Hybrid waters, as they are usually formed at dammed rivers, very often show severe and similar ecological problems. Because they are usually neither flowing nor standing waters, neither limnophilic nor rheophilic species find a suitable habitat here. Only less specialized "common species" can adapt and use these habitats.
In addition, only very few species of flora and fauna can settle on the concrete slabs that have so far usually been built into the banks, which means that classic riparian vegetation is completely absent. Contact with the surrounding areas is largely interrupted both hydrologically and ecologically.
In the past, water-side embankments directed towards the river were usually secured with embankment concrete slabs in reservoirs. Whenever dam heights or renovations become necessary, the slabs must be renewed. This process is not only costly, but also does not lead to any improvement in the ecological functions of dam-regulated areas. The standard construction method for dam raisings also requires a widening of the air-side dam contact area and often the replacement of the hinterland drainage. This results in a considerable intervention in the riparian forests (mostly FFH areas) and the need for corresponding compensation areas.
Construction with Eco-Berms
Due to this problem, the LEW has developed a new approach for ecological dam raising and dam restoration, which is implemented and tested within the framework of the LIFE-Project INADAR funded by the European Commission. Core of the new approach is the installation of so-called eco-berms at the water-side embankments of reservoirs. The aim will be to further investigate the special structural conditions, the stability and the deformation behavior during the construction of the test sections.
A restoration with eco-berms on the water side leads to technical challenges, as the construction of new dam fills on soft river sediments can lead to both stability and settlement problems. This is particularly the case when a second sealing element has to be installed on the water-side embankment at the same time.
Stability problems (terrain break under the water-side fills) are usually accompanied by comparatively large settlements, which lead to severe shear deformations of the concrete slabs lying on the water-side embankment.
Fig.: Example of the stabilization issues