Investigating the evolution and formation of coastlines and the response to sea-level rise
Ortiz, Alejandra C.
MetadataShow full item record
To understand how waves and sea level shape sandy shoreline profiles, I use existing energetics-based equations of cross-shore sediment flux to describe shoreface evolution and equilibrium profiles, utilizing linear Airy wave theory instead of shallow-water wave assumptions. By calculating a depth-dependent characteristic diffusivity timescale, I develop a morphodynamic depth of shoreface closure for a given time envelope, with depth increasing as temporal scale increases. To assess which wave events are most important in shaping the shoreface in terms of occurrence and severity, I calculate the characteristic effective wave conditions for both cross-shore and alongshore shoreline evolution. Extreme events are formative in the cross-shore shoreface evolution, while alongshore shoreline evolution scales linearly with the mean wave climate. Bimodal distributions of weighted wave heights are indicative of a site impacted more frequently by tropical storms rather than extra-tropical storms. To understand how offshore wave climate and underlying geometry of a carbonate reef platform shapes evolution of atolls, I simulate the hydrodynamics of a simplified reef flat, using XBeach, a two-dimensional model of infragravity wave propagation. The reef flat self-organizes to a specific width and water depth depending on the offshore wave climate and characteristics of the available sediment. Formation of a sub-aerial landmass, like a motu, can be initiated by a change in offshore wave climate (like a storm), which can create a nucleation site from mobilization and deposition of coarse sediment on the reef flat. Once a motu is present, the shoreline should prograde until reaching a critical reef-flat width. Our conceptual model of reef-flat evolution and motu formation is governed by understanding the hydrodynamics of the system and subsequent response of sediment transport.
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2015
Showing items related by title, author, creator and subject.
Benthuysen, Jessica A. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2010-06)In a stratified rotating fluid, frictionally driven circulations couple with the buoyancy field over sloping topography. Analytical and numerical methods are used to quantify the impact of this coupling on the vertical ...
Magde, Laura S. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1997-03)The formation of new oceanic crust is the result of a complex geodynamic system in which mantle rises beneath spreading centers and undergoes decompression melting. The melt segregates from the matrix and is focused to ...
Griffith, David R. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2013-09)Steroidal estrogens are potent endocrine disrupting chemicals that are naturally excreted by vertebrates (e.g., humans and fish) and can enter natural waters through the discharge of treated and raw sewage. Because ...