Sediment Dynamics In Estuaries Research Articles

Evolution of suspended sediment concentration profiles in the partially and periodically stratified Changjiang Estuary during dry season

A better understanding of how the vertical profile of suspended sediment concentration (SSC) is influenced by multiple factors is required to better understand the hydrodynamics and sediment dynamics of estuaries. Based on in situ measurements obtained during a spring-neap cycle in the estuarine turbidity maximum (ETM) of the Changjiang Estuary in January 2015, we investigate the intratidal evolution and controlling mechanisms of SSC profiles. The results show that during the dry season the ETM was characterized by periodic salinity stratification, low SSC, suspended sediments with reduced grain size, and low sediment availability for resuspension. Three types of SSC profiles were identified, i.e., profiles with two-layer, linear and quasi-uniform structures. The shapes of the SSC profiles varied with time and generally deviated from the equilibrium profile due to the highly variable hydrodynamic and sediment conditions. During ebbs of spring and intermediate tides, the SSC profiles generally evolved from a two-layer to a quasi-uniform structure via a linear structure. Analysis shows that the linear and quasi-uniform profiles occurred under the combination of vertically well-mixed salinity, negligible resuspension, low settling velocity associated with very fine grains, and shallow water depth. Such an evolution pattern can be well reproduced using a one-dimensional numerical model, with the diffusion coefficient being parabolically distributed in the water column and the four factors mentioned above. The findings reported here imply a high variability of SSC profiles in estuarine environments.

Prediction of the Turbidity Distribution Characteristics in a Semi-Enclosed Estuary Based on the Machine Learning

This study addresses the critical challenge of predicting sediment behavior in a semi-enclosed estuary, where the interplay between artificial freshwater discharge and seawater significantly impacts turbidity. Such environments are characterized by complex hydrodynamic interactions that lead to cycles of sediment settling and resuspension, influenced by tidal forces. To tackle this problem, we employed machine learning, leveraging its capability to analyze and predict complex non-linear phenomena. Our approach involved extensive transect observations conducted over two years, encompassing 11 ebb tide and 9 flood tide cycles. These observations were crucial for training the machine learning model, ensuring it captured the nuanced dynamics of sediment behavior under varying hydrodynamic conditions. The necessity of this research lies in its potential to enhance our understanding of sediment dynamics in estuaries, a vital aspect for environmental management and engineering projects. The findings demonstrate a promising alignment between the machine learning model’s predictions and the theoretically assumed sediment behavior, highlighting the model’s effectiveness in deciphering and predicting turbidity patterns in these challenging environments.

SO SÁNH MỘT SỐ ĐẶC ĐIỂM ĐỘNG LỰC VÀ TRẦM TÍCH VEN BỜ CHÂU THỔ SÔNG HỒNG VÀ DƯƠNG TỬ

The Red river delta coastal area (Vietnam) and Yangtze river delta coastal area (China) not only play an important role in developmental process of each country but also show typical characteristics of hydrodynamics and sediment dynamics of estuaries and delta coastal areas. Based on previous studied results of hydro-sediment dynamics in two delta coastal zones that were published, this paper gives a comparison of hydrodynamics and sediment dynamics of the coastal zones of Red river and Yangtze river. The results showed that there are some similar features of these two regions such as riverine hydrology, decreased fluvial sediment flux due to the dam, grain size of suspended sediment, alongshore sediment and morphological change. Besides, these two regions also have some distinct characteristics such as tidal regime and residual field currents.

Hydrodynamics and Cohesive Sediment Transport in the IJzer Estuary, Belgium: Case Study

The quantification and monitoring of sediment dynamics in estuaries has received plenty of attention in recent years due to both economic and environmental interests. Numerical models have been widely applied for predicting the morphodynamic evolution of these areas. However, the degree of uncertainty of these models is often very high due to the lack of measurements necessary for a complete model calibration and validation. In this paper, different methods have been integrated to overcome these limitations. The hydrodynamics and suspended sediment transport in the IJzer estuary were estimated by means of field data and with the use of a two-dimensional hydrodynamic model coupled to a morphodynamic model. Tidal pumping was recognized as the main driving mechanism of sediments inside the estuary. Erosion-deposition areas calculated with the numerical model were compared to the locations and volumes of dredged material. Model results and measurements were generally in good agreement. Additional support for the morphodynamic model results came from airborne hyperspectral images acquired in 2001 and 2005.