Distribution of Time-Averaged Suspended Sediment Concentration Due to Waves

According to the mechanism of sediment suspension under waves, namely, the main reason of sediment suspension changes from the turbulent mixing in the bottom boundary layer to the periodic motion of the water particle near the free water surface, a three-layer model of sediment concentration distribution due to waves is presented along the whole water depth based on the concept of the finite mixing length. 1he determination of the parameters in the model is discussed and an empirical formula is suggested. Comparisons between the calculated results and the measurements indicate that the resuits of the model agree well with the data from both the large and small scale flume experiments.

Distributions of surficial sediments and its response to dynamic actions in the Xiamen Bay sea area, China

Sediment distribution is important for morphodynamic evolution and shoreline changes in coastal zones and estuaries. In the study, the data of 230 surface sediment samples collected from the Xiamen Bay sea area in September 2008 are used to investigate the spatial distribution and sediment transport pathway. The grain size distribution of surficial sediments in the Xiamen Bay area is shown distinctly in this study. In addition, the Grain Size Transport Analysis model is used for conveying trend analysis of the sediment in this area, particularly for determining the sediment movement trend. The results indicate that eight sediment types are present for samples, with clayey silt comprising the highest percentage in the study area at 65.22%. Moreover, in the different subareas, the characteristics of grain size parameters are obviously different owing to different sediment sources and hydrodynamic conditions. Furthermore, runoff, tides, and waves are the main forces dominating sediment dynamics on the seabed and tidal flats, and the sediment movement trend is closely related to hydrodynamic conditions.

Numerical Simulation on Hydraulic Performances of Quarter Circular Breakwater

Quarter circular breakwater （QCB） is a new-type breakwater developed from senti-circular breakwater （SCB）. The superstructure of QCB is composed of a quarter circular front wall, a horizontal base slab and a vertical rear wall. The width of QCB＇ s base slab is about half that of SCB, which makes QCB suitable to be used on relatively finn soil foundation. The numerical wave flume based on the Reynolds averaged Navier-Stokes equations for impressible viscosity fluid is adopted in this paper to simulate the hydraulic performances of QCB. Since the geometry of both breakwaters is similar and SCB has been studied in depth, the hydraulic performances of QCB are given in comparison with those of SCB.

THE EFFECT OF RECLAMATION IN AREAS BETWEEN ISLANDS IN A COMPLEX TIDAL ESTUARY ON THE HYDRODYNAMIC SEDIMENT ENVIRONMENT

The Oujiang Estuary is a very complex tidal estuary with many islands, which is located in Zhejiang Province, China. Reclamation of areas between islands will create a great amount of land. In this article, the feasibility of reclamation of areas between Lingkun Island and Niyu is studied from the angle of its impacts on the hydrodynamic sediment environment. First, the natural hydrodynamic and sediment conditions and the seabed evolution are analyzed according to in-situ data. Second, numerical models of tidal current and sediment movement under the combined action of wave and current are set up with irregular triangular grid to carry out numerical simulations. The following conclusions are drawn from the study. （1） The areas between Linkun Island and Niyu are not a tidal passage. Wenzhou Shoal has been aggraded gradually, a condition favorable for reclamation. （2） The reclamation is feasible as far as its effect on surrounding hydrodynamic sediment environment is concerned. （3） The reclamation has great favorable socio-economic impacts.

Experimental study of breach process of landslide dams by overtopping and its initiation mechanisms

The present paper studies the physics of the breach erosion process, particularly, the breach initiation process in over- topped landslide dams. Due to great complexities involved, only homogeneous landslide dams are considered. The flume experime- nts of dam overtopping are conducted to study the breach growth process. And in order to reveal the effects of the seepage during the breach development, the permeability characteristics of the dam materials are also taken into consideration. With the experimental observation, the details of the breach growth are examined, and the whole breach process could be distinguished into five stages, i.e., Stage I, the seepage erosion, Stage II, the formation of the initial breach, Stage III, the erosion toward the head, Stage IV, the expan- sion and incision of the breach, and Stage V, the re-equilibration of the river channel through the breach. It is shown that once trigge- red the entire breach process goes continually without stop, which highlights the significant impact of the early stages on the later deformation of the dam. Evidence shows that the initial breach of the dam is most likely to take place in the downstream slope of the dam, near the upper edge of the seepage face. The experimental results show a ＂headcut＂ mechanism of the breach initiation.

NUMERICAL STUDY ON THE THREE-DIMENSIONAL CHARA-CTERISTICS OF THE TIDAL CURRENT AROUND HARBOR ENTRANCE

A three-dimensional （3-D） numerical model is established to investigate the tidal current motion characteristics around the harbor entrance. Computational approaches consist of the finite difference method, time-splitting technique, C-grid, and a high-order turbulence closure model. The Ocean General Circulation Model （OGCM） inundation scheme is incorporated in the model. An engineering application, Lianyungang Harbor, China, is used as a real-life case. The model is validated by showing that the simulated results agree well with the field data. In the approach channel, the tidal current shows a deflection effect especially in the bottom layer. As for Lianyungang Harbor, a jet flow forms at the tip of the northern breakwater, which drives a circulation flow at the inner side of the harbor entrance. In the vertical, the flow is significantly stratified at the entrance section within the channel, where the flow direction varies between layers and the speed distribution is quite uniform. These 3-D features become less evident to the offshore. Additionally, the sensitivity analysis shows that the flow deflection is related to the channel depth. Simulation results also imply that the siltation rate at the entrance section of the approach channel tends to be more uniform by the 3-D flow motion feature, and could be more significant with the increase of the channel depth.

A type of dynamic mechanism of river hydraulic geometry

Large-scale structure of river flow is the main driving force for bed erosion-deposition and bank deformation.The structure shapes and retains a corresponding hydraulic geometry form.Therefore,the most stable flow structure is the probable natural river plane formation.Natural coordinate transformation and perturbation methods were adapted to deform the governing equations of sine-generated river basic flow and disturbance flow independently.The stability and retention of perturbation waves were analyzed in our model to explain why meandering rivers followed a certain type of flow path.Computation results showed that all types of perturbation waves in meandering rivers were most stable when the meandering wave number was about 0.39–0.41.We believe that this type of stable flow structure shaped a certain meandering river.The statistical average length-width ratios of Yalin,Habib and da Silva and Leopold and Wolman somewhat confirmed our most stable river meandering wave number.In some ways,meandering rivers always tend to diminish internal turbulence intensity.

Seabed deposition and erosion change and influence factors in the Yangshan Deepwater Port over the years

The seabed scouring and silting are very important to the construction of port and waterway engineering.Seabed deposition and erosion change is complicated due to the influence of sediment supply,human activities and other factors.The Yangshan Deepwater Port is the new deep water harbor,which is an important part of the Shanghai International Shipping Service Center.Its construction has received much attention.At present,the water depth from the 1st to the 3rd harbor district is currently suitable under regular dredging and tidal current action.The fourth harbor district will be built in the world’s largest fully-automated deep water wharf.In the study,bathymetry change of the entire sea area of the Yangshan Deepwater Port and the 4th harbor district(i.e.,PhaseⅣproject)waters were analyzed quantitatively using multiyear bathymetric,hydrological and sediment data.The results show that from 1998 to 2010,seabed changes are characterized by large volumes of erosion and sedimentation,which the southern part was deposited and the northern part was eroded in the inner harbor waters,but the seabed of the Kezhushan inlet was eroded.Seabed changes of PhaseⅣproject waters generally show a scour tendency in recent few years with the annual scour rate about 0.7 m.Among the many factors,the existence of Kezhushan inlet and its influence of the western water flow play an important positive role in water depth changes under the ebb tide action.