About 60 people attended the Streambank Erosion Workshop held in Tarcutta on 12th September. Hosted by Murrumbidgee Landcare Inc in partnership with Tarcutta Valley and Kyeamba Valley Landcare Groups, the aim of the workshop was to provide landholders with a range of ideas and practical solutions and for dealing with streambank erosion.
Engineering Solutions for Erosion Control
Tim Smith, Licensing Officer with the Office of Water, spoke about the pros and cons of various structural works to solve large scale erosion problems. Rock armouring, rock and log groynes, log pins, and sausage gabions were all potential options in certain situations.
“Structural works must never be regarded as permanent solutions to erosion” was one key point that Tim raised. “Vegetation is the best long-term defence against bank erosion, the roots bind the banks together and vegetation is self-renewing.”
Low-Cost Erosion Control Techniques
Cam Wilson from Earth Integral spoke about his practical experience dealing with erosion, and gave some examples of low-cost solutions using local resources such as logs and rocks. The techniques Cam spoke about were mostly suited to 1st and 2nd order streams where smaller scale works would have an influence on erosion.
Cam also mentioned the effect that well managed deep-rooted pasture has on reducing surface run-off into waterways. Willow management rather than willow eradication was another possible method to prevent erosion – especially while more suitable vegetation was still establishing.
The role of water plants
Alison Elvin, a consultant with Natural Capital, spoke about the role of different plant species to prevent erosion, not only in the riparian area but throughout the whole catchment.
Cumbungi (bulrush) was recommended as a good pioneer species near waterways. Other rushes and tussock sedges such as Carex, many of which are actively controlled by landholders, were also recommended around wetlands and streams. Rows of vegetation, including trees, shrubs and grasses, planted across slopes in the landscape have the potential to reduce the damaging peak flows experienced during high rainfall events.
Erosion in the Tarcutta Creek Catchment
Aleksandra Rancic, Senior Natural Resource Officer at the Office of Environment & Heritage, spoke about the causes of erosion, both natural and human induced. Clearing of vegetation has resulted in reduced ‘roughness’ in channels and an increase in flow due to less water being taken up by trees in the catchment. This increases the energy of flowing water, which results in increased erosion.
Planting more perennial species throughout the catchment will reduce erosion. Planting shrubs and trees along streams will increase roughness, reducing the energy of flow, preventing erosion.
It was clear there was no simple solution to the erosion that was seen along Tarcutta Creek during the field trip that afternoon. Despite the extensive riparian planting along the creek at Peter McCallum’s property, there were still large areas of land that had disappeared after the floods. Tim Smith thought that the plantings probably helped to a large extent, but the flow energy during the floods was so extreme that erosion was inevitable. Revegetating the eroded areas was the cheapest and possibly the best option. Leaving fallen trees in the creek was also recommended, as they will help to slow flood flows and will not increase flood levels much at all. Redirecting flow away from eroded banks using fallen trees was possible in some situations.