Darne Weir, France

Introduction

Classified as a Natura 2000 site, the Laussonne River is located in a biodiversity hotspot. The Laussonne hosts fish species of national and international importance such as the Thymallus thymallus and Salmo trutta fario. Yet, the presence of dams inhibits the full ecological potential of this river.

Near the city of Le Puy en Velay, in Haute-Loire, France, the Darne Weir is an old water intake built in 1806 on the Laussonne River to feed a mill. The site is located in the Auvergne (Haute Loire) at approximately 150 m from the confluence with the Loire in the commune of  Coubon, in the district of La Darne. It is the first weir on the Laussonne River before its confluence with the Loire River blocking several kilometres of upstream habitat.

Project context and opportunity

The removal of the Darne Weir is part of a larger action plan, called “river basin contract”. The project partners plan to remove two other barriers on the Laussonne, upstream from the Darne Weir to cumulate the ecological benefits. If the Darne Weir would not be removed, removing other barriers further upstream would bring limited ecological gains, as the Laussonne River would remain disconnected from the Loire River.

Project aims

The Darne Weir removal will reconnect and restore the ecological continuity of the entire Laussonne River with the Loire River, particularly for the benefit of important fish species. In this area, the Loire is flow unimpeded for 200 km.

The project will restore riverbanks with bioengineering techniques and local vegetation to stabilise and improve the functionalities of the riverbanks, and benefit biodiversity. The objective is to restore good hydromorphological functions, not only continuity.  Because of its urban location, the project will encourage communication with many inhabitants to make the local population discover the importance the Laussonne.

Project achievements

The project faced challenges from flooding, which altered the site’s morphology and required updates to topographic surveys and studies. Following these adjustments, the permit application was re-submitted to the administration and preparatory works commenced in September 2025, including site installation and fish rescue operations.

The removal was completed on October 2025, allowing for the reconnection of nearly 26 km of the river, restoring natural flow and improving ecological connectivity.

Overall, the project successfully adapted to changing conditions and delivered significant ecological and hydrological benefits.