Examination Of Estuarine Sediment Dynamics

This dissertation investigated the dynamics of estuarine shorelines in the Albemarle-Pamlico Estuarine System (APES). Shoreline change is influenced by human activities (e.g., shoreline modification), and natural processes (e.g., waves, storms, and sea-level rise) on variable temporal and spatial scales in the coastal zone. This research examined the spatio-temporal dynamics of shoreline change, the drivers of that change, and the role of shoreline erosion in the sediment dynamics of the larger estuarine system. Historical rates of change were found to be comparable to previous studies at -0.5 ± 0.07 m yr−1. Decadal and sub-annual rates of change were highly variable over the study, both spatially and temporally. However, linear regression models indicate that the large changes in shoreline position observed in high-frequency (bi-monthly) surveys are captured within the long-term (historical) average rate of shoreline change. Simulations from a coupled hydrodynamic and wave model indicate that waves and storms (hurricanes) are important drivers of shoreline change. Wave energy along different shorelines was found to be dependent on shorezone characteristics such as shoreline orientation, wind direction and fetch, and nearshore bathymetry. The role of shoreline erosion in the sediment dynamics of the larger estuarine system was also investigated for a region of the APES, the Tar-Pamlico estuary. Shoreline erosion and shoreline modification were examined within the estuary in order to explore the significance of erosion as a source of fine sediment to the estuary. Sediment storage was also evaluated for the Tar-Pamlico estuary using rates of sediment accumulation determined from the radionuclide tracers of 210Pb and 137Cs. A fine sediment budget was constructed for the Tar-Pamlico estuary. The budget indicates that eroding wetland shorelines represent a significant (43% of total fine sediment input) source of material to the estuary. Also, the majority of fine sediment is retained within zones of accumulation within the estuary, with only about 7% potentially exported to the adjacent Pamlico Sound. Overall, this research highlights the dynamic process of estuarine shoreline change, and the role of that change in the functioning of the larger estuarine system. Coastal managers need to incorporate an understanding and accommodation of these processes into future management plans for North Carolina's estuarine shorelines.

The background for the Workshop on Cohesive Sediment Dynamics - . !!!!!. Special Reference to Physical Processes in Estuaries is briefly outlined in Chapter I. Here I wish to acknowledge those whose support I consider to be pivotal to this under taking. My deepest appreciation goes to Cynthia Vey, whose organizational skills and dedicated effort made the completion of this volume possible. Thanks are also due to Gail Terry for workshop organization, Jean Branson for word processing and Lillean Pieter for helping with drawings. Finally, I must express my sincere appreciation to Arthur Ezra 9f the National Science Foundation for providing support (through Grant No. CEE-8401185) for the workshop, and to Hsiang Wang for depart mental encouragement. With deepest regret, I must note the untimely death of Ranjan Ariathurai, 39, on June 5, 1985, before this volume could be published. He was a guiding force to many within the small group of researchers in cohesive sediment dynamics, and his professional brilliance and inspirational personal qualities constituted the true spirit . behind the workshop. I trust this volume will serve, albeit in a small way, as a fitting memory to this spirit, and to the remarkable professional contributions Ranjan made during his short career. Professor Ray B. Krone Professor Emmanuel Partheniades Department of Civil Engineering Department of Engineering Sciences University of California University of Florida Davis, California Gainesville, Florida TABLE OF CONTENTS CHAPTER PAGE I. INTRODUCTION Ashish J. Mehta •••••••••••••••••••••••••••••••••••••••••••••••••••• 1 II.

Covers the movement of mud, sand, and gravel on the continental shelf in the nearshore zone, on beaches, and in estuaries. A multi-disciplinary treatment integrating marine geology, oceanography, and engineering. Presents concepts in engineering sediment distribution patterns that improve the prediction of erosion and deposition rates. Reviews background material as well as the results of recent research.

This volume is the product of the International Conference on Cohesive Sediment Transport (INTERCOH 2003) held at the Virginia Institute of Marine Science, U.S.A., during October 1-4, 2003. The topics included in this monograph range from basic research on cohesive sediment dynamics to practical applications. Also included with this book is a database that contains all experimental results as well as a comparison of numerical simulation results supported by the COSINUS project. * Provides fundamental knowledge of the dynamics of cohesive sediments * Presents practical applications of new finds on sedimentary processes * Includes valuable ready-for-use data

Many estuaries are located in urbanized, highly engineered environments. Cohesive sediment plays an important role due to its link with estuarine health and ecology. An important ecological parameter is the suspended sediment concentration (SSC) translated into turbidity levels and sediment budget. This study contributes to investigate and forecast turbidity levels and sediment budget variability at San Francisco Bay-Delta system at a variety of spatial and temporal scales applying a flexible mesh process-based model (Delft3D FM). It is possible to have a robust sediment model, which reproduces 90% of the yearly data derived sediment budget, with simple model settings, like applying one mud fraction and a simple bottom sediment distribution. This finding opens the horizon for modeling less monitored estuaries. Comparing two case studies, i.e. the Sacramento-San Joaquin Delta and Alviso Slough, a classification for estuaries regarding the main sediment dynamic forcing is proposed: event-driven estuary (Delta) and tide-driven estuary (Alviso Slough). In the event-driven estuaries, the rivers are the main sediment source and the tides have minor impact in the net sediment transport. In the tide-driven estuaries, the main sediment source is the bottom sediment and the tide asymmetry defines the net sediment transport. This research also makes advances in connecting different scientific fields and developing a managerial tool to support decision making. It provides the basis to a chain of models, which goes from the hydrodynamics, to suspended sediment, to phytoplankton, to fish, clams and marshes.

Cohesive sediment, or mud, is encountered in most water bodies throughout the world. Often mud is a valuable resource, synonymous with fertile land, enriching the natural environment and used as an important building material. Yet mud also hinders navigation and consequently, dredging operations have been carried out since ancient times to safeguard navigation. Unfortunately, many mud deposits are now contaminated, endangering the eco-system and increasing the costs of dredging operations. The transport and fate of mud in the environment are still poorly understood and the need for basic research remains. This text contains the proceedings of the INTERCOH-2000 conference on progress in cohesive sediment research. It was the sixth in a series of conferences initially started by Professor Ashish Mehta in 1984 as a "Workshop on Cohesive Sediment Dynamics with Special Reference to the Processes in Estuaries". During these conferences the character of the first workshop has always been maintained, that is, small scale and dedicated to the physical and engineering aspects of cohesive sediments, without parallel sessions, but with ample time for discussions during and after the presentations, and followed by a book of proceedings containing thoroughly reviewed papers. INTERCOH-2000 was integrated with the final workshop of the COSINUS project. This project was carried out as a part of the European MAST-3 programme, and almost all European cohesive sediment workers were involved. INTERCOH-2000 focused on the behaviour and modelling of concentrated benthic suspensions, i.e. high-concentrated near-bed suspensions of cohesive sediment. Special attention was paid to: sediment - turbulence interaction; flocculation and settling velocity; high-concentrated mud suspensions; processes in the bed - consolidation; processes on the bed - erosion; field observations on mud dynamics; instrumentation; and numerical modelling.

The purpose of this work is to investigate via data analysis and numerical modeling the SPM (suspended particulate matter) dynamics of a heavily contaminated partially urban estuary, the Lower Passaic River estuary (LPR), NJ. Accordingly, I investigate the quantity and mechanics of variation of fine and coarse SPM in the LPR via data analysis. Data analysis focuses on the parameters that affect SPM dynamics at six moored stations occupied during the Fall and Spring seasons, from near the estuary mouth to tidal freshwater. A 3D hydrodynamic model (Delft3D-FM) is used to analyze the effects of estuary topography on the dynamic distribution of bed shear stress and to interpret the observations. Moored data from a station seaward of the LPR are used for model calibration. This work will address three primary issues. The first is to determine bulk settling velocity (Wsb) values and the factors that affect Wsb along the estuarine salinity gradient. The second is to determine the quantity of fine and coarse SPM throughout the water column distributed in Rouse-like and Modified-Rouse profiles, and to (a): investigate the dynamical importance of advection in influencing SPM profile structure for fine and coarse SPM, and (b) determine how the SPM concentration varies with particle size, river flow, and tidal range. Finally, Delft3D-FM was set up on a grid of a generic, convergent estuary similar to the LPR. This grid was used to investigate how oceanographic factors (e.g., channel curvature and tidal range to depth ratio), natural and man-made roughness elements (e.g., grains, meanders, and bridge pilings), and external forcing by river inflow influence the distribution of bed shear stress in a stratified estuary similar to the LPR.

The ability to predict the movement of cohesive sediment within coastal, estuarine or inland waters has a significant economic and ecological importance in the development of new engineering works and the maintenance of existing installations. Dynamics of estuarine muds clearly describes the most up-to-date developments in this field and contains information about improved procedures and how they can be applied to a variety of engineering projects. Drawing on a wide range of new data and new concepts in mud research, this concise volume presents the main processes of cohesive sediment behaviour, namely, erosion, transport, deposition and consolidation. It includes subsections on Knowledge, intended to show the practising engineer which parameters are important in each of the processes and Procedure, which will enable broad estimates of erosion, transport, deposition and consolidation to be made based on knowledge of the site conditions. Dynamics of estuarine muds is essential reading for the practising engineer who is involved in coastal, estuarine or inland water construction. A companion volume to Dynamics of marine sands, this excellent book provides invaluable information about this complex topic in a readily accessible manner.

Abstract : The knowledge and understanding of sediment transport is essential for the development of effective management strategies for nutrient and sediment loading in estuarine systems. Estuarine suspended sediment (in high concentrations), has the ability to adversely impact upon surrounding ecosystems, such as the Great Barrier Reef, Australia. Due to a recent decline in water and sediment quality, it has recently been mandated that a number of tropical, coastal estuarine systems in Queensland, such as the Fitzroy River estuary, have their sediment loading reduced. In order to meet these requirements, a greater understanding of the sediment transport dynamics and driving processes (such as flocculation and settling velocity) needs to be achieved, and the accuracy of estimation improved. This research project was motivated by the need to improve the general accuracy of field measurements for estuarine suspended sediment transport and dynamics. Field-based measurements (especially settling velocity) are necessary for the parameterisation of sediment transport models. The difficulty in obtaining accurate, in situ data is well documented and is generally limited to methods that isolate a water sample from its natural environment, removing all influences of estuarine turbulence. Furthermore, the water samples are often extracted from points (Eulerian) where the history of the suspended particles is generally unknown. These sampling methods typically contain intrinsic errors as suspended sediment transport is essentially Lagrangian (i.e., flows with the net motion of flow-field) in nature. An investigation into different drogue systems conducted in parallel with a study into the tidal states of the Fitzroy River estuary led to the development of a novel Lagrangian drogue device, the LAD. Additionally, the water-tracking ability of the LAD was tested and found to accurately follow a parcel of estuarine water over a slack water period. Therefore the LAD was deployed in the Fitzroy River to assist in the further understanding of complex sediment transport processes such as flocculation and settling velocity in a natural estuarine flow field. The final device (the LAD - Lagrangian Acoustic Drogue) was developed, utilizing the principals of acoustic backscatter intensity-derived SSC measurements. The investigation of a series LAD deployments (during slack water) in the Fitzroy River estuary, revealed the dominant suspended sediment processes and also gave an insight into the prevailing flow-patterns. Results showed the presence of a settling lag mechanism between low and high tide, which can initiate a net sediment flow upstream with each flood tide. The bulk settling velocity showed comparable results at both low and high water. The LAD derived bulk settling velocity as a function of concentration (SSC), yielding a strong positive correlation (r2 = 0.73). Also the importance of flocculation in the bulk settling and clear up of the water column during periods of still water (high and low tide) was demonstrated as all in situ settling velocities (0.33 - 1.75 mm s-1) exceeded single grain approximations (0.47 mm s-1). This research demonstrates the potential for Lagrangian drogue studies as an effective measuring platform for the accurate quantification of estuarine suspended sediment dynamics. The application of the LAD in the Fitzroy River has lead to a significant improvement in the understanding of the system's real sediment transport processes. This research has provided an effective and accurate technique for measuring real settling velocities for input into numerical models or for the validation of existing model outputs. Furthermore, this technique shows great potential for application in other estuarine systems.