An improved meander migration formulation based on streambank erosion processes

Authors: Langendoen, Eddy; MOTTA, DAVIDE - University Of Illinois; ABAD, JORGE - University Of Illinois; GARCIA, MARCELO - University Of Illinois

Submitted to: International Conference on Fluvial Hydraulics
Publication Type: Proceedings
Publication Acceptance Date: 6/10/2010
Publication Date: 9/8/2010
Citation: Langendoen, E.J., Motta, D., Abad, J.D., Garcia, M.H. 2010. An improved meander migration formulation based on streambank erosion processes. In Proceedings of International Conference on Fluvial Hydraulics -- River Flow 2010. pp. 1027-1033.

Interpretive Summary: Application of one-dimensional channel evolution computer models, such as the ARS computer model CONCEPTS, is problematic in meandering streams because of the strong three-dimensional nature of the flow that increases the forces exerted by the flowing water on the stream bank at the outside of a meander bend compared to those exerted on stream banks in straight channels. Current two-dimensional computer models developed specifically to simulate the migration of meandering streams, however, employ simplified empirical relationships to determine channel migration and therefore stream bank erosion. To model the mechanics of meander migration more physically, researchers at the USDA, ARS, National Sedimentation Laboratory in collaboration with scientists at the University of Illinois combined the stream bank erosion component of the USDA CONCEPTS model with the meander model RVR MEANDER developed by the University of Illinois. The performance of the proposed approach is compared to that of the more simple classic method through the application to planform evolution of the Mackinaw River, Illinois. The application shows that the improved physically-based method of bank retreat is required to capture the complex long-term migration patterns of natural channels. The presented methodology improves the accuracy and reduces the uncertainty in model outcome for streams with a meandering planform. One-dimensional channel evolution models are widely used by federal and state agencies, such as the US Geological Survey, the US Bureau of Reclamation, the US Corps of Engineers, the Natural Resources Conservation Service and the US Environmental Protection Agency, to design stream-channel conservation measures and assess their long-term stability and benefits.

Technical Abstract: The migration rate calculated by models of river meandering is commonly based on a method that relates the migration rate to near-bank excess velocity multiplied by a dimensionless coefficient. Notwithstanding its simplicity, since the early 1980s this method has provided important insight into the long-term evolution of meander planform through theoretical exercises. Its use in practice has not been as successful, which is largely due to the heterogeneity in floodplain soils and vegetation. As a result, calibration of the dimensionless coefficient is difficult. With the ongoing effort in both the United States and Europe to re-naturalize highly modified streams, it cannot be expected that this simple method will accurately simulate the response of meandering streams to in-stream and riparian management practices over engineering time scales. This paper presents a new approach that relates meander migration rates to physically-based streambank evolution. The University of Illinois RVR-Meander model that simulates two- dimensional flow and morphodynamics of meandering streams is integrated with the streambank erosion algorithms of the US Dept. of Agriculture channel evolution computer model CONCEPTS. The performance of the new model is compared to that of the more simple, classic method by simulating the evolution of a meandering reach on the Mackinaw River, Illinois, USA. The simulated migration of the channel centerline by the two methods only showed minor differences in the more sinuous upper part of the reach. The new model performed significantly better than the classic approach in the less sinuous, lower part of the reach.