Nature-based solutions for coastal defence

May 2021: Climate change induced extreme weather events are increasing the risk of flooding and costal erosion along shorelines. To protect critical infrastructure such as ports and to build resilience in coastal communities, researchers are recommending combining conventional flood protection measures such as dikes with managed grazing on salt marshes. Salt marshes can reduce the intensity of oncoming waves while grazing small herbivores can prevent erosion by increasing the amount of vegetation that binds the soil together.

Information

Many cities, ports, industry facilities, and residential communities are situated along the world’s coastlines and are being at increased risk of flooding from storms and risk of coastal erosion. The combination of sea level rises, and higher frequencies of extreme weather events due to climate change are accelerating coastal erosion and increasing the risk of damage from flooding. To mitigate these risks, traditional flood protection measures include building dikes, dams, and walls. New evidence suggests that combining conventional dikes with grazing on natural salt marsh habitats may provide a more sustainable and cost-effective alternative to purely ‘engineered’ flood protection. This approach is an example of a nature-based solution for building up costal defences. The salt marshes reduce wave forces on conventional dikes and the addition of grazing by both cattle and small herbivores, such as geese and/or hares, combined with artificial mowing significantly reduces salt marsh erosion and further increases the resilience of costal infrastructures. Small herbivores contribute to less erosion by changing the vegetation to plants with high root densities that bind the soil together.

Implications and opportunities

Sustainable and cost-effective flood and erosion prevention is key to building long-term resilience in coastal communities. To manage salt marshes effectively and deliver long-term protection for coastal regions, researchers recommend moderate or rotational livestock grazing on salt marshes. Further, coastal communities should avoid high intensity grazing in sediment poor areas and leverage the benefits of small grazers. When planning protective measures for coastlines, planners should consider the width and stability of salt marshes to ensure their long-term viability. Studying the developments in Cwm Ivy (Wales), researchers suggest that a nature-based approach to flood protection offers additional benefits for flora and fauna, alongside acting as a natural carbon sink to sequester carbon from the atmosphere. This approach encourages adaptation to shifting shorelines and offers benefits over fully engineered systems that aim to stop changes to coastlines and floods.

Limitations

Combining salt marshes with dikes and managed grazing has been shown to deliver flood protection in the UK at a pilot location; however, other flood prevention measures might be more appropriate in different geographical contexts and all recommendations should be seen within their geographic limitations.

Sources

Marin‐Diaz, B., Govers, L.L., van Der Wal, D., Olff, H. and Bouma, T.J., 2021. How grazing management can maximize erosion resistance of salt marshes. Journal of Applied Ecology, May.

Morris, S., (2021). ‘It wasn’t pretty at first’: the Welsh wildlife haven born out of disaster’. Available at: https://www.theguardian.com/uk-news/2021/may/10/wales-wildlife-haven-born-out-of-disaster-cwm-ivy