Bioswale

Bioswales are linear, vegetated trenches designed to collect, convey, filter, and infiltrate storm water run-off, reducing pollution and slowing down flow into waterways. These are landscape features made with a layered soil mix, vegetation, and mulch to naturally purify water, which helps prevent flooding, promotes biodiversity, and recharges groundwater. UN Habitat describe the 5 benefits of bioswales as being;

• Water Collection and Infiltration: Capture and direct run off from impervious surfaces like roads and side walks, allowing water to percolate into the ground.
• Cooling and Aesthetic Benefits: The vegetation helps lower temperatures in urban areas and enhances the visual appeal of public spaces.
• Slows Down Water; The slope and planted vegetation slow down water flow, reducing erosion and preventing flooding.
• Groundwater Recharge: Instead of directing all runoff into storm drains, bioswales allow water to seep into the soil, replenishing groundwater levels.
• Filtration and Pollutant Removal: As water moves through the bioswale, plants, soil, and microbes help filter out pollutants such as heavy metals, oil, and sediment.

Swales are also natural or man-made linear depressions (or ditches), usually grass covered, with shallow-sloping sides. although less biologically active than bioswales, they used as common components in the drainage strategies of residential, commercial and municipal schemes.

Approved Document H - Drainage and Waste Disposal, describes ‘swales’ as:

‘…grass-lined channels which transport rainwater from a site as well as controlling flow and quality of surface runoff. Some of the flow infiltrates into the ground. There may be an overflow at the end into another form of infiltration device or a watercourse. They are particularly suitable for treatment of runoff from small residential developments, parking areas and roads.’

The functions of swales is to:

• Slow the movement of water through the landscape after heavy rainfall;
• Reduce peak flows;
• Form a temporary reservoir;
• Direct water to a storage or discharge system and
• Facilitate the absorption of water into the ground.

Swales are frequently located alongside road verges, near the source of water run-off and can form a network linking storage ponds and wetlands. They can offer an efficient way of capturing rainwater and may form part of a sustainable urban drainage system (SuDS).

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