Thesis Defense: Andrew Moodie, Ph.D. Candidate
Defense Date: Friday, April 3rd, 2020
Time: 12:30 p.m.
Zoom Meeting Link: https://riceuniversity.zoom.us/j/531455798
Assessing deltaic landscape management strategies based on studies from the Yellow River delta, China
Deltaic environments possess an abundance of natural resources that promote human welfare, but these delicate environments are threatened by a multitude of natural and anthropogenic factors. This dissertation is motivated by a need to understand the impact of anthropogenic channel management on river-delta resiliency. The unanticipated civil disruption associated with flooding and channel relocation via avulsion is at odds with society’s desire for landscape stability, so channel engineering that restricts mobility and floodplain connectivity is common, but this engineering diminishes sediment dispersal necessary to sustain deltas and coastlines. On the Yellow River delta, China, engineered diversions have been implemented to approximate natural delta evolution; the Yellow River fluvial-deltaic system is used throughout this dissertation as a case study, to identify best practices for promoting deltaic sustainability that are exportable to other deltas around the world. In three chapters, this dissertation addresses the following questions: 1) how do sediment transport mechanics change in high concentration flows, and how does this impact diversion effectiveness, 2) what factors dictate the timing and location of natural deltaic avulsions, and 3) what is the channel response to artificial diversions, and what diversion length optimizes societal benefit while minimizing cost. First, a study of density stratification in the Yellow River reveals that fine sediment extracts turbulent energy from the river flow, modulating the vertical distribution of sediment and impacting effectiveness of water and sediment extraction efforts to deliver sediment to the coast. Second, a numerical model is developed to simulate the processes that lead to natural deltaic avulsion, and it is found that deltaic lobe progradation profoundly impacts the location and timing of avulsion. Third, simulating artificial diversions along a deltaic channel course reveals autogenic channel behavior that leads to system nonlinearity and emergence of an optimal diversion length.
Overall, this dissertation research indicates that the sustainability of coastal landscapes is achievable, but will require continued study and careful management of delicate coastal landscapes.