Anthropocene Coasts最新文献

Hangzhou Bay is located in China on the south side of the Changjiang Estuary and is vulnerable to extreme weather, such as typhoons in the summer and autumn. In this study, a three dimensional suspended sediment numerical model was developed that considers the dynamic factors of advection, mixing, wave, and sediment-induced stratification to simulate and analyze the effect of typhoons on water and sediment transport in Hangzhou Bay. The model validations show that the model can sufficiently reproduce the variability of the suspended sediment concentration (SSC) during typhoon conditions. The simulation results show that the high SSC in the bottom layer was mainly distributed in the leading edge of the south coast, and generally exceeded 10 kg·m⁻³. During typhoons, the water and suspended sediment transport in Hangzhou Bay presented a pattern of "north-landward and south-seaward" circulation, which promoted the convergence of suspended sediment in the center part of the bay. During Typhoon Rumbia in 2018, the water and sediment flux across the section from Nanhui Cape to Qiqu Archipelago (NQ section) increased by 18.13% and 265.75%, respectively, compared with those before the typhoon. The wave-induced bottom shear stress during typhoons has a very significant impact on the bottom SSC. The sensitivity experiments show that the wave-induced bottom shear stress greatly promotes the sediment resuspension during typhoons, which indirectly makes the sediment-induced stratification stronger than the direct effect of waves on the vertical mixing. The strong winds brought by typhoons mainly enhanced the vertical mixing, which has a stronger effect on surface SSC than waves. The suppression of vertical mixing by sediment-induced stratification during typhoons should not be ignored, especially for high turbidity coastal waters, such as Hangzhou Bay.

The sediment load in the Yangtze River downstream of the Three Gorges Dam (TGD) has substantially declined in recent decades. The decrease is more profound below the TGD, e.g., a 97% decrease at Yichang, compared with that at the delta apex, 1200 km downstream, e.g., a 75% decrease, implying along-river sediment recovery. Two large river-connected lakes, i.e., Dongting and Poyang Lakes, may play a role in the re-establishment of the river’s morphodynamic equilibrium, but a quantitative data-based understanding of this interaction is not yet available. In this work, we collected a series of field data to quantify the sediment gain and loss in the river-lake system in the middle-lower Yangtze River, and evaluate the lake’s response to the reduction in riverine sediment supply. We find that Dongting Lake and Poyang Lake shifted from net sedimentation to erosion in 2006 and 2000, and back to a sedimentation regime again after 2017 and 2018, respectively. Natural morphodynamic adaptation and sand mining play an important role in the regime changes in the Dongting Lake whereas sand mining dominates the abrupt changes in the Poyang Lake. The Dongting and Poyang Lake contributed maximum by 38% (2015) and 17% (2006) (respectively) to the sediment recovery in the erosion regime, whereas the riverbed erosion dominates the main sediment source. These changes in the relative contribution of sediment sources also indicates a response time of ~ 20 years in the lakes towards a new equilibrium state. It is noteworthy that the lakes’ buffer effects may be overestimated as the supplied sediment from the lakes is rather small compared to the significant dam trapping in the upstream basin and sediment source from downstream degradation. The results imply that river management and restoration should take into account of the river-lake interactions and feedback impact at decadal time scales.

Advection scheme is one of the core challenges in the computational fluid dynamics, which restricts the capacity of model performance in many research areas including the oceanographic modelling studies. Here in this study, we compared the newly developed algorithm HSIMT (advection scheme with High-order Spatial Interpolation at the Middle Temporal level) with the well-known scheme MPDATA (Multidimensional Positive-Definite Advective Transport Algorithm), in the 1-dimensional idealized simulation and the 3-dimensional realistic river plume simulations. The river plume simulation was done with a mainstream ocean model ROMS (Regional Ocean Modeling System). The results showed that in the 1-dimensional test both HSIMT and MPDATA can converge to the analytical results, but HSIMT converges much faster and does not produce overshooting around the sharp front. Accuracy of HSIMT is also free from the choice of timestep, unlike MPDATA. In the ROMS simulation of a surface-trapped river plume, HSIMT also showed great advantages. Results simulated by MPDATA is highly relied on the model resolution, but when the resolution is high enough the results approached to that simulated by HSIMT. The results of this study could assist the further understanding on capacity of advection schemes and further promote the developments of ocean models.

For operational use there is a need to identify a set of measures that quantify the resilience. The ‘CoastRes’ project, a component of the UK Climate Resilience Programme, examined how an operational interpretation of resilience might be applied to the coast, building on existing approaches to shoreline management in the UK. The development of the methodology and resulting Coastal Resilience Model has been reported elsewhere. For this communication, we provide a brief summary of the management framework, the Coastal Resilience Model (CRM) and the preparation of the datasets, so that the limitations of the data available at a national scale are clear. We then illustrate how the Coastal Resilience Model has been implemented as the web-based CRM Portal. The purpose of the portal is to allow users to explore (i) the implications of future change on local and national resilience; and (ii) their own view of the relative importance of the Performance Measures that make up the Coastal Resilience Index. By exploring the influence of these weightings it is hoped that Stakeholders can develop a shared understanding of what is important for coastal communities. The CRM Portal can be accessed at: https://coastalresilience.uk/crm/.