A Graph-Theoretic Monte Carlo Framework for Comparing Delta Surface Dynamics and Subsurface Structure in Numerical Models and Physical Experiments

As climate changes and populations grow, a deeper understanding of deltaic surface and subsurface processes will help design sustainable management practices of delta resources. Numerical delta models are useful tools for understanding the relationship between the surface and subsurface, but quantitatively linking surface dynamics to subsurface structures remains difficult. The challenges stem from uncertainty in the numerical model parameters and the selection of informative post-processing metrics. In this work a Monte Carlo- and metric-based probabilistic framework is proposed for testing how well a numerical delta model captures the link between surface dynamics and subsurface structure. Probabilistic analysis of three graph-theoretic metrics describing morphology, morphodynamics, and subsurface structure shows that, at the laboratory scale, certain delta surface features, including channelization and channel stability, are informative of the spatial organization of sediment in the subsurface. Other surface features, such as sheet flows, are less informative. The surface dynamics metrics are also applied to data from a laboratory-scale physical experiment to show key differences in the numerical and experimental surface dynamics. The experimental morphology is more channelized than the numerical model and also undergoes more dramatic morphologic changes. These differences are likely due to a combination of numerical model resolution limitations, assumptions in the numerical model physics, and differences in flow field extraction in the numerical model and physical experiment.

Automated summary

This study proposes a probabilistic framework based on Monte Carlo and metrics to test the ability of numerical delta models in capturing the link between surface dynamics and subsurface structures. The results show that certain delta surface features are informative of the spatial organization of sediment in the subsurface, while others are less informative. Key differences between experimental and numerical surface dynamics are likely due to limitations in numerical model resolution and assumptions in the model physics.