Controls on the Flux Distribution of Delta Networks

Abstract

Deltas are highly-populated coastal landscapes. They are naturally low-lying, making them vulnerable to relative sea-level rise.The flux distribution of delta networks controls which parts of a delta receive enough sediment to keep up with sea-level rise, versus which parts of a delta risk inundation. Bifurcations are the gatekeepers of delta distributary networks, controlling how much water and sediment enters each channel. Understanding of how bifurcations evolve and respond to upstream and downstream controls is therefore important for predicting the dynamics of delta network flux distribution. In this thesis, I start by developing a numerical model demonstrating how downstream deposition qualitatively affects bifurcation flux partitioning dynamics, allowing for ongoing dynamics. Next, I present a set of experiments designed to test this model, and argue that the observed irregular switching dynamics can best be interpreted as reflecting a combination of downstream control and upstream bar dynamics. I then extend the numerical model to show how coupling between bifurcations can lead to chaotic flux partitioning in a simple delta network. Finally, I conclude with lessons learned about the controls on the flux partitioning of delta networks, and present ongoing work on how bifurcations are influenced by relative angle, and how bifurcations are affected by noise.