Relationships between sediment connectivity and hypsometry in an intertidal microtidal estuary

Using the Tauranga Harbour estuary (New Zealand) as a case study, we quantify functional surface sediment connectivity between twenty geomorphic regions across five grainsize classes, applying graph theory to depth-averaged numerical model outputs. Our results show that estuarine surface sediment connectivity patterns can be resolved on both local and system-wide scales, and how these patterns vary systematically with hydrodynamic energy, grainsize, and the morphological and geometric properties of sub-basins and the larger estuary. We show that flood-dominant, infilled (divergent) sub-basins act as sediment sinks, whereas ebb-dominant, less-infilled (convergent) sub-basins function as sediment sources. However, these source–sink relationships are spatially variable and driven by non-linear interactions between hydrodynamics and local morphology, with greater connectivity for fine sediments. For coarse sediments, dominant transport pathways are confined to the deeper regions. Connectivity analysis can provide an effective framework for exploring sediment transport pathways in shallow estuarine systems with multiple sub-basins. Hence, the approach can also improve predictive understanding of sediment exchange for integrated estuary management.