Classifying Estuaries Based on Sediment Transport Processes

Abstract

Estuarine Turbidity Maxima (ETM) arise from various sediment transport processes, each responding differently to anthropogenic and climatic pressures. This study makes a step toward constructing an explanatory parameter space for sediment trapping in estuaries by systematically investigating ETM formation across a wide range of idealized, M2-dominated estuarine configurations using a width-averaged numerical model. The sensitivity of sediment transport processes to four key estuarine parameters - estuary length, bed roughness, river discharge, and tidal amplitude - is examined. Additional simulations explore the influence of bed slope, width convergence, and settling velocity. Through decomposition of sediment transport contributions in the model results, four distinct sediment transport regimes are identified, each named after its dominant import process: the Baroclinic Regime, the Dispersive Regime, the Sediment Advection Regime, and the Internally Generated Tidal Asymmetry Regime. This regime-based classification represents a novel framework for linking estuarine parameter configurations to dominant sediment dynamics. In a schematic straight, flat channel configuration, only the Baroclinic and Sediment advection regimes can govern ETM formation. The Internally Generated Tidal Asymmetry regime becomes dominant in ETM formation only when the channel is sloping or converging. The Dispersive regime cannot produce an ETM. While the individual balances, or regimes, have been discussed, this study newly identifies the region of parameter space where each regime dominates. Despite its limitations, the proposed parameter space successfully captures the dominant transport processes in the Loire and Scheldt Estuaries. This process-based characterization of ETM dynamics offers insight into the physical conditions that favor high sediment concentrations in tidal estuaries.