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Coastal mangroves, thriving at the interface between land and sea, provide robust flood risk reduction. Projected increases in the frequency and magnitude of climate impact drivers such as sea level rise and wind and wave climatology reinforce the need to optimize the design and functionality of coastal protection works to increase resilience. Doing so effectively requires a sound understanding of the local coastal system. However, data availability particularly at muddy coasts remains a pronounced problem. As such, this paper captures a unique dataset for the Guyana coastline and focuses on relations between vegetation (mangrove) density, wave attenuation rates and sediment characteristics. These processes were studied along a cross-shore transect with mangroves fringing the coastline of Guyana. The data are publicly available at the 4TU Centre for Research Data (4TU.ResearchData) via https://doi.org/10.4121/c.5715269 (Best et al., 2022) where the collection Advancing Resilience Measures for Vegetated Coastline (ARM4VEG), Guyana, comprises of six key datasets. Suspended sediment concentrations typically exceeded 1 g L−1 with a maximum of 60 g L−1, implying that we measured merely fluid-mud conditions across a 1 m depth. Time series of wind waves and fluid-mud density variations, recorded simultaneously with tide elevation and suspended sediment data, indicate that wave–fluid-mud interactions in the nearshore may be largely responsible for the accumulation of fine, muddy sediment along the coast. Sediment properties reveal a consolidated underlying bed layer. Vegetation coverage densities in the Avicennia-dominated forest were determined across the vertical with maximum values over the first 20 cm from the bed due to the roots and pneumatophores. Generalized total wave attenuation rates in the forest and along the mudflat were between 0.002–0.0032 m−1 and 0.0003–0.0004 m−1 respectively. Both the mangroves and the mudflats have a high wave-damping capacity. The wave attenuation in the mangroves is presumably dominated by energy losses due to vegetation drag, since wave attenuation due to bottom friction and viscous dissipation on the bare mudflats is significantly lower than wave dissipation inside the mangrove vegetation. Data collected corroborate the coastal defence function of mangroves by quantifying their contribution to wave attenuation and sediment trapping. The explicit linking of these properties to vegetation structure facilitates modelling studies investigating the mechanisms determining the coastal defence capacities of mangroves.

Building high dykes is a common measure of coping with floods and plays an important role in agricultural management in the Vietnamese Mekong Delta. However, the construction of high dykes causes considerable changes in hydrodynamics of the Mekong River. This paper aims to assess the impact of the high-dyke system on water level fluctuations and tidal propagation in the Mekong River branches. We developed a coupled 1-D to 2-D unstructured grid using Delft3D Flexible Mesh software. The model domain covered the Mekong Delta extending to the East (South China Sea) and West (Gulf of Thailand) seas, while the scenarios included the presence of high dykes in the Long Xuyen Quadrangle (LXQ), the Plain of Reeds (PoR) and the Trans-Bassac regions. The model was calibrated for the year 2000 high-flow season. Results show that the inclusion of high dykes changes the percentages of seaward outflow through the different Mekong branches and slightly redistributes flow over the low-flow and high-flow seasons. The LXQ and PoR high dykes result in an increase in the daily mean water levels and a decrease in the tidal amplitudes in their adjacent river branches. Moreover, the different high-dyke systems not only have an influence on the hydrodynamics in their own branch, but also influence other branches due to the Vam Nao connecting channel. These conclusions also hold for the extreme flood scenarios of 1981 and 1991 that had larger peak flows but smaller flood volumes. Peak flood water levels in the Mekong Delta in 1981 and 1991 are comparable to the 2000 flood as peak floods decrease and elongate due to upstream flooding in Cambodia. Future studies will focus on sediment pathways and distribution as well as climate change impact assessment.

In estuaries suspended sediment concentration (SSC) is one of the most important contributors to turbidity, which influences habitat conditions and ecological functions of the system. Sediment dynamics differs depending on sediment supply and hydrodynamic forcing conditions that vary over space and over time. A robust sediment transport model is a first step in developing a chain of models enabling simulations of contaminants, phytoplankton and habitat conditions. This works aims to determine turbidity levels in the complex-geometry delta of the San Francisco estuary using a process-based approach (Delft3D Flexible Mesh software). Our approach includes a detailed calibration against measured SSC levels, a sensitivity analysis on model parameters and the determination of a yearly sediment budget as well as an assessment of model results in terms of turbidity levels for a single year, water year (WY) 2011. Model results show that our process-based approach is a valuable tool in assessing sediment dynamics and their related ecological parameters over a range of spatial and temporal scales. The model may act as the base model for a chain of ecological models assessing the impact of climate change and management scenarios. Here we present a modeling approach that, with limited data, produces reliable predictions and can be useful for estuaries without a large amount of processes data.

Previous work on morphodynamic evolution in the Yangtze Estuary (YE) is based on measured historical bathymetries. To evaluate the sensitivity of sand–mud interaction in the estuarine morpho-dynamics, a process-based morphodynamic model, Delft3D, is used to examine the morphodynamic behaviour from 1958 to 1997. Different scenarios concerning sand and mud and their combination are designed systematically. The scenarios considering multiple fractions, and especially with four fractions, improve the hindcasting evolution, suggesting the importance of including both sand and mud fractions and a sediment gradient setting of medium grain.