Shoreline Wave Research Articles

Rising sea levels and the increase of shoreline wave energy at American Samoa

American Samoa is experiencing rapid relative sea level rise due to increases in global sea level and significant post-2009 earthquake land subsidence, endangering homes and critical infrastructure. Wave and water-level observations collected over a fringing reef at Faga‘itua Bay, American Samoa, in 2017 reveal depth-limited shoreline sea-swell wave heights over the range of conditions sampled. Using field data to calibrate a one-dimensional, phase-resolving nonhydrostatic wave model (SWASH), we examine the influence of water level on wave heights over the reef for a range of current and future sea levels. Assuming a fixed reef bathymetry, model results predict rising sea levels will escalate nearshore extreme water levels that are dominated by an increase in nearshore sea-swell wave heights. Model results provide insight into how and at what reef depths rising sea levels reduce reef capacity to dissipate wave energy, compounding shoreline threats. This study aims to bring increased attention to the immediate threats to American Samoa’s way of life, and to demonstrate the utility of SWASH for extrapolating wave transformation to future sea level.

On ST6 Source Terms Model Assessment and Alternative

We present the study of the ST6 balanced set of wind energy input and wave energy dissipation due to wave breaking source terms, offered as the option in operational wave forecasting models and based on theoretical self-similarity analysis and numerical simulation of the wave energy radiative transfer equation. The study relies on the classical limited fetch wind wave excitation problem with constant wind blowing orthogonally to the shoreline toward the open ocean. It is found that the ST6 model exhibits asymptotic quasi self-similar behavior for fetches exceeding ≃25 km, as well as non-universal wave energy growth for shorter fetches, depending on the shoreline wave energy levels. We construct the alternative model PGZ-2 from a self-similar consideration, which reproduces field experimental data almost in the whole fetch span and reduces wave energy evolution dependence on the shoreline energy level. We assert that the PGZ-2 model is more accurate than the ST6 model. Moreover, it has a wider area of applicability.

Dynamics of the Wave‐Driven Circulation in the Lee of Nearshore Reefs

AbstractNearshore rocky reefs with scales of order 10–100 m are common along the world's coastline and often shape wave‐driven hydrodynamics and shoreline morphology in their lee. The interaction of waves with these reefs generally results in either two or four‐cell mean circulation systems (2CC and 4CC, respectively), with diverging flows behind the reefs and at the shoreline in the 2CC case and flows that diverge in the lee and converge at the shoreline in the 4CC case. By applying a phase‐resolving wave‐flow model to conduct a detailed analysis of mean momentum balances for waves interacting with nearshore reefs, we develop an understanding of the drivers of 2CC and 4CC flow dynamics and how they vary for different reef geometries and wave and water level conditions. The 2CC or 4CC patterns were primarily driven by alongshore pressure gradients toward the exposed (nonreef fronted) or reef‐fronted beach. These alongshore pressure gradients were dependent on the cross‐shore setup dynamics governed by the balance between pressure (i.e., related to the setup) and radiation stress gradients, and mean bottom stresses exerted on the water column. If shoreline wave setup in the lee of the reef was less than the exposed beach, a 4CC pattern developed with convergent flow at the shoreline in the lee of the reef; otherwise, a 2CC emerged with divergent flow at the shoreline. Across the parameter space investigated, reef roughness, distance to the shoreline, and beach slope were the three parameters most likely to change the flow patterns between 2CC and 4CC.

Tidal Modulated Shoreface Facies in Eocene Agbada Formation, Niger Delta Basin, Nigeria

Tidal influence shoreface are shoreface deposit generated by wave induced tidal action. The extent of the tidal impact from lower to upper shorefaces depend mostly on the tidal range thereby controlling the impact of different shoreline wave action on sediment distribution across shorefaces. The Tidally influenced shoreface sediment display wave generated structure, however the structure are strongly associated with tidal generated structures and trace fossil consistent with tidal depositional setting. Shoreface successions in Titun well display a wide range of variability, largely restricted to the lower and middle shoreface intervals. This variation was controlled by relative wave dominance and intermittent pulsating nature of associated tidal bed deposition. The successions were subdivided into three end members, although a complete gradation between them exists. High energy shoreface consist almost entirely of erosively based amalgamated tide and wave beds with minimal bioturbation. Intermediate energy shoreface consist of stacked laminated to burrowed intervals, recording repeated erosive storm bed emplacement, followed by opportunistic colonization, and commonly overprinted by resident fairweather burrowing. Weakly storm-affected low energy shorefaces typically show intense bioturbation with minimal preservation of high energy beds. Based on the association of the facies, facies vertical build-up patterns, sedimentary structures and trace fossil content, the T1 sands in Titun well are interpreted as a prograding tidally influence shoreface deposit. This interpretation is supported by presence of tide generated structures and marine trace fossil, due to the prevalence of several tidal imprint as suggested by several mud drapes and flasers, couplets of sands and shale’s in heterolithic sequences, and bidirectional current structures (herringbone cross stratification), a tidally influence shoreface geological model is suggested for deposit.

The influence of submerged coastal structures on nearshore flows and wave runup

Engineered and natural submerged coastal structures (e.g., submerged breakwaters and reefs) modify incident wave fields and thus can alter hydrodynamic processes adjacent to coastlines. Although submerged structures are generally assumed to promote beach protection by dissipating waves offshore and creating sheltered conditions in their lee, their interaction with waves can result in mean wave-driven circulation patterns that may either promote shoreline accretion or erosion. Here, we analyse the mean flow patterns and shoreline water levels (wave runup) in the lee of idealised impermeable submerged structures with a phase-resolved nonhydrostatic numerical model. Waves propagating over submerged structures can drive either a 2-cell mean (wave-averaged) circulation, which is characterised by diverging flows behind the structure and at the shoreline, or 4-cell circulation, with converging flows at the shoreline and diverging flows in the immediate lee of the structure. The numerical results show that the mode of circulation can be predicted with a set of relationships depending on the incoming wave heights, the structure crest level, and distance to the shoreline (or structure depth). Qualitative agreement between the mean flow and proxies for the sediment transport using an energetics approach suggest that the mean flow can be a robust proxy for inferring sediment transport patterns. For the cases considered, the submerged structures had a minimal influence on shoreline wave setup and wave runup despite the wave energy dissipation by the structures due to alongshore wave energy fluxes in the lee. Consequently, these results suggest that the coastal protection provided by the range of impermeable submerged structures we modelled is primarily due to their capacity to promote beach accretion. • A phase-resolved model simulates hydrodynamic interactions with submerged structures. • Waves can drive 2-cell or 4-cell mean circulation and sediment transport patterns. • Bottom shear stresses presented an overall similar pattern to the mean currents. • We develop a predictor for the flow patterns based on wave and structure parameters. • The submerged structures had limited influence on shoreline setup and wave runup.

Utilising Natural Attributes of Tropical Islands for Beach Protection

This study reveals the coastal protection benefits of small artificial reefs on tropical islands. A monitored case study involving field and computer modelling investigations, as well as construction of a 95 m long reef and 12,000 m3 of local sand nourishment in a tropical lagoon on the north-east coast of Mauritius, is presented. Monitoring showed that a large salient widened the beach by 50 m in one year. The salient has continued to grow slowly and has remained stable for four years, including during a cyclone. Only a simple and inexpensive artificial reef was needed in the shallow lagoon to rebalance the shoreline wave conditions, because most wave energy was lost by breaking further offshore on the natural reef. With rising sea levels, inshore reefs with nourishment can overcome increases in wave height, wave set-up and wave run-up at the shoreline, which are jointly responsible for erosion and the flooding of homes by erosion and over-topping. To find suitable nourishment sources, regional computer modelling identified the following dominant circulation patterns: currents both coming into the lagoon over the reef crest (driven by breaking wave energy) and exiting via relict river channels or zones of lower waves. Sand for nourishment may be extracted from the exit locations with reduced environmental impact, because net currents are driving sand out of the lagoon system into deeper water. These relict sands have the same grain size as the natural beach and are readily accessible.

SHORELINE SENSITIVITY INDEX TO OIL SPILLS IN NUSA PENIDA MARINE PROTECTED AREA (MPA), BALI

The Shoreline Sensitivity Index(SSI) is one crucial aspect to know in protecting the coast from all threats, including oil spills. This study aims to determine the shoreline's sensitivity for oil spills based on several oceanographic parameters: shoreline type, tidal range, slope, and wave high in Nusa Penida, Map Protection Area (MPA). The weight overlay method was employed to apply the geographic information system (GIS). Each parameter component was scored as five categories before the weighted overlay. The shoreline sensitivity level of Nusa Penida island is divided into five categories: very low sensitive, low sensitive, medium sensitive, high sensitive, and very high sensitive. As the results, the SSI was categorized during the east monsoons (from June to August) and during the west monsoons (from December to February) is at a low sensitivity level to very high sensitivity. SSI during east monsoons there is about 60.05% (627.33 ha) in the medium, 9.39% (98.11 ha) in the high, and 2.39% (24.99 ha) in the very high sensitive. The SSI during the west season is about 78.16% (816.95 ha) with the medium, 19.43% (203.11 ha) with the high, and 2.39% (24.99 ha) with the very high sensitive. The difference in wave height during east and west monsoons greatly affects the sensitivity level of the Nusa Penida coastal area. However, sensitivity level in Jungutbatu and Lembongan Villages are not affected by the east or west monsoons.Keywords: Shoreline Sensitivity; GIS; Nusa Penida; Oil Spill.

Methodological Reconstruction of Historical Seismic Events From Anecdotal Accounts of Destructive Tsunamis: A Case Study for the Great 1852 Banda Arc Mega‐Thrust Earthquake and Tsunami

AbstractWe demonstrate the efficacy of a Bayesian statistical inversion framework for reconstructing the likely characteristics of large pre‐instrumentation earthquakes from historical records of tsunami observations. Our framework is designed and implemented for the estimation of the location and magnitude of seismic events from anecdotal accounts of tsunamis including shoreline wave arrival times, heights, and inundation lengths over a variety of spatially separated observation locations. The primary advantage of this approach is that all of the assumptions made in the inversion process are incorporated explicitly into the mathematical framework. As an initial test case we use our framework to reconstruct the great 1852 earthquake and tsunami of eastern Indonesia. Relying on the assumption that these observations were produced by a subducting thrust event, the posterior distribution indicates that the observables were the result of a massive mega‐thrust event with magnitude near 8.8 Mw and a likely rupture zone in the north‐eastern Banda arc. The distribution of predicted epicentral locations overlaps with the largest major seismic gap in the region as indicated by instrumentally recorded seismic events. These results provide a geologic and seismic context for hazard risk assessment in coastal communities experiencing growing population and urbanization in Indonesia. In addition, the methodology demonstrated here highlights the potential for applying a Bayesian approach to enhance understanding of the seismic history of other subduction zones around the world.

In-situ Observations of Infragravity Response during Extreme Storms on Sand and Gravel Beaches

Billson, O.J.; Russell, P.; Davidson, M.; Poate, T.; Amoudry, L.O., and Williams, M.E., 2020. In-situ observations of infragravity response during extreme storms on sand and gravel beaches. Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 382–386. Coconut Creek (Florida), ISSN 0749-0208.Infragravity waves (frequency = 0.005 – 0.05 Hz) play a key role in coastal storm impacts such as flooding and beach/dune erosion. They are known to dominate the inner surf zone on low-sloping sandy beaches during storms. However, in large wave conditions, their importance on different beach types, of variable swell and wind-waves dominance, is largely unknown. Here, a new dataset is presented comprising in-situ observations during storm wave conditions (significant wave height of 3.3 m, peak periods of 18 s and return periods up to 1 in 60 years) from two contrasting sites: a low-sloping sandy beach and a steep gravel beach. Wave measurements were collected seaward of the breakpoint by wave buoys and bed-mounted acoustic Doppler current profilers, and through the surf zone using arrays of pressure transducers. Wave spectra showed contrasting evolution from the shoaling zone to the inner surf zone at the two sites. At the sandy beach, gravity band energy dissipated gradually as depth reduced, while infragravity band energy simultaneously increased, resulting in strongly infragravity-dominated wave spectra in the inner surf zone. At the steep gravel site, a rapid drop in short wave energy was observed, with limited growth of infragravity energy so that inner surf zone spectra showed a low energy peak in the infragravity band. The normalized bed slope parameter indicated whether infragravity waves were generated by bound long wave release or breakpoint forcing, showing that the former (latter) was dominant on the sandy (gravel) beach. In spite of these differences, the shoreline wave spectra under storm wave conditions were infragravity-dominated on both the sandy and gravel beaches.

Extreme Water Levels for Australian Beaches Using Empirical Equations for Shoreline Wave Setup

AbstractEmpirical equations for wave breaking and wave setup are compared with archived shoreline wave setup measurements to investigate the contribution of wind waves to extreme Mean Total Water Levels (MTWL, the mean height of the shoreline), for natural beaches exposed to open ocean wind waves. A broad range of formulations is compared through linear regression and quantile regression analysis of the highest measured values. Shoreline wave setup equations are selected based on the availability of local beach slope data and the ability of the quantile regression to show a good representation of the highest measured levels. Wave parameters from an existing spectral wave hindcast are used as input to the selected equations and are combined with a storm tide time series to quantify the relative contribution of shoreline wave setup to the extreme MTWL climate along Australian beaches. A multipass analysis is provided to understand the ability to capture the shoreline wave setup estimates with and without considering beach slope. The national scale analysis which does not include beach slope indicates there are multiple contributing factors to MTWL. Examples are provided at two locations of differing local beach slope to show the importance of including local beach slope in determining the contribution of waves to MTWL. A tool is in development for further investigation of wave setup for Australian beaches.

Artificial wave breakers promote the establishment of alien aquatic plants in a shallow lake

We surveyed the occurrence of three emergent alien aquatic plants, Gymnocoronis spilanthoides, Alternanthera sessilis, and Alternanthera philoxeroides, in Lake Kasumigaura from 2013 to 2017. To determine the effects of shoreline modification on the expansion of alien aquatic plants, we compared the relative occurrence of alien aquatic plants in varying shoreline conditions modified by shoreline hardening and wave breakers. The distribution of alien aquatic species increased continually in Lake Kasumigaura over the study period, although the rate of expansion differed among years. Furthermore > 64.6% of the vegetative fragments were found within 2 km of the nearest patch. The construction of artificial wave breakers, which were installed parallel to the shoreline, had a positive influence on alien aquatic plant patch establishment. Especially, parallel wave breakers increased the patch establishment of G. spilanthoides by about 2.27-fold compared to the natural environment. Perpendicular wave breakers increased alien patch establishment by about 1.63-fold. For lakeshore management, it is important to consider both alien plant suppression and levee protection. We further suggest prompt action to prevent the expansion of alien aquatic species around pumping stations, which can also result in the relocation and expansion of invasive species.

Effects of reef morphology variations on wave processes over fringing reefs

Many low-lying tropical and sub-tropical atolls fringed by coral reefs are susceptible to coastal inundation during extreme wave events. Previous studies have shown that the infragravity (IG) wave is the dominant component of shoreline run-up compared to the sea and swell (SS) wave and the wave-induced setup. To better understand both the SS and IG wave dynamics over a fringing reef with various morphologies, a series of laboratory experiments were conducted in a wave flume based on an idealized fringing reef profile. The shoreline responses of waves to different reef morphologies with/without the reef crest, the lagoon and the reef surface roughness were examined. IG wave resonance on the reef flat was identified by a spectral analysis of the shoreline wave records. Subsequently, a numerical model based on the Boussinesq equations was validated by the experimental data. The model was then applied to investigate the impacts of varying reef morphologic features (fore-reef slope, reef-crest width, lagoon width, and reef roughness coefficient) on the shoreline wave motions.

Wave tank experiments on the power capture of a float-type wave energy device with a breakwater

The objective of this study is to discuss the configuration and hydrodynamic performance of a float-type shoreline wave energy converter coupled with a breakwater. The energy converter is designed to extract wave power by making use of the wave-induced pitch motion of the float which is hinged on a breakwater. Meanwhile, the float is connected with hydraulic pistons, generating the high pressure water stream to drive alternators for electricity generation. A scale model was built in the laboratory at Hohai University, and the friction force was employed as the power take-off damping source. During the experiments, variations in several key parameters, including the wave elevation, wave energy converter (WEC) response (decay motion, free response, or damped motion of the WEC with varying damping levels), and wave-induced tensile forces on the steel wires were instantaneously measured. With these data, the wave reflection coefficient, instantaneous output power, and wave energy conversion efficiency of the model were estimated. The experimental results show that the developed WEC is effective in dissipating the incident wave energy, especially for longer waves, and is able to extract wave energy at a meaningful rate from regular waves. The average output power and wave energy conversion efficiency of the model under the resonance state can be up to 0.13 W and 32.6%, respectively. Although the WEC model harnesses more energy under longer waves, further examination reveals that the device is more efficient when installed in less energetic seas. Meanwhile, the water depth and the spacing between the breakwater and the float are significant factors for the posture and motion characteristics of the float during the process of interaction with water waves.

Numerical Study on Optimization of the Float in a Shoreline Wave Energy Converter

Peng, W.; Fan, Y., and Zhang, J., 2018. Numerical study on optimization of the float in a shoreline wave energy converter.. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 1296–1300. Coconut Creek (Florida), ISSN 0749-0208.In this paper, the hydrodynamic performance of the float in a shoreline wave energy converter is investigated under regular waves. A numerical model is built based on the Navier-Stokes solver coupled with immersed boundary method, volume of fluid method and the mechanics model of float. Making use of the laboratory measurements, the numerical model has been proved to be a reliable tool in reproducing wave deformations and the dynamics of the float. Then, the model is employed to test the sensibility of float performance to changes in some variables under various waves: spacing between breakwater and float, length of float. From numerical estimations, it can be concluded that the nondimensional motion amplitude of float will decrease with the increasing float length or spacing between breakwater and float. With different loads, the dynamic of float shows different variation trend against the length of float, which implies further investigations may be needed in the future on the effect of power take-off damping load. Last but not the least, the interactions between water waves and two types of floats (rectangle and convex) are simulated and discussed. With the help of snapshots of water particle velocity field and the water surface profile from numerical calculation, the flow pattern and external forces from the fluid field acting on the float can be estimated. Then, the motion amplitudes of floats are computed and compared, and the convex floats are proved to capture more power than the rectangular ones.

On the shoreline wave energy potential and its conversion in Morocco

The efficiency of a wave energy converter (WEC) device for wave energy conversion depends on many factors, among which the incident wave conditions. In this paper, the case of Moroccan Atlantic shoreline wave energy resource will be presented through the exploitation one year of data records in terms of wave height and period variations. It is found that with its 3 000km Atlantic coastline the global potential of offshore wave energy is nearly of 75 000MW which makes the country able to reinforce significantly its renewable energy resources. As a part of this work, the flow behavior inside the chamber of an oscillating water column (OWC) device has been analyzed by means of a numerical flow simulation code. The flow is set to be incompressible, three dimensional (3D), viscous and unsteady. The turbulence has been modeled with the classical (k-ε) turbulent model. Computations have been carried out on the geometry of Pico plant built in Azores. Local flow characteristics have been determined in order to obtain an accurate understanding of the flow behavior inside the chamber.

Future Reef Growth Can Mitigate Physical Impacts of Sea‐Level Rise on Atoll Islands

AbstractWe present new detail on how future sea‐level rise (SLR) will modify nonlinear wave transformation processes, shoreline wave energy, and wave driven flooding on atoll islands. Frequent and destructive wave inundation is a primary climate‐change hazard that may render atoll islands uninhabitable in the near future. However, limited research has examined the physical vulnerability of atoll islands to future SLR and sparse information are available to implement process‐based coastal management on coral reef environments. We utilize a field‐verified numerical model capable of resolving all nonlinear wave transformation processes to simulate how future SLR will modify wave dissipation and overtopping on Funafuti Atoll, Tuvalu, accounting for static and accretionary reef adjustment morphologies. Results show that future SLR coupled with a static reef morphology will not only increase shoreline wave energy and overtopping but will fundamentally alter the spectral composition of shoreline energy by decreasing the contemporary influence of low‐frequency infragravity waves. “Business‐as‐usual” emissions (RCP 8.5) will result in annual wave overtopping on Funafuti Atoll by 2030, with overtopping at high tide under mean wave conditions occurring from 2090. Comparatively, vertical reef accretion in response to SLR will prevent any significant increase in shoreline wave energy and mitigate wave driven flooding volume by 72%. Our results provide the first quantitative assessment of how effective future reef accretion can be at mitigating SLR‐associated flooding on atoll islands and endorse active reef conservation and restoration for future coastal protection.

Projected atoll shoreline and run-up changes in response to sea-level rise and varying large wave conditions at Wake and Midway Atolls, Northwestern Hawaiian Islands

Atoll islands are dynamic features that respond to seasonal alterations in wave conditions and sea level. It is unclear how shoreline wave run-up and erosion patterns along these low elevation islands will respond to projected sea-level rise (SLR) and changes in wave climate over the next century, hindering communities' preparation for the future. To elucidate how these processes may respond to climate change, extreme boreal winter and summer wave conditions under future sea-level rise (SLR) and wave climate scenarios were simulated at two atolls, Wake and Midway, using a shallow-water hydrodynamic model. Nearshore wave conditions were used to compute the potential longshore sediment flux along island shorelines via the CERC empirical formula and wave-driven erosion was calculated as the divergence of the longshore drift; run-up and the locations where the run-up exceed the berm elevation were also determined. SLR is projected to predominantly drive future island morphological change and flooding. Seaward shorelines (i.e., ocean fronted shorelines directly facing incident wave energy) were projected to experience greater erosion and flooding with SLR and in hypothetical scenarios where changes to deep water wave directions were altered, as informed by previous climate change forced Pacific wave modeling efforts. These changes caused nearshore waves to become more shore-normal, increasing wave attack along previously protected shorelines. With SLR, leeward shorelines (i.e., an ocean facing shoreline but sheltered from incident wave energy) became more accretive on windward islands and marginally more erosive along leeward islands. These shorelines became more accretionary and subject to more flooding with nearshore waves becoming more shore-normal. Lagoon shorelines demonstrated the greatest SLR-driven increase in erosion and run-up. They exhibited the greatest relative change with increasing wave heights where both erosion and run-up magnitudes increased. Wider reef flat-fronted seaward shorelines became more accretive as all oceanographic forcing parameters increased in magnitude and exhibited large run-up increases following increasing wave heights. Island end shorelines became subject to increased flooding, erosion at Wake, and accretion at Midway with SLR. Under future conditions, windward and leeward islands are projected to become thinner as ocean facing and lagoonal shorelines erode, with leeward islands becoming more elongate. Island shorelines will change dramatically over the next century as SLR and altered wave climates drive new erosional regimes. It is vital to the sustainability of island communities that the relative magnitudes of these effects are addressed when planning for projected future climates.

Modeling wave processes over fringing reefs with an excavation pit

The excavation of reef-flat sand and aggregate for engineering projects is a common practice on atoll islands, with attendant coastal management and hazard mitigation issues. To assess the impact of reef-flat excavation pits on wave transformation, a numerical study is carried out based on one-dimensional weakly dispersive, highly nonlinear Boussinesq equations. Model simulations are compared to field observations made at Majuro Atoll, Republic of the Marshall Islands (Ford et al., 2013a), at a 75-m-wide fringing reef flat with a 17-m-wide, 4-m-deep excavation pit and at an adjacent unmodified reef flat. With a calibrated empirical breaking model and uniform friction coefficient, the numerical model is shown to satisfactorily reproduce the observed sea and swell (SS) and infragravity (IG) frequency band wave heights for a moderate amplitude wave event. By removing the lateral morphological differences of the field experiment, the model shows that an excavation pit reduces/increases shoreline IG/SS wave heights compared to numerical tests without the pit, in qualitative agreement with Ford et al. (2013a). An EOF analysis demonstrates that the reduction in IG wave heights is associated with modifications of the ¼ and ¾ wavelength IG standing modes across the reef caused by the pit. Model tests are used to evaluate the effects of cross-reef pit location and width on wave transformation. Shoreline wave heights are least affected by a pit located near the reef crest, and both SS and IG wave heights increase as the pit location moves shoreward. Shoreline wave heights are an increasing function of pit width as the increase in SS wave height exceeds the decrease in IG wave height produced by the pit. The effects of incident wave height and spectral bandwidth are also examined for the reef with and without pit. It is found that both shoreline SS and IG wave heights increase with the increasing incident wave height for both profiles. The numerical model results also demonstrate that the shoreline response is sensitive to the bandwidth of the incident wave spectrum, and larger IG shoreline wave heights are excited for narrower spectral bandwidths until wave reflection limits the forcing.

Where is the best site for wave energy exploitation? Case study along the coast of northern Latium (ITALY)

The present work proposes a siting process for the detection of a suitable site for wave energy exploitation. The choice of a suitable site is based on the good agreement between energy availability, environmental sustainability, and equipped facilities to exploit wave energy. The case study in the northern Latium coast is explicative because in this area there are several activities that affect marine ecosystems, and the introduction of renewable energies promote the reduction of anthropic pressures. The nearshore wave power is studied through the numerical wave model (CMS-Wave), and available wave buoys along the coast were used to compare numerical results. In correspondence with Civitavecchia harbour, the largest nearshore wave energy was found; the large depth in front of the breakwater allows to conserve a great part of offshore wave power, with an average dissipation rate of 10 % less than offshore, with mean annual available wave energy of 25.4 MWh/m and seasonal fluctuation of 5.4 MWh/m. This area appears to be an optimal site for nearshore and shoreline wave energy device tests and installations, for energy availability (intermediate level respect Mediterreanean Sea), low potential environmental impact, easier accessibility, and policy oriented towards a larger sustainability of harbour activities.

Extreme wave events in the central Mediterranean: Geomorphic evidence of tsunami on the Maltese Islands

Field evidence from the Maltese Islands is presented of extreme wave activity in the central Mediterranean Sea. An extensive range of extreme wave signatures, both erosional and depositional, is here presented for the first time and indicates a wave attack from the NE. Existing models of runup and boulder detachment imply that the extreme wave signatures lie beyond the capabilities of storm waves. These considerations, taken together with the range of evidence available, point toward tsunami as the agency responsible, which is consistent with the evidence from Mediterranean marginal coasts opposed to the Maltese Islands. Evidence from existing boulder detachment, tsunami runup and wave velocity models suggests that tsunami with shoreline wave height of up to ∼4 m, and with local velocities of >10 ms–1 would have been required in order to form the signatures observed.