The importance of topographic complexity for estuarine dispersion and mixing

The project will study the re-distribution of water and its properties in estuaries, and propose simplified parameterizations to represent those processes. Focus will be placed on the re-distribution caused by features of the estuarine geometry: a) meanders in the channel, b) constrictions in cross-sectional area, and c) the shape of the connection to the coastal ocean.

The project’s goals will be pursued with field measurements and computer models that explore different forces altering water motions in an estuary, such as tides, river discharge, and morphological features. Analyses will be anchored on a theoretical framework that describes salt transport in estuaries. Findings of this study should provide key connections to processes that determine the water quality and the ecology of estuaries.

The study will train two PhD students and include activities that engage local environmental groups.

The study will seek to determine the role of topographic features on dispersion, stratification and mixing in shallow and tidally dominated estuaries. Features to be considered include meanders, constrictions, and estuary’s mouth geometry. The objectives will be pursued with field observations at the North River (MA) estuary, idealized numerical simulations, and realistic numerical simulations.

Idealized simulations will explore amplitude, shape and longitudinal scale of topographic features, varying the forcing from tides, river discharge and overall geometry. Measurements will combine drone photogrammetry, shipboard measurements, and moorings. Analysis of results, with the approach of Dronkers and van de Kreeke (1986), will provide the “parametrization of the influence of topographic complexity on estuarine dispersion and mixing.” In terms of broader impacts, the proposal would support two graduate students.

Graduate students will mentor high school students, and together with the PIs will organize lectures for the North and South Rivers Watershed Association.

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.