Healthy Riparian Zones Limit Losses

Data from the Ex-Cyclone Oswald Flood Recovery Program shows properties with intact and healthy riparian zones suffer significantly less damage and loss to farm productivity, infrastructure and assets during major flood events than those with riparian zones not intact. This is the key message of site assessment data from one target area in the Condamine Alliance (Queensland) region for the program.

The estimated 2013 Ex-cyclone Oswald flood damage and loss to landholders in the area totalled $5.4 million across nearly 8000 ha of land and 107 km of creek frontage. The landholders on the floodplain bore the brunt of the loss, at an estimated average cost of damage of $822 per ha and up to $50,000 per km of creek frontage. In contrast, the average cost of damage and loss on properties with healthy riparian zones was only about one third of those where riparian areas were not intact. The assessment data also showed that in most cases, the more intact and healthy riparian zones were, the lower the cost of damage and loss to the landholder. In fact, the estimated cost of damage and loss from three landholders with the best riparian zones were just over $200 per ha and $13,000 per km of creek frontage.

The Ex-cyclone Oswald flood damage was caused by higher water velocity and erosive forces of flood waters than previous flood events. Soil type and condition, vegetation cover and water velocity all influence the extent of damage and loss to a property in a flood event. The lack of a good riparian zone, coupled with the removal of in-stream snags, rocks and bends, increases the risk of higher water velocity and subsequent damage from extreme weather events. The impacts are cumulative and rise exponentially as more riparian cover is lost.

Landholders can help mitigate erosion risk and the associated damage and loss on their property by increasing vegetation cover along creek banks and adjacent areas to slow water down. Retaining the natural ‘roughness’ in streams is also something landholders can do to help mitigate the risks of extreme weather events to their property and farm productivity. Snags, rocks and bends within the creek contribute to the ‘roughness’ in streams which helps reduce water velocity. Additionally, healthy riparian zones usually consisting of a ground layer, shrub layer and tree layer work together to minimise the erosive force of the water. The wider the riparian zone, the more effectively water is slowed down and erosion reduced.

These principles are being used to inform riparian restoration works being undertaken by landholders involved in the flood recovery program. Often, earthworks are required to repair creek bank erosion prior to vegetation being restored. Landholders are required to have appropriate approvals and licences from the Department of Natural Resources and Mines before undertaking any in-stream works.

The collective effort of all landholders from the headwaters to the floodplains is needed to ensure good riparian vegetation cover is maintained along our rivers and creeks to help slow the water down and reduce future risks of flood related damage.

Article and photo from the Condamine Alliance “Limit your losses from extreme weather events” article.