摘要:

Research on estuarine sediment transport processes has received increasing attention in recent years, attention related to concerns about water clarity, pollutant distribution and transport, dredge spoil disposal, creation and maintenance of channels and basins for navigational purposes, and shoreline erosion. Still, the geophysical community that addresses these concerns and the underlying fundamentals of sediment transport in an estuary is widely but relatively sparsely distributed around the world. The need to draw these researchers together to discuss ideas and outlooks led to the AGU Chapman Conference on Sediment Transport Processes in Estuaries that was held at the Universidad Nacional del Sur in Bahía Bianca, Argentina, from June 13 to June 17, 1988 [Perillo and Lavelle, 1988]. The meeting sought to provide a timely impetus to further progress in sediment transport research in estuaries, promote communication among researchers using different investigatory approaches, and develop collaborations among estuarine scientists in developed and developing nations

ISSN:0148-0227    

DOI:10.1029/JC094iC10p14287

年代:1989

数据来源: WILEY

摘要:

Estuaries are large bodies of water within which interactions of physical, chemical, and biological processes with suspended and bottom sediments are complex. The goals of estuarine sediment transport research are broad and place diverse requirements on instruments and methods of observation. Processes of sediment advection often are investigated with methods that provide synoptic observations over expanded geographical regions, i.e., remote sensing and rapid shipboard reconnaissance techniques. In contrast, time series data collected within an estuary by anchored ships or by moored or semipermanently emplaced instruments are used for the study of the processes or mechanics of sediment resuspension and deposition. Understanding the mechanics of estuarine sediment transport also provides important insights into the regional or advective processes active in estuaries. This paper reviews the present status of methods used for sediment transport research in estuaries. It explores some fundamental sediment transport equations to define measurement requirements, describes various classes of instruments to meet the measurement requirements, and presents examples of individual instruments that have been combined into operational measurement systems. Some potentially important methods under development are also discussed.

ISSN:0148-0227    

DOI:10.1029/JC094iC10p14289

年代:1989

数据来源: WILEY

摘要:

Several transport processes must be considered in any evaluation of the behavior of cohesive sediments in estuaries influenced by currents and waves. Focusing on the need to understand the evolution of the suspension concentration profiles to hydrodynamic forcing, it is shown that a physical framework identifying the various mass transport components which govern suspension profile dynamics is beginning to emerge. Unfortunately, our knowledge of these components, including those associated with the generation, transport, and dewatering of fluid muds, remains incomplete. A combination of field and laboratory based research is essential for providing data bases free of significant lacunae and for resolving major interpretative ambiguities which arise from laboratory to prototype scaling and from practical limits to field measurements.

ISSN:0148-0227    

DOI:10.1029/JC094iC10p14303

年代:1989

数据来源: WILEY

摘要:

Real estuaries are fundamentally inhomogeneous. This is evident in their irregular boundaries, waters of varying density, fluid motions that arise from multiple unsteady forcings, and sediments that are mixtures of various grain sizes. In the paper, a review is given of the influence of one of these heterogeneities, namely, mixed particle size, on the transport of sand as bed load. Essential early studies and recent complete theories are discussed. Present‐day investigators commonly assume a reference transport function (RTF) which is any established formulation for the flux of bed load under steady unidirectional flow over a substrate of monosized particles. The aim of the modern work is to develop a procedure which yields tailored values of sheltering‐exposure coefficients for the different size fractions. These coefficients are correction factors which when applied to the acting bed shear permit the use of the RTF to compute fraction transports over a mixed bed. There are strong interactions among the various size fractions; for instance, minor admixture of a coarse‐end ingredient disproportionately reduces the overall mobility of a finer‐grained bed. However, coarse fractions are more mobile in a bed of mixed sizes than they are in a bed of the same uniform size. Recommendations are made for an estuarine field study utilizing a modified Helley‐Smith bed load yiel

ISSN:0148-0227    

DOI:10.1029/JC094iC10p14315

年代:1989

数据来源: WILEY

摘要:

The gaps in current understanding of the erosion, transport and deposition of sediment in estuaries are briefly reviewed. It is concluded that future work should give priority to (1) the formation, movement and entrainment of high concentration near bed layers; (2) particle interactions, including flocculation, cycling processes, and chemical and biological interactions; (3) intertidal mudflat processes, sediment exchanges in shallow water and wave induced mud transport; (4) development of improved parameterization of exchange processes for inclusion in 3D mathematical models. (5) development and use of new instrumentation for field measurements, especially of intermittent events, and over the long term. This work should be carried out within interdisciplinary studies involving physicists, sediment dynamicists, biologists, and chemists.

ISSN:0148-0227    

DOI:10.1029/JC094iC10p14327

年代:1989

数据来源: WILEY

摘要:

To describe the transport of cohesive sediments, it is necessary to specify the erosion flux at the bed. Experiments on the erosion of soft mud layers in a steady flow were performed in the Delft Tidal Flume and in an annular flume. The results were analyzed using the erosion rate function as derived by Parchure and Mehta. It is concluded that a reasonable description is possible. However, the floc erosion rate appeared to be a function of the bed shear stress. In one case the erosion rate function needed to be adjusted slightly in order to obtain agreement between measured and calculated suspension concentrations.

ISSN:0148-0227    

DOI:10.1029/JC094iC10p14341

年代:1989

数据来源: WILEY

摘要:

The geomorphologic and sediment transport characteristics of the middle reach of the Bahía Blanca estuary (Argentina) are presented. A large intertidal sedimentary structure divides the curved‐funnel‐shaped reach into the Main channel, which includes the waterway, and the Vieja channel. The right margin of the study area is bordered by a low marsh/tidal flat complex. Sedimentological and low‐penetration seismic data show that the area is formed mostly by relict sediments of Pleistocene and Pliocene ages. Present‐day deposits are very thin and are concentrated on the left platform between the navigation route and the intertidal structure. Comparison of detailed bathymetric surveys separated by 6.75 years resulted in a net erosion for all the area of 2.4×106m3. Assuming that the volume of sediments dredged from the navigation channel (510,000 m3in 6 years) was originated on the erosional sectors of the study area, approximately 250,000 m3/yr are still exported from the reach. Net accumulation (up to 2 m) is concentrated on the left margin, while erosional zones (up to 4.5 m) are located on the right margin of the Main channel and the middle portion of Vieja channel. Sediment transport calculations from 15 current meter stations distributed in the area indicate a net bed load transport of sand‐sized material directed towards the mouth of the estuary. The results suggest that dynamically, the middle reach of the Bahía Blanca estuary does not behave as a meander as was expected from its general shape. Although a preliminary estimation may indicate that the dredged sediment may proceed from the right margin, the general circulation of the estuary indicates that all reaches interchange sediments with their adjacent sectors. Sediments deposited in the middle reach are coming from the erosional processes acting in the inner reach and on the flanks of tidal f

ISSN:0148-0227    

DOI:10.1029/JC094iC10p14351

年代:1989

数据来源: WILEY

摘要:

A general algorithm for determining suspended sediment concentrations in the surface waters of estuaries has been developed for use with satellite data. The algorithm uses a three‐parameter general optical equation to relate suspended sediment concentrations to water reflectances that have been corrected for sun angle effects, atmospheric path radiance, and tidal excursion. Using data collected by the advanced very high resolution radiometer on five different dates, reflectances were determined using two different methods, one providing maximum correction for haze and the other providing minimum sensitivity to pigments. For both methods, in situ and remotely sensed samples from Delaware Bay acquired within 3.5 hours of each other agreed to within 60% at the 95% confidence level. Pixel and subpixel scale spatial variations and variability associated with in situ measurements produced about 50% of the differences. Chlorophyll concentrations of>50 μg/L produced a discrepancy in the reflectance method that provided the best haze correction. The parameter values may be adjusted to allow for variations in sediment size and pigment variations, allowing application of the calibration to estuaries having optically different suspended sedimen

ISSN:0148-0227    

DOI:10.1029/JC094iC10p14363

年代:1989

数据来源: WILEY

摘要:

Optical beam transmittance meters integrated into Aanderaa current meters were used to measure long time series of suspended matter concentration simultaneously with current velocity and salinity in the turbidity maximum of the Weser estuary (shallow coastal plain estuary of the North Sea). They cover the spectrum from 10 min to several months. The time histories of concentrations and fluxes are discussed for characteristic locations within the turbidity maximum. The analyses demonstrate that the tidal dynamics of deposition into and resuspension of particles from temporally and spatially limited material sources at the bottom is the dominant process in the turbidity maximum while the nontidal gravitational circulation acts as a long‐term source and sink. There is a remarkable repeatability of concentration patterns during similar discharge condition

ISSN:0148-0227    

DOI:10.1029/JC094iC10p14373

年代:1989

数据来源: WILEY

摘要:

In 1985 a field survey was performed in the Weser estuary (northern Germany) covering a 30‐km‐long section to study the turbidity maximum in its complete extension. Moored instruments as well as shipborne vertical profilers were used in the survey. The measured data were employed in close connection with numerical simulations using a three‐dimensional finite‐difference model. The common aim of the investigations was to arrive at a better understanding of the hydrodynamics and the transient and spatial dynamics of the turbidity maximum in the Weser estuary. The overall behavior of the turbidity maximum resembles a cyclic process, wherein deposition, resuspension, and advection of resuspended sediments are the dominant processes. The conceptual model, derived from the measurements, was confirmed by the numerical simulations. This is demonstrated by the calculated distribution of suspended sediment along the estuary as well as by the calculated deposition and resuspension rates at the estuarine bed for a tidal cycle. Detailed analyses of measured data (moorings) demonstrate a close relationship between the local near‐bottom velocity gradient, stratification, and turbulence on the one hand and the suspended sediment concentration on the other. A comparison between numerical results and measured data leads to an improved parametrization of the bottom shear stress, wherein the bottom shear stress is calculated from the near‐bottom Reynolds stress, with consideration of the stratification. With this parametrization, it is shown that the model is able to reproduce some of the essential features reflected in the measured suspended sediment co

ISSN:0148-0227    

DOI:10.1029/JC094iC10p14381

年代:1989

数据来源: WILEY