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The following is a short summary of the habitat type and how to create/enhance it to a "good" condition. For an informed position, please refer to official up-to-date UKHAB documentation or the UK Government's Condition Assessment Sheet.
Synonyms: Balancing Pond, Bio-Retention Strips
A swale, in the context of sustainable drainage, is a shallow channel designed to store and convey surface water runoff. Consists of vegetated and gently sloped features designed to manage water runoff, filter pollutants and increase rainwater infiltration. May include gravel layers, perforated under-drains and overflow drains (Source: Natural England).
Swales are often damp, particularly in the lowest part, but have a range of soil conditions, which mean that they can support a high diversity of plants. The vegetation in a swale is often lightly managed, with plants being allowed to grow tall and provide visual interest. Plants should be selected that can withstand periods of drought. With most low-maintenance swales, it is advisable to establish vegetation by seeding with a variety of native species, including wetland, wet grassland, and dry grassland mixtures, chosen according to the local setting and conditions and predictions of how often the swale will convey water (Source: Natural England).
If the gradient is suitable, swales may include stop logs or check-dams designed to slow the flow. Inlets and outlets and other places that are subjected to high flow rates, that could cause erosion, may need to be armoured. On permeable ground, where the underlying geology is suitable, water may also infiltrate. A swale can also remove pollutants. This may be valuable where water is to be discharged into a natural waterbody. Adequate space should be made available to ensure that bioremediation objectives are met. (Source: Natural England).
Assessment Questions:
- Is the feature specifically constructed to manage water runoff?
- Does it have a gentle slope and is it vegetated?
- Is it designed to filter pollutants and increase rainwater infiltration?
- Is it integrated into an urban or built environment?
If YES, then it is likely 'Urban - Bioswale'
How to Create / Enhance to a "Good" condition
Minimum size information can be read here. Should not be created in areas with high density (source). Costing information can be read here.
How to get a "moderate" rating
In a management plan aiming to achieve ‘moderate’ condition the plan will show the following:
A variety of flower species will be planted, with a focus on attracting insects like bees and butterflies along with other wildlife. Plants will be selected based on how appropriate they are to the size and design of the green roof. The species mix will ensure that there are flowers at all different times of year, providing nectar through the seasons.
The seed mix will be mostly native species. Where non-native plant species are present, they will not be harmful to wildlife. The planting mix will exclude invasive non-native species (INNS).
Source: Natural England
How to get a "good rating"
In addition to the characteristics for moderate condition, to get a ‘good’ condition the plan will show the following:
Management will seek to ensure a varied vegetation structure, with at least two physically different habitat elements or vegetation types or heights. The variety will mean that no single vegetation type covers more than 80% of the habitat area.
Steps will be taken to ensure the habitat is composed of 100% native species that are suitable for wetland environments, including the structural vegetation types, or native species characteristic of pond edges.
Source: Natural England
Useful Resources
Guide 2 - Bioretention areas
Please note that this is a simple guide to help identify the habitat. For a definitive description, please refer to UKHab documentation. Joe's Blooms takes no responsibility for the content of external links.