Design & implementations
Lessons, risks, implications...
The recurrence of mudslides in the department and the impacts on the inhabitants and the search for solutions to the problems faced by local residents. The work done by the Agriculture chamber as a result of the departmental regrouping facilitated the choice and the location of development measures. The multiplicity of actors involved in this departmental approach is important: communes, metropolis, unions, agriculture chamber, farmers, researchers, etc. The project managers note a positive development of the acceptance of soft hydraulics measures by the agricultural profession over the last ten years. In the short term, these works are also cheaper alternative measures compared to the implementation of conventional retention basins (but In the long term, the costs of compensation and maintenance are important).
Policy, general governance and design targets
Silt mobilized by rainfall on bare plots is carried downstream, where there are sensitive issues such as villages in the valleys (Figure 1). Mudflows impact both the receiving area (villages and local residents) and the emitting area (loss of soil for farmers).
Several factors have led to an increase in the risk of this phenomenon occurring since the 1950s:
Climate changes favouring heavier rains earlier in the season.
The decrease in grassland (-44% cattle between 1979 and 2000) and the increase in agricultural areas with little coverage during Spring and early summer.
Theimplementation of land consolidation actions leading to an extension of the field size and the removal of landscape elements (hedges, rural roads, embankments, etc.).
Urbanisation is also accompanied by the artificialisation of soils (+1047 ha/year between 1984 and 2000) and the progressive removal of buffer zones such as orchards and meadows.
As a result, the frequency of muddy water flows has increased, and they occur earlier and earlier in the season.