Removing two weirs in the Bois Jean River, Belgium

Introduction

The Bois Jean Basin, a transboundary sub-catchment of the Semois (Meuse), is located in 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.

Project context and opportunity

Since 2023, over 300 barriers to river connectivity have been identified in the Semois Valley National Park. From these, the project’s team selected 7 sub-catchments for complete restoration. These were chosen for their ecological importance, and because the fragmentation situation is known and offers opportunities for barrier removal.

The project is also innovative in its approach: it works in full cooperation with private landowners, who agree to barrier removal on the condition that an alternative water supply is secured for their ponds, which are home to sensitive or protected species. This demonstrates how ecological restoration and landowner interests can be aligned through smart, integrated design. The proposed ecological intake will maintain pond function while eliminating the need for river fragmentation.

Project aims

The removal of barriers in the Bois Jean Basin will have a substantial ecological impact by improving river connectivity and restoring key habitats. These weirs 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 removing these barriers – the only barriers in the catchment – the project’s team aims to open approximately 15 km of river, facilitating fish migration and improving overall habitat quality. This project will also help advocate for further barrier removal projects and hopefully contribute to the removal of more barriers in the Semois Valley.

Project achievements

The Bois Jean Weir Removal Project was launched to restore ecological connectivity in the Bois Jean sub-basin, a tributary of the Semois River located within the Parc national de la Vallée de la Semois in southern Wallonia, Belgium. Until recently, the ecological function of the stream was severely limited by two small artificial barriers – concrete and stone weirs approximately 1.5 metres high – originally built to feed three private ponds downstream. These structures blocked fish passage, disrupted sediment transport, and fragmented nearly 15 kilometres of upstream habitat. By removing these barriers, the project has reconnected 14.9 km of free-flowing habitat, restored natural sediment dynamics, and improved hydromorphological conditions throughout the Bois Jean valley. The site now functions as an open and resilient headwater system, contributing to Good Ecological Status (GES) under the EU Water Framework Directive and advancing regional goals for biodiversity recovery and climate adaptation.

Beyond ecological outcomes, the project demonstrates an effective model of cooperation with private landowners, balancing restoration with practical land use needs. With both weirs now removed and ecological functions restored, the Bois Jean project stands as a tangible example of small-scale but high-impact river restoration in a protected and transboundary landscape.