ALBERT

Description: In-channel structures are often installed in alluvial rivers during restoration to steer currents, but they also modify the streambed morphology and water surface profile, and alter hydraulic gradients driving ecologically important hyporheic exchange. Although river features before and after restoration need to be compared, few studies have collected detailed observations to facilitate this comparison. We created a laboratory mobile-bed alluvial meandering river and collected detailed measurements in the highly sinuous meander before and after installation of in-channel structures, which included one cross-vane and six J-hooks situated along one bar unit. Measurements of streambed and water surface elevation with sub-millimeter vertical accuracy and horizontal resolution were obtained using close-range photogrammetry. Compared to the smooth gradually varied water surface profile for control runs without structures, the structures created rapidly varied flow with sub- to super-critical flow transitions, as well as backwater and forced-morphology pools, which increased volumetric storage by 74% in the entire stream reach. The J-hooks, located along the outer bank of the meander bend and downstream of the cross-vane, created stepwise patterns in the streambed and water surface longitudinal profiles. The pooling of water behind the cross-vane increased the hydraulic gradient across the meander neck by 1% and increased local groundwater gradients by 4%, with smaller increases across other transects through the intra-meander zone. Scour pools developed downstream of the cross-vane and around the J-hooks situated near the meander apex. In-channel structures significantly changed meander bend hydraulic gradients, and the detailed streambed and water surface 3D maps provide valuable data for computational modeling of changes to hyporheic exchange. This article is protected by copyright. All rights reserved.