Swale & Rain Garden Construction
Build a swale (level trench on contour) or rain garden to slow, spread, and sink water into your landscape. These earthworks recharge groundwater, reduce erosion, and create productive planting zones.
Version History
Version 1.0 Current
Effective: 2026-03-30Initial version
Procedure Details
Check for underground services before digging. Wear sturdy boots. Do not build swales on slopes steeper than 1:3 without engineering advice. Never dam flowing waterways without permits.
You will need:
- A-frame level or laser level for finding contour
- Shovel, mattock, or small excavator
- String line and stakes
- Mulch for the mound
- Plants for the mound (nitrogen fixers, deep-rooted species)
- Gravel or rock for inlet areas (optional)
Procedure Steps (Version 1.0)
Use an A-frame level or laser level to find the contour line across your slope. Mark with stakes every 2-3 metres.
Dig a trench along the contour line. Typical dimensions: 30-50cm deep, 30-60cm wide. The bottom must be level along its entire length.
Place the excavated soil on the downhill side to form a mound (berm). This is your planting zone.
Check the trench is level by filling with water — it should pool evenly along the entire length, not flow to one end.
Mulch the berm heavily (15-20cm of straw, wood chips, or leaves) to protect the disturbed soil.
Plant the berm with a diverse mix: nitrogen-fixing trees/shrubs, deep-rooted comfrey, ground covers, and productive species.
For a rain garden variant: dig a basin (not a trench) at a low point, line with gravel, and plant with water-loving species.
After the first significant rain, check the swale. Water should pool evenly and infiltrate within 24-48 hours.
Record the date, dimensions, materials used, and planting details. Take before and after photos.
Monitor infiltration rate after subsequent rains. If water sits for more than 48 hours, the swale may need a spillway.