fence under waterWe live on the Wairua River in Whangarei. Kate lives in Helena Bay. The headwaters of the Wairua start on Kate's property and they're crystal clear. The water is a completely different colour when it gets to our place, and even worse when it empties into the Kaipara Harbour beyond Dargaville.

The Wairua isn't vastly different from many other rivers around New Zealand, passing through farmland and open country, getting browner and browner as it goes. You wouldn't want to drink it, some days you wouldn't even want to put a foot in it. If everyone did their bit, fencing off and managing riparian margins and adjoining wetlands, it would improve water quality hugely. We might even be able to swim in the river one day.

Waterways should be fenced, and not just for environmental reasons - there are compelling commercial reasons as well.

Why?

  • Fencing off waterways and planting water margins beautifies and adds value to your property.
  • Keeping stock out of waterways can reduce stock losses.
  • Stock management is easier if you don't have to round them up out of a stream, river or swamp.
  • Pasture growth is improved by using fertilizer on productive land and not sending it down the river to the sea.
  • Fencing helps to reduce bank erosion and drainage maintenance costs.
  • Conserves your soil - rather than seeing it wash downstream every time it rains.
  • Stock health is improved by eliminating access to unsafe water supplies.
  • Production is increased by removing access to liver fluke breeding areas. If you're not sure whether liver fluke is a threat on your property - talk to your vet.
  • Your Regional Council may have funding available to help you with fencing costs.
  • Future generations will have something to thank you for.

Putting a fence around a body of water such as a pond or dam is pretty straightforward. Fencing off flowing water is usually more worrisome. For most property owners there a fear of significant damage to fences due to flooding, a fear that is often unfounded. From personal experience - I watched 1000 metres of new fencing on my own property disappear from sight (one strainer post only being visible as a pressure wave in the swollen river) - then reappear unscathed when the flood waters receded. There was a fair bit of debris hung up on some sections but I didn't even have to tighten a single wire. It's all in how the fences are set out, and how they're built. One thing I learnt though, is to clear the debris sooner rather than later. It's no fun finding a dead possum in the debris you're clearing three weeks later on a hot April afternoon, even with gloves on …

fence under water

March 2007. There was a fence here yesterday …


Flood proofing fence lines comes down to design. Bear in mind that the fence doesn't have to hold wild animals in; it just needs to keep the grazing stock out of waterways. Stock-proof doesn't necessarily mean 7 wire and batten. Dairy cattle can be kept behind as little as a 1 or 2 wire and post electric fences, or 3-5 wire and post electric for dry-stock or 4 wire electric for sheep.

Design tips:

If you're planning to fence off a river or stream, take photos of peak water levels at every flood event - the photos are great for reference when setting out your new fencing.

  • 7 wire and batten or mesh fences are not a good mix with flowing water, try to use an option without battens, or with fewer wires.
  • Avoid running fence lines at right angles to the river flow wherever possible - fence lines parallel to the flow will come under much less pressure.
  • Use fewer wires on the fence in flood-prone areas.
  • Staple wires on the downstream side of posts, use un-barbed staples so wires "ping off" leaving the posts intact and upright.
  • Use hanging fence sections where panels hinge upward as floodwaters rise.
  • Run shorter strains with "blow-out" sections of fence or use electric polywire and temporary fence standards in real problem areas.
  • For problem areas that are constantly washing out - instead of stapling wires to posts - staple wire onto battens which are attached to the downstream side of tops of posts with light wire - under flood pressure the tie-wire breaks and the fence section collapses intact. When the floodwaters recede, stand the fence up again and secure with new tie-wires.
  • If all else fails - set permanent fences further back and use temporary electric fences to graze between permanent fences and the waterway.
  • Talk to other property owners or visit properties that have fenced off waterways to see how they've handled fencing challenges.

You will never regret investing the effort (or money) into fencing off waterways, especially if you then put a little more work into planting out fenced off margins. We are now being rewarded with the results on our property in areas we fenced off and planted several years ago.

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