River morphodynamics with creation/consumption of grain size stratigraphy 2: numerical model

Abstract

As a river-carrying sediment mixture aggrade, it creates a stratigraphic signature that records this evolution. This stratigraphy is characterized by the vertical/horizontal variation of substrate grain size distribution. If a river degrades, it mines this stratigraphy, and transfers the sediment so accessed farther downstream. Although several numerical models tracking the creation/consumption of stratigraphy are available, none has been tested against experiments under plane bed regime conditions. Here nine physical experiments modelling the creation/consumption of stratigraphy are described. These are compared with nine corresponding numerical experiments using a model that tracks stratigraphy. The results justify the numerical model, and in particular the scheme to track stratigraphy. This scheme can be used at field scale to characterize e.g. the response of a river to an increased/decreased sediment supply. The numerical model shows a discrepancy with the experiments, however, whenever a distinct delta front forms, because the model does not describe sediment sorting across an avalanche face.

Keywords:

• Laboratory flume
• mobile-bed equilibrium
• sediment mixture
• sediment transport
• stratigraphy

Acknowledgements

The research reported here represents a contribution of the National Center for Earth-surface Dynamics, a Science and Technology Center funded by the National Science Foundation of the USA (EAR-0203296). This research was motivated by the large-scale experiments on the morphodynamics of gravel-bed rivers conducted in the Streamlab facility at St Anthony Falls Laboratory, USA. Special thanks are due to Astrid Blom, who provided not only the sediment corer used herein, but also important advice in conducting the experiments. Thanks are also due to Tzu-Hao Yeh, who provided advice and assistance in plotting the stratigraphic patterns.

Additional information

Notes on contributors

Enrica Viparelli

currently at Department of Civil and Environmental Engineering, University of Illinois Urbana-Champaign, 205 North Mathews Ave, 61801, currently at Department of Civil and Environmental Engineering, University of Illinois Urbana-Champaign, 205 North Mathews Ave, 61801 Urbana IL USA.

Octavio E. Sequeiros

currently at Shell Intl. Exploration and Production, B.V., Kessler Park 1 2288 GS Rijswijk, The Netherlands.