Soil bioengineering: when plants protect us from risks

Effective and sustainable, soil bioengineering techniques enable us to manage the risks of riverbank erosion. Learn more about these innovative and biodiversity-friendly methods from the publication of the book Génie végétal en rivière de montagne (Soil Bioengineering in Mountain Rivers) and the conclusion of the Géni’Alp project.

When concrete goes green

Mountainous areas face extreme and unpredictable hazards. Protecting human infrastructure has often been the role of civil engineering, which has been using mineral, concrete wall and rip-rap techniques along riverbanks since the 1950s. However, despite being effective, these works can disrupt the continuity of ecosystems and often form a blot on the landscape.

Protection rhymes with vegetation 

Gentler, more eco-friendly techniques would allow these works to integrate more harmoniously into the landscape; one such technique is soil bioengineering.  This ecological engineering technique uses living plant materials to fight erosion and promote the stabilisation of riverbanks. Just as resistant as some civil engineering techniques, these methods are often less expensive and contribute to maintaining vegetation and ecological corridors (areas which connect natural habitats and favour biodiversity). 
Soil bioengineering, which is increasingly used on plains and along rivers and waterways, remains marginal in mountainous areas due to the significant constraints found there.
 

A collaborative project between research and professionals

Developing and experimenting its use in mountainous regions: this is a challenge met by the Géni’Alp project, launched in 2010 by Irstea Grenoble, the Association Rivière Rhône-Alpes and Hepia school in Geneva. Uniting 11 organisations from the Franco-Swiss border area (associations, regional authorities, engineering schools, public establishments) and piloted in France by the Rhône-Alpes region, this project has boosted the use of soil bioengineering in the region.

Six experimental work sites in the heart of mountainous areas have subjected plant techniques to severe testing, pushing their limits higher and further. Given altitude and gradient, the main specific restrictions in the mountain soil bioengineering work sites, a review of the plant species used has been carried out. In fact, the choice of suitable plants is essential as, along with their root systems, they will ensure the sustainability of the works.

Training days have taken place on experimental work sites. They have brought together managers, contracting authorities, technicians and researchers. The aim was also to show managers about the use of these techniques in altitude or on steep-sloped rivers. The feedback on these works will be a great learning tool for all of these stakeholders.

Meanwhile, many soil bioengineering sites have been used as research land within the framework of a thesis dedicated to monitoring biodiversity and the functioning of these restored ecosystems.

The technical publication Génie végétal en rivière de montagne summarises all of the experience and knowledge acquired throughout the project. This book, which combines engineering, hydrology, botany and ecology, provides all the key elements to contracting authorities so that biodiversity and ecosystems are taken into account in their development projects on mountain riverbanks. It supplies background information on soil bioengineering, its limits and the questions to consider before launching a project. Many work sites, not only those from the project, but also those from feedback on an Alpine scale, are presented in detail. It also includes a guide to the species. This original guide describes both ecosystem models and the species to choose for the projects. Unusually, this flora contains a key to determining dormant willows, especially from their buds and branches.

This book will be available at no charge in January 2014 on a dedicated website; in the meantime, you can consult the website of the Géni’Alp project, which is full of resources and documents.

Book website: ouvrage.geni-alp.org

Available January 2014

Géni’Alp website: www.geni-alp.org