The Waikato Regional Council monitors soil stability to get a measure of the quantity of soil in place (stable) and how much has been subjected to erosion and has the potential to generate sediment. It provides information about how particular land use disturbances and natural erosion is affecting the soil resource across the region. Accelerated erosion can lead to the loss of the soils productive capability, damages to fences, tracks, roads and houses, damage to native habitats or animal habitats, adverse effects on the aesthetic and cultural values associated with land and sediment being generated that could enter waterways.
Measuring the stability of the soil gives us an understanding of its natural stability – how it has been affected by natural erosion processes and an understanding of how land management practices have affected its stability and accelerated erosion. The soil resource is important for farming, forestry, conservation and residential/commercial use so it is important to understand how well the soil resource is remaining in place and what are the factors influencing erosion.
In 2012 stable surfaces made up 51% of the regional land area. Stable surfaces show no signs of past natural erosion and are completely vegetated (unless the topsoil is disturbed by land use activities e.g. cultivation, tracking).
Unstable surfaces made up of erosion prone, eroded and eroding surfaces accounted for 41 % of the region. Almost 19 % of the sample contains land that has been recently eroded, or is currently eroding, these areas require careful management and limit the range of productive uses available.
Extensively disturbed surfaces for example surfaces are those where the soil has been partly or completely removed, re-contoured, or covered by buildings and pavements rural buildings, roads, urban areas, lakes made up 7.3% of the regions area.
The changes in soil stability between 2007 and 2012 are shown in Figure 1. The percentage of sample points within the stable surfaces category has significantly increased over the past five years from 49.8% in 2007 to 51.3% in 2012. The change has largely been seen as an increase in stable surfaces with intact soil i.e. no disturbance by land use processes.
Unstable surfaces are up from 39.3% in 2007 to 41.4% in 2012 and have increased significantly. This is largely due to a significant increase in eroding surfaces disturbed by natural processes up from 7.5% in 2002 to 9.1% in 2012.
Waikato Regional Council – land and soil
Ministry for the Environment
The indicator is updated as aerial photography for the region becomes available generally every five years.
Soil Scientist - Science and Strategy Directorate