Urbanization-driven simplification of deltaic channel networks: Landsat super-resolution reveals the hidden loss of small channels

Study region Dongjiang Delta, China, where rapid urbanization since the 1980s has significantly altered deltaic channel networks and hydrological connectivity. Study focus The topology of channel networks controls drainage efficiency and hydrological connectivity in river deltas. However, existing studies have predominantly focused on main distributaries and overlooked the widespread small channels. As such, we quantitatively examined how urbanization has altered the channel network and hydrological connectivity of the Dongjiang Delta, using a super-resolution technique to reconstruct high-resolution historical channel networks. New hydrological insights for the region Our results reveal a hidden pathway of hydrological degradation, i.e., the selective loss of small channels can substantially reduce the complexity and connectivity of the channel network even when main distributaries remain. Specifically, the loss of small channels caused decreases in the geometric and structural fractal dimensions of the channel network, indicating reduced space-filling capacity and weakened topological connectivity. Furthermore, we found a significant increase in the mean connectivity distance, signifying a reduction in river–floodplain connectivity of the Dongjiang Delta. Spatial analysis confirmed a positive relationship between urban expansion and the loss of river–floodplain connectivity, driven by both local direct effects and regional spillover effects. Our findings show that small channels are more susceptible to urbanization while playing crucial hydrological roles. Therefore, protecting and restoring small channels should be integrated into regional monitoring and coastal flood management.