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Severe gully erosion

On this page: What causes erosion?, Accelerating erosion, Where does the eroded soil go?, Reducing erosion, Identifying risk factors, Reducing the risk

Erosion is a natural process, but people can greatly accelerate the rate of erosion by removing vegetation and using inappropriate land management practices. In the Waikato region, eroded soil often ends up in our waterways, causing poor water quality. Good land management reduces erosion.

What causes erosion?

Gravity, wind and water can wear away the soil surface and move soil far from where it was formed. This process is called erosion.

The rate of soil erosion depends on the:

  • type of soil
  • climate
  • vegetative cover
  • topography (slope and aspect)
  • land management practices.

Accelerating erosion

Soil scientists classify 43 percent of land in the Waikato region as having high potential for erosion.

People often accelerate the rate of erosion by removing vegetation and having inappropriate land management practices. Sometimes the vegetation is removed intentionally (for example during logging, cultivating or grazing). Sometimes introduced pests remove it for us (possums, goats, rabbits, deer and pigs).

Once the vegetation is removed, the land is very vulnerable to erosion. Large amounts of soil can be lost from cultivated land during storms. In some cases as much as 35 cm of soil has been lost over thirty years.

Where does the eroded soil go?

We lose most eroded soil from the land. Soil particles moved during erosion are often washed and blown into our waterways.

This is bad for our waterways because:

  • it decreases the water clarity (less light for plants to photosynthesize)
  • fine sediments can suffocate fish and other water life
  • increased nutrients encourage undesirable plants and animals.

Eventually the water carries the soil particles downstream to the coast, causing increased sediment in our harbours. More sediment in our harbours means:

  • less habitat for kai moana (seafood)
  • poor water clarity
  • flooding problems upstream
  • infilling of harbours restricting recreation
  • changes in habitats.

Hill country erosion, Mahoenui

Reducing erosion

Identifying risk factors

Forty-three percent of land in the Waikato region has a high potential erosion risk.

The risk of erosion increases if land:

  • has little vegetation on it
  • is steep
  • is on the bank of a river or lake
  • is disturbed
  • has erosion prone geology (for example mudstone or pumice)
  • is under pressure from high stock density or machinery
  • is in an area of high and intensive rainfall.

Cultivation also leaves soils vulnerable to erosion. The compacted soils left in wheel tracks often act as channels for water. When it rains, water can then undercut and remove the surrounding soil.

Find out more about:

Reducing the risk

Common ways to reduce erosion include:

  • planting trees on hills and stream banks
  • fencing gullies and waterways to prevent stock access
  • removing wild goats and rabbits (they eat the vegetation)
  • keeping stock off steep pasture when it is wet
  • minimising the use of earthworks and using appropriate practices
  • planting cover crops when land is left fallow
  • ripping wheel tracks in cultivated land where runoff and erosion along wheel tracks is a problem
  • retiring unproductive land
  • not cultivating steep land.

    In many communities, groups of people are working together to care for their local environment. One way they are doing this is through local care groups. Another way is the Trees for Survival Trust - check it out under our Resources for Teachers information.

    Waikato Regional Council manage soil conservation programmes to minimise erosion and the amount of sediment entering water. We are also designing a land monitoring programme based on soil quality monitoring at key representative sites.

    Waikato Regional Council and the Department of Conservation work together to control wild goats under our Regional Pest Management Strategy (RPMS). The RPMS also sets standards for rabbit control. It is the land occupier’s responsibility to ensure these standards are met.

    For policy information on accelerated erosion check out our Waikato Regional Plan and  Regional Policy Statement.