Vegetation protects against stream bank erosion by more than 80%

Stream bank erosionEvery year thousands of cubic meters of valuable soil is lost from local properties during rain and flood events to rivers and streams.

A study was undertaking by Alluvium Consulting in 2010/2011 which looked at the role of vegetation in protecting stream banks from erosion. The study found that stretches of stream that have been cleared experience much greater erosion than those that are vegetated.

During the study, cleared sections were compared to vegetated reaches on the same river and assessed after a flood event.

The sections with established vegetation reduced erosion rates by 80 – 95% due to the structurally diverse vegetation.

The study concluded that diverse range of vegetation including trees, shrubs and grasses will more effectively protect against erosion due to extensive root networks. Trunks and branches further reducing erosion will also reduce stream velocity.

While grass alone can limit erosion due to its coverage of the bank surface area, it is less effective at increasing the cohesive properties of the soil and reducing the stream velocity near the bank.

Soil cohesion is a measure of the bonds between individual soil particles or “stickiness” of the soil and is a key factor which impacts on the erosion rates in streams. Sand is an un-cohesive soil type, whilst clay is highly cohesive. Cohesive soils are typically more resistant to erosion as the “stickiness” of the soil reduces bed failure and bank scouring from flooding.

Riparian vegetation can increase the cohesive properties of soils by reinforcing via their root networks. The longer and more extensive the root network, the greater the degree of reinforcement.

Native riparian vegetation must be of a high quality and contain diverse structural elements comprising of in-stream, bank and floodplain vegetation.

Structural works like gradient reinstatement (bank battering); pylons or logjams may be required in addition to riparian vegetation to provide an appropriate level of protection from flood related stream erosion.

For more information on programs that help you control erosion on your property, contact Reef Catchments 07 4968 4200 or info@reefcatchments.com

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