A new nearshore numerical model approach to assess the natural coastal response during time-varying storm and hurricane conditions, including dune erosion, overwash and breaching, is validated with a series of analytical, laboratory and field test cases. Innovations include a non-stationary wave driver with directional spreading to account for wave-group generated surf and swash motions and an avalanching mechanism providing a smooth and robust solution for slumping of sand during dune erosion. The model performs well in different situations including dune erosion, overwash and breaching with specific emphasis on swash dynamics, avalanching and 2DH effects; these situations are all modelled using a standard set of parameter settings. The results show the importance of infragravity waves in extending the reach of the resolved processes to the dune front. The simple approach to account for slumping of the dune face by avalanching makes the model easily applicable in two dimensions and applying the same settings good results are obtained both for dune erosion and breaching.
UAVs (Unmanned Aerial Vehicles or “drones”) for routine survey applications at the coast have come of age, and are no longer ‘the latest thing’ more suited to the specialist researcher or amateur enthusiast. Off-the-shelf, survey-grade UAV equipment, data processing and analysis tools are now readily available to practicing coastal engineers, managers and researchers. Within the regulatory constraints that determine their use in many countries, UAVs provide an efficient and cost-effective survey tool for topographic mapping and measurement in the coastal zone. At the practical level, the specialist training required to operate off-the-shelf UAV suited to coastal surveying is now comparable in time and degree of difficulty to learning how to use the equivalent survey capabilities of professional hand-held RTK-GPS equipment. While incremental improvements to both the flight technology and data processing will no doubt continue to occur, from the coastal practitioner's perspective, no more step changes in UAV technology or ease of useability are required. In particular, survey-grade UAVs that incorporate internal RTK-GPS for high accuracy positioning and requiring a single operator only to safely deploy in the field, remove the need for separate and time-consuming on-ground surveying of ground control points (GCPs), previously required during post-deployment data processing. A coastal engineering application of UAV is used here to exemplify the practical use and potential benefits of this now mature survey technology. Over the past 2 years, rapid post-storm deployment of UAV surveying has been successfully integrated into an established coastal monitoring program spanning 4 decades at Narrabeen Beach, Australia. This has extended the scope of this program to include detailed measurements of dune and beachface erosion spanning the full 3.5 km long embayment at a spatial scale and temporal resolution that were previously unfeasible. For both the researcher and practicing coastal engineer, UAVs now provide a practical option for routine coastal surveying.
A computational procedure has been developed for simulating non-hydrostatic, free-surface, rotational flows in one and two horizontal dimensions. Its implementation in the publicly available SWASH (an acronym of Simulating WAves till SHore) is intended to be used for predicting transformation of surface waves and rapidly varied shallow water flows in coastal waters. This open source code ( ) has been developed based on the work of ). The governing equations are the nonlinear shallow water equations including non-hydrostatic pressure and provide a general basis for describing complex changes to rapidly varied flows typically found in coastal flooding resulting from e.g. dike breaks and tsunamis, and wave transformation in both surf and swash zones due to nonlinear wave–wave interactions, interaction of waves with currents, and wave breaking as well as runup at the shoreline. The present paper provides a complete description of the numerical algorithms currently used in the code. The code is benchmarked using some analytical problems. Moreover, the numerical results are validated with various cases of laboratory data with the principal aim to convey the capabilities of the SWASH code. In particular, emphasis is put on an analysis of model performance and associated physical implications. Serial and parallel performance scalings are also presented.
The unstructured-mesh SWAN spectral wave model and the ADCIRC shallow-water circulation model have been integrated into a tightly-coupled SWAN + ADCIRC model. The model components are applied to an identical, unstructured mesh; share parallel computing infrastructure; and run sequentially in time. Wind speeds, water levels, currents and radiation stress gradients are vertex-based, and therefore can be passed through memory or cache to each model component. Parallel simulations based on domain decomposition utilize identical sub-meshes, and the communication is highly localized. Inter-model communication is intra-core, while intra-model communication is inter-core but is local and efficient because it is solely on adjacent sub-mesh edges. The resulting integrated SWAN + ADCIRC system is highly scalable and allows for localized increases in resolution without the complexity or cost of nested meshes or global interpolation between heterogeneous meshes. Hurricane waves and storm surge are validated for Hurricanes Katrina and Rita, demonstrating the importance of inclusion of the wave-circulation interactions, and efficient performance is demonstrated to 3062 computational cores.
Coastal defence structures are proliferating as a result of rising sea levels and stormier seas. With the realisation that most coastal infrastructure cannot be lost or removed, research is required into ways that coastal defence structures can be built to meet engineering requirements, whilst also providing relevant ecosystem services—so-called ecological engineering. This approach requires an understanding of the types of assemblages and their functional roles that are desirable and feasible in these novel ecosystems. We review the major impacts coastal defence structures have on surrounding environments and recent experiments informing building coastal defences in a more ecologically sustainable manner. We summarise research carried out during the THESEUS project (2009–2014) which optimised the design of coastal defence structures with the aim to conserve or restore native species diversity. Native biodiversity could be manipulated on defence structures through various interventions: we created artificial rock pools, pits and crevices on breakwaters; we deployed a precast habitat enhancement unit in a coastal defence scheme; we tested the use of a mixture of stone sizes in gabion baskets; and we gardened native habitat-forming species, such as threatened canopy-forming algae on coastal defence structures. Finally, we outline guidelines and recommendations to provide multiple ecosystem services while maintaining engineering efficacy. This work demonstrated that simple enhancement methods can be cost-effective measures to manage local biodiversity. Care is required, however, in the wholesale implementation of these recommendations without full consideration of the desired effects and overall management goals.
The present work describes the validation of an SPH-based technique for wave loading on coastal structures. The so-called DualSPHysics numerical model has been used for the scope. The attention is focused on wave impact on vertical structures and storm return walls. For vertical quay walls, the numerical results have been compared with analytical and semi-empirical solutions. Later on, the wave impact on storm return walls has been modelled and the results have been compared with experimental data. Regular and random waves have been simulated. Despite the model limitations (e.g. lack of an active wave absorption system), good agreement is achieved with the formulae predictions and experimental results which proves that DualSPHysics model is becoming an alternative to some classical approaches and can be used as complementary tool for the preliminary design of coastal structures.
Wind wave reanalyses have become a valuable source of information for wave climate research and ocean and coastal applications over the last decade. Nowadays, wave reanalyses databases generated with third generation models provide useful wave climate information to complement, both in time and space, the instrumental measurements (buoys and alimetry observations). In this work, a new global wave reanalysis (GOW) from 1948 onwards is presented. GOW dataset is intended to be periodically updated and it is based on a calibration of a model hindcast with satellite altimetry data, after verification against historical data. The outliers due to tropical cyclones (not simulated due to insufficient resolution in the wind forcing) are identified and not taken into account in the process to correct the simulated wave heights with the altimeter data. The results are validated with satellite measurements in time and space. This new calibrated database represents appropriately the wave climate characteristics since 1948 and aims to be the longest and up-to-date wave dataset for global wave climate variability analysis as well as for many coastal engineering applications. ► We present a global wave dataset (1948–2008), which may be periodically updated. ► The dataset is corrected using altimetry data. ► Tropical cyclones are identified and not considered in the correction. ► The results and the corrections are compared with buoy and satellite altimetry. ► The correction is remarkable for high wave heights and coastal regions.
In the present work, the OpenFOAM® newly developed wave generation and active absorption boundary condition presented in the companion paper (Higuera et al., submitted for publication) is validated. In order to do so the simulation of some of the most interesting physical processes in coastal engineering is carried out and comparisons with relevant experimental benchmark cases presented. Water waves are found to be generated realistically and agreement between laboratory and numerical data is very high regarding wave breaking, run up and undertow currents. ► Relatively large simulations show good results and reasonable computational time. ► The new wave generation presents a realistic behaviour. ► The reproduction of the surf zone hydrodynamics is also very accurate. ► The five cases indicate that OpenFOAM is a suitable tool for coastal engineering.
Over the last decades, population densities in coastal areas have strongly increased. At the same time, many intertidal coastal ecosystems that provide valuable services in terms of coastal protection have greatly degraded. As a result, coastal defense has become increasingly dependent on man-made engineering solutions. Ongoing climate change processes such as sea-level rise and increased storminess, require a rethinking of current coastal defense practices including the development of innovative and cost-effective ways to protect coastlines. Integrating intertidal coastal ecosystems within coastal defense schemes offers a promising way forward. In this perspective, we specifically aim to (1) provide insight in the conditions under which ecosystems may be valuable for coastal protection, (2) discuss which might be the most promising intertidal ecosystems for this task and (3) identify knowledge gaps that currently hamper application and hence need attention from the scientific community. Ecosystems can contribute most to coastal protection by wave attenuation in areas with relatively small tidal amplitudes, and/or where intertidal areas are wide. The main knowledge gap hampering application of intertidal ecosystems within coastal defense schemes is lack in ability to account quantitatively for long-term ecosystem dynamics. Such knowledge is essential, as this will determine both the predictability and reliability of their coastal defense function. Solutions integrating intertidal ecosystems in coastal defense schemes offer promising opportunities in some situations, but require better mechanistic understanding of ecosystem dynamics in space and time to enable successful large-scale application.
This paper intends contributing to the development of an economically and environmentally sustainable coastal infrastructure, which combines rubble mound breakwaters with Wave Energy Converters (WEC). The energy is produced by collecting wave overtopping in a front reservoir, which is returned to the sea through turbines. Wave loadings and average wave overtopping rate at the rear side of the rubble mound breakwater and in the front reservoir are discussed on the basis of physical 2-D model tests carried out at Aalborg University (DK). The experiments have been analyzed and compared with results from model tests and wave load design formulae by Nørgaard et al. (2013) for traditional rubble mound crown walls. The existing prediction methods seem unable to predict the hydraulic performances and loadings on the front reservoir and thus new prediction formulae are proposed based on the new experiments. The formulae are provided with the aim to be of direct use to engineers in the preliminary design of a first prototype of combined breakwater and wave energy converter.
Horizontal and vertical forces acting on a two-dimensional horizontal plate due to solitary waves are investigated by conducting a series of laboratory experiments as well as CFD calculations. A total of 133 cases were tested, including four water depths, four submergence depths and three elevations above the SWL, and five wave amplitudes. Following the experiments, computational results obtained by the CFD package OpenFOAM are presented for both vertical and horizontal forces. The comparisons made with the calculations show that OpenFOAM's InterFoam solver, that we specialized to Euler's equations here, can successfully simulate the data in many cases. With the wave force data presented here, it will now be possible to compare numerical predictions of various shallow-water wave equations with the experiments. The data will also be useful to estimate the tsunami loads on submerged structures, such as breakwaters, and elevated structures, such as coastal-bridge decks. The case of the flat plate, either submerged or elevated, is considered in this paper (Part I), while the case of a plate with girders will be discussed in a companion paper under the same title (Part II).
The present work presents a fully comprehensive implementation of wave generation and active wave absorption for second-order long-crested monochromatic and random waves in a WCSPH-based (Weakly Compressible Smoothed Particle Hydrodynamics) model. The open-source code DualSPHysics is used for the scope. The numerical flume resembles a physical wave facility, so that, the moving boundaries mimic the action of a piston-type wavemaker. The second-order wave generation system, capable of generating both monochromatic (regular) and random (irregular) waves, is implemented jointly with passive and active wave absorption. A damping system is defined as solution for passive absorption and is used to prevent wave reflection from fixed boundaries in the numerical flume. The use of active wave absorption allows avoiding spurious reflection from the wavemaker. These implementations are validated with theoretical solutions and experimental results, in terms of water surface elevation, wave orbital velocities, wave forces and capacity for damping the re-reflection inside the fluid domain.
Sand nourishments are a widely applied technique to increase beach width for recreation or coastal safety. As the size of these nourishments increases, new questions arise on the adaptation of the coastal system after such large unnatural shapes have been implemented. This paper presents the initial morphological evolution after implementation of a mega-nourishment project at the Dutch coast intended to feed the surrounding beaches. In total 21.5 million m dredged material was used for two shoreface nourishments and a large sandy peninsula. The Sand Engine peninsula, a highly concentrated nourishment of 17 million m of sand in the shape of a sandy hook and protruding 1 km from shore, was measured intensively on a monthly scale in the first 18 months after completion. We examine the rapid bathymetric evolution with concurrent offshore wave forcing to investigate the feeding behaviour of the nourishment to the adjacent coast. Our observations show a large shoreline retreat of (150 m) along the outer perimeter of the peninsula, with locally up to 300 m retreat. The majority (72%) of the volumetric losses in sediment on the peninsula (1.8 million m ) were compensated by accretion on adjacent coastal sections and dunes, confirming the feeding property of the mega nourishment. Further analyses show that the morphological changes were most pronounced in the first 6 months while the planform curvature reduced and the surf zone slope flattened to pre-nourishment values. In the following 12 months the changes were more moderate. Overall, the feeding property was strongly correlated to incident wave forcing, such that months with high incoming waves resulted in more alongshore spreading. Months with small wave heights resulted in minimal change in sediment distribution alongshore and mostly cross-shore movement of sediment.
A 2DH numerical, model which is capable of computing nearshore circulation and morphodynamics, including dune erosion, breaching and overwash, is used to simulate overwash caused by Hurricane Ivan (2004) on a barrier island. The model is forced using parametric wave and surge time series based on field data and large-scale numerical model results. The model predicted beach face and dune erosion reasonably well as well as the development of washover fans. Furthermore, the model demonstrated considerable quantitative skill (upwards of 66% of variance explained, maximum bias − 0.21 m) in hindcasting the post-storm shape and elevation of the subaerial barrier island when a sheet flow sediment transport limiter was applied. The prediction skill ranged between 0.66 and 0.77 in a series of sensitivity tests in which several hydraulic forcing parameters were varied. The sensitivity studies showed that the variations in the incident wave height and wave period affected the entire simulated island morphology while variations in the surge level gradient between the ocean and back barrier bay affected the amount of deposition on the back barrier and in the back barrier bay. The model sensitivity to the sheet flow sediment transport limiter, which served as a proxy for unknown factors controlling the resistance to erosion, was significantly greater than the sensitivity to the hydraulic forcing parameters. If no limiter was applied the simulated morphological response of the barrier island was an order of magnitude greater than the measured morphological response.
The steep offshore slope and abrupt transition to a shallow lagoon are conducive to formation of energetic breaking waves in fringing reef environments. This paper describes an extension of a one-dimensional, shock-capturing Boussinesq-type model to account for these processes in two dimensions and the numerical formulation to facilitate adaptive time integration and code parallelization. The governing equations contain the conservative form of the nonlinear shallow-water equations to capture shock-related hydraulic processes. The finite volume method with a Godunov-type scheme provides a compatible, conservative numerical procedure. A two-dimensional TVD (Total Variation Diminishing) reconstruction procedure evaluates the flow variables on either side of the cell interface, while a Riemann solver supplies the flux and bathymetry source terms at the interface. A well-balanced scheme eliminates depth-interpolation errors in the domain and preserves continuity across moving boundaries over irregular topography. Time integration of the governing equations evaluates the conserved variables, which in turn provide the horizontal velocity components through systems of linear equations corresponding to series of one-dimensional problems. The application of the model to fringing reef environments is validated with laboratory experiments performed at Oregon State University as well as field data collected in Hawaii. The model describes the flux-dominated wave breaking processes through the Riemann solver without predefined empirical energy dissipation and reproduces transitions between sub and supercritical flows as well as development of dispersive and infra-gravity waves in the processes. ► Development of conservative Boussinesq-type model for breaking waves over reef bathymetry. ► Efficient and robust mathematical and numerical formulation is outlined. ► Model is validated with laboratory and field data.
The contribution of seagrasses to coastal protection is examined through the review of the most relevant existing knowledge. Seagrasses are the largest submerged aquatic vegetation ecosystem protected in Europe and it is worth examining their contribution to coastal protection. The review performed highlights incident energy flux, density, standing biomass and plant stiffness as the main physical and biological factors influencing the efficiency of the protection provided by seagrasses. The main conclusion achieved is that seagrass meadows cannot protect shorelines in every location and/or scenario. The optimal conditions for enhancing the protection supplied might be achieved in shallow waters and low wave energy environments, with high interaction surface, at the vertical and horizontal dimension, between water flow and seagrasses. Likewise, the most favorable protection might be provided by large, long living and slow growing seagrass species, with biomass being largely independent of seasonal fluctuations and with the maximum standing biomass reached under the highest hydrodynamic forcings. It is shown that seawater warming, increasing storms and sea level rise, together with the increasing population and anthropogenic threats in the coastal area may lead to rates of change too fast to allow seagrasses to adapt and keep their coastal defense service. Finally, to amend the decline of seagrasses and consequent coastal protection loss, different artificial and natural adaptation measures are provided.
Computer modeling of sediment transport patterns is generally recognized as a valuable tool for understanding and predicting morphological developments. In practice, state-of-the-art computer models are one- or two-dimensional (depth-averaged) and have a limited ability to model many of the important three-dimensional flow phenomena found in nature. This paper presents the implementation and validation of sediment transport formulations within the proven DELFT3D three-dimensional (hydrostatic, free surface) flow solver. The paper briefly discusses the operation of the DELFT3D-FLOW module, presents the key features of the formulations used to model both suspended and bedload transport of noncohesive sediment, and describes the implemented morphological updating scheme. The modeling of the three-dimensional effects of waves is also discussed. Following the details of the implementation, the results of a number of validation studies are presented. The model is shown to perform well in several theoretical, laboratory, and real-life situations.
Using shoreline water-level time series collected during 10 dynamically diverse field experiments, an empirical parameterization for extreme runup, defined by the 2% exceedence value, has been developed for use on natural beaches over a wide range of conditions. Runup, the height of discrete water-level maxima, depends on two dynamically different processes; time-averaged wave setup and total swash excursion, each of which is parameterized separately. Setup at the shoreline was best parameterized using a dimensional form of the more common Iribarren-based setup expression that includes foreshore beach slope, offshore wave height, and deep-water wavelength. Significant swash can be decomposed into the incident and infragravity frequency bands. Incident swash is also best parameterized using a dimensional form of the Iribarren-based expression. Infragravity swash is best modeled dimensionally using offshore wave height and wavelength and shows no statistically significant linear dependence on either foreshore or surf-zone slope. On infragravity-dominated dissipative beaches, the magnitudes of both setup and swash, modeling both incident and infragravity frequency components together, are dependent only on offshore wave height and wavelength. Statistics of predicted runup averaged over all sites indicate a − 17 cm bias and an rms error of 38 cm: the mean observed runup elevation for all experiments was 144 cm. On intermediate and reflective beaches with complex foreshore topography, the use of an alongshore-averaged beach slope in practical applications of the runup parameterization may result in a relative runup error equal to 51% of the fractional variability between the measured and the averaged slope.
The Overtopping BReakwater for Energy Conversion (OBREC) is an overtopping type wave energy converter, totally embedded into traditional rubble mound breakwaters. The device consists of a reinforced concrete front reservoir designed with the aim of capturing the wave overtopping in order to produce electricity. The energy is extracted through low head turbines, using the difference between the water levels in the reservoir and the sea water level. This paper investigates the nature and magnitude of wave loadings exerting on various parts of the structure. The results improve the overall knowledge on the device behavior, completing the highlights from the complementary test campaign carried out in the same wave flume in 2012 (Vicinanza et al., 2014). The formulas provided have been used to design the first OBREC prototype breakwater in operation since January 2016 at Naples Harbour (Italy).