Collaborative Research: Towards the closure of a classic problem: The role of vertical and lateral transport in driving estuarine exchange flow and salt flux

The objective of this project is to advance understanding of how vertical mixing affects estuarine circulation and exchange of salt with the coastal ocean. This study will develop a new modeling framework that explicitly incorporates all key drivers of estuarine circulation and allows for a plethora of model runs to examine the effects of a large range of physically important parameters. A novel machine learning approach will be used to analyze the model results and to establish functional relationships between physical processes. While the project focuses on the Delaware Estuary, the outcomes from this project will be applicable to a broad range of estuary systems, helping with the understanding of processes that impact estuarine water quality and pollutant transport. The goal of this project is to advance the understanding of how density-driven, tide-driven, and advection-driven lateral and vertical transport contribute to estuarine exchange flow and salt flux. For this purpose, the plan is to perform and analyze a comprehensive set of numerical hydrodynamic simulations based on a broad external forcing parameter space of estuaries due to tides, river discharge, and channel geometry to provide insights into the role of lateral mixing and advection on the exchange flow and salt flux and to develop physics-based parameterizations within a tidally averaged but cross-sectionally resolved framework. The methodology employed incorporates a systematic salt and momentum budget analysis to reveal key physical mechanisms paired with a deep neural network approach to link the external estuarine forcing to dominant salt and momentum fluxes. Of particular interest in estuaries is the relationship between salt intrusion length L and the river charge Q. By explicitly including all key drivers of the estuarine circulation, the modeling framework will resolve previously missing physical processes to provide a general Q-L relationship for a broad range of estuarine systems, addressing shortcomings of earlier work. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.