Planting vegetation to stop stream bank erosion: where’s the evidence?

Posted on June 19, 2017

Increased rates of stream bank erosion and sediment movement in disturbed catchments have been attributed to changes in catchment hydrology caused by land clearing, channel modification, the trampling activities of livestock and the removal of riparian vegetation. Given that these effects are human-induced, it’s commonly assumed that they can also be reversed by human intervention, for example by restricting access of livestock to streams and restoring streamside vegetation. However, only a few studies have quantified the impact of riparian management on bank erosion. A review of research carried out in New Zealand identified only nine relevant studies, most of which relied on qualitative or semi-quantitative methods of analysis. Several of these studies reported that managed stream banks were in better condition than unmanaged banks, but most cited livestock control as the most influential factor; only two studies specifically attributed reduced stream bank erosion to the presence of riparian vegetation. The New Zealand experience is similar to that encountered elsewhere, with North American researchers commenting that despite the widespread use of riparian interventions to control bank erosion, quantitative assessments of their effectiveness are rare. However, this doesn’t necessarily mean that riparian restoration is ineffective, especially in the case of tree plantings, because the stabilising effects of tree root systems may take decades or even centuries to develop fully.  Therefore, there’s a need for long-term monitoring of bank condition, preferably using quantitative methods such as erosion pins and Lidar data analysis.  And because erosion processes can vary across a catchment, different types of riparian intervention may be needed at different sites.

Reference: Hughes, A.O. 2016. Riparian management and stream bank erosion in New Zealand. New Zealand Journal of Marine and Freshwater Research 50(2), 277-290.