Author(s): Pietro Beretta Piccoli; Youichi Yasuda

Linked Author(s): Youichi Yasuda

Keywords: Gravel mounts; Stacked boulders; Refuge areas; Flood stages

Abstract: To improve the ecology inside channelized rivers, three different designs of alternated mounts are tested: arrowhead-shaped gravel mounts (Case 1); rectangular stacked boulders constructions with further stacked boulders along both sides of the channel (Case 2) and finally, a combination of both with arrowhead-shaped gravel mounts with stacked boulders reinforcements along their shape and the sides of the channel (Case 3). Experiments are conducted under same discharge and channel slope. The swimming requirements for small fishes (B. L. < 0.30 m) are simulated using two thresholds scaled to experimental dimentions: time-averaged velocity ≤ 0.1 m/s and standard deviation std (V) ≤ 0.07 m/s. The space inside stacked boulders constructions account to 30% of their volumes and it is expected to shield the fishes against the flooding’s force. For Case 1, the meandering flow generates pockets with reduced velocity and standard deviation behind each mount. The water surface is wavy, the volume with suitable swimming conditions is small compared to the mounts’ volume and the gravel becomes unstable under increased discharges. Stacked boulders of Case 2 are significantly more stable and generate the largest suitable volumes of all models, but the water surface rise is large. The positive aspects of both previous models are combined in Case 3 as the stacked boulders increase the arrowhead-shaped gravel mounts’ stability. The water surface is flat and its rise is manageable. Each mounts generates a suitable swimming volume equal 40% of its own. Based on these results, the construction of Case 3 is considered the best.

DOI: https://doi.org/10.3850/978-90-833476-1-5_iahr40wc-p0056-cd

Year: 2023