Date of Award

Fall 12-2018

Level of Access

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Earth Sciences

Advisor

Peter Koons

Second Committee Member

Sean Smith

Third Committee Member

Samuel G. Roy

Abstract

Bedrock channels are responsible for balancing and communicating tectonic and climatic signals across landscapes, but it is difficult and dangerous to observe and measure the flows responsible for removing weakly-attached blocks of bedrock from the channel boundary. Consequently, quantitative descriptions of the dynamics of bedrock removal are scarce. Detailed numerical simulation of violent flows in three dimensions has been historically challenging due to technological limitations, but advances in computational fluid dynamics aided by high-performance computing have made it practical to generate approximate solutions to the governing equations of fluid dynamics. From these numerical solutions we gain detailed knowledge of the motions and forces of flowing water, which deepens our understanding of earth processes responsible for shaping landscapes.

By simulating hydraulic forces generated by flowing water in bedrock channels with interconnected zones of weakness, I explore the implications of fluvial stresses, boulder impact, and rock fabric heterogeneity on landscape form. I use a Smoothed Particle Hydrodynamics (SPH) solver to simulate flow over landscapes and I use stress-strength analysis to calculate earth fabric failure using the Failure Earth Response Model (FERM). SPH modeling is used to simulate the hydraulic mobilization of a boulder in a bedrock channel and to quantify the forces associated with its subsequent rolling, sliding, and impact two-meter freefall. FERM model results reveal that strength gradients in fractured bedrock topographies exert more control on volume of eroded material and channel form than the overall strength of the surrounding bedrock.

Finally, SPH model results are calibrated with three-dimensional water velocity measurements collected by an acoustic doppler current profiler in the Penobscot River. SPH modeling is used to explore the influence of in-stream logging structures on channel velocity, which has implications for the habitat of federally-protected diadromous fish species in the Penobscot River. Model results show that even at low discharges, the presence of in-stream structures changes the velocity structure at ~102 m length scales.

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