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Abstract: Comparing with the studies on large estuarine systems, such as the Chesapeake Bay and the San Francisco Bay, the processes of stratification and transport in small and shallow estuaries are relatively less studied. The St. Lucie Estuary (SLE) is a riverine estuary located on the east coast of south Florida. It is small and shallow, with mean depth of 2.4m. To study the estuarine processes in the SLE, a hydrodynamic model was developed based on the Environmental Fluid Dynamics Code (EFDC) [Hamrick, J.M., 1992. A three-dimensional environmental fluid dynamics computer code: theoretical and computational aspects. The College of William and Mary, Virginia Institute of Marine Science, Special Report 317, 63 pp.]. The model was calibrated and verified using observational data obtained in 1999 and 2000, respectively. The model variables used for model data-comparisons are water elevation, velocity, temperature, and salinity. The model is then applied to study the hydrodynamic processes in the SLE. It is found that freshwater inflow plays a major role in the stratification and net flushing of the SLE. Stratification generally increases with freshwater inflow. But when the inflow is persistently large for a relatively long period, the estuary can suddenly change from very stratified to well mixed within a few tidal cycles and the stratification collapses. This finding suggests that large and persistent freshwater inflows do not always increase estuarine stratification. Instead, it may cause the stratification to collapse within a short period of time. In addition to gauged tributaries, ungauged lateral inflows can also be important to small and shallow estuaries like the SLE. Although small individually, the ungauged streams and surface runoffs can be a significant portion of the total inflow and affect salinity distribution significantly. Flushing time affects a wide range of hydrodynamic and water quality processes in the estuary. The model results indicate that commonly used formulas, such as the tidal prism formula and the Knudsen formula, may significantly underestimate the flushing time. [Copyright &y& Elsevier]

Offshore drilling for oil and gas has been conducted since the early 1900s. Oil and gas under the seabed continue to be an important part of the energy resources of the United States. The need to balance the value of these resources against the potential for environmental damage is an important concern. This article explains why and how the Minerals Management Service (MMS) of the US Department of the Interior uses research in physical sciences to help fulfill its environmental goals, and it provides background information on the role of physical sciences in decision-making for Outer Continental Shelf (OCS) oil, gas, and other minerals development. Established in the 1970s, the MMS’ Environmental Studies Program is a highly focused marine research program designed to provide the environmental information necessary for OCS energy and nonenergy minerals planning and development activities. The physical sciences research supported by MMS includes physical oceanography, oil-spill risk analyses, atmospheric sciences, and sand and gravel studies. Instead of giving a comprehensive review on physical sciences research in MMS, this article presents sample MMS studies and illustrates how these studies are utilized to support decision-making in environmental management. [ABSTRACT FROM AUTHOR]

A time-dependent three-dimensional hydrodynamic model of Lake Okeechobee was validated and used to understand the physical processes associated with vertical mixing in the lake. The lake has relatively uniform water depths in the open water areas, and the localized bathymetry irregularities are small, which enables the Lake Okeechobee Hydrodynamic Model with a grid resolution of 912 x 923 m to represent the hydrodynamic processes reasonably well. This work presents the results of a 7-week simulation that uses measured bathymetry, relative humidity, total solar radiation, wind velocity, inflow, and outflow. Surface elevation, velocity field, and temperature are computed and compared with observed data. Conservation equations for mass, momentum, and temperature transport are solved to provide values for water depth, current velocities, and water temperatures. The statistical comparisons between the simulated and observed results indicate that the model represents the circulation and temperature distribution of the lake very well. The model was run for a 7-week verification period, during which water levels receded because of dry conditions. The model also indicates that well mixed circulation patterns for the top and bottom layers result from high wind events. Diurnal thermal stratification impacts may result in a two-layer flow and affect the horizontal dispersion in Lake Okeechobee. The model results indicate that wind is the major driving force of horizontal and vertical water movement; however, during calm periods, geostrophic currents would be significant. DOI: 10.1061/(ASCE)0733-950X(2002)128:3(114) [ABSTRACT FROM AUTHOR]

The US Minerals Management Service performs oil-spill risk analyses using, in part, a statistical model of hypothetical oil-spill trajectories. The “Oil-spill Risk Analysis” (OSRA) model is driven by analyzed sea surface winds and model-generated ocean surface currents. The OSRA model calculates thousands of oil-spill trajectories over extended areas of US waters and tabulates the frequencies with which the simulated oil spills contact the geographic boundaries of designated natural resources within a specified number of days after the simulated spill events are initiated.The limits of computer mass storage and speed impose constraints on the number of oil-spill trajectory simulations and the time step of the numerical integration generating the spill trajectories. Also, the model winds and ocean currents have limited spatial and temporal resolution, producing sensible limits on the spatial density of the simulated oil spills and on the numerical integration time step. This investigation attempted to determine the smallest practical spatial interval between simulated oil spill release sites and the shortest integration time step beyond which the frequencies of oil-spill contact essentially do not change. In addition, we investigated the number of hypothetical oil spills initiated per day from a single location and two methods of numerical integration to generate the spill trajectories—simple forward time stepping and the fourth order Runge–Kutta method.Applying the OSRA model to the Gulf of Mexico using 9 years of winds and ocean current data, we found a smallest distance between simulated spills of 6 nautical miles and a shortest integration time step of 1 h using the fourth order Runge–Kutta integration method. A 20-min time step would be needed with simple forward time stepping. Initiating hypothetical spills eight times per day produced essentially the same contact probabilities as initiating spills once per day. These intervals were practical for OSRA model runs over the US portion of the Gulf of Mexico using commonly available desktop personal computers. [Copyright &y& Elsevier]