Zachary Little

Zachary Little

Years participated in RESESS:

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An Overview

Major: Environmental Science, Geography, GIS Science
Academic Affiliation: University of Maryland Baltimore County
Research Mentors: A. Brad Murray and Katherine Ratliff
Communications Mentor: Rachel Havranek


Zachary’s fascination with the geosciences developed during his childhood trips along the coastlines of Ocean City, Maryland and family hikes within Gunpowder Falls State Park. He now aspires to pursue graduate school to study coastal and fluvial geomorphology with the goal of becoming either a professor of coastal and fluvial geomorphology or a coastal manager for the government.


Modeling river delta evolution under different wave climates

Deltas, dynamic landforms that are heavily inhabited by humans, result from a combination of river and coastal processes (Neinhuis and Ashton, 2013). As river sediment lengthens a river course and builds a delta lobe, wave driven alongshore transport reshapes the coastline. River lengthening promotes channel aggradation and eventually avulsions. Coastal processes affect river lengthening, and therefore avulsions. On the other hand, avulsions change where the sediment is delivered to the coastline, affecting coastline shape and processes. In previous numerical modeling analyses, Ratliff and others (2018) began to investigate how this coupling affected delta morphology and avulsion dynamics. As a simplification, the initial work involved symmetric wave climates - wave climates that produce no net alongshore sediment transport on average. Here we broaden these initial investigations by implementing asymmetric wave climates (and net alongshore sediment transport). In the numerical model experiments we manipulate four parameters: wave height; degree of asymmetry of wave climate; effectiveness of waves at smoothing coastlines (ratio of “high angle” to “low angle” waves); and critical threshold channel superelevation for avulsions. As expected increasing asymmetry yields asymmetric delta shapes; however, increasing wave heights can inhibit delta asymmetry. Lowering superelevation threshold for avulsions also tends to inhibit delta asymmetry. Unexpectedly, the migration of asymmetric deltas inhibited avulsions in the downdrift direction. In addition, the rotation of the coastline on the updrift side of asymmetric deltas produced avulsions that only minimally change channel lengths (and also minimal change in sediment flux out of the river mouth). As migration of an asymmetric delta becomes sufficiently pronounced, the erosive updrift side of the delta impinges on the river mouth - tending to slow progradation and inhibiting avulsions.