Southeasterly Waves Research Articles

Changes in the Behavioral Characteristics of the Gangmun and Anmok Beaches following the Construction of Artificial Reefs

Kim, J.; Kim, I.; Nam, J.; Song D., and Lee, H., 2019. Changes in the behavioral characteristics of the Gangmun and Anmok beaches following the construction of artificial reefs. In: Lee, J.L.; Yoon, J.-S.; Cho, W.C.; Muin, M., and Lee, J. (eds.), The 3rd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 91, pp. 26-30. Coconut Creek (Florida), ISSN 0749-0208.On the East coast of South Korea, there is only a small significant difference between low and high tides, meaning that seasonal wave directions appear clearly in recorded data. During summer, southeasterly waves dominate, and northward longshore drift occurs. In addition, the southward transport of littoral sediment occurs under the northeasterly waves that are dominant during winter. However, recent changes in the coastal environment, due to the development of coastal flooding prevention facilities, harbor development projects, and unusual weather conditions, have shown a tendency to increase the erosion of coastal areas. In other words, there is a repeating cycle of positive feedback, in which structures introduced to prevent a certain kind of coastal erosion cause different kinds of coastal erosion. In this study, we used field survey data to analyze the behavioral characteristics of the Gangmun and Anmok beaches for a period of seven years. The results show that the Gangmun and the Anmok beaches are very vulnerable to the effects of artificial constructs. Coastal erosion on Gangmun beach occurred through northward sediment transportation, caused by a dike that was built to avoid the closure of the mouth of Gyungpo stream. After an artificial reef and the groin were constructed to solve this erosion problem, the coastline stabilized. In the case of the Anmok beach, an imbalance in the sand budget supplied from the Namdae stream was brought about by the expansion of the Gangneung harbor, leading to significant beach erosion. After artificial reefs were installed on both beaches to prevent erosion, the area of each beach was increased and each beach's status was stabilized, as a salient beach.

Morphodynamic and Hydrodynamic Controls On the Stratigraphic Architecture of Intertidal Compound Dunes On the Open-Coast Macrotidal Flat In the Northern Gyeonggi Bay, West Coast Of Korea

Abstract The morphodynamics and hydrodynamics of intertidal dunes were investigated to understand their controls on the stratigraphic architecture of the dunes on the open-coast macrotidal tributary channel and channel bank in the northern Gyeonggi Bay, west coast of Korea. Simple dunes migrate seaward as fast as 1–4 m/day on the tributary channel that is ebb dominated with pronounced tidal asymmetry. In contrast, simple and compound dunes migrate either landward or seaward at slower rates of 0.1–2 m/day and 2–3 m/month, respectively, on the southern channel bank, where currents are flood dominated with smaller tidal asymmetry. The tributary channel migrates laterally at variable rates ranging from 1 to 18 m/month with greater rates occurring during the summertime rainy season. In the event of large waves that coincide with the dominant current, westerly to northwesterly waves during winter to spring accentuate the ebbward migration of compound dunes, whereas southerly to southeasterly waves during the summer result in the floodward migration. Deviations to this seasonal trend are possible when the large waves occur during subordinate current stage. The displacement of compound dunes onto the migrating tributary channel produces a composite succession in which a coarsening-up compound-dune succession overlies a fining-up point-bar succession. The master bedding surfaces of the compound dunes dip opposite to or oblique to the directions of accretion surfaces of the point bar. Recognition of nontidal events from the intertidal compound dunes is not straightforward because the reversal and displacement of the dune profile requires shorter response time compared to subtidal counterparts. Tidal asymmetry, tidal cycle in the event of waves, seasonality in wave intensity and direction, and the migration of the tributary channel are seen to exert an important control on the stratigraphic architecture of compound dunes and point bars in the intertidal environment over time and space.

Environmental cues for mass nesting of sea turtles

Mass nesting of Olive Ridley sea turtles at Rushikulya rookery exhibit interannaul variability in population size as well as location of nesting site. This year mass nesting was observed over sand spit (0.25 million) and sporadic nesting (0.05 million) at the rookery and the nesting population surpassed all previous records. The present study examines multiple environmental cues (beach width, volume, shoreline change, foreshore slope, sediment grain size, littoral environmental observation, wind speed and direction) during mass nesting events to assess the factor(s) which favour mass nesting and also the reasons for the record mass nesting over a new site (sand spit). Analysis of results indicates that beach/spit to the north of the river mouth with medium width, mild slope and medium sand grain is a favoured location for mass nesting. Near shore oceanographic conditions conducive for mass nesting are low saline near shore surface water, low energy and relatively longer period south southeasterly waves. Local wind burst with a few days lag/lead of the new/full moon appears as one of the most important factors which trigger mass nesting. Environmental cues for selection of mass nesting site and the factor triggering the mass nesting revealed in the present study are of paramount importance for rookery management and conservation of the vulnerable sea turtles.

Maintaining a way of life for São Miguel Island (the Azores archipelago, Portugal): An assessment of coastal processes and protection

Traditional hard engineering structures and recently emerging soft engineering alternatives have been employed to protect vulnerable coastlines. Despite negative publicity, they have ensured community survival where socio-economic benefits outweigh adverse impacts. This is especially true for Small Islands (SI) where increasing sea levels and storm intensities threaten already limited land availability. This paper presents coastal vulnerability in São Miguel Island (the Azores SI archipelago) and considers SI issues with regard to coastal land loss. Regional wave statistics using 1998 to 2011 wind record showed: periods ranging from 7 to 13s (circa 83%); wave heights between 1 and 3m (circa 60%); and increasing trends in westerly (p=0.473), easterly (p=0.632) and southeasterly (p=0.932) waves. Sea level analyses between 1978 and 2007 indicated a statistically significant rising trend (2.5±0.4mmyr−1; p=0.000), while between 1996 and 2007 it was 3.3±1.5mmyr−1 (p=0.025), agreeing with other global sea level studies. Based on 2001 and 2008 population data and using zonal statistics, circa 60% of the Island's population was found to reside within 1km of the sea and the percentage of total population was linearly correlated with distance from the shoreline (r2=99%). Three case studies show hard coastal engineering solutions preserved Azorean coastal lifestyle and had little or no observed negative impacts on their environs. Although hard engineering is likely to remain a valuable and feasible coastal protection option, an inventory of São Miguel's population distribution, surf breaks, bathymetry and coastal erosion rates showed the potential of using multifunctional artificial reefs as a soft engineering solution. These offshore submerged breakwaters offer coastal protection while providing additional benefits such as surfing amenity and beach widening. Consequently, findings of this work can inform other SI communities.

Links between wave forcing, offshore islands and a macro‐tidal headland‐bound bay beach

ABSTRACTProfiles were analysed in conjunction with wave climate to assess offshore island influences on an embayed beach at Tenby, Wales. Time series analyses showed medium and short‐term beach oscillation, with volume exchanges between zones lagging by up to six months. Dominant southerly and southwesterly waves caused sub and low tidal longshore drift from south towards north, while less frequent southeasterly waves generated counter drift. Modelled inshore breaking waves had less energy than offshore ones and the former behaved differently between the low and high tidal zones (spring tidal range of 7 · 5 m). Variations in wave direction from directly behind the islands resulted in reduced wave heights and statistical analyses agreed with wave model results. These were correlated to morphological change and it was concluded that offshore islands change wave dynamics and modify the morphology of embayed beaches in their lee. Consequently, this work provides significant new insights into offshore island influences, shoreline behaviour and especially tidal setting Copyright © 2013 John Wiley & Sons, Ltd.

Rotation on two adjacent open coast macrotidal beaches

Beach profiles, gale climate, atmospheric variations and wave models (RCPWave) were used to assess beach rotation at two adjacent macrotidal open coast beaches, Pendine and Cefn Sidan Sands, West Wales. Results identified an 11 year record of rotation on both beaches where negative phase relationships were established between volume change at beach extremities within both subaerial and intertidal zones. In the absence of headlands to trap sediment, it is asserted that the driving force for beach rotation is the presence of two estuary complexes that act as surrogate headlands. Wave models found agreement with statistical analyses and showed that under dominant south-westerly waves, sediment movement is towards the estuary complexes, while subdominant south-easterly waves generate counter drift. This was supported by illustrations of sediment pathways for varying wave directions. NAO Index values change from positive to negative trends through time and were correlated to morphological change in both littoral settings. Beach volume change lagged NAO variation by six months at Pendine Sands and by up to two years at Cefn Sidan Sands, with opposing correlations observed at beach extremities. This suggests that rotation is caused by a reversal in NAO trends. These new findings are likely to be exhibited at other open coast locations and this work should be repeated elsewhere to inform coastal management strategies.

An operational model to simulate post-accidental radionuclide transfers in Toulon marine area: preliminary development

As part of its development of post-accident management tools, the French Institute for Radiological Protection and Nuclear Safety is setting up a model to simulate radionuclide dispersion in the Toulon marine area (one of France’s main military ports). The model is based on the MARS 3D code developed by IFREMER. It reproduces hydro-sedimentation phenomena in the Bay of Toulon with a horizontal spatial resolution of 100 m and 30 vertical sigma levels and also factors in radioactive decay and dissolved/particulate distribution of the radionuclides studied. With no tide, the major currents in this area are generated by the wind. The model effectively reproduces the resulting hydrodynamic phenomena, which were measured throughout the summer of 2009 in the channel that links the Little Bay to the Large Bay of Toulon. When the Mistral (wind from the West/Northwest) blows, a surface current quickly appears, which pushes water southwards from the Little Bay, and which is offset by a bottom current (upwellings). When the wind blows from the East, the currents move in the opposite direction, and southeasterly waves, dependent on wind strength and fetch, occur in the Large Bay. Here, we give an example of the simulated dispersion of radionuclides released directly into the surface waters near the Arsenal, demonstrating the constraint relative to dispersion generated by the half-closed configuration of the Little Bay. Sediment in the Little Bay also forms an area where the most highly reactive radionuclides would accumulate, and where the lack of waves has the effect of considerably limiting the phenomena of resuspension.

Patterns, rates and possible causes of saltmarsh erosion in the Greater Thames area (UK)

The estuary-dominated coast of the Greater Thames in England has experienced rapid lateral erosion and internal dissection of saltmarshes. This paper provides an overview of saltmarsh development in this area, and re-examines the role of environmental and human forcing factors. It draws on documentary evidence, including historical maps, survey data and time-series data of forcing factors. Lateral marsh retreat began in the 19th century in the Medway and Blackwater Estuaries, followed by other estuaries in the Greater Thames region at the beginning of the 20th century. The outer estuaries and the wider parts of the inner estuaries especially have experienced erosion. Erosion has been modest in wave-sheltered areas, e.g., the Colne and the inner Crouch. In the 1960s and, more widely, the 1970s, a phase of rapid erosion took place, with erosion rates of up to ca. 16 ha year −1 per site, notably along the open coast of Dengie and Foulness, and in the Blackwater and Thames Estuaries. At all sites, vertical sediment accretion was well able to keep up with sea level rise over the past century. Evidence indicates that there may have been several causes for the erosion of saltmarshes. These are notably land claim and embankment construction (increasing the tidal range and current velocities) and a continuous rise of, especially, high and extreme water levels. The latest episode of rapid erosion in the 1970s is largely attributed to changes in the wind/wave climate. For example, erosion at wave-exposed sites coincided with a peak in high magnitude waves combined with a high incidence of southeasterly waves. The study shows that many factors, including natural forcing factors and human activities, have to be taken into account when explaining saltmarsh development.

Avaliação das condições hidrodinâmicas de dois recifes costeiros do litoral norte do estado da Bahia

Sedimentologic analyses associated with the study of recent foraminifers tests were assessed in order to evaluate their relationship with hydrodynamics and sediments transportation. Fifth-six samples of surface sediments were collected from the top of reefs. Sedimentologic data suggest the influence of littoral drift action, southerly and south-easterly waves during the winter and easterly and north-easterly during the summer, on the transport of sediment and forams. Planktonic species and ecologic preferences of bentonic genera are indicative that these organisms have brought over from high fertility zones. The small number of principal species suggests that Amphistegina lessonii , Quinqueloculina bicarinata , Quinqueloculina lamarckiana and Quinqueloculina sp are the most resistant to the stressing conditions imposed by the transport. Nevertheless: (i) the higher percentage of accessory and constant species, (ii) the dominance of yellow tests, (iii) the relatively small values of abrasion and dissolution recorded to Itacimirim reef, suggest that is a rather calm depositional environment than Praia do Forte. This finding is corroborated by the divergence and convergence patterns of the easterly and south-easterly waves in the adjacent shelf.

Coastal dynamics and impact of coastal protection works on the Spurn Head spit (UK)

The erosion of the glacial tills along the Holderness Coast (eastern England) has released material which has led to the formation of a 4.5 km sand and gravel spit, Spurn Head, across the mouth of the Humber estuary. This paper examines the sedimentology and geomorphology of the spit and of the tidal flat behind it (Spurn Bight), and assesses the effects of coastal defences on the nearshore dynamics. A study of the coastal dynamics was carried out by analysing wind data and modelling wave shoaling and refraction at the estuary mouth, and on the tidal flat. The geomorphology and sedimentology of the beaches and the tidal flat were studied to assess the response of the spit system to different weather conditions. The results show that only 6% of the longshore drift produced by cliff erosion in Holderness is transported along Spurn Head, mainly by waves from the north and the north-east. This drift is stored in an area of sand and gravel banks at the tip. Medium-size sand is carried around the tip by south-easterly waves, leading to the formation of a small area of tidal sand waves. Waves from the southwest, which originate within the estuary, spread the sand over the tidal flat, but are not able to carry it towards the most northern inner part of the spit. Coastal defences built along the spit have slowed its rate of landward migration and prevented overwash processes. The defences have not been maintained for the last 30 years so that the spit is now likely to be breached in the winter months whenever surge conditions exist.

A Simulation Model of a Complex Recurved Spit

A simulation model of a particular coastal spit is presented to illustrate the value of such models in studying the processes that lead to spit formation. Hurst Castle spit in Hampshire was chosen for the model as it has a distinctive form due to the operation of several easily identified wave types. The processes forming the spit have been discussed by W. V. Lewis. The main ridge, which is composed of shingle, is prolonged by westerly waves, while storm waves build it up. The recurves are formed of material drifted round the end of the main ridge by waves from a southerly point. Waves from the northeast, coming down the Solent, build the lateral recurves. These become longer and more numerous toward the distal end of the spit. The computer program simulates the operation of waves from the west, storm waves, southeasterly waves, and waves from the northeast. In addition, a depth factor simulates the increasing depth of water offshore. This accounts for the increase in number of recurves toward the distal end. A refraction factor allows the curvature of the main ridge to be simulated. The proportion of random numbers allocated to these variables can be adjusted in the data input to elucidate the part they play in the formation of the spit. The close fit of the standard spit to the real spit suggests that the controlling variables are being correctly simulated.

Protection des côtes contre l'érosion maritime et formation des plages de sable Deux problèmes sur la côte du Mozambique

Protection des côtes contre l'érosion maritime et formation des plages de sable Deux problèmes sur la côte du Mozambique