Removing a weir in the Gérinaux Stream, Belgium

Introduction

The Gérinaux stream is a tributary located in southern Wallonia (Belgium), flowing into the Hermeton river, which itself joins the Upper Meuse catchment. The upstream section of the Hermeton is classified as an ecologically important axis for fish movement. As one of the last tributaries in this upper basin suitable for fish spawning, the Gérinaux stream features a favourable gradient for salmonids as well as good water quality and oxygenation.

The area hosts a local population of brown trout, along with other species such as the bullhead and brook lamprey. The surrounding landscape within the municipality of Philippeville is made up of meadows, forests, and small rural villages, with the project site situated right between Vodecée upstream and Sautour downstream.

Project context and opportunity

Decades ago, a concrete weir creating a 1.6-metre waterfall was constructed to supply a pond on public land, but it is now obsolete. Situated 900 metres from its confluence with the Hermeton, it stands as the main obstacle on the stream, dividing wild trout into separate upstream and downstream populations.

Removing this single, obsolete structure presents a high-impact opportunity to fully reconnect 6 km of upstream habitat, and improve sediment dynamics, backed by local fishers, municipal authorities, and regional environmental services.

This area is also occupied by beavers, which, once the works are completed, will help establish a new dynamic balance within the stream. Their presence should help maintain valuable wetland areas without creating completely fixed and impassable barriers like the concrete weir targeted by this removal project.

Project aims

The primary goal of the project is to restore full longitudinal ecological continuity along the Gérinaux stream by completely removing the weir and safely managing the adjacent beaver dam.

Expected outcomes include:

• Ecological Restoration: Reopening 6 km of upstream habitats and spawning grounds, facilitating free movement, sediment transport, and genetic mixing for brown trout, bullhead, and river lamprey. Additionally, restoring natural flow will enhance water oxygenation and reduce its warming during the summer period.
• Stakeholder Cooperation: Strengthening partnerships between the local fishing association, the City of Philippeville, the Province of Namur, the Walloon Region (SPW-DNF), and the Haute-Meuse River Contract.