Riverine Systems
River Nairn
Aberarder, Scotland, United Kingdom Restoring a wandering gravel-bed river using online wetlands. Beginning as a steep mountain stream in the Highlands, the River Nairn historically wandered through a wide valley of wetlands and wooded floodplain. But between 1750 and 1860, the river was straightened and embanked, most likely to improve the valley for agriculture, leaving the channel perched above its floodplain. The gradual in-filling of the channel with gravel had increased flood risk to surrounding property, and the river corridor lacked naturally occurring physical features. In 2013, the landowner and regulator discussed two solutions to address the flood risk of the river: the traditional approach of regular dredging or a process-based restoration approach. They chose the latter for the project, which involved embankment removal, channel realignment, and restoration of wetland areas (creating online wetlands by reconnecting them to the river channel) to facilitate sediment storage without compromising flood risk. The project team also placed large wood in the channel to facilitate natural physical processes such as the development of riverine habitats. Construction began in 2017 and finished in just four weeks. Within two weeks of completion, sea trout (Salmo trutta) were already using typical spawning locations, with Atlantic salmon (Salmo salar) following a few weeks later.
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