Bioswales 101: A Beginner’s Guide+ 15 Bioswale Benefits

Last Updated on September 27, 2022 by admin

Green Infrastructure is a landscaping feature that helps clean water and air and provides much-needed greenery in urban environments. One type of this infrastructure is bioswales. Bioswales are low-impact solutions that use vegetation, topsoil, rocks, and other natural materials to filter pollutants from runoff before they enter the storm sewer system. This means less pollution entering our local waterways!

This article will cover the basics of bioswales, including how they work and how to build one. We also list 15 critical benefits of bioswales that extend beyond their primary use and discuss how they can increase property values and improve neighborhood aesthetics.

Table of Contents

• What is a Bioswale?
• Why are Bioswales Used?
• How do Bioswales Work?
• How to Build a Bioswale
• Bioswale Location
• Bioswale Design
• Bioswale Vegetation
• Bioswale Maintenance
• Bioswale Benefits
• When Should you Use a Bioswale to Filter Stormwater Runoff?

What is a Bioswale?

Why are Bioswales Used?

Stormwater runoff is water that comes from rainfall or melting snow that does not soak into the ground. When this water runs off hard surfaces like roads and sidewalks, it can pick up pollutants like oil, grease, and pesticides. This polluted water can then end up in rivers and lakes, where it can harm plant and animal life.

Bioswales are one way to reduce stormwater pollution. They work by intercepting runoff water and allowing it to percolate into the ground rather than running off into sewers or drains. In this way, bioswales can help to improve water quality and reduce flooding.

How do Bioswales Work?

Bioswales work by using vegetation, topsoil, rocks, and other natural materials to filter pollutants from runoff before they enter the storm sewer system. Unlike traditional methods that rely on filters or chemicals to remove impurities, bioswales use living plants to break down contaminants.

The most common type of bioswale is a grassy swale, which uses grasses and other types of vegetation to filter out pollutants. As water flows through the bioswale, the plants take up nutrients and help to break down any harmful chemicals. Bioswales are designed to be low-maintenance, and they can be used in a variety of settings, from residential neighborhoods to commercial parking lots. In addition to their pollution-reducing benefits, bioswales also help to reduce the risk of flooding and soil erosion.

How to Build a Bioswale

There are a few things to consider when building a bioswale, such as location, size, shape, vegetation, and maintenance. A bioswale is a type of landscaping designed to remove excess water from an area. Bioswales are typically built in urban areas with a risk of flooding. The primary focus should be to grade the bioswale so that you can redirect excess water away from roads and buildings and into the bioswale.

Building a bioswale is not as difficult as you might think. The first step is to choose a location for your bioswale. The site should be in an area where stormwater runoff collects, such as at the end of a street or parking lot. Once you have chosen a location, you will need to excavate the area so it slopes away from the impervious surface. After excavating the site, you will need to add a layer of gravel. This helps to improve drainage and prevents the soil from becoming waterlogged. The gravel layer should be at least 6 inches deep. However, if you can place a foot or 1.5 feet of gravel, the bioswale will be more effective.

One foot of soil should be placed on top of the gravel layer. Next, vegetation is placed on top of the gravel. It is often a wise choice to choose a native plant pallet. The plants selected for the pallet should be able to tolerate heavy rainfall and flooding. This is environmentally friendly and can also help reduce maintenance by choosing plants well-suited to the environment. Finally, bioswales typically have a drainage overflow. This helps to ensure that any runoff that could not percolate into the ground will be directed towards the storm sewer.

Bioswale Location

Bioswales are often placed next to roads, in parks, and within pocket parcels within a neighborhood that can be utilized for stormwater management. They can also be placed in courtyards or within other site developments to improve their stormwater management system. Bioswales can be used as a stand-alone stormwater management tool or in conjunction with other green infrastructure practices such as infiltration trenches and pervious pavement.

Bioswale Design

The bioswale design is site-specific and will be based on the hydrology and topography of the area. Bioswales are often designed with a natural shape that follows the contours of the land. This helps to reduce erosion and allows for maximum infiltration. The size of bioswales varies. However, they should be designed to maximize infiltration and accommodate maintenance operations. Additionally, the size of the bioswale should take into account how much stormwater runoff it will handle. This is mainly dependent on the tributary area on the runoff coefficient. The depth of the bioswale should be at least 18 inches to allow for proper percolation. However, constraints, such as a high groundwater table, need to be taken into account.

The bottom of the bioswale should be graded so that it slopes towards the outlet at a minimum slope of 2%. This helps to ensure that water will flow towards the outlet and not pool in the bioswale. The vegetation chosen for the bioswale should be native and should be able to tolerate the conditions of the site, such as flooding, drought, nutrient loads, or high pH levels.

Bioswales should also have an outlet that is connected to the storm sewer system. This helps to ensure that any excess stormwater can overflow into the drainage system.

When designing a bioswale, it is crucial to consider the following:

• The type of soil that will be used. Loamy soils are ideal for bioswales as they are able to absorb and filter large amounts of water. However, other soils that allow for percolation work as well.

• The climate of the area. Bioswales should be designed to withstand the amount and intensity of rainfall typical for the location.

• The amount of space available. Bioswales can be designed to fit a variety of space constraints.

• The surrounding land use. Bioswales should be located in areas where they will be most effective at removing pollutants from runoff water.

When properly designed and located, bioswales can play a pivotal role in improving water quality and protecting the environment.

Bioswale Vegetation

The type of vegetation you choose will depend on the climate and soil conditions at your site. Plants should be deep-rooted so that they can effectively absorb water. Grasses, sedges, shrubs, and trees are all good options for bioswale vegetation.

A native plant pallet is always the best option as these plants already acclimate to the local climate and soil conditions. Non-native plants may not be as effective at filtering water and may require more maintenance.

Bioswale Maintenance

Bioswales will need to be maintained regularly to ensure that they continue to function correctly. This includes removing debris, trimming vegetation, and replanting as required. Depending on the size of your bioswale, you may need to hire a professional landscaper to help with maintenance tasks.

It is also important to keep an eye on the condition of your bioswale and make any necessary repairs. This may include fixing erosion problems or repairing the outlet connection to the storm sewer system.

Bioswale Benefits

The benefits of bioswales include improved water quality, reduced flooding, and enhanced habitat for wildlife. In addition, bioswales can help to beautify a landscape and increase property values. Bioswales are an effective and environmentally-friendly way to manage stormwater, and their benefits make them an excellent addition to any community. Below is a list of 15 key benefits of bioswales.

1. Improved Water Quality: By removing pollutants from stormwater before it is discharged into natural water bodies, bioswales help to enhance the quality of water in our rivers and lakes. The plants and soil in bioswales also absorb excess nutrients that can lead to harmful algal blooms.
2. Reduced Flooding: Bioswales help to reduce flooding by slowing the flow of stormwater and allowing the water to seep into the ground instead of running off impervious surfaces. By allowing water to infiltrate, bioswales can reduce the strain on city sewer systems during heavy rains.
3. Aquifer Recharge: Bioswales allow stormwater to seep into the ground. This infiltration helps to recharge groundwater sources that are needed for irrigation or to provide raw water for drinking water plants.
4. Increased Property Value: Bioswales mitigate flooding and provide significant aesthetic benefits. Homes located near bioswales can exhibit increased property value due to the aesthetic appeal of these landscaped features, the reduced flooding, and the improved water quality in nearby waterways.
5. Enhanced Neighborhood Aesthetics: As is the case with all landscaping, bioswales can significantly improve neighborhood aesthetics. This is particularly true for neighborhoods with limited to no existing greenery.
6. Improved Air Quality: The plants in bioswales help to improve air quality by absorbing emissions from cars and trucks, reducing the amount of smog and other air pollutants in the atmosphere.
7. Reduced Urban Heat Island Effect: Bioswales can help to cool the air temperature in urban areas. This is because the plants in bioswales evaporate water which has a cooling effect on the surrounding air. This process helps to offset the heat island effect caused by impermeable surfaces like asphalt and concrete, which absorb and retain heat from the sun. Depending on the plant palette, bioswales’ shade can also help reduce the air temperature.
8. Reduced Energy Consumption: Bioswales can help to reduce the energy consumption of nearby properties by cooling the air around them through evapotranspiration.
9. Low Maintenance Requirements: Bioswales require minimal maintenance once they are established. The primary maintenance task is to remove any debris that may have accumulated in the bioswale.
10. Help Reduce Maintenance of Storm Sewers: Since bioswales filter pollutants from runoff before they enter the storm sewer system, they can help reduce the maintenance requirements for the storm sewer system. For example, less particulate matter entering the storm sewer means less maintenance on stormwater treatment filters.
11. Quieter Neighborhoods: The plants in bioswales can help muffle noise from nearby roads, making for more peaceful neighborhoods. 
12. Healthier Communities: The plants in bioswales absorb harmful particulates from car exhaust fumes, improving air quality and making for healthier communities. In addition, being around nature has been shown to positively impact mental health, providing people with a sense of calmness and well-being.
13. Provides Habitat for Wildlife: By providing food and shelter, bioswales can provide habitat for various animals, including birds, butterflies, and small mammals.
14. Cost-Effective Green Infrastructure: lower cost than many other forms of green infrastructure, such as green roofs and porous pavement. Bioswales can be designed to fit the needs of a particular site, making them a versatile and cost-effective solution for stormwater management.
15. Enhanced Stormwater Management: Bioswales are often used as part of a site’s overall stormwater management plan. When incorporated into a comprehensive plan, bioswales can help manage small rain events without using grey infrastructure. These types of holistic stormwater management plans can provide the above benefits and help the site comply with and exceed regulatory standards. They can also help the site qualify for LEED Certification or Envision Certification.

When Should you Use a Bioswale to Filter Stormwater Runoff?

Bioswales often provide optimal benefits in urban environments. This is because rural settings already have large green spaces that are essentially acting as natural bioswales.

Bioswales can be found all around the world. Many benefits come from bioswales, including cleaner water, green infrastructure, and some other benefits.

Bioswales filter stormwater runoff to ensure that water from rooftops and hard surfaces is adequately treated before entering the environment. Without bioswales, runoff pollutants can go into sewers, streams, and rivers, eventually polluting our water systems.