Experimental and 2D numerical modelling of morphology and bank erosion in meandering channels of different sinuosity

Authors: KARKI, SAROJ - Kyoto University; NAKAGAWA, HAJIME - Kyoto University; KAWAIKE, KENJI - Kyoto University; HASHIMOTO, MASAKAZU - Tohoku University; HASEGAWA, YUJI - University Of Hiroshima; Langendoen, Eddy; ATA, RIADH - Electricite De France (EDF); TASSI, PABLO - Electricite De France (EDF); EL KADI ABDERREZZAK, KAMAL - Electricite De France (EDF)

Submitted to: International Hydro-Science & Engineering International Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/30/2019
Publication Date: 9/1/2019
Citation: Karki, S., Nakagawa, H., Kawaike, K., Hashimoto, M., Hasegawa, Y., Langendoen, E.J., Ata, R., Tassi, P., El Kadi Abderrezzak, K. 2019. Experimental and 2D numerical modelling of morphology and bank erosion in meandering channels of different sinuosity. In Proceedings of International Hydro-Science & Engineering International Proceedings. September 1-6, 2019, Panama City, Panama 10 pp.

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 scientists of three Japanese universities and Electricity of France conducted laboratory experiments and computer model evaluations of bank erosion in meandering streams with two different magnitudes of channel curvature and with and without bank protection measures. The locations of bank erosion were different for the two planform curvatures, and were greatest for the channel with the lower curvature. 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: River bank erosion is a serious problem in meandering rivers as they continuously evolve due to erosion-deposition phenomena adjusting their geometric characteristics like sinuosity, the radius of curvature, deflection angle, etc. It is therefore important to understand the channel morphological changes and identify probable bank erosion locations in order to appropriately plan and implement riverbank protection works. Through experimental and numerical analysis, the objective of this study is to identify the channel morphological changes including the locations where the erosion of banks will be higher. In addition, the suitability of different arrangement of impermeable groynes for mitigating bank erosion are examined. Experiments were conducted in two different sine-generated meandering channels of varying sinuosity and curvature under the erodible bed and bank composed of non-cohesive sediment. From the experiments, it was observed that the higher sinuosity channel exhibit more uncertainty in bed morphology compared to the lower sinuosity channel, which showed distinct pool-bar patterns. The location and the extent of bank erosion also differed according to the sinuosity. Bank erosion was higher in lower sinuosity channel which shows the greater necessity of bank protection. The numerical simulation reasonably reproduced the phenomena observed in the experiments. Simulation results with the implementation of groynes showed that, groynes placed beginning from downstream of the outer bank apex are more effective in shifting high bed shear stress zone away from the outer banks for low sinuosity channel whereas in higher sinuosity channel, groynes placed exactly from the apex are slightly better.