Collaborative Research: Effects of wind events on circulation and salinity dynamics in a curved estuary

This project builds on observations in the Neuse Estuary (North Carolina) that have been collected previously and expands upon them through 3-d modeling with a widely used model called ROMS (short for Regional Ocean Modeling System). Unique features of the Neuse Estuary include a close to 90 degree bend and a micro-tidal environment, with wind forcing thus thought to be dominant over tides. Wind effects on estuaries are understudied because usually tides are more prevalent and cause most of the mixing. In this case, the proposed model experiments will investigate how wind forcing at different angles relative to the two connecting estuary legs as well as the duration and intervals of the wind events affect circulation and salinity distributions in a model set-up that resembles the Neuse Estuary. The results from this work will inform communities around the Neuse Estuary how to better interpret water quality time series, knowing more about the circulation features that affect residence and flushing times of the estuary. The results will also help enhance prediction and management of water quality in the Neuse Estuary. More specifically, the project will investigate how the circulation and salinity distribution in estuaries with curved sections respond to wind events using simulations on idealized and real estuary domains. Of primary interest is how interaction between estuary legs parallel and perpendicular to the wind, and lateral circulation and mixing in the connecting curved region, impact the strengths of horizontal and vertical salinity gradients and the distance that high salinity water extends upstream. Also of interest is how wind event duration and interval between wind events relative to timescales associated with wind mixing, wind-driven currents, and the baroclinic response, control the circulation and salinity distribution. To address these questions, simulations on idealized estuary domains using ROMS will be conducted. Three sets of simulations will be performed in which parameters are varied systematically: 1) constant wind at varying angles to a straight estuarine channel; 2) constant wind on an estuary with perpendicular legs connected by a curved region, varying wind speed, direction, freshwater inflow, and radius of curvature; and 3) finite length wind events, varying event duration and separation. Finally, simulations on a realistic Neuse Estuary domain will be conducted to examine how theory developed from idealized simulations can be applied to a real wind-dominated estuary. This work will advance understanding of wind effects on estuary dynamics by extending it to more general estuarine geometries that have bends and more realistic situations in which wind varies with time.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.