Enhanced grass swales

From LID SWM Planning and Design Guide
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This article is about installations designed to capture and convey surface runoff along a vegetated channel, whilst also promoting infiltration.
For underground conveyance which promotes infiltration, see Exfiltration trenches.
For conveyance along planted channels, on both surface and underground, see Bioswales.

Overview[edit]

The fundamental components of an enhanced grassed swale are:

Additional components may include:

Planning considerations[edit]

Design[edit]

Swales should be designed to meet the following criteria:

  • Minimum residence time of 5 minutes.
  • Maximum flow velocity 0.3 m/s
  • Bottom width between 0.6 - 2.4 m
  • Minimum length 30 m
Slope variations
< 2 % Use underdrain to distribute water for infiltration
2 - 5 % Design swale for surface flow, consider check dams
5 % Check dams required to reduce effective slope to 2 – 3 %

Maximum depth of flow

  • 50% height of grass for regularly mown swales, to maximum of 75 mm.
  • 33% height of vegetation for infrequently mown swales.

Materials