Reduce sediment loss

The primary sources of sediment loss on a farm are topsoil loss from cultivation and redrilling of paddocks, discharge from tracks, races and critical source areas, and streambank erosion. Erosion of land, particularly hilly areas that are not appropriately managed, can also contribute significant loads of sediment through things such as slips and grazing damage (plugging).

This sediment can be transported to waterways, causing the water to be dirty and sediment to accumulate on the streambed. This can impact insects and fish by smothering habitat, reducing feeding efficiency, and clogging gills. Sediment can also reduce the aesthetic appeal of waterways and make them unsafe for swimming, as well as result in drainage issues, with sediment removal sometimes required to alleviate this risk.

Reducing sediment loss leads to improved grass growth and milk production. It enhances water quality and ecosystem health, and can reduce maintenance requirements around channel clearing.

Options for reducing sediment loss

There are several options for reducing sediment loss and maintaining soil structure:

• Think about the suitability of each paddock for cultivation and assess the risk of soil erosion before work is undertaken, e.g. topography and soil type, proximity to waterways, and erosion susceptibility.
• Plan crop rotations and re-sowing to minimise the time that soils are bare, especially during the high-risk winter months.
• Consider direct drilling, strip-tillage, or non-invasive tillage to reduce risk of sediment loss.
• Manage or retire and plant erosion-prone land to minimise soil losses.
• Plan and prepare a winter grazing plan to minimise soil damage and erosion during winter months. Select appropriate paddocks and intensive winter grazing that are away from waterways, 10° or less slope and are not vulnerable to pugging or erosion.
• Graze pastures and crops from top to bottom or strategically, to minimise sediment and contaminant loss to critical source areas and waterways.

Other options, depending on farm characteristics, include measures such as riparian buffers and planting, streambank stabilisation, stock exclusion, retiring of land, constructed wetlands or sediment traps, deferred grazing, and prevention of runoff from bridges and culverts. Guidance documents such as this one from Manaaki Whenua – Landcare Research may help you identify what measures are best for your farm to reduce sediment loss. Our erosion webpage also provides some useful information.

Regulatory requirements

Your regional council may have restrictions on certain farm practices to manage the risk of sediment loss from farms. These are likely to focus on high-risk erosion areas and critical source areas due to these areas typically contributing a large amount of sediment to waterways. Reducing sediment loss may be a key objective in your Farm Environment Plan or Freshwater Farm Plan, with actions to work towards addressing this.