Erosion control by agricultural and forestry techniques and soft hydraulics in the Bas-Rhin

National Id
France_12
Summary
The Bas Rhin department is sensitive to muddy water flows occuring during Spring and early summer storms, which impact farmers and villages located downstream of agricultural plots. In order to reduce this risk, the Agriculture Chamber and the local authorities are working together to develop ways of combating these phenomena, which are harmful to downstream areas. Within this partnership framework, a diagnosis of the erosion and mudslides risks is carried out by the Alsace Agriculture Chamber at the commune level, and gives rise to proposals for concerted crop rotation (preventive measures) and soft hydraulic developments (curative measures). On the basis of these recommendations, the installation of hedges, weirs and grass strips is carried out by different project leaders depending on the territory (municipalities or intercommunal). Concerted crop rotation is coordinated by the Agriculture Chamber, and also allows for the gradual transition of some crops to no-till techniques, while the communities manage the implementation of soft hydraulic works.
Reviewed by
Fribourg-blanc
The in-depth description of the case study
Location description
The Bas-Rhin department is located in the North-East of France. The Rhine plain land-use is mostly dedicated to Spring crops with no landcover during winter. Crops are located on the top of the hills and on the slope, while villages lie in the lower land.
NUTS Code
Alsace
RBD code
FRC
Transboundary
0
NWRM(s) implemented in the case study
Longitude
7.686808
Latitude
48.682818
Remarks
The project covers a wide area, with several hundred towns and villages.
Light or indepth?
In-depth
Project scale
Large
Project scale specification
The policy was conducetd over a long period in the region.
Application scale
Region
Installation date
2008
Age
12
Key lessons
The combination of preventive measures (crop rotation, no-tillage cultivation) and curative measures have reduced the risk of mudflow.
Success factor(s)
Success factor type
Attitude of relevant stakeholders
Success factor role
main factor
Comments

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 description
The Bas Rhin department is regularly subject to muddy water flows. These occur during Spring and summer storms on silty hills with Spring crops (beets, corn, etc.).
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.
Information on runoff reduction
The effectiveness of soft-hydraulic measures has been demonstrated by modelling of watersheds concerned with muddy casting phenomena. The visual observation of the various carriers of project confirms the retention of sediments by the soft hydraulic developments. The co-benefits of this work are landscape improvement, restoration of habitat for small wildlife, and softening of tensions between farmers and inhabitants of villages that have been impacted by past muddy water flows. The measures are also considered less expensive in the short term than the construction of mud ponds.

Partners

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