Storm Wave Events Research Articles

Projected sea level rise and changes in extreme storm surge and wave events during the 21st century in the region of Singapore

Abstract. Singapore is an island state with considerable population, industries, commerce and transport located in coastal areas at elevations less than 2 m making it vulnerable to sea level rise. Mitigation against future inundation events requires a quantitative assessment of risk. To address this need, regional projections of changes in (i) long-term mean sea level and (ii) the frequency of extreme storm surge and wave events have been combined to explore potential changes to coastal flood risk over the 21st century. Local changes in time-mean sea level were evaluated using the process-based climate model data and methods presented in the United Nations Intergovernmental Panel on Climate Change Fifth Assessment Report (IPCC AR5). Regional surge and wave solutions extending from 1980 to 2100 were generated using ∼ 12 km resolution surge (Nucleus for European Modelling of the Ocean – NEMO) and wave (WaveWatchIII) models. Ocean simulations were forced by output from a selection of four downscaled ( ∼ 12 km resolution) atmospheric models, forced at the lateral boundaries by global climate model simulations generated for the IPCC AR5. Long-term trends in skew surge and significant wave height were then assessed using a generalised extreme value model, fit to the largest modelled events each year. An additional atmospheric solution downscaled from the ERA-Interim global reanalysis was used to force historical ocean model simulations extending from 1980 to 2010, enabling a quantitative assessment of model skill. Simulated historical sea-surface height and significant wave height time series were compared to tide gauge data and satellite altimetry data, respectively. Central estimates of the long-term mean sea level rise at Singapore by 2100 were projected to be 0.52 m (0.74 m) under the Representative Concentration Pathway (RCP)4.5 (8.5) scenarios. Trends in surge and significant wave height 2-year return levels were found to be statistically insignificant and/or physically very small under the more severe RCP8.5 scenario. We conclude that changes to long-term mean sea level constitute the dominant signal of change to the projected inundation risk for Singapore during the 21st century. We note that the largest recorded surge residual in the Singapore Strait of ∼ 84 cm lies between the central and upper estimates of sea level rise by 2100, highlighting the vulnerability of the region.

Synchronised patterns of erosion and deposition observed at two beaches

A similarity in the observed variability through time of two or more individual beaches (here quantified by synchronous changes in shoreline position and subaerial sand volume) can have significant implications to the increased focus worldwide on the need for expanded coastal monitoring. If it can be established that one or a select few beach sites exhibit ‘regionally representative’ behaviour in response to varying and/or changing wave and other climatic forcing, then this will assist to guide the extent and scope of the ongoing monitoring effort required. In this study, two beaches located on the southeast Australian coastline of similar size and orientation but separated by 35km, were simultaneously monitored and compared for a period spanning 3years. Intensive sub-aerial surveys were conducted each month at both sites using ATV-mounted RTK-GNSS. The purpose was to establish whether detailed, embayment wide patterns of erosion and deposition quantified at either site were indicative of the behaviour observed at the other.During the data collection period, storm wave events caused substantial fluctuations in monthly sub-aerial sand volumes (in the range of 60–70% of mean volume), including month-to-month changes at the berm and episodic foredune erosion and recovery. Principal component analysis of the two beaches revealed that both were dominated by oscillation (corresponding north–south behaviour) rather than rotation (contrasting north–south behaviour) over this three-year period. Comparison of alongshore-averaged volume time-series between the two sites indicated a similar total range (68m3/m and 78m3/m) and the average difference between the two sites (4.5m3/m) was found to be of the order of 50% of the average monthly change (9.7m3/m and 10.2m3/m). Corresponding spatial patterns in the occurrence of erosion/accretion along the two sites were also compared and found to closely correspond. Five synchronised ‘snap-shot’ observations from historical aerial photogrammetry and surveys at both sites spanning the period 1974 to 2011 (one per decade) suggest coherence between the sites extends beyond the three-year intensive monitoring period reported here.

Extreme storm wave influence on sandy beach macrofauna with distinct human pressures

We evaluated the influence of storm waves on the intertidal community structure of urbanized and non-urbanized areas of a sandy beach on the northern coast of Rio de Janeiro, Brazil. The macrofauna was sampled before (PREV) and after two storm wave events (POEV I; POEV II) in 2013 and 2014. Significant differences in community structure between PREV and POEV I in the urbanized sector demonstrate higher macrofauna vulnerability, and the community recovery within 41days on this scenario of less frequent events in 2013. On the other hand, significant differences in the macrofauna only in the urbanized sector between PREV and POEV II also highlight macrofauna vulnerability and community recovery failure within 42days on this scenario of more frequent storm in 2014. Urbanization and wave height were the variables that most influenced species, indicating that high storm wave events and increasing urbanization synergism are a threat to the macrofauna.

Storm Swash Deposition On An Embayed Rock Coastline: Facies, Formative Mechanisms, and Preservation

Abstract Storm swash terraces mark the most distal, landward deposition of storm wave events on high-energy rock coasts. They form a potential, but as yet unexploited, sedimentary archive of past storminess. This paper describes storm swash terraces at Morgan Bay, Eastern Cape, South Africa. They form as steeply seaward dipping (30–60°), partially vegetated terraces comprising alternating beds of organic-rich sand, mud, and gravel. The terraces are up to 5 m thick, and the basal elevations range from 0.5 m amsl in the embayment, to 6.5 m amsl on the headland margins. Regardless of location, they are always fronted by a rocky shore platform on which most storm wave energy is attenuated. Six sedimentary facies are delineated on the basis of their lithological and paleontological characteristics and the nature of each bounding surface. Deposits in the most exposed headland locations are thicker and coarser-grained than those formed in the embayment. Composition of the depositional terrace reflects the fronting shore platform, indicating a short source-to-sink transport distance. The thickest storm deposits form where the backing topography is high and accommodation is limited. Storm swash terraces have a high preservation potential with successive storms depositing material in an aggradational manner: reworked material is incorporated into subsequent depositional units. The spatial controls on facies partitioning in each terrace appear to be a function of position in the embayment, the availability of material to seaward, and the presence of accommodation space. Areas of particularly limited accommodation space produce aggradational storm sequences that form especially good archives of marine storminess.

Interannual Variability of Two Offshore Sand Banks in a Region of Extreme Tidal Range

Lewis, M.J.; Neill, S.P., and Elliott, A.J., 2015. Interannual variability of two offshore sand banks in a region of extreme tidal range.Offshore sand banks play important roles for coastal flood protection and fisheries, and they are sources of marine aggregates. An 11-year record (1991–2002) of annual bathymetric surveys from two sand banks (Nash and Helwick) in the Bristol Channel (U.K.) were analysed. Both sand banks have a history of commercial dredging, and have dimensions of the order 10 km by 1 km, with a crest height rising to around 20–25 m above the surrounding sea bed. The crest at Nash Bank is exposed on the lowest spring tides, while Helwick Bank is always covered to a depth of at least 3 m. The volume of Nash Bank decreased over 10 years, and dredging was estimated to be responsible for around one third of this reduction. The volume of Helwick Bank also decreased over an 8-year period, but at a rate six times greater than the loss due to dredging. Significant interannual variability of sand bank morphology was calculated at both sites. The time during which waves alone could induce sediment transport over the sand banks was calculated between each survey date (the effective wave climate). The change in sand bank volume correlated well to the effective wave climate: a linear regression score of 77% (−0.88 Pearson correlation at the 95% significance level) and 69% (0.83 Pearson correlation at the 95% significance level) were found at Helwick and Nash, respectively. A one-dimensional morphodynamic model (UNIBEST-TC), simulated storm wave–induced changes to sand bank morphology that were consistent with those observed. Therefore, the interannual variability within storm wave events could be responsible for the observed natural variability of sand bank volume and morphology observed at both sites. We conclude that it is important to understand anthropogenic impacts upon sand banks within the context of natural variability.

Reconstrução paleoambiental da Laguna de Maricá, RJ, com base em foraminíferos bentônicos

Com o objetivo de avaliar a evolução costeira baseada na distribuição dos foraminíferos bentônicos e nos aspectos sedimentológicos, duas testemunhagens foram realizadas na Laguna de Maricá, Rio de Janeiro. Duas biofácies foram reconhecidas: (i) biofácies Ap-At (Ammonia parkinsoniana - A. tepida) correspondendo à metade inferior de ambos os testemunhos, caracterizada pela abundância de foraminíferos calcário-hialinos, entre os quais destacam-se Ammonia parkinsoniana e A. tepida, associada à intercalação de lama siltosa e lama arenosa com conchas desgastadas e quebradas, sugerindo eventos de ondas de tempestades; e (ii) biofácies Ac-As (Ammotium cassis - A. salsum) compreendendo à metade superior dos testemunhos, caracterizada por espécies aglutinantes, como Ammotium cassis, A. salsum, Trochammina inflata, Miliammina fusca e Ammobaculites spp., associados à lama siltosa e à ocorrência de alguns micromoluscos, indicando uma fase de baixa energia hidrodinâmica. Este registro da distribuição de foraminíferos calcários e aglutinantes relaciona-se principalmente com a dinâmica de abertura e fechamento da barreira arenosa da Laguna de Maricá.

Distribution and thickness of sedimentary facies in the coastal dune, beach and nearshore sedimentary system at Maspalomas, Canary Islands

Numerous studies have shown that most beaches and coastal dune systems of the world are currently eroding but very few have investigated the combined sediment budgets of subaerial and nearshore submarine systems. In the case of the dune field of the Maspalomas Natural Special Reserve (in the south of Gran Canaria), the adjacent Maspalomas and El Ingles beaches and the adjacent submarine platform, the sediment budgets have been severely affected by erosion over the past few decades. The objectives of this study were to investigate the availability of sand within the modern sedimentary system, including the coastal dunes, the beaches and the submerged shelf, but also to assess local sediment sinks. An isopach map generated on the basis of topo-bathymetric data and seismic-reflection profiles revealed that sediment thickness varies from 0–22 m in the study area. Expanses of relatively low sediment thickness were identified in the south-western sector of the coastal dune field along Maspalomas beach, and in the nearshore region to the south of this beach. These localized sediment-deficit areas earmark Maspalomas beach as the most vulnerable shore strip threatened by erosion. The shallow seismic data also revealed that the submarine platform south of Maspalomas represents a marine terrace cut into an ancient alluvial fan, thus documenting an influence of the geomorphological heritage on the present-day morphodynamics. A side-scan sonar mosaic of this nearshore platform enabled the delimitation of areas covered by rock, boulders and gravel, vegetated sand patches and a mobile sand facies, the latter including ripple and megaripple fields. The megaripple field in a valley close to the talus of the marine terrace has been identified as a major sediment sink of the Maspalomas sedimentary system. It is fed by south-westerly storm-wave events. The sediment deficit in the coastal dune field and along Maspalomas beach can therefore only be explained by a currently faster loss of sediment to an offshore sink than can be compensated by the supply of sand from outside the system.

Multitemporal Analysis of a Gravel-Dominated Coastline in the Central Canadian Arctic Archipelago

Abstract ST-HILAIRE-GRAVEL, D.; FORBES, D.L., and BELL, T., 2012. Multitemporal analysis of a gravel-dominated coastline in the central Canadian Arctic Archipelago. This study assesses the stability of Arctic gravel coasts across a range of timescales, based on field and remote-sensing studies of three coastal sites near Resolute Bay, Nunavut. It considers shore-zone sensitivity to ice, wind, and wave forcing at storm-event and annual timescales within a longer-term context, including coastal emergence resulting from postglacial isostatic uplift partially counteracted by accelerating sea-level rise. Another long-term factor associated with climate change is the potential for increased seasonal depth of thaw in the beachface and nearshore. The coast in this area is ice bound on average for 10 months of the year, but the annual duration of ice cover has decreased over the past 30 years (1979–2009) by 0.95 d/y. A longer open-water season has implications for the number and timing of storm-wave events, with i...

Historical trends in Southern Ocean storminess: Long‐term variability of extreme wave heights at Cape Sorell, Tasmania

Atmospheric re‐analyses indicate increased Southern Ocean (SO) storminess over the past few decades. A southern Australia waverider record provides a 23‐year record of storm waves generated in the SO. Statistical models to estimate long‐term trends in frequency and intensity of severe storm waves, based on time‐dependent versions of the Peak over Threshold model, are applied to investigate SO storminess trends. Significant increase in frequency of storm wave events observed in the corrected ERA‐40 re‐analysis significant wave height (HS) record is supported by increasing frequency of synoptic storms which drive large wave events at the site in both ERA‐40 and NCEP‐NCAR re‐analyses. However buoy data show a small decrease in storm wave event frequency, consistent with previous studies investigating trends in SO mean HS from altimeter records. Re‐analysis winds, with apparent increasing trend, may have influenced prior SO research conclusions, particularly related to weakening of the SO CO2 sink.

Wave-Sediment Interactions on an High Energy Beach System

Please click here to download the map associated with this article. The North coast of Northern Ireland is exposed to high-energy swells and frequent storm events and therefore beach systems found along this coast tend largely to be dissipative in character. Bedrock-framed coastlines formed by basalt cliffs, shore platforms and smaller sandy embayments dominate this study area. West Strand beach at Portrush (located 55°12′N/6°40′W) is a high-energy system shaped by a headland-embayment with a sandy beach to the north and boulder beach to the south. It is characterised by a microtidal regime and predominant local winds are west and south westerly. The research work aims to examine this high-energy beach under multiple storm scenarios and to investigate hydrodynamic and morphodynamic behaviour at the site. For the analysis, a wave propagation model was used to compare wave energy dissipation from storm wave events as well as examining currents and sediment transport through the analysis of the spatial distribution of radiation stress. Real data from deep-water wave parameters (significant wave height, period and direction), wind direction and speed, and recent high-resolution bathymetry data were used as an input to the propagation model. The methodology was applied to West Strand beach (9 km2) at a scale of 1:250.

Oceanographic processes and sediment mixing on a sand flat in an enclosed sea, Manukau Harbour, New Zealand

Studies of oceanographic and sedimentary processes on intertidal sand flats in an enclosed sea were undertaken to gain a better understanding of the factors controlling the mixing and dispersal of sediment bound contaminants. Field investigations included a 90 day process experiment during which wind, waves, tidal currents, tides, depth of disturbance and sand flat morphology were measured, and 27 months of sand flat profile monitoring. Sediment entrainment by strong spring tidal currents is restricted to the middle and lower regions of the sand flat which are inundated during the peak tidal flows. The upper 2–3 cm of sediment is re-worked across the middle and upper sand flat by mild storm wave events ( H s = 70 cm), which occurred four times during the 90 day experiment. Numerous ridges and runnels in the upper sand flats are wave-formed features and are maintained by the lack of currents of sufficient magnitude to re-work the features. The ridge and runnel morphology is testimony to large infrequent storm events which re-work the sediment to depths of 20 cm. Such storms are an important mechanism for the release of contaminants and were recorded on 3 occasions in the 27 month profile record.

BEACH CHANGES BY STORM WAVES

Monitoring of beach profiles was carried out during one-year period at two sites located 3 km apart along a Pacific beach, Japan. These two sites are composed of beach sand with different grain size: 0.76 mm and 0.26 mm. It was found that the shoreline did not move even in storm wave events at the site with 0.7 6-mm sand, where the "seesaw mode" profile change took place in the subaerial portion of the beach. It was also found that the shoreline was not always retreated by storm waves at the 0.26-mm sand site, where the "parallel mode" profile change dominated, at the time of presence of bars working as a submerged breakwater to protect the beach from erosion.

Theoretical and observational estimates of nearshore bedload transport rates

Sediment transport rates in a shallow (< 3 m) nearshore region are estimated using theoretical models and using bedform migration rates measured from vertical aerial photographs covering a 10-yr interval. Aerial photographs of the study area in Nantucket Sound, Massachusetts, showed low-amplitude (tens of centimeters), long wave- and crest-length (tens to hundreds of meters), shore-normal sand waves in distinct geometrical patterns. The waves migrated an average of 10–20 m yr−1 over a 10-yr period; the migration distances and bedform dimensions were used to calculate an average volume transport rate for the area. This rate was compared to bedload transport rates calculated using a Meyer-Peter and Müller model and a Bagnold model; field observations of steady currents and directional waves provided data for the calculations. Theoretical rates based solely on asymmetrical tidal currents are as much as an order of magnitude smaller than the observed rates, but inclusion of storm wave effects in the theoretical predictions brings them into better agreement with observations. This suggests that even in tidally dominated, protected regions with low background wave energy, infrequent storm wave events significantly modify sand transport rates and patterns.

Tidally driven sediment transport on the East China Sea continental shelf

Time series measurements were made from an instrumented tripod deployed on the seabed at two locations off the Changjiang on the continental shelf of the East China Sea. The first station (M3; June 1980) was positioned 150 km east of the river mouth in 39-m depth in an area of relict sand. The second station (M4; August 1981) was positioned 80 km east of the river mouth in 47-m depth over a silty-sand bottom sediment. Measurements included current speed, temperature and salinity at z = 218cm, speed and direction at z = 100cm, mean and fluctuating component of pressure for tidal and wave analyses, nephelometer measurements at z = 30cm and half-hourly bottom photographs. Data record lengths were 565 and 263 h for Stas M3 and M4, respectively. During the sampling period at both stations, tidal currents were the dominant bottom velocity component, with U 218 reaching 53 cm s −1 at M3 and U 100 reaching 44 cm s −1 at M4. Tidal current velocities were used to estimate the movement of bottom sediment and the net particle flux at the sampling locations. At Sta. M3, bedload transport was the dominant mode of grain movement. Threshold of grain motion was exceeded on 65% of all tidal cycles and over 17% of the time. The net bedload transport rate over the sampling period was estimated to be 1.7 × 10 −5gm cm −1s −1 in a northerly direction (357°T) or, extrapolated over an annual period, 5.4 × 10 4kg km −1 y −1. At Sta. M4, near the river mouth, significant semidiurnal variations in suspended sediment concentrations were observed. Advective transport of suspended sediment occurred during all tidal cycles, while resuspension of the silty bottom sediment was possible during the velocity maximums associated with spring tidal cycles. Mean suspended sediment concentrations (at z = 30cm) during neap tidal cycles was 8.4 mg I −1 and during spring tidal cycles was 29.7 mg I −1, with an overall station average of 16.5 mg l −1. Net transport of suspended load (at z = 30cm) over the sampling period was 0.11 mg cm −2 s −1 toward 62°T. The observed patterns of sediment transport are in agreement with the qualitative model presented by Chin (1979, Oceanic Selections, 2, 130–142); with bottom sediment at Sta. M3 showing a net drift towards the east northeast and the relict sand deposits farther seaward on the continental shelf migrating in a northerly direction. Major storm or gravity wave events capable of causing significant sediment transport did not occur during the field experiments and it is not known how these other forcing mechanisms would alter the observed sedimentation patterns.

Wave stress and coral community structure in Hawaii

The most significant factor determining the structure of Hawaiian reef coral communities is physical disturbance from waves. Sequential analysis of community structure off the west coast of the island of Hawaii shows that variation of wave energy and storm frequency clearly affects organization in time and space. Normal conditions of low wave stress maintain four well-defined reef zones; diversity is highest at intermediate depths and decreases in physically rigorous shallow areas and stable deep reef slopes. Intermediate level storm wave events cause variable effects within the reef zones, but the zonation pattern, as a whole, is maintained. Diversity increases in zones that are dominated by a single species largely through nonlethal fragmentation and transport, but decreases in the zone of most equitable species distribution. Conversely, severe infrequent storm disturbances that cause massive mortality to all coral species wipe out the pattern of community structure and return the entire community to a low diversity early successional stage.