Environmental issues caused by river dams and dam rehabilitation – starting point & challenges
Today, the banks of most water bodies with dams are usually covered with wave breakers made of concrete. However, these dams do not provide a suitable ecological habitat. In addition, hybrid waters (common at rivers with dams) tend to have similar ecological issues. As they are usually neither flowing nor standing waters, neither limnophilic nor rheophilic species can find a suitable habitat there. Only less specialized “common species” can adapt and use these habitats.
In addition, only few species of flora and fauna can settle on the concrete slabs built into the river banks, which leads to an absence of natural vegetation along the river banks. Classical dams interrupt contact with the surrounding areas both hydrologically and ecologically.
Whenever dam elevations or renovations become necessary, the slabs must be renewed. Usually, the old concrete surface is simply exchanged by new concrete elements – without improving the environment for flora and fauna. Not only is this process of dam elevation and restoration costly, it does not lead to any improvement in the ecological functions of dam-regulated areas.
When dams have to be elevated, the dam becomes broader on the landside. This increases land consumption and has a negative impact on the nearby riparian forests (usually FFH areas).In addition, the approval procedures are time-consuming and the cost for restoration and elevation of dams are considerably high.Dam construction with eco-berms
LEW Wasserkraft, Obere Donau Kraftwerke AG (ODK) and their project partners have developed a new approach for ecological dam raising and dam restoration which has been implemented and tested within the framework of the LIFE project INADAR funded by the European Commission. At the core of the new approach is the installation of so-called „eco-berms“ at the water-side embankments of reservoirs – ecological dams made from natural materials.
The standard construction method for the elevation of a dam causes further land requirements on the downstream face of the dam. Eco-berms allow for an elevation using the water (upstream) side of the dam, where a membrane and a layer of gravel are put in place (read more about how it works here). The ecological benefit: precious habitat for flora and fauna can be created by using dead wood and other structural elements along the banks.
Construction challenges
One aim of the project was to further investigate the special structural conditions, the stability and deformation behavior during the construction of the test sections. A dam restoration with eco-berms on the water side leads to technical challenges: The construction of new dam fills on soft river sediments can lead to both stability and settlement issues. 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 (e.g. 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 stabilization issues in the construction of eco-berms
Next chapter: our solution approach with eco-berms – continue reading here!