Collaborative Research: Grain to Channel Scale Experimental and Numerical Investigation of Cohesive Sediment Transport

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Each year, the United States loses billions of dollars in property and large areas of habitat to erosion. To mitigate erosion-related damages and habitat losses, restoration projects import sediment to eroded areas. The success of these restoration efforts depends on their ability to retain sediment, so that restoration design requires a good understanding of sediment transport. Currently, there are established methods for predicting the transport of non-cohesive sediment, such as sand and gravel, relative to flow conditions and sediment particle size. However, it remains difficult to predict the transport of cohesive sediment, such as clay or mud, which is ubiquitous in aquatic ecosystems and consists of very fine particles. Predicting cohesive sediment transport is challenging because these fine particles have a strong tendency to stick together and form aggregates. These aggregates greatly change the effective size of the sediment particles and their interaction with the flow. This project will combine experiments and numerical simulations at a range of scales to understand how fine cohesive particles form aggregates and how aggregation controls the transport of sediment in water. Predictive equations for cohesive sediment transport will be developed. The results of this study will help improve designs of restoration projects to mitigate erosion-driven property and habitat losses. Next-generation environmental scientists and engineers will be trained at the graduate, postdoctoral, and undergraduate levels. Science videos about erosion will be created and disseminated to the public. Demonstration experiments will be used to raise K-12 students’ interest in environmental science and public understanding of erosion. This study will combine multiscale experiments and numerical simulations to understand the fundamental physical factors governing cohesive sediment transport. The study will directly address key challenges related to the multiscale and multiphysics nature of cohesive sediment transport dynamics that currently inhibit understanding of these processes. This includes the fact that transport that occurs at channel and ecosystem scales is controlled by the micro- to mesoscale interactions between nanometer-size clay particles, which are the main contributors to sediment cohesiveness, and by the multiphysics couplings between particle mechanics and fluid flow. The planned research will combine nano- to microscale confocal imaging and coarse-grained molecular dynamics (CGMD) simulations, micro- to mesoscale millifluidic experiments and computational fluid dynamics (CFD) simulations, and channel scale flume and outdoor stream experiments and CFD simulations to fundamentally understand the critical impacts of clay aggregation and gelation on channel-scale cohesive sediment transport.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.