摘要 :
The scientific focus of this project is to better understand and predict reference concentration above the seabed. Models of sediment transport depend on parameterization of the near-bed concentration of suspended sediment (or ref...
展开
The scientific focus of this project is to better understand and predict reference concentration above the seabed. Models of sediment transport depend on parameterization of the near-bed concentration of suspended sediment (or reference concentration ) in terms of dynamical and sedimentological measures. We will evaluate the accuracy and suitability of existing expressions for reference concentration, and based on our field investigations, provide improved definition of this important parameter. This work will be accomplished as part of an ONR-sponsored Mine Burial Research Program. It will be coordinated with other investigators who are working together to understand the oceanographic and seafloor processes that affect bottom mines. The principal goal of this research is to develop specification of the near- bed reference concentration that is tested and supported by high-quality field measurements in shallow-water marine environments.
收起
摘要 :
The Coastal Engineering Technical Note (CETN) herein provides information and procedures for analyzing instantaneous measurements of currents and suspended sand to estimate longshore sand transport during storms. The information a...
展开
The Coastal Engineering Technical Note (CETN) herein provides information and procedures for analyzing instantaneous measurements of currents and suspended sand to estimate longshore sand transport during storms. The information and procedures described in this CETN will assist others in developing similar and improved measurement techniques. Longshore sand transport is a primary factor in many coastal engineering studies and influences coastal erosion, impoundment at structures, channel infilling, and morphological behavior of ebb shoals, spits, and capes. A significant portion of longshore sediment transport occurs during coastal storms. To quantify and characterize longshore transport induced by the combined influences of waves and currents, the Sediment Transport Processes (STORM) Work Unit has measured currents and instantaneous concentration of suspended sand across the surf zone during storms.
收起
摘要 :
The goals of this work are to obtain better understanding of sediment mobilization, transport, and deposition across the wave bottom- boundary layers (WBBL) in the surf and swash zones and to improve predictive capabilities for be...
展开
The goals of this work are to obtain better understanding of sediment mobilization, transport, and deposition across the wave bottom- boundary layers (WBBL) in the surf and swash zones and to improve predictive capabilities for bed load and suspended sediment transport as a function of environmental parameters, including wave heights, breaker characteristics, sediment properties, beach slope, bottom roughness, local water depth, wave frequency spectra, and the presence of low frequency circulations such as along shore currents and undertow.
收起
摘要 :
The scientific focus of this project is to improve our understanding of near-bed suspended sediment concentration (i.e., 'reference concentration or Cref') in the coastal environment. Models of sediment transport require parameter...
展开
The scientific focus of this project is to improve our understanding of near-bed suspended sediment concentration (i.e., 'reference concentration or Cref') in the coastal environment. Models of sediment transport require parameterization of Cref in terms of hydrodynamical and sedimentological measures. We will evaluate the accuracy and suitability of existing expressions for Cref, and based on our field results, provide an improved expression for this important parameter.
收起
摘要 :
Scientific objectives of this project are: (1) Develop a nested set of models tostudy the interactions of sedimentation processes on the shelf, including the effects of river supply, plume transport and initial deposition of sedim...
展开
Scientific objectives of this project are: (1) Develop a nested set of models tostudy the interactions of sedimentation processes on the shelf, including the effects of river supply, plume transport and initial deposition of sediments; (2) Analyze the effects on the resulting sediment sequences of a range in river discharge characteristics from a storm flood dominated system to a more continuous discharge system; (3) Analyze the effects on the resulting sediment sequences of the temporal coherence of river discharge events and ocean storms, and (4) Establish the importance and determine the effects of climate change on sediment supply and distribution on a continental margin.
收起
摘要 :
The long-term objective is to determine the hydrodynamic processes controlling sediment transport and the associated morphologic response on tidal flats. The objectives of this project are to analyze the data from the Skagit Flats...
展开
The long-term objective is to determine the hydrodynamic processes controlling sediment transport and the associated morphologic response on tidal flats. The objectives of this project are to analyze the data from the Skagit Flats deployment of June, 2009 and complete several papers that document our findings. The themes of analysis are: to ascertain the influence of freshwater inflow on the barotropic and baroclinic dynamics of Skagit Flats, and then to ascertain their consequences for sediment transport and trapping; to determine the processes causing tidal and high-frequency (up to surface gravity- wave frequency) variations in bottom stress, turbulence and suspended sediment concentrations, including the possible formation and destruction of fluid mud layers and episodes of rapid sediment accumulation and erosion; to quantify the mechanisms causing tidal asymmetry in bottom stress and sediment transport rate on Skagit Flats and determine the implications of these asymmetries for the sediment balance and morphological structure of the flats.
收起
摘要 :
Magnitude-frequency analysis of gauging station records (1950-1982) on the Lower Mississippi shows that there is a clearly defined dominant flow of about 30,000 cu m/s. This lies within an effective range of channel-forming flows ...
展开
Magnitude-frequency analysis of gauging station records (1950-1982) on the Lower Mississippi shows that there is a clearly defined dominant flow of about 30,000 cu m/s. This lies within an effective range of channel-forming flows between 17,000 and 40,000 cu m/s, which are responsible for transporting a disproportionately large percentage of the sediment load. The 33-year period of record is sufficiently long that the occurrence of an extreme high-flow event does not significantly change these results. Hydrographic survey data, long- profile records, and stage-discharge relationships from calibrated one- dimensional flow models indicate that the dominant discharge corresponds to 'bar-full' discharge on the lower Mississippi and that the effective range of flows occurs between the stage that just tops mid-channel bars and that which significantly overtops the bank. Historical trends in bar growth suggest that bar-top elevations have generally risen to the dominant flow elevation over the last 30 years.
收起
摘要 :
The energy sources that result in sediment particle associations, reorientation, and disaggregation are presented in terms of processes and mechanisms. Based on electron microscopy observations and theoretical considerations, the ...
展开
The energy sources that result in sediment particle associations, reorientation, and disaggregation are presented in terms of processes and mechanisms. Based on electron microscopy observations and theoretical considerations, the observed and modeled microfabric forms and signatures are associated with processes and mechanisms operating in various micro- and macroenvironments. The interplay of geological, chemical, and biological processes and mechanisms during transport, deposition, and burial of particulate material largely controls and ultimately determines the physical nature, properties, and observable micro- and macrocharacteristics of soft sediments and their indurated equivalents. Discrete events such as suspended sediment transport, flocculation, and slumping may be indentified and/or observed in the field or laboratory. More often, the sedimentary material is studied to understand and infer processes and mechanisms responsible for its fundamental properties, origin, significance, and stratigraphic position in the geological record. The particle-to-particle development and ultimate nature of a sedimentary deposit and its variability in time and space depend on multiple process that include some important mechanisms that occur extremely fast and others that progress over eons. As defined in this study, mechanisms are the specific energy sources that drive microfabric development. Two or more related mechanisms constitute that broader classification termed process. In the continuum of microfabric development, the fundamental processes in which the individual mechanisms operate are described as (1) physiochemical, (2) bioorganic, and (3) burial diagenesis.
收起
