Investigating Transient Rip Current Dynamics (Current Work)
Waves that propagate towards a coastline from many different directions (directionally spread) can create waves with short crest-lengths. These waves inject vorticity into the surf-zone and create small scale eddies. Small surf-zone eddies can coalesce into larger eddies and lead to strong intermittent offshore directed flows known as transient rip currents (TRCs). My PhD work is focused on understanding TRC dynamics and how these small eddies lead to TRCs through the use of wave-resolved numerical models, like FUNWAVE-TVD. Currently, this work focuses on the development of a model setup of directionally spread waves on an alongshore uniform barred beach that validates well with observations collected in a series of lab experiments conducted in a large wave basin. My future work will also include integrating machine-learning techniques with numerical modeling to improve the representation of TRC dynamics in coastal models.
This plot shows vorticity computed from output from a wave-resolved numerical model (FUNWAVE-TVD). Vorticity in the surf-zone (0-100 m) is created from short-crested wave breaking induced from directionally spread waves generated from a wavemaker (black line) on alongshore uniform bathymetry (grey contours).
Exploring The Controls of Stratification on Phytoplankton Blooms in San Francisco Bay
Historically, San Francisco Bay has not exhibited classic eutrophication conditions despite high ambient nutrient concentrations; however, a shift in precipitation and freshwater flow patterns may change the stratification dynamics, which modulate phytoplankton dynamics. To better understand the risk of these future conditions, I utilized observations to map out a probabilistic relationship between observed chlorophyll levels and stratification strength. Stratification strength was quantified by computing the horizontal Richardson number (Rix) from tidal velocity and salinity data. Conditional probabilities were calculated for observing a level of chlorophyll or higher given the stratification strength (Rix quantile) in the 3 days prior (Figure to the left). This relationship does not capture the full complex dynamics of phytoplankton, but helps to capture the simplified relationship between stratification and phytoplankton. This relationship could be used to better understand the implications of shifts in stratification, due to precipitation changes under climate scenarios, on phytoplankton dynamics and help forecast eutrophication risk.
Hydrodynamic Modeling of San Francisco Bay with a Community Model
As a member of the modeling team at the San Francisco Estuary Institute (SFEI) I helped develop and validate a hydrodynamic model of the San Francisco Bay using Delft-3D Flexible Mesh as a part of the San Francisco Bay-Delta Community Model project. The model is forced with tides, freshwater and stormwater flow, river flow from the Sacramento-San Joaquin River Delta, wastewater treatment plants, and winds. The figure on the right shows the model domain and freshwater inputs. This model is used for various SFEI projects trying to understand the impact of the hydrodynamics of the Bay on biogeochemical processes, including through biogeochemical modeling. A report of the model setup and validation of the hydrodynamics can be found here and further work to couple and validate biogeochemical modeling can be found here.
Developing A Microbial-Physical Model in Waikīkī, Hawaiʻi
For my masters degree, I developed a microbial model of the pathogenic bacterium Vibrio vulnificus by using the fact that V. vulnificus growth-rates are dependent on environmental temperature and salinity. This microbial model was then coupled to a hydrodynamic model of the Ala Wai Canal in Waikīkī, Hawaiʻi. This coupled microbial-hydrodynamic model was run and used to analyze the dynamics of V. vulnificus in the Ala Wai Canal. The analysis highlighted the delicate balance between changes in in-situ growth-rates (i.e. changes in temperature and salinity) and changes in transport out of the canal, which was controlled by tides and stream input to the canal. This interplay is particularly observed during rain events, where transport is increased, but growth-rates are also increased. During rain events, V. vulnificus concentrations in the canal increased only when transport was not strong enough to advect V. vulnificus faster than their growth could compensate.
This work is written up in my masters thesis and is also in prep for publication.