Improved numerical modelling of morphodynamics of rivers with steep banks

Authors: Langendoen, Eddy; MENDOZA, ALEJANDRO - University Of Pittsburgh; ABAD, JORGE - University Of Pittsburgh; TASSI, PABLO - Electricite De France (EDF); WANG, DONGCHEN - Electricite De France (EDF); ATA, RIADH - Electricite De France (EDF); EL KADI ABDERREZZAK, KAMAL - Electricite De France (EDF); HERVOUET, JEAN-MICHEL - Electricite De France (EDF)

Submitted to: Advances in Water Resources
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/3/2015
Publication Date: 7/1/2016
Publication URL: https://handle.nal.usda.gov/10113/62656
Citation: Langendoen, E.J., Mendoza, A., Abad, J.D., Tassi, P., Wang, D., Ata, R., El Kadi Abderrezzak, K., Hervouet, J. 2016. Improved numerical modelling of morphodynamics of rivers with steep banks. Advances in Water Resources. 93(PartA):4-14.

Interpretive Summary: Steep streambanks represent an abrupt change in channel geometry resulting in highly complex three-dimensional flow and sediment transport processes, which greatly affect bank erosion and river planform adjustment. A number of depth-averaged two-dimensional computer models are available to simulate morphologic adjustment of both bed and banks. Unfortunately, these models use overly simplified conceptual models of riverbank erosion, are limited by inflexible structured mesh systems to resolve the flow and river topography, or are unable to accurately account for the flow and sediment transport adjacent to streambanks of arbitrary geometry. Researchers at the USDA, ARS, National Sedimentation Laboratory in collaboration with scientists from the University of Pittsburgh and the French National Hydraulics Laboratory-Chatou (LNH) are developing a new comprehensive model of river morphologic adjustment combining LNH TELEMAC model of riverbed evolution with the bank erosion modules of the USDA channel evolution computer model CONCEPTS. The performance of the new model is evaluated for initiation and development of meander planform. The model is able to simulate a much greater variety and complexity in meander shapes than has been currently published in the literature. Simulated meander development agrees closely with theoretical conceptual models of meander evolution. These efforts are part of the ongoing improvement of computer models to evaluate dam decommissioning scenarios during which large amounts of sediments are released that can adversely change the morphodynamics of downstream river reaches.

Technical Abstract: The flow and sediment transport processes near steep streambanks, which are commonly found in meandering, braided, and anastomosing stream systems, exhibit complex patterns. The interactions between bed and bank morphologic adjustment, and their governing processes are still not well understood. Increasingly, multi-dimensional computer models of riverine morphodynamics are used to aid in the study of these processes. A number of depth-averaged two-dimensional models are available to simulate morphologic adjustment of both bed and banks. Unfortunately, these models use overly simplified conceptual models of riverbank erosion, are limited by inflexible structured mesh systems, or are unable to accurately account for the flow and sediment transport adjacent to streambanks of arbitrary geometry. A new model is introduced that resolves these limitations. The model combines the river morphodynamics computer models TELEMAC-2D and SISYPHE of the open source TELEMAC- MASCARET suite of solvers with the bank erosion modules of the CONCEPTS channel evolution computer model. The performance of the new model is evaluated for initiation and development of meander planform. The model is able to simulate a much greater variety and complexity in meander wavelengths. Simulated meander development agrees closely with the unified bar-bend theory of Tubino and Seminara (1990), and the rate of meander planform adjustment is greatly reduced if the wavelength of alternate bars is similar to that of meanders.