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Kong, J.; Pan, M.; Shen, C.; Hua, G., and Zhao, H., 2016. Analysis of the morphological changes and related sediment transport mechanisms of the Baisha Shoal in the Qiongzhou Strait, China. The morphological changes and evolutionary mechanism of the Baisha Shoal in the Qiongzhou Strait were investigated using various methods, including bathymetric chart comparisons, geomodeling, hydrodynamic modeling, and hydrologic statistical analysis. Water depths were extracted from digitized charts to explore the evolution of the Baisha Shoal and to quantitatively estimate the changes in the shoal area within the 5-m isobath. The grain-size trend analysis (GSTA) model was introduced to explain the features of bed sediment distribution and to analyze the sources of the sediment. Tidal flow models and wave models were adopted to simulate the tidal flows and wave fields around the Baisha Shoal and to reveal the sediment transport dynamics. Further comparisons based on a Mann-Kendall trend analysis and remote-sensing image data from different years were used to discuss the reason for the recent evolution of the Baisha Shoal. The results show that the formation of the Baisha Shoal was caused by the combined effects of reciprocating flow in the eastern and western directions and waves from the NE direction. However, in recent years, the Baisha Shoal has demonstrated an unsteady geomorphological state and is transitioning from a deposition-dominated state to an erosion-dominated state. Erosion has become most significant since 2004, as reflected in the shoal area within the 5-m isobath, which is decreasing by 0.732 km2/y. The analysis demonstrated that a reduction in sediment load and increased sand mining are the two most significant factors that are progressively altering the shoal morphology. If these issues cannot be resolved, the strong dynamic surroundings will aggravate the erosion of the Baisha Shoal. This study on the Baisha Shoal highlights the necessity of combining different approaches to better understand coastal evolutionary features, dynamic mechanisms, and evolutionary causes, as well as to guide future coastal protection engineering design. [ABSTRACT FROM AUTHOR]

Abstract: While previous studies have documented contaminants in fish, sediments, water, and wildlife, few specifics are known about the spatial distribution of contaminants in the Columbia River Estuary (CRE). Our study goal was to characterize sediment contaminant detections and concentrations in reaches of the CRE that were concurrently being sampled to assess contaminants in water, invertebrates, fish, and osprey (Pandion haliaetus) eggs. Our objectives were to develop a survey design based on sedimentation characteristics and then assess whether sediment grain size, total organic carbon (TOC), and contaminant concentrations and detections varied between areas with different sedimentation characteristics. We used a sediment transport model to predict sedimentation characteristics of three 16km river reaches in the CRE. We then compartmentalized the modeled change in bed mass after a two week simulation to define sampling strata with depositional, stable, or erosional conditions. We collected and analyzed bottom sediments to assess whether substrate composition, organic matter composition, and contaminant concentrations and detections varied among strata within and between the reaches. We observed differences in grain size fractions between strata within and between reaches. We found that the fine sediment fraction was positively correlated with TOC. Contaminant concentrations were statistically different between depositional vs. erosional strata for the industrial compounds, personal care products and polycyclic aromatic hydrocarbons class (Indus–PCP–PAH). We also observed significant differences between strata in the number of detections of Indus–PCP–PAH (depositional vs. erosional; stable vs. erosional) and for the flame retardants, polychlorinated biphenyls, and pesticides class (depositional vs. erosional, depositional vs. stable). When we estimated mean contaminant concentrations by reach, we observed higher contaminant concentrations in the furthest downstream reach with a decreasing trend in the two upstream reaches. Contaminant survey designs that account for sedimentation characteristics could increase the probability that sampling is allocated to areas likely to be contaminated. [Copyright &y& Elsevier]

A numerical model for simulation of embankment dams' gradual breaching because of overtopping, named embankments breach software (EBS), is introduced in this paper. The model solves the equations for the depth-averaged flow (modified for shallow water flow on steep slopes), the turbulence model, the sediment transport, and the bed elevation change in a coupled manner. An upwind cell center finite volume method is applied for developing the discrete form of the differential equations. A linearized scheme with second-order accuracy in space and explicit time integration on unstructured triangular meshes is utilized in this model. To simulate the flow over dry sloping surfaces of the embankment dam configuration, the developed model considers a powerful wetting and drying technique. Furthermore, the abilities of the model enhanced simulation of sudden bank failure of the breach channel because of the base erosion and transport of the failed solid material. [ABSTRACT FROM AUTHOR]

Summary: Overbank sedimentation is an important process in river floodplain ecosystems and is a component of the floodplain geomorphologic evolution. The impact of suspended sediment supply on floodplain processes is still unclear because sediment deposition can be influenced by many factors. We quantified the effect of sediment supply (suspended sediment) and transport formulas on simulated floodplain processes using a coupled two-dimensional hydrodynamic and sediment transport model (MIKE21C). Erosion and deposition depths, net sedimentation depth and total volume were quantified based on the last time step of the simulation period. The MIKE21C model was validated by comparing simulated water surface elevations to those from a one-dimensional hydrodynamic model. We compared the sediment transport model simulated suspended sediment concentrations (SSCs) to measured concentrations at a gage station. Erosion and deposition processes were simulated using five hydrograph scenarios as a function of high and low SSC and two sediment transport equations, and . A specific location could be an erosional or depositional zone at different time steps of the simulation. Thus, floodplain deposition is a discontinuous function of river discharge and varies spatially and temporally over the floodplain. Large flows with high SSC were more effective for floodplain deposition than lower discharges, which dominantly caused sediment scour. Coupled hydrodynamic and sediment transport models that account for feedback processes between topography and hydraulics should be given first preference for future floodplain restoration projects. From a restoration perspective, larger flows are required for greater floodplain deposition rates and maintenance of dynamic processes. The equation simulated higher transport rates than the . For future studies, transport equations should be selected based on the study objectives and field characteristics. The current model might be used to analyze the impact on floodplain processes from altered SSC due to Libby Dam operation. [Copyright &y& Elsevier]

Abstract: The Minas Basin, the eastern end of the Bay of Fundy, is well known for its high tide ranges and strong tidal currents, which can be exploited to extract electricity power. The properties of the tidally-induced sediment transport in the Minas Basin, where significant changes in tidal processes may occur due to a recently proposed tidal power project, have been studied with a three-dimensional hydrodynamic model, an empirical bed load sediment transport model and surface sediment concentrations derived from the remotely-sensed images. The hydrodynamic model was evaluated against independent observational data, which include tidal elevation, tidal current (in the full water column and bottom layer), residual current profile and tidal asymmetry indicators. The evaluation shows that the model is in good agreement with the observations. The sediment transport includes two components, bed load and suspended particulate load. The bed load is calculated using the modelled bottom shear stress and the observed grain size data. The estimated features of bed load transport roughly agree with the observed patterns of the erosion and deposition in the Minas Basin and Cobequid Bay. The transport of the suspended load is estimated using the modelled velocity fields and the surface sediment concentration derived from remote-sensing images. The comparisons between the modelled results and the limited observations illustrate that the observed directions of suspended sediment transport are basically reproduced by the model. The modelled net suspended sediment input into the Minas Basin through Minas Passage is 2.4×106 m3 yr−1, which is comparable to the observed value of 1.6×106 m3 yr−1. The variations of the bed load and the suspended load in space and time are also presented. The total net transport, defined as the mean value of the sum of bed and suspended load transports during the tidal cycle, shows strong spatial variability. The magnitude of the transport flux ranges from 0.1 to 0.2kgm−1 s−1 in Minas Channel and Minas Passage, 0.1kgm−1 s−1 in Cobequid Bay, to 0.01kgm−1 s−1 in the central Minas Basin and Southern Bight. In Minas Channel, the sediment transport follows the structure of the tidal residual circulation, which features a large anticlockwise gyre. The sediment in Minas Passage moves eastward and deposits into the central Minas Basin. However, the sediment from the eastern part of the Basin moves westward and deposits in the central Minas Basin as well. In the Cobequid Bay, sediment moves eastward and deposits in the upper bay. [Copyright &y& Elsevier]

Abstract: Sediment is an important environmental factor for aquatic ecosystem and oyster productivities of Apalachicola Bay located in Florida, USA. Based on the data analysis in this study, surface wind speed is highly correlated to the turbidity of water column, which results from sediment resuspension and transport in the Apalachicola Bay. In this paper, an application of a 3D sediment transport model to predict the wind-induced sediment transport in Apalachicola Bay is described. The sediment model is coupled with a 3D hydrodynamic module in the Environmental Fluid Dynamics Code (EFDC) model that provides information on estuarine circulation and salinity transport under normal temperature conditions. The hydrodynamic model was calibrated with field observations of water levels and salinity. The sediment transport model solves the transport equation with sources and sinks terms to describe sediment deposition and resuspension. The coupled hydrodynamic and sediment transport models were used to investigate wind-induced total suspended sediments (TSS) resuspension and transport in the bay. For the period June 1–July 30, 2005 two storm events with strong winds gave model results of TSS concentrations that compared well with the field observations. Model simulations reasonably reproduce the sudden increase of sediment concentrations during the storm events. Maximum sediment concentrations in the bay during the two storm events were 10 times or more than those in the pre-storm conditions. Spatial sediment transport from model simulations indicate active sediment resuspension and transport near areas of highly productive oyster beds. The model predictions of TSS and salinity can be used as inputs to an oyster dynamic model (Wang, H., Huang, W., Harwell, M., Edmiston, L., Johnson, E., Hsieh, P., Milla, K., Christensen, J., Stewart, J., Liu, X., 2008. Modeling eastern oyster population dynamics in response to changing environment in Apalachicola Bay, Florida. Journal of Ecological Modeling 211, 77–89) to support the ecological study of oyster growth and mortality in the aquatic ecosystem of Apalachicola Bay. [Copyright &y& Elsevier]

Abstract: The predictive skills of an integrated physical–biogeochemical modeling system (CH3D-IMS) for shallow estuarine and coastal ecosystems are assessed using available field data in the Indian River Lagoon estuarine system, Florida during 1998–2000. The cornerstone of the modeling system is the circulation model CH3D (Curvilinear-grid Hydrodynamics in 3D), which is coupled to models of wave (SMB), sediment transport, water quality (nutrients: N, P, and Si, three phytoplankton species, zooplankton, and dissolved oxygen), light attenuation, and seagrass. To resolve the complex geometry and bathymetry of the estuarine system, the modeling system uses a boundary-fitted non-orthogonal curvilinear grid in the horizontal direction and a terrain-following sigma grid in the vertical direction. While water level and salinity data were collected continuously (at 15-min intervals) at 10 fixed stations, most water quality data were collected at much longer time scales (bi-weekly to quarterly) during ship surveys at more than 30 stations. Sediment-water quality data were collected at 24 stations once in 1998. Model skills for hydrodynamic and water quality simulations are assessed in terms of the absolute relative errors and the relative operating characteristic (ROC) scores. Both methods indicate that the modeling system has skills in simulating water level, salinity, dissolved oxygen, chlorophyll, and dissolved nutrients, with the ROC score between 0.6 and 0.862, indicating skills for most of the variables. Skills for simulating total suspended solids (TSS) and particulate nutrients are lacking, with ROC score and: between 0.5–0.6. Simulated diffuse attenuation coefficient, which depends on TSS, chlorophyll a, and dissolved organic matter, has an ROC of 0.55. Using high frequency time-varying field data collected during two episodic events in the study period, the skills of CH3D-IMS improved significantly for both TSS and particulate nutrients. Model skills for particulate nutrients are found to be very sensitive to nutrient concentrations in the sediment column which were sampled in 1998. Sensitivity tests were conducted to determine the sensitivity of model skill to bottom boundary condition, open boundary condition, and model parameters/coefficients. Results suggest that model skills can be improved with more detailed sediment-water quality data, addition of a coastal ocean domain, and improved knowledge of model parameters/coefficients. Parameter estimation method (e.g., modified Gauss–Newton method) can be used to reduce the effort required to select optimal model coefficients for the baseline simulation. [Copyright &y& Elsevier]

Abstract: Ocean circulation influences nearly all aspects of the marine ecosystem. This study describes the water circulation patterns on time scales from hours to years across Torres Strait and adjacent gulfs and seas, including the north of the Great Barrier Reef. The tridimensional circulation model incorporated realistic atmospheric and oceanographic forcing, including winds, waves, tides, and large-scale regional circulation taken from global model outputs. Simulations covered a hindcast period of 8 years (i.e. 01/03/1997–31/12/2004), allowing the tidal, seasonal, and interannual flow characteristics to be investigated. Results indicated that the most energetic current patterns in Torres Strait were strongly dominated by the barotropic tide and its spring-neap cycle. However, longer-term flow through the strait was mainly controlled by prevailing winds. A dominant westward drift developed in summer over the southeasterly trade winds season, which then weakened and reversed in winter over the northwesterly monsoon winds season. The seasonal flow through Torres Strait was strongly connected to the circulation in the north of the Great Barrier Reef, but showed little connectivity with the coastal circulation in the Gulf of Papua. Interannual variability in Torres Strait was highest during the monsoon period, reflecting variability in wind forcing including the timing of the monsoon. The characteristics of the circulation were also discussed in relation to fine sediment transport. Turbidity level in Torres Strait is expected to peak at the end of the monsoon, while it is likely to be at a low at the end of the trade season, eventually leading to a critically low bottom light level which constitutes a severe risk of seagrass dieback. [Copyright &y& Elsevier]

The development of tidal energy in Australia is still a challenge with few studies performed on the characterisation of the resource, due to the difficulty to acquire data and uncertainties about the influence of this anthropogenic activity on the marine environment. Changes in flow could lead to alterations in sediment transport and have further influence on the marine habitat. A case study in a promising area, Banks Strait (Australia), was created using high resolution 2D and 3D models validated against in situ data to investigate changes to hydrodynamic conditions with two scenarios of tidal farms (100 and 300 turbines). Comparison between 2D and 3D is performed to find the best compromise between model accuracy and computational time for preliminary assessment. Changes to current speed and bed shear stress over a 35 day period were found to be localised around the tidal farms and did not extent more than 7 km from the farm (300 turbines) for both 2D and 3D. The results showed that for near field and far field, 2D models are sufficient to give a first approximation of the hydrodynamic influence of tidal farm deployment on its environment. [ABSTRACT FROM AUTHOR]