Wattles, also called fibre rolls, are laid across a slope along the contour. Each one shortens the distance water can run downhill, so it never builds up enough speed to carry soil away. The steeper the slope, the closer together they need to be.
Spacing by slope
California’s transport department publishes this spacing for fibre rolls:
| Slope (horizontal : vertical) | Spacing between rows |
|---|---|
| Steeper than 2:1 | 10 ft (about 3 m) |
| 2:1 to 4:1 | 15 ft (about 4.5 m) |
| 4:1 to 10:1 | 20 ft (about 6 m) |
| Flatter than 10:1 | 50 ft (about 15 m) |
Where to place them
- At regular intervals down the slope face, following the contour.
- At every grade break, where the slope changes steepness.
- At the top and at the toe of the slope.
A worked example
Take a slope 18 m long, measured down the face, at 3:1, and 40 m wide. The table gives about 4.5 m between rows, so the face needs rows at roughly 4.5, 9 and 13.5 m, plus one at the top and one at the toe: five rows. Five rows of 40 m is 200 m of wattle, plus a little extra so the ends can turn uphill and stop water running round them.
What wattles cannot do
Caltrans is clear that fibre rolls will not solve slope stability problems, are difficult to install on steep or rocky slopes, and need maintenance: sediment has to be cleared and damaged rolls repaired or replaced. If a slope is moving, it needs a geotechnical fix first.
Choosing the material
The California Coastal Commission notes that fibre rolls typically last from six months to five years depending on materials, and recommends natural-fibre netting over plastic to protect wildlife. Coir sits at the longer-lasting end of natural fibres.
See our coir wattles or send us your slope dimensions for a quantity estimate.