Soil Erosion

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Soil Erosion

Soil erosion on hillside.

It is important that we have reliable information on the amount and type of soil erosion in our region. This is because:

  • Soil loss accelerates sedimentation and nutrient run-off and degrades water quality in adjacent or downstream water bodies;
  • Downstream erosion cause rivers to become filled in with silts and gravel increasing the risk of flooding;
  • The gradual loss of topsoil affects the general heath of the soil and reduces fertility and the productive capacity of the soil resource;
  • Some types of erosion can affect land stability for housing and other uses.

To gain a better understanding of the amount and type of soil erosion across the Marlborough Region, in 2009 a survey was undertaken to assess Soil State using region-wide aerial photography. Soil State characterises whether soil at a given site is on:

  • stable surfaces i.e. vegetated
  • erosion-prone unstable surfaces i.e. inactive vegetated surfaces
  • eroded, unstable surfaces i.e. recently disturbed and re-vegetating
  • eroding, unstable surfaces i.e. freshly disturbed and bare

What have we found out?

  • 52.5% of the region’s sample points are on stable surfaces
  • 11.5% of the region’s sample points are on erosion-prone but inactive surfaces
  • 36.0% of the region’s sample points are on actively eroded and eroding surfaces
  • We also found out that 11.56% of the region has bare soil
  • However most of the bare soil in the region (10.08%) was due to natural processes of which the most important by far was bare rock and scree (7%), with lesser amounts due to streambank deposition (1%) and sheetwash (1%) (Figure 1).
  • Significantly less bare soil in the region was due to land use activities (1.47%). By far the most important land use activity responsible for bare soil was tracks (0.87%), with lesser amounts due to cultivation and grazing pressure (Figure 2).