Farm planning: Fencing waterways

Planning fencing around waterways is of key importance, both for helping exlude stock and improve water quality. Dairy NZ shares some advice.

Fencing waterways protects freshwater from nutrients, effluent, and sediment by excluding stock and creating a buffer between water and the land. Fencing will help to maintain and improve water quality and create a habitat for birds and freshwater species.

Planning your fencing

Waterway fencing needs to be far enough back to allow for movement/flooding of the waterway.

Start by mapping your waterways and creating a fencing plan.

Consider the overall layout of your farm along with protecting waterways. New fencing can improve grazing management and stock control.

Plan out fence lines and crossing points.

Determining where your fence should go

Under the nationwide stock exclusion rules, all dairy cattle need to be excluded from all lakes and waterways with a bed wider than one metre. All new fences erected after 3 August 2020 need to be a minimum of three metres away from the waterway. If your fence was erected prior to 3 August 2020, it does not need to be moved, unless it needs to be replaced, in which case it needs to comply with the three-metre stock exclusion.

This rule is a minimum standard and regional council rules, and conditions of milk supply can be more stringent.

If you do need to erect a new fence or replace an existing fence, it’s best to create a variable width buffer. What we do know is that rainfall runoff from paddocks is not uniform and becomes concentrated into swales (common terms include critical source areas, depressions, run-off channels).

In these areas, there’s a benefit of leaving
a wider grass buffer in. In some instances, there will also be a benefit to exclude stock
as well.

This approach means you don’t have to retire large areas of land (beyond the minimum now required) and the land you do retire will be the most at-risk areas where the benefit is the greatest.

In these situations, the best approach is to leave the wide buffers in these swales in rank grass. You may even want to consider a sediment trap. Where there are no swales, the use of riparian planting can provide instream water quality benefits and biodiversity benefits.

Extend fenced area to include seeps, wetlands, swamps, and springs

Additional benefits

Reduces stock losses
Provide habitat for birdlife

Limitations

May result in loss of grazing land
Needs stringent weed control
Higher cost if planting required

Fencing in flood-prone areas

Use fewer upright posts and less wire. This way, less debris will catch on the fence. Do not use netting, as it will trap debris.
Put wires on the downstream back side of posts so the staples pop and the wire drops, rather than pulling out the posts and strainers.
Use un-barbed staples so wires can pop off more easily.
Erect fences parallel with the way the stream floods so the fence does not collect debris.
Have fences further back where active erosion is occurring
Construct separate ‘blow-out’ sections across flood channels.

Maintaining access to drains

Build an electric fence that can be dropped or removed to allow access. E.g., use pinlock insulators so that the wires can easily be lowered for machinery to cross.
Position the fence so that a long reach digger can reach over the top.
For wide waterways, place a fence far enough back to allow a digger to work between the fence and the bank. This approach still allows for a wide grassy margin, and you can plant low growing plants on the waterway margin if you wish.
Do not cut off gateways that give diggers access to neighbouring paddocks.

Planting waterways

Using the right plants and techniques will help maximise the success of riparian planting and ensure you’re getting value for money by getting it right the first time.

Planting fenced riparian areas adds further benefit to the environment, as plants function like a sieve, helping to filter out sediment and nutrients before they enter waterways. Stabilising riparian plants help prevent land erosion and increase the habitat for native wildlife.

What to plant and where

When deciding what to plant and how wide the riparian margin should be, you need to consider the orientation of the waterway.

One of the benefits of riparian planting is that it provides shade to the river, reducing water temperature and excessive plant growth.

Rivers need at least 70% shade for these benefits to be achieved.

The table below suggests heights of vegetation for different stream orientations.

Both banks planted

North-South flowing stream	East-West flowing stream	Meandering stream
Plant height needs to be at least 80% of the stream width	Plant height needs to be at least 150% stream width	Plant height needs to be at least 75% stream width

One bank planted

North-South flowing stream	East-West flowing stream	To create more shade
One bank planted North–South does not achieve 70% shade for aquatic weed control but is likely to slow aquatic weed growth, improve temperature, and water quality	Plant height = 3x stream width and overhanging canopy. Taller vegetation on the North bank.	Have taller plants, plants overhanging the channel, and/or meandering channels.

Within riparian margins, there are three planting zones where different types of plants should be planted. Planting the upper and lower banks with vegetation will help improve conditions in waterways for animals that live in there as well as improve terrestrial biodiversity. Leaving rank grass near laneways, bridges, culverts and in swales where excess rainfall runs off paddocks will help filter out sediment and phosphorus.

Planting zones

Grass strip

Grass strips should be left between any riparian planting and fences to avoid plants tripping electric wires. Also, leave rank grass in areas where swales enter waterways.

Upper bank zone

The upper bank zone is on higher ground but may still be partially flooded every couple of years. Use flaxes, grasses, shrubs, or trees, which provide shade and shelter.

Lower bank zone

The lower bank zone is prone to flooding so plants need to be tolerant of waterlogging. Use plants such as sedges and rushes, which are well rooted and can survive many days under water.

Effective planting technique

1. Remove grass and weeds.

Four to six weeks before planting, spray one-metre diameter circles with a glyphosate-based herbicide at the location each plant will be planted.

2. Dig a hole that’s big enough to accommodate plant roots without them being curled up or bent in the hole.

On drier soils, ensure the base of the stem is one to two centimetres below the soil surface.

Mulch around plants will help keep soils damp, reduce weeds, and provide nutrients.

Good mulches include straw, staked down cardboard, or wool.

3. Put a stake beside plants (unattached) so they can be easily seen when weeding and identified if they have died and need replacing.