Geology topics

Robert A. Baltzer

Publications and source records attributed to Robert A. Baltzer.

7 recordsLinked to original sources

USGS1995

Robustness of de Saint Venant equations for simulating unsteady flows

Long-wave motion in open channels can be expressed mathematically by the one-dimensional de Saint Venant equations describing conservation of fluid mass and momentum. Numerical simulation models, based on either depth/velocity or water-level/discharge dependent-variable formulations of these equations, are typically used to simulate unsteady open-channel flow. However, the implications and significance of selecting either dependent-variable form - on model development, discretization and numerical solution processes, and ultimately on the range-of-application and simulation utility of resulting models - are not well known. Results obtained from a set of numerical experiments employing two models - one based on depth/velocity and the other on water-level/discharge equation formulations - reveal the sensitivity of the two equation sets to various channel properties and dynamic flow conditions. In particular, the effects of channel gradient, channel width-to-depth ratio, flow-resistance coefficient, and flow unsteadiness are analyzed and discussed.

Conference Paper↗

USGS1994

Simulating effects of highway embankments on estuarine circulation

A two‐dimensional, depth‐averaged, finite‐difference, numerical model was used to simulate tidal circulation and mass transport in the Port Royal Sound, South Carolina, estuarine system. The purpose of the study was to demonstrate the utility of the Surface‐Water, Integrated, Flow and Transport model (SWIFT2D) for evaluating changes in circulation patterns and mass transport caused by highway‐crossing embankments. A model of a subregion of Port Royal Sound including the highway crossings and having a grid size of 61 m (200 ft) was derived from a 183‐m (600‐ft) model of the entire Port Royal Sound estuarine system. The 183‐m model was used to compute boundary‐value data for the 61‐m submodel, which was then used to simulate flow conditions with and without the highway embankments in place. The numerical simulations show that, with the highway embankments in place, mass transport between the Broad River and Battery Creek is reduced and mass transport between the Beaufort River and Battery Creek is increased. The net result is that mass transport into and out of upper Battery Creek is reduced. The presence of the embankments also alters circulation patterns within Battery Creek.

Journal of Waterway, Port, Coastal and Ocean Engin↗

USGS1991

Tidal mass exchange between a submersed aquatic vegetation bed and the main channel of the Potomac River

Tidal mass exchange between a submersed aquatic vegetation (SAV) bed and the main channel of the Potomac River was investigated. Water levels were recorded at 5 minute intervals from August (when plants were present) through December (when plants were absent). Velocities were measured during individual tidal cycles both in the presence and absence of plants. Flow patterns were found to be altered significantly when plants were present. SAV impeded flow onto the shoal causing a water level phase lag between the bed and the channel, a reduction in flow speed and a change in flow direction. The phase lag was enhanced when the low frequency (subtidal) water level in the channel was below normal. The phase lag was further enhanced during spring tides. Ebb flow in the presence of plants was perpendicular to the edge of the SAV bed in the direction of the pressure gradient established by the lagging water level. Flood flow did not follow such a predictable pattern despite the strongest pressure gradients occurring during flood tides. In the absence of plants the flow speed increased by nearly an order of magnitude and the water-level phase lag disappeared.

Conference Paper↗

USGS1990

Horizontal density-gradient effects on simulation of flow and transport in the Potomac Estuary

A two-dimensional, depth-integrated, hydrodynamic/transport model of the Potomac Estuary between Indian Head and Morgantown, Md., has been extended to include treatment of baroclinic forcing due to horizontal density gradients. The finite-difference model numerically integrates equations of mass and momentum conservation in conjunction with a transport equation for heat, salt, and constituent fluxes. Lateral and longitudinal density gradients are determined from salinity distributions computed from the convection-diffusion equation and an equation of state that expresses density as a function of temperature and salinity; thus, the hydrodynamic and transport computations are directly coupled. Horizontal density variations are shown to contribute significantly to momentum fluxes determined in the hydrodynamic computation. These fluxes lead to enchanced tidal pumping, and consequently greater dispersion, as is evidenced by numerical simulations. Density gradient effects on tidal propagation and transport behavior are discussed and demonstrated.

Conference Paper↗

USGS1989

Implementation of a hydrodynamic model for the upper Potomac Estuary

A vertically integrated, two-dimensional hydrodynamic/transport model has been implemented for the upper extent of the Potomac Estuary between Indian Head and Morgantown, Md. The model computes water-surface elevations, flow velocities, and time-varying constituent concentrations by numerically integrating finite-difference forms of the equations of mass and momentum conservation in conjunction with transport equations for heat, salt, and dissolved constituents. Previous, preliminary calibration efforts have been extended and validity of the model implementation improved. Field-measured and model-computed water levels compare within ?? 2 cm and maximum computed flood and ebb flow discharges are within 3% of measured values. Indications are that further improvements can be effected.

Conference Paper↗

USGS1988

Simulation technique for modeling flow on floodplains and in coastal wetlands

The system design is premised on a proven, areal two-dimensional, finite-difference flow/transport model which is supported by an operational set of computer programs for input data management and model output interpretation. The purposes of the project are (1) to demonstrate the utility of the model for providing useful highway design information, (2) to develop guidelines and procedures for using the simulation system for evaluation, analysis, and optimal design of highway crossings of floodplain and coastal wetland areas, and (3) to identify improvements which can be effected in the simulation system to better serve the needs of highway design engineers. Two case study model implementations, being conducted to demonstrate the simulation system and modeling procedure, are presented and discussed briefly.

Conference Paper↗

USGS1987

NONHOMOGENEOUS TERMS IN THE UNSTEADY FLOW EQUATIONS: MODELING ASPECTS.

A study is in progress to identify the relative significance, effects, and benefits attributable to the use of one-dimensional, unsteady, open-channel, flow-simulation models employing a variety of nonhomogeneous terms in their equation formulations. Nonhomogeneous terms being analyzed include those representing bed slope, frictional resistance, nonprismatic channel geometry, lateral flow, and (surface) wind stress. After an initial theoretical discussion, the results of a set of numerical experiments are presented that demonstrate cause-and-effect relationships and intercomparisons achieved by neglect or improper treatment of important nonhomogeneous terms. Preliminary results of this study are discussed and presented in this paper, both in the form of qualitative considerations and quantitative tabular findings. These results are expected to yield a definitive set of guidelines and suggestions useful to model engineers.

Conference Paper↗