Erosion control

How to reduce and prevent erosion

Stock management

Exclude stock from erosion-prone areas to reduce pressure on banks and allow vegetation to establish. Use lighter stock classes or lower stocking rates to reduce pressure on steep land.

Fencing

Fence off waterways and streams to reduce stock or equipment pressure, and allow vegetation to establish and stabilise the bank. Ensure the fence is put back far enough to allow for water movement when water levels are high and erosion events occur.

Planting erosion-control species

The best long-term solution for erosion control on banks is to plant a combination of natives with poplars and hybrid willows. Natives have a deep root structure for stabilising banks but they take longer to establish. Poplars and willows are faster growing, so they provide erosion control while the native plants are establishing.

Low natives such as sedges and rushes will survive flooding on the lower banks and help reduce soil being washed away.

Trees such as poplars and hybrid willows are good for steeper upper banks and hillsides. They are fast-growing and have a strong, deep root system that will help control erosion. Ongoing maintenance is required with these trees to keep them manageable. In wind-prone areas plant shelter belts at right angles to prevailing winds.

Erosion control structure

If erosion is severe and or threatening core infrastructure, an immediate solution is hard structures such as rock and gabion baskets, flumes and detention dams. These types of structures will likely require consent from your regional council and assistance from an engineer.

Drain banks should be gradually sloped, with a shallow 'V' formation rather than an unstable 'U' shaped bank.

Culverts should be sized to cope with high flows as well as allow for fish passage.

Locate bridges and culverts where there are regular stock crossing points to prevent stock from accessing water.

Nib walls and diversion channels before crossings help to avoid the movement of runoff into waterways.

Grazing and crop management

Soil that is exposed to wind and rain, is at higher risk to erosion. Ensuring that there is good pasture cover in winters, not overgrazing especially on steep slopes, select cropping paddocks carefully, avoid cultivation during dry, windy weather and explore alternative options to full cultivation for crops e.g. no-till.

Sheet, rill, and gully erosion

Movement of soil overland in sheets or channels:

• Occurs on any sloping surface where the soil is exposed.
• Sheet erosion will often remain relatively unseen.
• Gully erosion is usually very active and visible but can also start as tunnels under the surface.

How to avoid sheet, rill, and gully erosion

• Exclude stock from erosion-prone areas.
• Use cut-offs on races to direct water into paddocks.
• Avoid overgrazing.
• Select cropping paddocks carefully, limiting cropping on steep slopes and critical source areas.
• Plant erosion control species.
• Maintain good pasture cover over winter.

Mass movement

Earthflow, slips, and slumps:

• Usually occurs on steep land.
• Can also occur in moderate to gently sloping areas.

How to avoid or minimise mass movement

• Plant erosion control trees such as hybrid willow species or poplars.
• Use lighter stock classes or lower stocking rates to reduce pressure on steep land.
• In severe cases, retire land from grazing and change land use to plantation forestry or native forest.
• Surface water controls may be required to divert water from critical areas. Call your regional council for more information.

Streambank erosion

Occurs on streambanks, particularly:

• In flood plains.
• On the outside of bends.
• In areas prone to high flows or floods.

Wind erosion

Usuall occurs:

• All land where there is exposed soil and dry, windy conditions.
• Particularly problematic with Loess soil on the Canterbury plains.

How to avoid or minimise wind erosion

• Place shelter belts at right angles to prevailing winds. Aim to block about 50% of the wind to prevent wind eddying or funnelling on the downward side of the shelter.
• Use minimum or no tillage cultivation practices to retain topsoil.
• Avoid cultivating crops during dry weather or strong winds to minimise soil loss.
• Do not over-cultivate soils. This will leave them more vulnerable to wind erosion.