|Garcia, Marcelo -|
|Motta, Davide -|
|Abad, Jorge -|
Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: September 20, 2011
Publication Date: N/A
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 stream flow. The topography and flow dynamics in meander bends increase 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. Scientists at the USDA-ARS National Sedimentation Laboratory in collaboration with researchers from the University of Illinois have developed a new model that combines the stream bank erosion component of the 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 several test cases for both homogeneous and heterogeneous floodplain soil distributions. The applications show that the improved physically-based method of bank retreat better captures the complex long-term migration patterns of natural channels than the classic method.
Technical Abstract: The RVR Meander platform for computing long-term meandering-channel migration is presented, together with a method for planform migration based on the modeling of the streambank erosion processes of hydraulic erosion and mass failure. An application to a real-world river, with assumption of homogeneous floodplain soils, shows significant improvements in prediction over the classic migration approach based on the product of a calibrated dimensionless migration coefficient and the excess velocity at the outer bank. The proposed approach is also able to reproduce features such as downstream skewness of meander bends, compound loops, and preferential migration of some portions of a bend, and in general provides more complex planform shapes. The impact of floodplain heterogeneity on rates and patterns of meander migration is also analyzed. Since heterogeneous distributions of floodplain soils are difficult to describe deterministically, a Monte Carlo approach is adopted to examine the effects of floodplain soils and their distribution on channel-planform development. Focusing on the process of hydraulic erosion of the bank soils, governed by critical shear stress and erodibility coefficient in an excess shear stress relation, we show that migrated centerlines exhibit larger variability for increasing length scales of floodplain-soil heterogeneity, though the relation appears to be less than linear.