A process-based, idealized study of salt and sediment dynamics in well-mixed estuaries
Estuaries are among the most important ecosystems as they are habitats for many species including phytoplankton/zooplankton, fishes, birds and mammals. Estuaries are also economically important because they accommodate a large number of harbors and industries. Furthermore, estuaries are important to human populations, as estuaries are usually surrounded by densely populated cities, providing huge amounts of fresh water for human drinking and irrigation.
Estuarine conditions can change signiﬁcantly by natural causes and human activities. To sustain the economic development and the great diversity of living species, we need to predict estuarine responses to natural variations or anthropogenic impacts to reduce potential negative effects. To reach that, a good understanding of the dominant physical mechanisms of estuarine dynamics is needed.
In this research, I focus on two important factors, which control the estuarine water quality and strongly affect the long-term estuarine transport of nutrients, pollutants and sediments. Namely, the salinity and turbidity of the water. Turbidity is the cloudiness or haziness of water, and is strongly related to suspended sediment concentration SSC. To systematically study the dynamically coupled water motion, salt intrusion and sediment transport, a three-dimensional idealized, process-based model is developed for well-mixed estuaries, combining a perturbation method with a finite element method. By using this semi-analytical approach, the contributions of different longitudinal/lateral processes such as (secondary) gravitational circulation, and processes varying at the tidal timescale (e.g., tidal advection), are evaluated explicitly.
The model results provide good insight into the dominant physics of the salt and sediment transport in well-mixed estuaries, and can be used to better understand and predict the occurrences of salt intrusion and estuarine turbidity maxima (regions with the highest turbidity levels).