Culverts removal in the Antrogne, Belgium

Introduction

The Antrogne basin, a sub-catchment of the Semois (Meuse), is located in the heart of the Semois Valley National Park in Belgium. This area was selected for restoration due to its ecological significance, supporting species like brown trout and bullhead, as well as its technical and financial feasibility for restoration efforts. Historically, it was also home to the pearl mussel and the Atlantic salmon.

Project context and opportunity

Since 2023, the project’s team has identified over 300 barriers to river connectivity in the Semois Valley National Park. From these, seven sub-catchments were selected for complete restoration, based on their ecological importance, known fragmentation status, and opportunities for barrier removal.

In the Antrogne basin, 46 structures or crossings were identified as potential obstacles to ecological continuity. A preliminary report recommended the modification or removal of seven key structures. Many of the observed structures, such as large bridges or temporary streams without fish habitats, were not considered problematic. The culverts selected for removal are crucial for trout reproduction, offering ideal spawning and nursery conditions in terms of sediment, water quality, slope and permanent water flow.

Project aims

The removal of barriers in the Antrogne basin will have a substantial ecological impact by improving river connectivity and restoring key habitats. These culverts currently restrict the movement of species such as brown trout and bullhead, impeding their ability to migrate and access critical spawning and feeding areas. By replacing these barriers with hydraulically transparent solutions, the project’s team aims to open approximately 6 km of river, facilitating fish migration and improving overall habitat quality. The project will also serve as a model to advocate for additional barrier removal projects within the Antrogne and the wider Semois Valley.

Project achievements

This removal project opened up approximately 6 km of stream in the Ardennes Forest, in the heart of the Semois Valley National Park, by removing three culverts.

While these culverts were still in a somewhat functioning state (in terms of the road – not the river), the project team was able to remove them through concertation with all stakeholders, mainly for ecological reasons. While these culverts were fairly ‘easy’ to remove, the bigger challenge is actually replacing them, for two reasons: (1) the right solution must be found based on local constraints, and (2) funding must be secured for the reconstruction, which is far more expensive than demolition.

Thankfully, in Wallonia, “open arch modular bridges” are starting to be used and luckily the project team managed to have access to restoration funding through the national park, which allowed them to finance the reconstruction of the bridges.