Machuan Peng

Incorporation of a Mass-Conserving Inundation Scheme into a Three Dimensional Storm Surge Model

Abstract The rapid rise and fall of coastal sea level due to tides and storm surge complicates the application of hydrodynamic models that use constant lateral boundaries in the region where sea level change falls within the tidal range or between the negative and positive surge extremes. In order to enable a hydrodynamic model for use in tidal or surge zones, an inundation and drying scheme must be incorporated into the hydrodynamic model. In this study, a mass-conserving inundation (wetting) and draining (drying) scheme is incorporated into a three-dimensional hydrodynamic model (the Princeton Ocean Model, often referred to as POM) for coastal ocean and estuarine systems. This coupled hydrodynamic and inundation modeling system is tested in an idealized lake/estuarine setting. The results show that: 1) incorporation of the inundation/drying scheme into the POM enabled its application in shallow water systems with time-dependent coastal boundaries; 2) the mass conservation constraint used in the inundation and drying scheme eliminates the problem of artificial flooding associated with the imbalance of water mass that is typical of a non-mass-conserving schemes; 3) using vertically-averaged flow as flooding velocity resulted in a reduced flooding area as compared to the cases that use the surface flow as the flooding velocity. This is partly due to the fact that vertically-averaged flow tends to be weaker and directed more parallel to the coastline than the surface flow.

Numerical Simulation of Salinity and Dissolved Oxygen at Perdido Bay and Adjacent Coastal Ocean

Abstract Environmental fluid dynamic code (EFDC), a numerical estuarine and coastal ocean circulation hydrodynamic model, was used to simulate the distribution of the salinity, temperature, nutrients, and dissolved oxygen (DO) in Perdido Bay and adjacent Gulf of Mexico. External forcing factors included the coupled effects of the astronomical tides, river discharge, and atmospheric winds on the spatial and temporal distributions of salinity and DO. Modeled time series were in good agreement with field observations of water level, nutrients, temperature, salinity, and DO. Perdido Bay and adjacent northern Gulf of Mexico coasts can be divided into two areas according to salinity, water level, and DO concentrations. The first area was lower Perdido Bay and the associated Gulf of Mexico coasts, acting primarily under the influence of tidal forcing, which increases the vertical stratification. The second division was upper Perdido Bay, which was influenced by both tidal forcing and freshwater inflow. Simulations also indicated winds influenced the salinity and DO distributions, with an enhanced surface pressure gradient. Tidal effects were also important for conducting salinity and water quality simulations in Perdido Bay. Low amplitude tides induced relatively weak vertical mixing and favored the establishment of stratification at the bay, especially along deeper bathymetry. Flood tides influenced the distribution of salinity and DO more than ebb tides, specifically along shallow bathymetry.

A Numerical Study of Storm Surge in the Cape Fear River Estuary and Adjacent Coast

Abstract The Cape Fear River Estuary (CFRE) region is a coastal domain that has experienced considerable threats and impacts from tropical cyclones. It is also an important nursery for juvenile fish, crabs, shrimp, and other biological species. Thus, predictions about the physical responses of the CFRE system to extreme weather events are important to the protection of life and property and to the economical well-being of local residents. In this study, the Princeton Ocean Model (POM) is used to simulate tropical cyclone storm–induced surge, inundation, and coastal circulation in the CFRE and the adjacent Long Bay using a three-level nesting approach. Hindcasts of the hydrodynamic responses of the CFRE system to historic events were performed for Hurricanes Fran, Floyd, Bertha, and Charley. Comparisons were also made for the modeling results and the observations.

Influence of physical forcing on bottom-water dissolved oxygen within Caloosahatchee River Estuary, Florida.

Environmental Fluid Dynamics Code, a numerical estuarine and coastal ocean circulation hydrodynamic and eutrophication model, was used to simulate the distributions of dissolved oxygen (DO), salinity, water temperature, and nutrients in the Caloosahatchee River Estuary. Modeled DO, salinity, and water temperature were in good agreement with field observational data from the Florida Department of Environmental Protection and South Florida Water Management District. Sensitivity analyses identified the effects of river discharge, atmospheric winds, and tidal forcing on the spatial and temporal distributions of DO. Simulation results indicated that vertical mixing due to wind forcing increased the bottom DO concentration. River discharge enhanced stratification in deep locations but propagated vertical mixing in the shallow upper estuary. Finally, tidal forcing heavily influenced bottom layer DO concentrations throughout the whole river estuary.