Alternated Gravel Mounts With Artificial Assembled Boulders Reinforcement Inside Channelized Rivers

Abstract

Alternated gravel mounts are expected to be a simpler and more cost-efficient alternative to traditional river restauration strategies. To improve their stability, two layers of assembled boulders are placed like fallen dominoes facing downstream around the triangular shape of each mount. Further assembled boulders are placed along both sides of the channel. The ecological improvements are quantified by the definition of refuge, i.e. anywhere inside the flow where fishes might escape the flooding’s force. In this paper, the needs of small sized fishes are considered (body length under 0.30 m). Point gauge and electrical-magnetic current meter are used to measure elevation and horizontal velocity components, respectively. The channel slope is kept at 0.01, while four different discharges are researched. The collected results are very promising: the introduction of assembled boulders is very important to maintain the model’s stability and flatten the water surface along the sides of the channel. The gravel mounts’ triangular shape successfully forces the flow to meander. Areas with slow flowing water are generated near the gravel bed along the channel’s sides. There, the requirements for the definition of refuge are met. As the water volume increases, the flow straightens, particularly inside the channel’s centre, but the refuge able areas are still forming. Each gravel mount is expected to generate a volume suitable for refuge as large as 40% of its own, with limiting factors such as flood’s discharge or shallow water conditions having little effect on this performance.