Waterway Erosion


2 min read

Exclude Stock Plant banks Other erosion control methods Recognising and repairing waterway erosion Severe erosion

Stream bank erosion refers to the loss of farm land due to the displacement of soil from riverbanks, which can also lead to excessive phosphorus in waterways. This page provides measures to mitigate erosion. Firstly, keep livestock away from banks to let vegetation grow, using fencing if necessary. Secondly, plant a mix of native plants, poplars, and hybrid willows on banks for long-term erosion control. Thirdly, use erosion control techniques like gradually sloping drain banks, appropriately sized culverts, and diversion channels. In severe cases, consider erosion control structures like rock riprap or detention dams, but you may need consent from your regional council.

Preventing stream bank erosion protects productive farm land from being lost and decreases the amount of soil and phosphorous entering waterways.

Stream erosion is a natural process but is accelerated by the removal of stabilising vegetation from stream banks and blockages in waterways that redirect water flow.

Reduce waterway erosion by following these steps:

1. Exclude stock

Exclude stock to reduce pressure on banks and allow vegetation to establish.

Fence back far enough to allow for some movement of the water channel when water levels are high.

2. Plant banks

The best long-term solution for erosion control is to plant a combination of natives with poplars and hybrid willows. Natives have a deep root structure for stabilising banks but they take longer to establish. Poplars and willows are faster growing, so they provide erosion control while the native plants are establishing.

Low natives such as sedges and rushes will survive flooding on the lower banks and help reduce soil being washed away.

Trees such as poplars and hybrid willows are good for steeper upper banks. They are fast growing and have a strong, deep root system to lock the bank together and will help control erosion. Ongoing maintenance is required with these trees to keep them manageable.

3. Other erosion control methods

Drain banks should be gradually sloped, with a shallow 'V' formation rather than an unstable 'U' shaped bank.

Culverts should be sized to cope with high flows as well as allowing for fish passage.

Locate bridges and culverts where there are regular stock crossing points to prevent stock accessing water.

Nib walls and diversion channels before crossings help to avoid the movement of runoff into waterways.

Recognising and repairing waterway erosion

Severe erosion

Rock riprap erosion control structure.

If erosion is severe and an immediate solution is required, an erosion control structure will provide protection.

Immediate solutions include hard structures such as rock (rock riprap) and gabion baskets, flumes and detention dams. Resource consent is usually required by regional councils and these are usually high in cost as they may require assistance from an engineer.

Contact your regional council for information about what solution would be most appropriate and any consent requirements. In some cases regional councils may be able to assist in planning or funding some of the work.

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Last updated: Sep 2023

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