Effect of sediment transport boundary conditions on the numerical modeling of bed morphodynamics

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

Submitted to: Journal of Hydraulic Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2016
Publication Date: 4/10/2017
Publication URL: https://handle.nal.usda.gov/10113/5763093
Citation: Mendoza, A., Abad, J.D., Langendoen, E.J., Wang, D., Tassi, P., El Kadi Abderrezzak, K. 2017. Effect of sediment transport boundary conditions on the numerical modeling of bed morphodynamics. Journal of Hydraulic Engineering. 143(4):04016099. doi:10.1061(ASCE)HY.1943-7900.0001208.

Interpretive Summary: Computer models are increasingly used to evaluate sediment management in rivers. Unfortunately, simulated sediment transport and resulting channel bed morphology are sensitive to the imposed sediment transport boundary conditions at the upstream end of the studied river model. Scientists of the USDA-ARS National Sedimentation Laboratory in collaboration with researchers of the University of Pittsburgh and the French National Hydraulics Laboratory-Chatou, have conducted a detailed analysis on the effects of the upstream sediment transport boundary condition (constant sediment feed and recirculating the sediment from the downstream end to the upstream end) on sediment transport rate and bed form dynamics (dunes and bars) using the computer model Telemac2D. The sediment-recirculating condition produced a more dynamic bed morphology, which resulted in greater variability of sediment transport rates and patterns. The findings will help with 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: Experimental sediment transport studies in laboratory flumes can use two sediment-supply methods: an imposed feed at the upstream end or recirculation of sediment from the downstream end to the upstream end. These methods generally produce similar equilibrium bed morphology, but temporal evolution can differ. The adjustment of natural rivers to sediment supply usually includes both modes. Nevertheless, computer models of river morphodynamics typically use a sediment-feed boundary condition, and can therefore produce inaccurate bed morphology. The effect of sediment transport boundary conditions on bed-form dynamics was analyzed through numerical experiments using the two-dimensional, depth-averaged sediment transport model Telemac2D-Sisyphe of the open-source TELEMAC-MASCARET system. Two different boundary conditions were imposed at the inlet (a constant sediment feed and sediment recirculated from the outlet) for two bed-form scales (dunes and bars). Sediment transport boundary conditions greatly influenced dune development. The sediment-recirculating condition produced a more dynamic bed morphology with dunes of higher amplitude. The resulting zones of higher shear stress had a direct impact on the hydrodynamics and patterns of sediment transport. In the case of the bar bed morphology, the simulated bars had similar mean length and height for both sediment boundary conditions. However, the sediment-recirculating case produced a more dynamic bed, where the dominant bar length varied over time. Finally, the simulated bed morphology with bars, agreed much better with that observed when using a calibrated sediment transport equation to match sediment transport rates instead of the standard empirical sediment transport equations available in literature.