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Coastal zones are constantly changing in response to meteorological and hydrodynamic conditions. Water levels associated with storms, coupled with wind-driven waves, can significantly reshape coastal and deltaic geomorphology. Conversely, coastal wetlands attenuate waves, surge, and currents. These interactions have profound implications for ecosystem function and human infrastructure. This article discusses how predictive numerical models and remote-sensing techniques can advance understanding of the dominant process response (and feedbacks) of coastal and deltaic systems to a wide range of natural and anthropogenic changes. Remote-sensing techniques can provide valuable information at large spatial scales (101-103 km2) and at temporal scales ranging from days to decades that can be used to parameterize and validate numerical models, especially in regions such as the Mekong Delta where in situ data are sparse. Applications to the Mekong Delta system illuminate how modeling tools can reliably predict and describe system dynamics. Numerical modeling supported by remote-sensing information is an effective approach for evaluating and examining restoration and protection strategies, and for ameliorating the effects of climate change, natural hazards, and anthropogenic alterations to coastal ecosystems and human communities. [ABSTRACT FROM AUTHOR]

This paper demonstrates the potential use of nearshore bathymetry estimated from video data in a coastal operational model for the Dutch Coast, which provides daily forecast of waves, water levels and (rip) currents. Two video techniques to obtain beach bathymetry from video data- Beach Wizard and CBathy are validated against jet ski surveyed bathymetry. Both methods show good agreement with surveyed data, and bathymetric features of the beach are adequately produced. To assess the applicability of video-derived bathymetry for the purpose of rip current predictions, a model is built for Egmond aan Zee in The Netherlands, in which rip current predictions based on videoderived bathymetry are compared with those based on the jetski survey. Results show that predicted maximum mean offshore-directed (rip) velocities are in good agreement when using surveyed bathymetry (reference model) and videoderived bathymetry. Finally, to address the rip current forecasting skill, this local model is forced by wave boundary conditions obtained from a larger-scale wave prediction model, in addition to the bathymetry from video. Results show that useful information can still be obtained regarding the rip currents' flow where maximum offshore-directed velocities obtained from the predictive model resemble adequately rip currents pattern in the reference model. This paper will discuss each component of the model system and the validation result on hindcasting and forecasting rip currents. [ABSTRACT FROM AUTHOR]

This study aims at developing a new set of equations of mean motion in the presence of surface waves, which is practically applicable from deep water to the coastal zone, estuaries, and outflow areas. The generalized Lagrangian mean (GLM) method is employed to derive a set of quasi-Eulerian mean three-dimensional equations of motion, where effects of the waves are included through source terms. The obtained equations are expressed to the second-order of wave amplitude. Whereas the classical Eulerian-mean equations of motion are only applicable below the wave trough, the new equations are valid until the mean water surface even in the presence of finite-amplitude surface waves. A two-dimensional numerical model (2DV model) is developed to validate the new set of equations of motion. The 2DV model passes the test of steady monochromatic waves propagating over a slope without dissipation (adiabatic condition). This is a primary test for equations of mean motion with a known analytical solution. In addition to this, experimental data for the interaction between random waves and a mean current in both non-breaking and breaking waves are employed to validate the 2DV model. As shown by this successful implementation and validation, the implementation of these equations in any 3D model code is straightforward and may be expected to provide consistent results from deep water to the surf zone, under both weak and strong ambient currents. [ABSTRACT FROM AUTHOR]

A new semi-empirical storm surge prediction (SESSP) method is presented that computes tropical cyclone induced storm surge levels as a function of space and time for various storm and geometry input parameters. It distinguishes between five components that contribute to the total surge: the normal, parallel, radial, Ekman, and inverse barometer surge. The parallel surge (caused by shore-parallel gradients in the wind stress) and radial surge (resulting from wind set-up due to the inflow angle of cyclonic wind fields) have not been adequately reported upon before. The empirical relations are derived using the results of thousands of numerical model simulations in which synthetic storms are simulated at coasts with varying cross-shore topography. Non-linear fitting procedures are used to derive surge response functions (SRFs). The SESSP method reproduces peak surge levels within 10 percent of the values computed by the hydrodynamic model. This study showed variable surge response at different types of coast. On steep coasts, surge is dominated by the inverse barometer effect. Along intermediate and mild sloping coasts, the wind set-up has the greatest contribution to the peak surge. The Ekman surge (caused by the Coriolis effect) typically peaks several hours before landfall and can either have a positive or negative contribution to the peak surge. The radial surge becomes relatively more important on mild-sloping coasts. SESSP's computational efficiency allows for the execution of ensemble forecasts with thousands of synthetic storms along large stretches of coast. • Fast method for predicting storm surges during tropical cyclones. • Surge predictions as a function of alongshore position, time, storm parameters and coastal geometry. • Distinguishes between five components that constitute the total surge. [ABSTRACT FROM AUTHOR]

The estuaries and coastal zones of the Vietnamese Mekong Delta located at the end of the Mekong Basin are susceptible to a large variety of natural threats and human interventions such as upstream dam construction, climate change and sea level rise. In this study, we investigated sediment dynamics and morphodynamic changes in the Mekong estuaries and coastal zone, using a well-calibrated Delft3D-4 model for a 10-years period simulation. For the first time, the impacts of different drivers were distinguished to guide future adaptation strategies and policies. Our investigations pointed out that the influences of upstream sediment reduction and large-scale sand extraction would cause substantial modifications in the subaqueous delta region. Besides human-induced impacts, modeling results also showed that the sediment volume and spatial distribution changed through the simulated period according to monsoonal variation. The influence of each driver, however, not only varied in space but also time. In the flood season, the Mekong and Bassac Rivers provided a large amount of sediment (more than 90%) that was deposited on the delta front due to coastal processes. The sediment quantity transported along the coastline changed with the monsoon and was in a dominantly south-west direction due to the northeast monsoon, especially in November, December and January. As a natural process, in the estuarine region, erosion and deposition occurred alternately, but the south-west coast region (belonging to the Ca Mau peninsula) was dominated by erosion. This is because of the formation of sand bars in front of the Bassac estuaries, which influences the capacity of sediment transportation to the south-west. Consequently, navigation capacity will reduce significantly in the estuaries and coastline erosion in the Ca Mau peninsula leads to substantial loss of houses and assets of local people. Urgent actions such as stopping sand mining or modifying dam designs are needed to sustain the delta coastline. • A well-calibrated Delft3D model against observed and remote sensing data. • Sediment transport is strongly driven by both river discharges and monsoons. • Long-term sand bar formation diverted the direction of current sediment flows. • Human activities will lead to the severe recession of the delta. [ABSTRACT FROM AUTHOR]

Coastal zones in the vicinity of tidal inlets are commonly utilised for navigation, fishing, sand mining, waterfront development and recreation and are under very high population pressure. Any negative impacts of climate change (CC) on inlet environment are therefore very likely to result in significant socio-economic impacts. CC driven variations in mean water level (i.e. SLR), wave conditions and riverflow are likely to affect the stability of, particularly, the thousands of Small Tidal Inlets (STIs, or bar-built/barrier estuary systems) around the world. The combination of their predominant occurrence in developing countries, socio-economic relevance and low community resilience, general lack of data, and high sensitivity to seasonal forcing makes STIs potentially very vulnerable to CC impacts. This article summarises potential CC impacts on the stability of STIs and discusses means by which these CC impacts maybe quantified using existing modelling tools. As presently available process based models cannot be confidently applied with concurrent time varying water level, wave and riverflow forcing over typical CC impact assessment time scales (~ 100 years), a ‘snap-shot’ simulation (~ 1 year duration) approach using process based coastal area morphodyamic models is proposed for qualitative assessments of CC impacts on STIs. As the modelling approach will by necessity depend on the level of data availability, two different ‘snap-shot’ modelling frameworks for ‘data rich’ and ‘data poor’ environments are presented. Process based multi-scale coastal area morphodynamic models and scale aggregated (or reduced complexity) morphodynamic models are identified as modelling approaches that may be pursued in the future to obtain more reliable assessments of CC impacts on STI stability. [ABSTRACT FROM AUTHOR]

Abstract: The recently developed Morphological Acceleration Factor (MORFAC) approach for morphodynamic upscaling enables numerical model simulations of coastal evolution at decadal to millennial time scales. Primarily due to the massive increase in modeling time scales it affords, the MORFAC approach is now standard in state-of-the-art commercially available coastal morphodynamic modeling suites. However, the general validity of the MORFAC concept for coastal applications has not yet been comprehensively investigated. Furthermore, a robust and objective method (as opposed to the subjective and inelegant trial and error method) for the a priori determination of the highest MORFAC that is suitable for a given simulation (i.e. critical MORFAC) does not currently exist. This communication presents some initial results of an ongoing, long-term study that attempts to rigorously and methodically investigate the limitations and strengths of the MORFAC approach. Based on the results of a strategically designed numerical modeling exercise using the morphodynamic model Delft3D, two main outcomes are presented. First, the main dependencies and sensitivities of the MORFAC approach to fundamental forcing conditions and model parameters are elucidated. Second, a criterion based on the Courant–Friedrichs–Levy (CFL) condition for bed form propagation that maybe used as a guide to determine the critical MORFAC a priori is proposed. [Copyright &y& Elsevier]