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R. T. Cheng

Publications and source records attributed to R. T. Cheng.

At least 37 records · Page 2Linked to original sources
USGS1993

Tidal and residual currents measured by an acoustic doppler current profiler at the west end of Carquinez Strait, San Francisco Bay, California, March to November 1988

Water-velocity profiles were collected at the west end of Carquinez Strait, San Francisco Bay, California, from March to November 1988, using an acoustic Doppler current profiler (ADCP). These data are a series of 10-minute-averaged water velocities collected at 1-meter vertical intervals (bins) in the 16.8-meter water column, beginning 2.1 meters above the estuary bed. To examine the vertical structure of the horizontal water velocities, the data are separated into individual time-series by bin and then used for time-series plots, harmonic analysis, and for input to digital filters. Three-dimensional graphic renditions of the filtered data are also used in the analysis. Harmonic analysis of the time-series data from each bin indicates that the dominant (12.42 hour or M2) partial tidal currents reverse direction near the bottom, on average, 20 minutes sooner than M2 partial tidal currents near the surface. Residual (nontidal) currents derived from the filtered data indicate that currents near the bottom are pre- dominantly up-estuary during the neap tides and down-estuary during the more energetic spring tides.

Water-Resources Investigations Report↗
USGS1992

Dispersion in tidally averaged transport equation

A general governing inter-tidal transport equation for conservative solutes has been derived without invoking the weakly nonlinear approximation. The governing inter-tidal transport equation is a convection-dispersion equation in which the convective velocity is a mean Lagrangian residual current, and the inter-tidal dispersion coefficient is defined by a dispersion patch. When the weakly nonlinear condition is violated, the physical significance of the Stokes' drift, as used in tidal dynamics, becomes questionable. For nonlinear problems, analytical solutions for the mean Lagrangian residual current and for the inter-tidal dispersion coefficient do not exist, they must be determined numerically. A rectangular tidal inlet with a constriction is used in the first example. The solutions of the residual currents and the computed properties of the inter-tidal dispersion coefficient are used to illuminate the mechanisms of the inter-tidal transport processes. Then, the present formulation is tested in a geometrically complex tidal estuary – San Francisco Bay, California. The computed inter-tidal dispersion coefficients are in the range between 5×10 4 and 5×10 6 cm 2 /sec., which are consistent with the values reported in the literature

Book chapter↗
USGS1992

A semi-implicit finite difference model for three-dimensional tidal circulation,

A semi-implicit finite difference formulation for the numerical solution of three-dimensional tidal circulation is presented. The governing equations are the three-dimensional Reynolds equations in which the pressure is assumed to be hydrostatic. A minimal degree of implicitness has been introduced in the finite difference formula so that in the absence of horizontal viscosity the resulting algorithm is unconditionally stable at a minimal computational cost. When only one vertical layer is specified this method reduces, as a particular case, to a semi-implicit scheme for the solutions of the corresponding two-dimensional shallow water equations. The resulting two- and three-dimensional algorithm is fast, accurate and mass conservative. This formulation includes the simulation of flooding and drying of tidal flats, and is fully vectorizable for an efficient implementation on modern vector computers.

Conference Paper↗
USGS1990

Residual currents and long-term transport

Estuaries, bays, and contiguous coastal seas of the world are the most valuable and yet most vulnerable marine ecosystems. For centuries, society has placed enormous value on coastal areas for living, working, and recreation. In nearly all regions of the world, the largest population is distributed along the coastlines. The marine ecosystems provide food, shelter, and spawning grounds for fisheries, and refuge and sanctuary for wildlife. Dramatic increases in the population living in coastal regions have changed the pattern of land use and the movement of sediments. Obviously, these changes have not come without a price. Accompanying the coastal population increase is competition for the use of estuarine and coastal resources: the diversion of fresh water for irrigation and the discharge of waste water into these systems. The changing patterns of water use have resulted in deterioration of water quality, and in irreversible impacts on many marine ecosystems. All of these alterations directly affect the economic development and the quality of life in adjacent regions.

Book↗
USGS1989

A general method for generating bathymetric data for hydrodynamic computer models

To generate water depth data from randomly distributed bathymetric data for numerical hydrodymamic models, raw input data from field surveys, water depth data digitized from nautical charts, or a combination of the two are sorted to given an ordered data set on which a search algorithm is used to isolate data for interpolation. Water depths at locations required by hydrodynamic models are interpolated from the bathymetric data base using linear or cubic shape functions used in the finite-element method. The bathymetric database organization and preprocessing, the search algorithm used in finding the bounding points for interpolation, the mathematics of the interpolation formulae, and the features of the automatic generation of water depths at hydrodynamic model grid points are included in the analysis. This report includes documentation of two computer programs which are used to: (1) organize the input bathymetric data; and (2) to interpolate depths for hydrodynamic models. An example of computer program operation is drawn from a realistic application to the San Francisco Bay estuarine system. (Author 's abstract)

Open-File Report↗
USGS1989

A vertically averaged spectral model for tidal circulation in estuaries

A frequency dependent computer model based on the two-dimensional vertically averaged shallow-water equations is described for general purpose application in tidally dominated embayments. This model simulates the response of both tides and tidal currents to user-specified geometries and boundary conditions. The mathematical formulation and practical application of the model are discussed in detail. Salient features of the model include the ability to specify: (1) stage at the open boundaries as well as within the model grid, (2) velocities on open boundaries (river inflows and so forth), (3) spatially variable wind stress, and (4) spatially variable bottom friction. Using harmonically analyzed field data as boundary conditions, this model can be used to make real time predictions of tides and tidal currents. (USGS)

Water-Resources Investigations Report↗
USGS1989

Recent progress on hydrodynamic modeling of San Francisco Bay, California

A hydrodynamic modeling study of the effects of freshwater inflow on circulation and mixing in San Francisco Bay has been underway since 1985. This paper describes the multidimensional hydrodynamic models being used on the study and review recent progress with their applications. Particular modeling considerations for San Francisco Bay and future modeling plans are discussed.

Conference Paper↗
USGS1985

Harmonic analysis of tides and tidal currents in South San Francisco Bay, California

Water level observations from tide stations and current observations from current-meter moorings in South San Francisco Bay (South Bay), California have been harmonically analysed. At each tide station, 13 harmonic constituents have been computed by a least-squares regression without inference. Tides in South Bay are typically mixed; there is a phase lag of approximately 1 h and an amplification of 1·5 from north to south for a mean semi-diurnal tide. Because most of the current-meter records are between 14 and 29 days, only the five most important harmonics have been solved for east-west and north-south velocity components. The eccentricity of tidal-current ellipse is generally very small, which indicates that the tidal current in South Bay is strongly bidirectional. The analyses further show that the principal direction and the magnitude of tidal current are well correlated with the basin bathymetry. Patterns of Eulerian residual circulation deduced from the current-meter data show an anticlockwise gyre to the west and a clockwise gyre to the east of the main channel in the summer months due to the prevailing westerly wind. Opposite trends have been observed during winter when the wind was variable.

California↗
USGS1983

Observations from remote weather stations in San Francisco Bay, California

Weather data collected at three remote weather stations in the San Francisco Bay estuarine system between November 1979 and September 1981 are compiled in this report. Measurements include average and maximum wind speed, wind direction, air temperature, atmospheric pressure, and irradiance. Data are presented in time-series plots with each graph covering one calendar month. Daily averages of all measurements are tabulated.

California↗