Hydrological Connectivity of Distributary-Confluence Geomorphic Unit: A Case Study of H-Shaped Features Within River Networks

Abstract

The H-shaped feature, characterized by a single connecting channel (CC) linking two inflows, is a common geomorphological unit in delta river networks. This structure plays a critical role in redistributing upstream flows, affecting the hydrological connectivity of the network. Despite previous studies on geometric structures and flow distribution, the mechanisms influencing hydrological connectivity remain poorly understood due to the complex structure of deltas and the interactions among various controlling factors. This study investigates the flow distribution and hydrological connectivity of H-shaped structures using numerical simulations and graph theory. Results indicate that, in H-shaped structures, the gravitational pressure caused by variations in Upstream Discharge Ratios (UDR) and CC topography generates uneven spatial velocity fields, resulting in different levels of diversion capacity in the CC. The hydrological connectivity indexes of the distributary subnetwork increase with the growing diversion capacity of the CC, whereas the confluence subnetwork exhibits the opposite trend. The CC's influence on downstream flow regulation and hydrological connectivity is influenced by the structure itself. Enhanced CC diversion capacity in H-shaped structures balances flow distribution and strengthens system resilience. The study emphasizes that simpler river network topologies concentrate flows in fewer channels while maintaining strong subnetwork exchanges, while complex networks distribute flows broadly but reduce inter-subnetwork connectivity. Therefore, we recommend that deltaic river network management consider their topological characteristics and implement strategies such as constructing additional CC or modifying existing channel topography to enhance flow exchange capacity. These findings offer valuable insights for global management and conservation of deltaic river networks.