Browsing by Author "Williams, Megan"

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    A snapshot of turbulence in the Northeastern Magellan Strait
    (2024) Lozovatsky, Iossif; Escauriaza, Cristian; Suarez, Leandro; Fernando, Harindra J. S.; Williams, Megan; Coppersmith, Ronald Scott; Mayorga, Nicolas
    First-ever measurements of the turbulent kinetic energy (TKE) dissipation rate in the northeastern Strait of Magellan (Seg-unda Angostura region) taken in March 2019 are reported here. At the time of microstructure measurements, the magnitude of the reversing tidal current ranged between 0.8 and 1.2 ms(-1). The probability distribution of the TKE dissipation rate in the water interior above the bottom boundary layer was lognormal with a high median value epsilon(MS)(med) = 1.2x10(-6) Wkg(-1). Strong vertical shear, (1-2)x10(-2) s(-1), in the weakly stratified water interior ensued a sub-critical gradient Richardson number Ri < 10(-1) - 10(-2). In the bottom boundary layer (BBL), the vertical shear and the TKE dissipation rate both decreased exponentially with the distance from the seafloor xi, leading to a turbulent regime with an eddy viscosity K-M similar to 10(-3) m(2)/s, which varied with time and location, while being independent of the vertical coordinate in the upper part of BBL (for xi > similar to 2 meters above the bottom).
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    Understanding Salinity Intrusion and Residence Times in a Small-Scale Bar-Built Estuary under Drought Scenarios: The Maipo River Estuary, Central Chile
    (2024) Soto-Rivas, Karina; Flores, Raul P.; Williams, Megan; Escauriaza, Cristian
    The Maipo River estuary is a low-inflow bar-built estuary that includes a protected wetland, which harbors a rich ecosystem. The estuary and wetland have been threatened by a persistent drought for more than a decade, which has resulted in greater salinity intrusion and increased residence times. Previous studies have described salinity and pollutants in estuaries; however, almost all have focused on deeper and/or wider estuaries with dimensions much larger than those of the small-scale Maipo River estuary. In this study, we used the numerical model FVCOM to simulate the dynamics of the Maipo River estuary under drought scenarios and explored the interactions between river discharge and tides in terms of saline intrusion and particle dispersal. The model was validated against observations collected during a field campaign near the river mouth. The simulations successfully reproduced the water surface elevation but underestimated salinity values, such that the vertical salinity structure observed in the field was not captured by the model in this shallow and morphologically complex estuary. Consequently, our model results provide qualitative insight related to salinity and baroclinic dynamics. Results of maximum saline intrusion showed an exponential decay with increasing river discharge, and the analysis of salinity intrusion time series revealed that droughts may cause permanent non-zero salinity levels in the estuary, potentially affecting ecological cycles. The incorporation of passive tracers showed that decreasing river discharge increases the residence time of particles by allowing the tracers to re-enter the estuary. Model results showed the formation of accumulation zones (hotspots) in the shallower zones of the estuary.