CSDMS 2016 annual meeting poster EnricaViparelli
Vertically continuous mass conservation in morphodynamic modeling of upper regime
Ricardo Hernandez Moreira, University of South Carolina Columbia South Carolina, United States. ricardo.hernandezmoreira@gmail.com
Astrid Blom, TU Delft Delft , Netherlands. Astrid.Blom@tudelft.nl
Abstract:
The vast majority of the morphodynamic models that account for the non-uniformity of the bed material are based on some form of the active layer approximation, which was first introduced in the 1970s and has been modified in different ways to meet different needs. In active layer-based models the deposit is divided in two or more layers with uniform characteristics in the vertical direction. The topmost layer is the active layer proper, which can interact with the bed material transport and whose characteristics can change in time. The other layers cannot interact with the bed material transport; they can exchange sediment with the other layers if the mean elevation of the deposit changes in time. In other words, the characteristics of these layers can only change in case of aggradation or degradation and the vertical sediment fluxes associated with e.g. bedform migration, infiltration of fine material and the dispersal of natural tracers and contaminants are not accounted for. To overcome the limitations associated with the discrete nature of the active layer approximation, Parker, Paola and Leclair introduced a continuous morphodynamic framework (PPL framework) that quantifies the vertical sediment fluxes within the deposit in terms of probability density functions of bed elevation, entrainment and deposition. The PPL framework was first implemented to model the grain size stratigraphy associated with dune migration at laboratory scale. However, due to the lack of information on the shape and the characteristics of the probability functions, the vertical sediment fluxes due to dune migration, changes in bedform size and aggradation/degradation were computed with sub-models. The use of sub-models has a serious drawback: the computational costs quickly become too expensive as the spatial scales increase. We recently demonstrated that if the probability density functions of entrainment and deposition are known, the computational costs for field scale applications of the PPL framework are comparable with those of active layer based models. Here we present an attempt to implement the PPL framework to describe the morphodynamics of the upper plane bed regime at laboratory scale. Our probability density functions are determined from time series of bed elevation measured in laboratory experiments performed at the University of South Carolina. The probability functions are implemented in a numerical model that is applied to compare the dispersal of tracer stones in the case of bed configurations changing from upper plane bed to sheet flow. Future work is needed to relate the probability functions to the flow and sediment characteristics and to extend the results to the case of non-uniform bed material.
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