Looping Network Meetings

#39 March 10, 2023

Monday, 15:00 CET

Tian Dong

The Three Scaling Regimes of Delta Land Building

Abstract:
Deltaic distributary channel networks (DCNs) are critical for providing ecosystem service and nourishing populated coastal economic hubs. Mitigating climate change-induced land loss on deltas thus requires understanding the organization of DCNs, yet distributary networks remain understudied compared to tributary river networks. Specifically, tributary networks self-organize to maximize channel length per unit catchment area for a given amount of runoff, producing a geometry quantified by Hack’s Law. Previous work has established a concept in deltas that is analogous to catchment area called nourishment area, which defines the extent of a delta a particle can travel between downstream of a given bifurcation and the shoreline, but the relationship of nourishment area to distributary pathway length has not been established. Herein, we relate nourishment area to the lengths of three different channel paths within that area, representing DCN’s topological structure and flux partitioning. Our dataset comprises ~6,000 nourishment areas and associated channel paths, extracted using a graph-theoretic approach from 30 deltas across scales and hydrodynamic forcings. We found power-law relationships between nourishment area (An) and distributary channel length (L) in deltas, akin to Hack’s Law. A geometric relation that accounts for a proxy of bifurcation angle explains some variability in the relationships. Finally, after normalizing by delta size, we discovered three scaling regimes between An and L: a nearly linear relationship at the micro-scale (mouth-bar), a power-law relationship at the mesoscale (delta-lobe), and no/weak relationships at the macroscale (regional-delta). Our findings highlight the complexity of land-building processes in coastal delta regions.

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