Choosing a fence line that make sense

Within reason, the wider the buffer between stock and  the stream the more effective it will be in filtering run-off.

The following sections will help you decide how wide a buffer to leave, based on the unique conditions of your project or the amount of 'threat' to the stream.

1. Position fences according to the slope of the land

• Where practical, position fences to include some flat land next to the stream. Run-off moves more slowly across flat land than sloping land, allowing more time for it to soak in.
• The steeper the slope draining into the stream, the wider the buffer width needs to be. As a rough guide, fence off 3 m for slight gradients, 3-5 m for gentle slopes and 10-20 m for steeper land.

2. Position fences according to the soils drainage ability

Free-draining soils

• In free-draining soils (above), most water will move through the soil and into the shallow groundwater then into the stream. The roots of riparian plants can help remove nutrients from shallow groundwater before it reaches the stream.
• Position fences to leave a minimum buffer width of 2 m on flat, free-draining ground.

Poorly drained soils

• On poorly drained soils, most water will flow over the surface of the ground, carrying soil and nutrients directly into the stream.
• Position fences to leave a minimum buffer width of 4 m on flat, poorly drained soils.

3. Position fences according to what you plan to plant

Consider if you will be leaving a grass margin or planting native plants.

Although it looks untidy, long grass does an excellent job of filtering sediment and nutrients from paddock run-off.

Native plants on the other hand shade the stream. This cools the water, reducing weed growth and providing better conditions for stream life. If you can only plant on one side of the stream, plant the north side as this provides more shade.

Think about which plants you plan to use: some need more space than others, and some need to be planted further back from the water than others. This will affect where you put the fencelines.

Carex plants helping to filter run-off and shade the stream.

Small plants

When planting small plants, such as the native sedge Carex secta and Coprosma propinqua, a 2 m wide buffer may be wide enough.

Large plants

When planting large plants plan to leave enough space, for example:

• Toitoi: 2.5 - 3 m buffer
• Flax: 3.5 - 4 m buffer
• Shrubs: 3 m buffer
• Narrow trees (eg cabbage tree and ribbonwood): 3 m buffer
• Other trees: 4 m buffer

Refer to Planting & Maintenance, for more information.

Plants correctly planted 1.5 m from fence to allow space for growth.

The 1.5 m rule

As a general rule, don’t plant within 1.5 m of the fence, otherwise as they grow, plants can short-out electric fences. Exceptions may be made when planting narrow plants such as cabbage trees, ribbonwoods and lacebarks.

4. Position fences to allow for natural waterway changes

Set permanent fencing back far enough to allow for bank erosion or for changing stream meanders, particularly in wide flood plains of U shaped valleys.

5. Be careful about fencing in flood prone areas

Erect permanent fences above any flood-prone areas and fence parallel with the way the stream floods, so the fence does not collect debris.

6. Fence-off low spots

Land run-off usually flows into a stream at low points. For example, water is channelled into naturally lower points in times of high rainfall; border dyke irrigation drains to low points and natural drainage channels form in the hill country.

These low points may contain wetlands, which also help remove nutrients and sediment from run-off. Consider fencing-off these areas.

7. Fence-off springs and drains

Excluding stock from springs, and drains that feed into streams, is particularly important. If stock defecate in these, the water quality of the whole stream is affected.


Above: Low points in paddocks are best fenced-off.

Below: Natural drainage channel fenced-off.

8. Where necessary, leave access for diggers

Drains, and streams in drainage schemes, may need to be mechanically cleaned from time to time to remove weeds, silt or debris. Planting and fencing can restrict access for drain maintenance.

Options for streams that require mechanical maintenance:

• Position a fence so that a digger can reach over the top and clear the channel. Plant low-growing plants or leave a grass margin between the fence and the stream.
• For bigger streams, place a fence far enough back to allow a digger to work between the fence and the bank. Plant the bank with low-growing plants or leave a grass margin. Taller species can be placed on the other side of the digger track, well away from the water.
• Use a temporary fence and leave gaps in plantings to allow the digger to get to the bank at certain spots.

South side is best for diggers

Plants on the north side of streams provide more shade to the stream when planted. It is therefore recommended that if you need to choose one side for digger access, you choose the south side.

• If drain clearance is an issue, talk to the Environment Canterbury river engineers.

9. Be careful fencing along stop banks

Environment Canterbury river engineers drive along the side of stop banks to check they are in good condition. For this reason they prefer that fences or plants are not placed on, or 3 m either side of, the stop banks. Tree roots can also affect the structure and integrity of stop banks.

The right fence for the right job

A sturdy well-maintained fence designed to suit your stock types is essential. One sheep or cattle beast getting though your fence can set your plantings back by years!

If you're running sheep or goats, you'll need a conventional post and 7-8 wire fence (preferably with netting).

Conventional fencing is also the safest option for cattle. A well-maintained three-wire electric fence can be a cheaper option for cattle, providing the power source is consistent and the fence is checked regularly.

An electrified outrigger can be a good idea for cattle, horses and goats to reduce fence damage and rubbing and leaning. If you're running deer, you will need a more expensive 2 metre mesh deer fence (adapted from Managing your bush block).

For a discussion on the uses and relative costs of the various types of fences, refer to Appendix 'QEII Covenant fencing: relative costs'.

When fencing flood prone areas:

• Use fewer uprights and less wire – this way less debris will catch. Do not use netting.
• Put wires on the downstream side of posts so the staples pop and the wire drops rather than rather than pulling out the posts and strainers.
• Use un-barbed staples so wires can pop more easily.

Refer to Planting & Maintenance - Hardy plant guide & Hardy plant table, for information on plants that can be planted in flood-prone areas.

Stock water options

Now that you've fenced off the waterway, what are the stock water options?

Troughs keep stock out of the stream.

Troughs

Putting in a reticulated stock water system can be expensive but costs will be offset by improved stock health and productivity.

Putting in trough water also allows you to deliver animal remedies and supplements though the trough water systems.

Alternative to troughs

If it is not possible to put in troughs, consider limiting the access for stock drinking.

When choosing the access points, avoid the outside of the bend. Here the water flows faster and the bank is the most prone to erosion. Banks on the inside of bends are less erosion-prone and usually shallower. Avoid positioning access points on steep banks.

At access points try setting fences so stock can reach their heads under the fence to drink, but can't get their hooves in the water. Gravel the area the stock will be standing on.

Note: This is not advised for large numbers of animals.

Checklist:

• Fence-off sufficient land to filter run-off
• Leave enough space for plants to grow
• Leave 1.5 metres between the fence and plants
• Fence-off low spots, springs and drains
• Allow for digger access where necessary.