Quick Green Roof 101 Tutorial

Growth media for green roof projects require a well-balanced blend to support vegetation. There are two flavors of green roofs:

  • High Line - green roof infrastructureExtensive: Extensive green roof systems have shallow profiles, with typically 3-4 inches of growth media. It’s primarily mineral and organics (no soil involved) made up of expanded shale and compost.
  • Intensive: Intensive green roof systems have a deeper profile (6”) and can support a much broader plant palette including perennials, shrubs and trees.

Learn more about green roofs.

High Line - purple crocuses in bloomA few crocuses were blooming (we loved the purple!) and a few trees were beginning to bud.

Beyond the Beauty: Why Soil Infrastructure Impacts Water Quality

A few states south, the Cheseapeake Bay Foundation has been fighting for years to curb pollution. Greenwire reporter Tiffany Stecker submitted on April 7, “Under a 2010 legal settlement between the nonprofit Chesapeake Bay Foundation and EPA, watershed states must adhere to a “pollution diet” and implement plans to meet individual nutrient-reduction goals by 2025. The states – Maryland, Virginia, Delaware, Pennsylvania, New York and West Virginia – and D.C. are required to submit reports on these efforts to EPA. The analysis released yesterday says the states collectively have reached 21 percent of the nitrogen reductions, 71 percent of the phosphorus reductions and 25 percent of the sediment reductions toward the 2025 goals.”

High Line - green roof - from rooftop to waterwayWhat does this mean? In laymen’s terms: In the past, we screwed up our waterways. Currently, we’re taking steps to reduce pollution by A) modifying our land applications and B) re-designing our built infrastructure via bioswales and green roofs (and innovative parks like the High Line) to absorb rain water during storm events. Looking ahead, we still have work to do from rooftop to runoff.

We checked in with our specialty soils guru, Dave L on how progress in the Chesapeake Bay intersects our work on land. He says,

“Bioretention facilities as well as green roof applications contribute to the amount of water introduced into the stormwater system and improve the quality of water output into this system. Overall these combined facilities improve the quality of outflow through filtration with properly blended soils and reduce the quantity of outflow by retaining water in their respective systems for plant uptake.”

Harvest Power has a lot of momentum in our specialty soils department that mixes up soils to specification – for green roofs, stormwater management, bioretention (including specs that meet Montgomery County Blends and MDE Table B.4.1 requirement), and beyond.

Want to learn more? Drop us a line.