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Research Project: Managing Water and Sediment Movement in Agricultural Watersheds

Location: Watershed Physical Processes Research

Title: Hydro-morphological response to the change in groynes position and angle in sine-generated meandering channels of different sinuosity

Author
item KARKI, SAROJ - Kyoto University
item NAKAGAWA, HAJIME - Kyoto University
item KAWAIKE, KENJI - Kyoto University
item Langendoen, Eddy

Submitted to: International Conference on Fluvial Hydraulics
Publication Type: Proceedings
Publication Acceptance Date: 3/31/2020
Publication Date: 7/7/2020
Citation: Karki, S., Nakagawa, H., Kawaike, K., Langendoen, E.J. 2020. Hydro-morphological response to the change in groynes position and angle in sine-generated meandering channels of different sinuosity. International Conference on Fluvial Hydraulics. July 7-10, 2020. Delft Netetherlands. pp. 644-652.

Interpretive Summary: Rates of stream bank erosion are, among others, influenced by the planform of the stream, which causes streamwise variations in the forces acting on the stream banks. This makes it difficult to identify locations with greatest risk of erosion and develop effective mitigation measures. Scientists from the USDA, ARS, National Sedimentation Laboratory in collaboration with researchers from Kyoto University, Japan, conducted laboratory experiments and computer model evaluations of bank erosion in meandering streams with two different magnitudes of channel curvature and with bank protection measures (groins) positioned at different locations along a meander bend. For the lower curvature channel, bank protection was more effective when placed downstream of the meander bend apex, whereas bank protection needs to begin upstream of the apex for higher planform curvature. The findings highlight the complexity and spatial variability of bank roughness on meandering rivers, and therefore the need for improved process description in computer models of river morphologic adjustment.

Technical Abstract: In this study, we investigated the effect of impermeable groynes position and orientation on the hydro-morphological evolution using a depth-averaged 2D numerical model in two laboratory scale sine-generated meandering channels having different sinuosity and deflection angle. Two positions- one starting exactly from the outer bank apex and the other starting from downstream of the outer bank apex and two orientation- one at 900 and the other at 1200 to the bankline were investigated. Results revealed that in low sinuosity channel, groynes positioned downstream of the outer bank apex are more effective in reducing the scour depth at the groynes tip, shifting high-velocity and high near-bank shear stress away from the banks. However, with increasing sinuosity, the position of groynes needed to be shifted upstream around the apex for improving the performance. Additionally, meandering channel morphology and flow field were more sensitive to the change in position of the groynes than their orientation.