Anthropocene Coasts最新文献

Saltwater intrusion in estuaries has become a serious environmental problem, such as in the Pearl River estuary (PRE). In this study, we used a fully validated three-dimensional hydrodynamic model EFDC to numerically investigate the saltwater intrusion in the PRE during the dry season of 2007-2008. Based on the measured salinity, an abnormally strong saltwater intrusion occurred in the Humen Channel in February 2008. The saltwater intrusion occurred twice a month to varying extents, with each saltwater intrusion happening 1-3 days before spring tide, and the stronger saltwater intrusion always occurred at the beginning of the month. Our model results show that caused by a long-term northerly wind during the dry season, the increased steady shear term in the salt transport flux were responsible for the abnormally strong saltwater intrusion in the Humen Channel. The abnormally strong saltwater intrusion has features of long duration, far-reaching upstream distance and great hazard to freshwater resources. The wind effects were revealed to mainly influence the bottom salinity in the middle reach of the PRE, especially near the Humen outlet.

The estuary is highly dynamic and sensitive to external and internal forcing. We examine a chain reaction of hydrodynamic and morphodynamic responses to a series of land reclamation projects during the period 1997 to 2017 in the North Branch of the Changjiang Estuary through the Digital Elevation Model (DEM) comparison and the numerical simulation by the Finite Volume Community Ocean Model (FVCOM). The results show that tidal amplification was further strengthened by the artificially reduced channel volume in the middle and upper segments of the North Branch due to the implementation of several large-scale land-reclamation projects in the first stage (1997–2007), and the channel siltation in the middle and upper segments was in turn further promoted by the increased tidal flows with flood dominance. In the second stage (2007–2017), tidal amplification was relaxed by the channel narrowing project at the lower segment and the waterway improvement project through channel dredging works at the middle and upper segments. Contemporary erosion volume was almost balanced by the accretion volume in the North Branch because of the weakening dominance of flood over ebb flows. Spatiotemporal variation in channel accretion and erosion patterns in response to estuarine engineering projects was vividly mirrored by the change of simulated bed shear stress in that the areas with increased (decreased) bed shear stress underwent severe erosion (accretion). These findings highlight again the dynamic feature of tide-dominated estuaries and the importance of simulation tools to the estuarine management.

Small island developing States, such as those in the Pacific, are often prone to multiple hazards that have potential to result in disaster and / or restrict development. Hazard data can be limited in resolution or omitted in or near SIDS’ coasts, but a growing and improved range of datasets are becoming available. Through an analysis of approximately 100 policy documents on hazards and disaster risk management in Pacific island nations, we found: limited information on hazards and how they manifest to disasters at local levels, thus not fully connecting drivers and subsequent risk; at times a non-specific multi-hazard approach prompting the need to address more specific hazards; and restricted temporal and spatial scales of analysis that potentially limit continuity of actions where mitigation methods evolve. These limitations suggest that appropriate and timely high resolution hazard data is needed from the top-down to underpin the design and development of local disaster risk management plans, simultaneous to local, bottom-up knowledge and interpretation to bring the realities of such hazard data to life. Developing and ensuring openly available hazard data will enable island States to develop more robust, inclusive disaster risk management plans and mitigation policies, plus aid inter-island comparison for communal learning.

Recent developments in process-based coastal area models such as XBeach provide new opportunities to predict coastal responses to primary forcing mechanisms such as storm hydrodynamic by using 2DH grids. However, due to the lack of measured data, there are few application scenarios of the models. Therefore, more measurement and research are needed. In this paper, the Typhoon Lekima that hitting Zhejiang Province during neap tide period was selected to simulate morphodynamic responses of the Huangcheng Beach by assuming encountering with different tide types. Cross shore measurements with eight cross-shore profiles (named S1 ~ S8 from north to south) of the Huangcheng Beach pre- and post- the Typhoon Lekima respectively were presented. Then a 2DH storm surge and wave coupled model was established with Delft3D Flow/Wave. The model was well calibrated with measured water levels and wave data and provided hydrodynamic boundary conditions of different typhoon and tide types coupling situations for a refined model. The refined model was built using XBeach and simulated the morphological responses of the Huangcheng beach with well verifications. On basis of the numerical results, bed level changes at the eight profiles were analyzed, and the character of erosion and deposition under different tide conditions were illustrated. The net sand volume changes were got smaller under the spring tide condition rather than middle tide and neap tide conditions. Further study of the distribution of wave induced current at different stages of collision, inundation and ebb shown that the stronger current under spring tide condition would increase the sediment transport rate and reduce the deposition volume at profiles S3 and S6 ~ S8, and the total amount of sediment involved in transportation had increased for the whole beach, leading to the reduction of net erosion volume at profiles S1, S2, S4 and S5.

Aquatic flexible vegetation plays a very important role in ecosystem, and has been widely used in river or coastal bank revetment. Flexible vegetation contributes to wave attenuation and soil retention. In this study, a fluid-structure bidirectional coupled numerical model (FSC model) was developed based on the codes in-house software HydroFlow^@ to study the interaction between water flow and flexible vegetation. The water wave was simulated using the non-hydrostatic numerical model. Based on the nonlinear theory of elastic thin rod, a dynamic numerical model of flexible vegetation (FV model) was developed using the Finite Element Method (FEM) to simulate the large bending deformation and finite extension of a thin rod. A domain extension method was used to transfer the contact force between waves and the vegetation stem in the coupling process. The FSC model was validated using available experimental results focusing on a single stem dynamic simulation coupling with the free surface open channel flow simulation. The numerical results were in good agreements with the experiments. Relative errors of maximum deflection were less than 10%. Asymmetrical bending during a wave period were captured well compared with the measurements.