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Fencing drains, seeps and wetlands

Keeping stock out of drains, seeps and wetlands is an important part of good farm management. By fencing stock out of wet areas you’ll lose less stock from bogging, stock will be easier to manage and water entering streams and rivers will be cleaner. Find out about how poorly managed drains can act as nutrient ‘highways’ and check out our tips for good drain management.



Photograph of a fenced seep.On this page: Fencing wet areas so they work for you, Drains as nutrient ‘highways’, Constructed wetlands, Clean Streams , Find out more

Drains, seeps and wetlands can be easily overlooked on the farm. But they are important features that can work for you if well managed.

Fencing stock out of drains, seeps and wetlands reduces stock losses from bogging and improves livestock management. It also allows these areas to function as natural sponges for removing farm pollutants, even if they are a long way from the nearest stream or river.

Fencing wet areas so they work for you

Drains, seeps and wetlands will only work as filters if they are not:

  • drained – nitrogen removing bacteria (denitrifying bacteria) need wet conditions to grow
  • grazed – particularly during the wettest parts of the year.

To exclude cattle from drains, seeps and wetlands, use an electric fence. It’s particularly important to keep cattle out when soils are wet. This:

  • protects the soil structure so it can act as a filter
  • protects these areas from direct contamination from stock effluent
  • stops the soil from being pugged and becoming a source of dirty runoff.

Drains as nutrient ‘highways’

Results from a NIWA (National Institute of Water and Atmospheric Research) study show that well vegetated open drains can remove up to:

  • 70 percent of nitrate
  • 40 percent of phosphate.

However, poorly managed drains can act as ‘highways’, particularly for the movement of:

  • nutrients – such as nitrogen and phosphate
  • faecal organisms – for example, the bacteria E. coli
  • sediment – such as eroded topsoil.

Many drains empty directly into waterways and can be a major source of pollutants in some areas. For open drains to be effective in removing farm pollutants make sure:

  • they have vegetation, for example, grasses, sedges and rushes – to trap and absorb farm nutrients and other pollutants
  • they are fenced from stock – to protect vegetation and soil structure, and to avoid direct input of stock effluent
  • you control weeds with herbicide, rather than digging – grassed drains are effective filters
  • you dig drains during maintenance in sections, rather than the whole lot at once. This ensures part of the drain remains vegetated, and still effective in removing farm pollutants and sediment.

Constructed wetlands

Many subsurface drains flow directly into waterways, bypassing the ‘sponge zone’ or waterway margin. One way to get around this is to construct a small wetland area between the end of a drain and the receiving waterway. Alternatively, drain outlets can be redirected to a wetland area. This will act as a natural barrier, filtering out any farm pollutants.

Clean Streams

‘Clean Streams’ aims to encourage and support farmers’ efforts to reduce the impacts of farming on waterways.

Order a copy of ‘Clean Streams – A guide to managing waterways on Waikato Farms’. This booklet explains how farming can affect waterways. It offers practical suggestions about what farmers can do, and what works best where on a farm.

Find out more

Managing farm drains, seeps and wetlands are only part of the ‘picture’. Find out more about fencing streams and rivers. Use our online calculation sheet for costing different fencing and planting options.

Find out more about nutrient management.

Check out our information on applying effluent to land and find out about threats to wetlands.