Abstract
Abstract. A one-dimensional model that is able to store the stratigraphy emplaced by a prograding delta is validated against experimental results. The laboratory experiment describes the migration of a Gilbert delta on a sloping basement into standing water, i.e., a condition in which the stratigraphy emplaced by the delta front is entirely stored in the deposit. The migration of the delta front and the deposition on the delta top are modeled with total and grain-size-based mass conservation models. The vertical sorting on the delta front is modeled with a lee-face-sorting model as a function of the grain size distribution of the sediment deposited at the brinkpoint, i.e., at the downstream end of the delta top. Notwithstanding the errors associated with the grain-size-specific bedload transport formulation, the comparison between numerical and experimental results shows that the model is able to reasonably describe the progradation of the delta front, the frictional resistances on the delta top, and the overall grain size distribution of the delta top and delta front deposits. Further validation of the model in the case of variable base level is currently in progress to allow for future studies, at field and laboratory scale, on how the delta stratigraphy is affected by different changes of relative base level.
Highlights
A fluvio-deltaic deposit can be considered composed of two parts: the delta top, where sediment is transported, eroded, and deposited by fluvial-type processes, and the delta front, where sedimentary processes are characterized by avalanches, deposition of sediment from suspension, and particle entrainment and deposition by submarine currents (Swenson et al, 2000)
This paper focuses on relatively coarse grained Gilbert deltas, with steep fronts and a thick delta front deposit compared to the delta top deposit (Edmonds et al, 2011)
In this study we present the validation against experimental observations of a one-dimensional delta migration model that is able to predict and record the spatial, i.e., vertical and streamwise, variation of the grain size distribution within the deltaic deposit, under the assumption that grain flows are the dominant delta front sedimentation process
Summary
A fluvio-deltaic deposit can be considered composed of two parts: the delta top, where sediment is transported, eroded, and deposited by fluvial-type processes, and the delta front, where sedimentary processes are characterized by avalanches, deposition of sediment from suspension, and particle entrainment and deposition by submarine currents (Swenson et al, 2000). In this study we present the validation against experimental observations of a one-dimensional delta migration model that is able to predict and record the spatial, i.e., vertical and streamwise, variation of the grain size distribution within the deltaic deposit, under the assumption that grain flows are the dominant delta front sedimentation process. A numerical model that needs to reproduce the stratigraphy emplaced by a prograding delta is composed of three sub-models (types 1–3) that respectively describe (1) the total sediment mass conservation in the system (e.g., Wright and Parker, 2005a, b), (2) the mass conservation of sediment in each grain size range (e.g., Hirano, 1971), and (3) the sorting process on the lee face (e.g., Blom and Parker, 2004; Blom et al, 2006). Due to the different depositional processes on the delta front and on the delta top (Fig. 1), these experimental results allow for the validation of both the grain-size-specific mass conservation submodel (type 2) and the lee-face-sorting sub-model (type 3). A brief discussion of the model sensitivity to the grain-size-specific bedload model is presented in the Appendix
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