Incision Sets the Growth Rate of Delta Channel Networks

Hongbo Ma , Tian Dong, John Shaw, Lawrence Vulis, Matthew Czapiga, Alejandro Tejedor, Andrew Moodie, Efi Foufoula-Georgiou

River deltas support large human populations and diverse ecosystems, but many are increasingly threatened by relative sea-level rise and sediment deprivation. Delta growth is widely viewed as a depositional process driven by sediment accumulation. However, the distributary channels that deliver sediment across deltas often extend before major episodes of subaerial land growth. Recent field observations suggest that, in many systems, these channels extend basinward by incision rather than deposition. Here, drawing on incisional growth theory, we derive an analytical solution that links channel-tip progradation to network topology, channel geometry, and river discharge. Analysis of observations based on this framework suggests that channel-tip progradation rates scale linearly with flow velocity at channel mouths, revealing an unexpectedly constant dimensionless ratio between the two—the progradation number—across deltas of widely varying sizes and growth rates. These findings suggest that incision is a predominant mechanism driving distributary channel growth and provide a simple framework for predicting channel-network expansion in delta restoration.