Coastal erosion is widespread under conditions of changing hydrodynamics and diminishing sediment supply, and exposure assessment to erosion hazard has received increasing attention. In this study, we explore the impact of spatial heterogeneity of land use within administrative units on exposure assessment of land use value to erosional hazard. We illustrate land use diversity using the Shannon’s diversity index (SHDI) and consider the distance effect by comparing five different buffer zones according to the distance to the coast (i.e., 0–1 km, 0–2 km, 0–3 km, 0–4 km, 0–5 km). Our results show that coastline change and socio-economic development are responsible for land use heterogeneity within the administrative units. Using a buffer zone of 1-km along the coast as the assessment unit leads to an increase in the number of townships that have high and very high exposure of land use value when compared with the assessment result that is based on the whole township area. Furthermore, the 1-km buffer zone can be divided into subunits if very high SHDI values exist within the administrative boundary. This study demonstrates that heterogeneity in land use identified at a fine spatial scale should be given full consideration in carrying out exposure assessment to hazards in a dynamic deltaic coast.

Human development of mega-deltas is influenced by the elevation of delta ground surface. The elevation, modulated by the largest tidal range, influences the inundation pattern during storm surges, or the degree of risk in the presence of a sea dyke. However, the tidal modulation may be interrupted by nature or human induced subsidence or sediment starvation. Thus, the dynamics of the elevation should be studied in order to optimize the techniques to maintain the tidally modulated elevation. Furthermore, appropriate engineering schemes may be adopted to improve the deltaic geomorphological condition.

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.

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.

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.

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.

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.

Microplastics are ubiquitous in the environment, eventually becoming part of the geological record as ‘technofossils’. However, research on the chronological characteristics of microplastics remains limited. This study reviewed dating methods, microplastic abundance, and microplastic polymer type in sedimentary cores globally. Furthermore, the ‘evolution’ of plastic types was compiled in sequence, and a microplastic chronological sequence in the sedimentary record was established. This microplastics chronological sequence was applied to 39 published cores with microplastic polymer analysis. The sediment age ranges determined by microplastic type were found to correspond to the published ages, indicating that microplastics could be useful for dating sedimentary cores on a centennial scale. Furthermore, good preservation and limited mobility of microplastics in burial records make microplastic dating an effective supplementary dating method for determining ages of Anthropocene sediments.

Delta evolution in the context of no sediment discharge has become a global concern, and an accretion-to-erosion conversion is occurring in the Yangtze estuary. This conversion could threaten Changjiang subaqueous delta development. Sediment erodibility is an important indicator of subaqueous delta vulnerability. However, the present and future erodibility of the Changjiang subaqueous delta remains unclear. In this study, 37 short cores were collected from the Changjiang subaqueous delta, and the critical shear stress of the sediment was measured using a cohesive strength meter (CSM) and compared with estimates based on an empirical Shields diagram. The sediment erodibility was analyzed by comparing the sediment critical shear stress with the bed shear stress simulated using a numerical model (i.e., FVCOM), and sediment activity was introduced to discuss the geomorphological change in the subaqueous delta. The CSM-derived critical shear stress is significantly higher than that derived from the empirical Shields formula, but it better shows the erodibility of the sediment. The annual surface sediment activity ranges from 5% to 30% based on the CSM, indicating low surface erodibility. Moreover, the critical shear stress in this region increases as water depth increases, but the bed shear stress shows the opposite trend. Therefore, the erodibility of the Changjiang subaqueous delta is lower than that of the shallow area, indicating no accretion-erosion conversion or continued vertical erosion under sediment starvation in the coming decades. These findings can provide suggestions for erosion assessment and management in large river deltas under decreasing sediment discharge.

Urban coastal wetlands are fragile ecosystems that provide important ecosystemic services. However, these ecosystems are subject to considerable external pressures from urban development, which leads to serious disturbances in their structure, functioning, and diversity as a result of the advancement of urban, agricultural, foraging, and drainage activities, as well as displacement of endemic species by invasive ones. Within the biological communities of these ecosystems, arthropods play an important trophic and ecological role as food resource, pollinating agents, biological controllers, organic matter decomposers, and nutrient cyclers. In this paper we characterize the taxonomic richness and abundance of the terrestrial arthropod fauna of the Aguada de La Chimba urban coastal wetland (Antofagasta Region, Chile) using various methods. From a total of 1,874 specimens, we identified 109 terrestrial arthropod species, where Insecta was the most represented taxon, with 85 species, 47 families, and 15 orders. The estimated species richness values were higher than the observed values for the different groups under study, and insects showed the highest species values in all estimators. Based on their origin, the communities identified included native (24%), naturalized (22%), and to a lesser extent, endemic species. We also characterize the major threats to this urban wetland and discuss the importance of building public–private partnerships with the local community for the success of biodiversity conservation programs in coastal ecosystems.

Two field campaigns in Dafeng and Jianggang were organized to compare spatial variations of hydrodynamic characteristics and sediment transport patterns on intertidal flats of different types with distinct human interferences along middle Jiangsu coast, China. The major contributors to the different patterns of sediment dynamics between the two tidal flats were offshore tidal current field and human interference. Offshore tidal force provide the basic setup of tidal current patterns on tidal flats, which is then modified by local morphology. Seawalls parallel to coast reduce tidal flat width, forcing tidal energy to dissipate within a shorter distance and thus influencing tidal flat morphology. Seawalls vertical to coast and major tidal current significantly reduce tidal current speed, which favors sediment deposition on tidal flats. Two seawalls built on both sides of the observational tidal flat profile caused much reduced current speed at Dafeng tidal flat, comparing to the offshore station. Being exposed to offshore radial tidal currents, hydrodynamics at Jianggang was much stronger than that at Dafeng. Residual currents at both areas showed net landward transport at the lower flat and net seaward transport at the upper flat, in favor to sediment accumulation at the middle flat. Sediment flux over tidal cycles showed net landward sediment transport at Dafeng, and net seaward transport at Jianggang, consistent with the convex-up accretion-dominated profile observed at Dafenge, and concave-up erosion-dominated profile observed at Jianggang. The instantaneons sediment flux changed significantly due to variations in velocity and sediment concentrations, but these terms counteracted with each other within tidal cycles, leading to the dominant role of Eulerian flux in determining net sediment flux over tidal cycles.

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/.