Large Swell Research Articles

Short-term dynamics of a high energy embayed beach: Stanwell Park, NSW, Australia

The three-dimensional variability of the subaerial beach is examined for Stanwell Park Beach, New South Wales (NSW), Australia. This embayed environment has previously been studied over long time scales (decades), but not over shorter time scales (days, weeks). Embayed beaches experience rotation events during which opposite accretion and erosion patterns are observed at the extremities of the beach. To analyse this phenomenon, the beach is mapped with 10 Real-Time Kinematic Global Positioning System (RTK-GPS) surveys collected from 10th February 2016 to 14th May 2016. This study aims to examine short-term changes (days, weeks) to the morphology of the subaerial beach of Stanwell Park Beach and any factors that may influence its behaviours. We show that a short-time beach rotation event occurs over one month, caused by a large eastern swell. However, swell with a southern direction generates rip current channels on the subaerial beach face. During this particular event, the amount of sediment transported is lower than during beach rotation events. Furthermore, Stanwell Park Beach has two lagoons that can open to discharge water accumulated in these lagoons. We show that during heavy rainfall, the lagoons open, transporting sediment in surf zone and thus causing erosion. This study provides a clear demonstration of the sensitivity of embayed beaches to short-term variability in wave climate.

Centrifuge modelling of the effect of base slab stiffness on long-term heave and swell pressure

Long-term heave of basement slabs is a significant problem in cities with overconsolidated clay, such as London. There is a dearth of data to calibrate the methods commonly used by designers to predict heave displacement and swell pressure. This paper presents results from two centrifuge tests aimed at reproducing the phenomenon of long-term basement heave. Reduced scale models of rectangular basements with different slab thicknesses underlain by overconsolidated clay were tested, to investigate the effect of base slab stiffness on heave behaviour. The centrifuge tests provided measurements of the profiles of vertical displacement, bending moments in the slab and contact pressure at the slab–soil interface. This is the first geotechnical centrifuge study to provide simultaneous measurements of vertical displacement and swell pressures during long-term basement heave. Whereas the flexible basement underwent significant differential heave and almost complete relaxation of swell pressures, the stiff basement generated large swell pressures and consequently large bending stresses. These results confirm that the prediction of high heave pressures is a self-fulfilling prophecy: a basement slab with high stiffness will beget large swell pressures. The experimental measurements of swell pressure and heave were compared to predictions by a simplified non-linear method of heave calculation. The simplified non-linear method produced acceptable predictions of total heave.

Influence of Embedment Conditions on Long-Term Basement Heave in Over-Consolidated Clay

Deep excavations in over-consolidated clays lead to swelling of the clay, which can exert large swell pressures on the basement slabs. In this paper, four prototype scenarios of basement construction in over-consolidated clay were investigated using both centrifuge modelling and finite element modelling. The main aim was to discern the effects of two aspects of embedment on long-term heave behaviour when relatively flexible and relatively stiff slabs were employed. The extension of diaphragm side walls below the formation level and the presence of a drainage layer between the slab and the clay were investigated. The results confirm that the use of a drainage layer would shorten the time of consolidation as expected. The variations in embedment conditions would also cause some redistribution of heave displacements, though the magnitude of such redistribution is relatively small, both when compared to the overall magnitudes of heave displacement and when compared to the effect of varying base slab stiffness on heave displacement.

The 2015 exceptional swell in the Southern Pacific: Generation, advection, forecast and implied extremes

A very severe storm in the Antarctic belt is analysed that sent a very large swell throughout the South-Pacific Ocean. The reasons for the storm were a deep depression passing over an anomalous warm sea area, with consequent increased intensity, more active wind input, gustiness, with also dynamical generation. Wind and wave model results are verified with scatterometer and altimeter data. We follow the swell evolution during the five days required to reach the Galapagos Islands and a buoy off the Peruvian coast. The first forerunners peaked at 0.032 Hz at these locations, well represented in the model thanks to a purposely extended frequency range used in the WAM model. A nonlinear combined analysis is carried out to estimate the overall maximum single wave heights that may have impinged on the Galapagos coasts. Single wave heights up to 6 m have been estimated. Once generated, the swell conditions at Galapagos and the buoy are perfectly anticipated. Including generation, useful forecasts extend till at least eight days before the event. The lack of any local communication is discussed. An analysis using ERA5 winds, but a respectively higher resolution long-term wave hindcast, shows that a similar, actually stronger, event happened in 2006. A simple, but sound method, based on physical principles and elementary geometry, is proposed to estimate, firsthand and after any time, the maximum height of a once generated swell. The results for the 2015 storm are correct within 5% of the model values.

Intense atmospheric rivers can weaken ice shelf stability at the Antarctic Peninsula

The disintegration of the ice shelves along the Antarctic Peninsula have spurred much discussion on the various processes leading to their eventual dramatic collapse, but without a consensus on an atmospheric forcing that could connect these processes. Here, using an atmospheric river detection algorithm along with a regional climate model and satellite observations, we show that the most intense atmospheric rivers induce extremes in temperature, surface melt, sea-ice disintegration, or large swells that destabilize the ice shelves with 40% probability. This was observed during the collapses of the Larsen A and B ice shelves during the summers of 1995 and 2002 respectively. Overall, 60% of calving events from 2000–2020 were triggered by atmospheric rivers. The loss of the buttressing effect from these ice shelves leads to further continental ice loss and subsequent sea-level rise. Under future warming projections, the Larsen C ice shelf will be at-risk from the same processes.

Sea ice-free corridors for large swell to reach Antarctic ice shelves

Sea ice can attenuate Southern Ocean swell before it reaches Antarctic ice shelves and imposes flexural stresses, which promote calving of outer ice-shelf margins and influence ice shelf stability. An algorithm is developed to identify sea ice-free corridors that connect the open Southern Ocean to Antarctic ice shelves from daily satellite sea ice concentration data between September 1979 and August 2019. Large swell in the corridors available to impact the ice shelves is extracted from spectral wave model hindcast data. For a selection of ice shelves around the Antarctic coastline, corridors are assessed in terms of duration and areal extent. The availability of large swell to impact certain ice shelves through the corridors is evaluated from spectral wave data for daily statistical properties and the number of large swell days per year. Results integrated over a large number of ice shelves are used to assess overall trends. Large variations are found between individual ice shelves for both corridors and available swell, with contrasting trends between the West and East Antarctic Ice Sheet. The findings indicate ice shelves likely to experience prolonged periods of appreciable outer margin flexure due to large swell action, such as the Fimbul, Shackleton and Ross Ice Shelves, which could exacerbate climate-driven weakening and decreasing buttressing capacity, with implications for sea-level rise.

The effect of additional limestone on expansive soil at Summarecon Emerald East Karawang

Expansive clay soils are soils that have large shrink and swell properties, and their behaviour is affected by water. The purpose of this study was to determine the physical properties and mechanical properties of expansive clay soil. In this study, land samples were taken at the Summarecon Karawang Project. Clay soil in stability with calcium carbonate (CaCO3) of 2%, 4%, 6%, and 8%. The location of study is at Summarecon Emerlad Karawang Timur. The soil character is potential to expand 7.4602%, type CH (Clay - High Compressibility). The result of study is by using carbonate content (CaCO3) the plastic limit increased 7.75%, cohesion increased by 19.44%, the plasticity index decreased by 45%, the specific gravity decreased by 2.8%, the CBR decreased by 58.78%, the swelling decreased by 66.35%. (R).

Atmospheric Drivers of Oceanic North Swells in the Eastern Caribbean

Large wintertime ocean swells in the Caribbean, known as north swells, generate high surf and expose communities, ecosystems, and infrastructure to hazardous conditions. Empirical orthogonal functions and cluster analyses using ERA5 reanalysis swell data are performed to characterize north swells in the eastern Caribbean and to establish a ranked list of historical events. ERA5 atmospheric and swell data are used to create basin-scale sea-level pressure, surface wind and swell composites for north swell events of different magnitudes. Additionally, storm events are identified in the mid-latitude North Atlantic Ocean. North swells are predominantly generated by storms that intensify off the North American east coast. However, there is a subset of moderately sized swells associated with a westward-located high-pressure system in the North Atlantic. While lower sea-level pressure and stronger surface winds are important for generating larger swells, the location of the low-pressure center and storm track as well the zonal speed of the storm are critical in the development of large eastern Caribbean north swells. The largest such events are associated with storms located comparatively further southeast, with a more zonal trajectory, and slower zonal speed. Large storms located further northwest, with a more southwest to northeast trajectory, and faster zonal speeds are associated with weaker north swells or in many cases, no significant north swell in the eastern Caribbean.

Busan Geoje Fixed Link

The Busan Geoje Fixed Link project is one of the landmark projects in South Korea, providing a road connection between Gaduk and Geoje Island near to the city of Busan at the Southern tip of the Korean peninsula. The project consists of two Cable Stayed Bridges, an Immersed Tunnel, rock tunnels and it has a total length is over 8 km.This paper will focus on the immersed tunnel part of the link and the particular challenges that the project faced in designing and constructing the tunnel, these challenges required a significant evaluation in immersed tunnel technology. The tunnel consists of 18 tunnel elements and has a total length of 3.6 km. The tunnel location was characterised by the following conditions:•a large depth, maximum depth of the tunnel is 48 m below sea level.•the tunnel is located in a seismic sensitive area.•the tunnel is founded largely on weak marine clay, but parts also on bedrock.•part of the tunnel was constructed on a sub sea embankment which is also founded on a weak marine clay.•the tunnel has been constructed in a location that is facing to the Sea of japan and is exposed to a severe wind and wave environment with large long period swell waves present for part of the year.Because for only a few months a year the wave- and weather circumstances were suitable for immersion, extensive numerical and physical model tests were carried out to predict the behaviour of the immersion system for the expected conditions. These model tests were used to determine the wind and wave climate that the immersion system could cope and a go, no-go range of conditions.Additionally, an accurate, sophisticated short and long term wave and weather forecast system was developed. This system enabled forecasts to be made within a 10 cm wave height accuracy, for periods leading up to the element transport and immersion operations which allowed the immersion operations to be possible within acceptable risks.The tunnel elements (TE) were built in batches in a pre-cast yard (PC). After inundation of the dock the elements were transported to a mooring location close to the PC-yard for fitting out and to wait for favourable immersion weather.The elements were immersed using two catamaran pontoons and placed in a previous dredged trench on the sea bed. A taut mooring configuration was used in order to reduce the wave influenced motions to a minimum. Anchor points were created by pre-installed plate anchors.Due to the total length and installation depth of the tunnel the traditional survey systems using towers and total stations were not suitable. Therefore new survey methods were developed, these included a tautwire system and an Ultra Short Base Line (USBL) acoustic system were used for the positioning of the elements during the immersion operation. Fine positioning of the TE’s under swell wave influence was done using a special designed External Positioning System (EPS) and placed on the pre-laid screeded gravel bed.

Trends in sandy beach variability EThekwini Municipality, South Africa

It is well-known that the coastal zone attracts human populations like no other. There is ever increasing demand on the coastal zone by tourists, residents and developers alike; it is named as the fastest growing sector of the blue economy. Hence, coastal zone processes require better understanding to be effectively managed in the context of sustainable development of the asset. While sea level may be rising over the long-term, and many global-resolution studies lament the loss of sandy beaches as a result, coastal managers work over far shorter time-scales thus require site specific information to manage the coastal zone on a daily and monthly basis. In this contribution we discuss nine years of morphological change along a sandy beach in Durban, South Africa. The beach is managed by the eThekwini Municipality who are responsible for maintaining a coastal zone of ca. 100 km. The morphological data of this study were collected on a near monthly basis over 9.6 km of sandy beach between October 2011 and March 2020. From these data, beach volume and area are calculated and the variation is documented over time in conjunction with wave data recorded from a proximal directional wave buoy. Over the study period, the beach has experienced a net loss of 177885m3 and 29,375 m2 in volume and area respectively. However, the beach response has not been uniform throughout the study area. The southern three-quarters of the beach were affected by significant losses while the northern one-quarter gained in volume and area over the same period. The summer wave climate is characterised by increased variability in swell origin with greater easterly contributions than other seasons, and typically lacks the frequency of large swell (>3.5 m) events (7% of events) common to autumn (20%), winter (35%) and spring (38%). Winter, followed by spring then autumn seasons have more focused swell origins and southerly contribution, particularly in terms of large swell events. During periods of reduced event frequency allow for partial beach recovery, while erosion is associated with periods of increase event frequency. The sediment budget has been significantly reduced though impoundments on the proximal river catchment, compounded by un-managed sand mining. Rather than sea level, these near-field controls on sediment availability likely play a major role in beach volume and area in response to wave climate. There is less sediment available to nourish the beach naturally following erosional events; artificial nourishment will likely be required to maintain the sandy beach in the future.

Microclinoform structure of the BT<sub>10</sub> horizon as a factor controlling the formation of gas fields in the southeastern part of the Yamalo-Nenets Autonomous Okrug

The microclinoform model of the Neocomian shelf reservoirs is becoming more and more supported by practicing geologists, since it allows to effectively address the problems arising in the development of complex reservoirs. According to modern concepts, the microclinoform structure is due to the intense progradation of delta complexes during periods of forced regression. The article demonstrates the effectiveness of the microclinoform concept in building a geological model of an accumulation in BT10 horizon of Zapadno-Chaselsky field, which is located in the southeastern part of the Russko-Chaselsky large swell in the southeast of the Yamalo-Nenets Autonomous Okrug. The microclinoform structure of the target was mapped based on the data volume of the second derivative of the wave field, which is more sensitive to changes in thicknesses, and porosities of sand reservoirs. As a result of comprehensive studies, correlation profiles and a GDE map of stratigraphic unconformity (top of BT10) were built reflecting the microclinoform structure of the target. The results were used to build a model of a gas reservoir and estimate its reserves. Hydrocarbon discoveries have already been made in the BT group of reservoirs at Zapadno-Chaselsky field and neighboring Yuzhno-Russkoye field that improves the potential of this interval within the southeastern part of the Yamalo-Nenets Autonomous Okrug. This poses the task of its more detailed study based on the microclinoform concept.

Analysis Of Reinforcement Testing Of Bamboo Cuts For Road Board Employment On Soil Soil

Soil is a support for a building that functions as a support for the construction load on it. There are several types of soil that have properties that are not suitable for constructing a construction, namely those that have low bearing capacity, low shear strength, and large soil swells. The research that the author is carrying out here is a research on the Juanda Sidoarjo Frontage Road Development Project along the 200 m length, mostly passing through a location that is in subgrade conditions in the form of soft clay soil up to 30 m. At that location, the frontage road is planned to use the road embankment. The use of road embankments on soft soil is predicted to cause problems with the stability of the bearing capacity of the subgrade and subgrade subsidence. On the other hand, the cost of road foundation construction needs to be reduced to make it more economical. In collecting the required data, the authors use interview techniques. While in the discussion used qualitative and quantitative research methods. From the results of the analysis conducted by the author on the finite element analysis method, the SF (safety factor) value using soil reinforcement with bamboo cerucuk mats is 2.0734 (meets the minimum requirements). Where (SNI 8460-2017) requires a minimum SF (safety factor) value with an additional load of SF > 1.5. So the strengthening of the bearing capacity of the soil using a bamboo cone mat is very influential on the strengthening of the carrying capacity of the soil. While in the discussion used qualitative and quantitative research methods. From the results of the analysis conducted by the author on the finite element analysis method, the SF (safety factor) value using soil reinforcement with bamboo cerucuk mats is 2.0734 (meets the minimum requirements). Where (SNI 8460-2017) requires a minimum SF (safety factor) value with an additional load of SF > 1.5. So the strengthening of the bearing capacity of the soil using a bamboo cone mat is very influential on the strengthening of the carrying capacity of the soil. While in the discussion used qualitative and quantitative research methods. From the results of the analysis conducted by the author on the finite element analysis method, the SF (safety factor) value using soil reinforcement with bamboo cerucuk mats is 2.0734 (meets the minimum requirements). Where (SNI 8460-2017) requires a minimum SF (safety factor) value with an additional load of SF > 1.5. So the strengthening of the bearing capacity of the soil using a bamboo cone mat is very influential on the strengthening of the carrying capacity of the soil. Where (SNI 8460-2017) requires a minimum SF (safety factor) value with an additional load of SF > 1.5. So the strengthening of the bearing capacity of the soil using a bamboo cone mat is very influential on the strengthening of the carrying capacity of the soil. Where (SNI 8460-2017) requires a minimum SF (safety factor) value with an additional load of SF > 1.5. So the strengthening of the bearing capacity of the soil using a bamboo cone mat is very influential on the strengthening of the carrying capacity of the soil.

Projections of Directional Spectra Help to Unravel the Future Behavior of Wind Waves

Based on a novel approach, present-day and future spectral wind-wave conditions in a high-emission scenario from a seven-member wave climate projection ensemble are compared. The spectral analysis at the selected locations aids in understanding the propagation of swell projected changes from the generation areas across the ocean basins. For example, a projected increase in the energy from Southern Ocean swells can be observed in all ocean basins and both hemispheres, which is especially relevant in the west coast of North America due to the penetration of these swells beyond 30°N. Similarly, a consistent decrease in the energy of large northern Atlantic swells is noted close to the equator. This work provides evidence that assessments based on only integrated wave parameters (e.g., significant wave height and mean wave period) can mask information about the sign, magnitude, and robustness of the actual wave climate changes due to the offset of positive and negative variations within the spectrum, leading to a significant underestimation of the change associated with certain wave systems.

Swell-Triggered Seismicity at the Near-Front Damage Zone of the Ross Ice Shelf

Abstract Ocean swell interacting with Antarctic ice shelves produces sustained (approximately, 2×106 cycles per year) gravity-elastic perturbations with deformation amplitudes near the ice front as large as tens to hundreds of nanostrain. This process is the most energetically excited during the austral summer, when sea ice-induced swell attenuation is at a minimum. A 2014–2017 deployment of broadband seismographs on the Ross Ice shelf, which included three stations sited, approximately, 2 km from the ice front, reveals prolific swell-associated triggering of discrete near-ice-front (magnitude≲0) seismic subevents, for which we identify three generic types. During some strong swell episodes, subevent timing becomes sufficiently phase-locked with swell excitation, to create prominent harmonic features in spectra calculated across sufficiently lengthy time windows via a Dirac comb effect, for which we articulate a theoretical development for randomized interevent times. These events are observable at near-front stations, have dominant frequency content between 0.5 and 20 Hz, and, in many cases, show highly repetitive waveforms. Matched filtering detection and analysis shows that events occur at a low-background rate during all swell states, but become particularly strongly excited during large amplitude swell at rates of up to many thousands per day. The superimposed elastic energy from swell-triggered sources illuminates the shelf interior as extensional (elastic plate) Lamb waves that are observable more than 100 km from the ice edge. Seismic swarms show threshold excitation and hysteresis with respect to rising and falling swell excitation. This behavior is consistent with repeated seismogenic fracture excitation and growth within a near-ice-front damage zone, encompassing fracture features seen in satellite imagery. A much smaller population of distinctly larger near-front seismic events, previously noted to be weakly associated with extended periods of swell perturbation, likely indicate calving or other larger-scale ice failures near the shelf front.

Evaluating the feasibility and advantage of a multi-purpose submerged breakwater for harbor protection and benthic habitat enhancement at Kahului Commercial Harbor, Hawai\u2018i: case study

Construction of breakwaters provides an engineering solution for coastal protection. However, little effort has been made toward understanding the ecological impact on local coral reef ecosystems and developing engineering structures that would enhance the coral reef environment. A submerged breakwater proposed for Kahului Commercial Harbor, Hawai‘i, provided an opportunity to design a multi-purpose ‘reef structure’ to mitigate wave impacts while providing new coral reef habitat. This design involved ecological and environmental considerations alongside engineering principles, serving as a model for environmentally sound harbor development. This field study evaluated environmental conditions and reef community composition at the proposed site in a gradient extending outward from the harbor, using in situ data with multivariate analyses. Benthic and topographic features in the area were assessed using a towed drop camera system to relate to biological factors. Results that support breakwater topography should follow the natural spur and groove and depth of the adjacent reef and orient with wave direction. A deep area characterized by unconsolidated substrata and low coral cover would be replaced with the shallow, sloping hard bottom of the breakwater, and provide an exemplary area for corals to flourish while protecting the harbor from large ocean swells. Surfaces on shallow sloping hard bottoms receive higher levels of irradiance that benefits coral growth. Optimal levels of water motion facilitate sediment removal and promote coral recruitment and growth. The design of the Kahului Harbor submerged multi-purpose structure serves as a model for design of shoreline modification that enhances, rather than degrades, the local coral reef environment.

Swell-dominated sediment re-suspension in a silty coastal seabed

Waves are fundamentally important for sediment re-suspension in estuary and coastal areas, especially for silty sediments, which can be easily suspended by waves, but the differential effects of swell and wind waves are still unclear. Integrated field observations were made from November 2012 to March 2013 including waves, currents, and suspending sediments on the offshore seabed of the Huanghe Delta to explore the mechanism of sediment re-suspension in silty coastal zones. During the five months of observation, there were more than 30 winter wind events that affected the study area and induced sediment re-suspension with varying suspended sediment concentration. The observed wave composition was separated into swell and wind waves using a bandpass filter. Results show that large swell (with significant height > 1.0 m) coming from the offshore direction (NE in our study area) dominated sediment resuspension in the coastal seabed due to the fact that this wind direction had the longest average fetch. Winds from the onshore direction usually had smaller swell due to their short fetches and caused limited sediment re-suspension. The residual currents caused by NE winds also transport larger sediment. An individual NE wind event could transport sediment 8–13.6 t/m2 and 5.1–8.2 t/m2 in directions parallel and perpendicular, respectively, to the isobaths, which is much higher than the sediment transportation during an individual NW wind event, which could transport 1.5–4 t/m2 and 0.6–5 t/m2 parallel and perpendicular, respectively, to the isobaths. Our research shows that large swell and the accompanying residual currents caused by NE winds (from offshore direction) are a vital driving force for sediment resuspension and transportation in the offshore zone.

Lidar Observations of the Swash Zone of a Low-Tide Terraced Tropical Beach under Variable Wave Conditions: The Nha Trang (Vietnam) COASTVAR Experiment

A field experiment was conducted at a tropical microtidal intermediate sandy beach with a low tide terrace (Nha Trang, Vietnam) to investigate the short-term swash-zone hydrodynamics and morphodynamics under variable wave conditions. Continuous 2D Lidar scanner observations of wave height at the lower foreshore, subsequent run-up and swash-induced topographic changes were obtained. These data were complemented by detailed real-time kinematic GPS topographic surveys. Variable wave and tide conditions were experienced during the field experiment with relatively large swell waves (offshore significant wave height, Hs = 0.9 m to 1.3 m; peak wave period, Tp = 8 to 12 s) concomitant with spring tides at the beginning of the period, followed by mild wind waves (offshore Hs under 0.5 m and Tp 5 s) and neap tides. This resulted in the following morphological sequence: berm erosion followed by rapid neap berm reformation and beach recovery within a few days. New insights into the link between intra-tidal swash dynamics and daily beach profile evolution were found using the Lidar dataset. While waves directly cause morphology changes on a wave-by-wave basis, tidal levels were found to be a key factor in determining the morphological wave-effect (accretive or erosive) due to modulated interaction between surf and swash hydro-morphodynamics.

Spatial and seasonal differences in the top predators of Easter Island: Essential data for implementing the new Rapa Nui multiple‐uses marine protected area

Abstract Reef fishes are an important component of marine biodiversity, and changes in the composition of the assemblage structure may indicate ecological, climatic, or anthropogenic disturbances. To examine spatial differences in the reef fish assemblage structure around Easter Island, eight sites were sampled during autumn and summer 2016–2017 with baited remote underwater video systems. To determine seasonal changes, quarterly (seasonal) sampling was conducted at five of those eight sites. Fifteen pelagic species of fishes were recorded during this study, some of which have not previously been recorded in scuba surveys, including the Galapagos shark (Carcharhinus galapagensis, Snodgrass & Heller, 1905) and tunas (Scrombidae). Significant spatial and seasonal differences were found in the fish assemblage. Fish assemblages from the south coast differed significantly from those along the west and east coasts, mainly due to the occurrence of top predators. Winter differed from other seasons, especially along the south coast where the island is more exposed to large oceanic swells and winds from Antarctica. Owing to the variety and high relative abundance of species recorded during this survey, baited remote underwater video systems seemed to be an effective method for studying top predators at Easter Island. The identification of priority zones for the protection of top predator species represents an important contribution of this study, in order to develop management and conservation strategies to be implemented in the newly created Rapa Nui multiple uses coastal marine protected areas.

Impact of swell on the wind-sea and resulting modulation of stress

Investigation of 37,106 ocean surface wave spectra from the Pacific, Atlantic Ocean, and Gulf of Mexico demonstrate that swell modulates the energy level of the high frequency tail of the wind-sea wave spectrum, altering sea surface roughness. With a mixture of sea and swell, the wind-sea part of spectra follows the well-known f-4 (equilibrium range) and f-5 (saturation range) power laws. Swell modulates the energy levels but does not change the power-law structure. For swell with minimal winds, the spectra follow the −4, −5 power-law paradigm, but energy correlates to swell steepness not wind speed. Swell shifts the transition between the two sub-ranges towards lower frequencies. For sea-swell mixtures, a modulation factor λ is proposed that depends on wind speed and swell steepness which allows parameterization of the spectral tail. Comparison of large swell with little wind to wind-sea spectra of same height and period, indicates that there is little difference in spectral shape and suggests that the Hasselmann Snl source term is likely the mechanism by which energy is transferred into the wind-sea tail causing the modulation. Analysis of 33,000+ directional spectra at Ocean Station Papa shows that the mean direction for the wind-sea high frequency tail is strongly correlated to wind direction, no matter the swell direction or steepness or level of swell dominance.An equation for the friction velocity of a sea state with swell (u*s) is developed, u∗s=λ1/2u∗o where u∗o is the friction velocity in the absence of swell, by neglect of the direct swell impact. Noting that this is only a partial estimate of the total measured stress, the prediction is evaluated for 3,000+ observed spectra yielding a correlation of 0.91 suggesting that it may be of consequence. Observations of u∗/u∗o suggest a dependence with swell steepness that is similar to that predicted by λ1/2. At low winds, λ1/2 overestimates the stress, but noting that it was derived absent the components from the swell frequencies. In the tail, the momentum transport is downward, while in the swell the transport is predominantly upward, suggests a possible correction for λ1/2. The case of a swell generated wind is discussed.

Long Period Beat Phenomena of Swells in a Coastal Water of Toyama Wan

The large swells invade the Toyama Wan from October to April every year,and cause wave disasters such as ship dragging anchor, grounding and so on, around the Toyama Wan. It is considered that the wave disasters are mainly caused by swells and water level fluctuations with long periods, and so beat phenomena of swells and periodic water level fluctuations are investigated using water level data observed from December, 2017 to March, 2018. The following results are obtained.