Plane trees rooted in the dikes of a navigation canal. Plane tree’s root system is very developed. It is very efficient at supporting the banks but also causes important risks regarding the structure of the backfills supporting the canal.
Large-sized larches and scots pines, rooted in a narrow dike, generating important risks of internal and external deterioration in dikes and dams.
Rooting of a larch in a dike, with a mixed-type root system (pivoting and tracing roots of great diameter and length). The root system colonized a great part of the dike’s backfill, generating an important risk of external erosion if the wind knocks down trees.
Wooded dike with a majority presence of poplars and black locusts, that have the particularity of developing very long roots that can go right through dikes and dams.
Protective dike against floods, delimited by the river and cultivated fields. Poplars are planted at the bottom of the dike, on the side of the fields. A riparian corridor is set on the bank, on the river side.The poplars that are in the “agricultural zone” produce crossing roots at the level of the foundation in order to draw water from the river, generating a risk of internal erosion.
Dike in a montainous zone colonized by large-sized conifers, generating multiple risks.
Channel parallel to the course at the bottom of the dike. The area at the foot of the slope is and has to be free from ligneous vegetation, as it generates a risk of clogging of the drainage system.

Define and prioritize issues and actions needed for territory protection against flood risk while insuring to environment a sound ecological condition

Context

Since the early 20th century, the revegetation of slopes and the river engineering works started a dynamic of reclosing of the environment. The incision of streams, as a consequence to the reduction of sediment supply and emphasized by the samples of materials in small river beds, has generated important modifications to fluvial processes.

In parallel, the revegetation of dikes, dams and banks showed a diminution of the pressure and maintenance done by men. This translated into the modification of hydraulic conditions during water flow.

For security reasons regarding dikes and dams and for the proper functioning of fluvial environments, it is necessary to control plant colonization in anthropized areas.

Grands peupliers en bordure de crête de barrage. Risque d’érosion externe en cas de renversement de l’arbre.
Jeunes pousses de peupliers ayant déstructuré le bajoyer bitumineux sur une digue de canal
Risque lié à la décomposition des racines. Galerie laissée en place par une racine décomposée au sein de matériaux à matrice cohésive.
Risque lié à l’arrachement d’un arbre. Le basculement de l’arbre entraine l’arrachement de la souche, qui peut importer avec elle, une partie plus ou moins grande de l’ouvrage hydraulique.

Issues

The risks involved with the implantation of ligneous species on dikes and embankment dams were highlighted in research works, led by C. Zanetti, M. Vennetier, P. Mériaux in the Irstea laboratory. The rooting of trees generates phenomenons of external and internal erosion, linked to the development of living root systems and to woody roots decay.

If the impact of vegetation on dikes and dams is negative, it is generally beneficial on banks where plants help with stabilizing and protecting the grounds.

Therefore, the development of vegetation has to be controlled, so that the positive and negative aspects of it can be combined.

Partners

Pays d’Aix Développement
Incubateur inter-universitaire IMPULSE
IRCE
France Active
BPI France
réseau entreprendre provence
ARRAA
INPI