Beach Elevation Research Articles

Dramatic typhoon-induced variability in the grain size characteristics of sediments at a meso-macrotidal beach

Knowledge of sediment grain size characteristics is important for a better understanding of the morphodynamic behavior of beaches worldwide. In this paper, dramatic changes in the grain size of sediments at Yintan Beach, South China in response to Typhoon Rammasun (tropical storm no. 1409) were analyzed on the basis of the collected sediments, beach elevation, and hydrological data from June 1 to July 31. Variations in beach geomorphology were interpreted using the digital elevation taken by LiDAR technology, while changes in sediment grain size were detected by sediment parameters and associated sediment components. The results show that the sediments of Yintan Beach were nearly pure sand before Rammasun and became coarser and slightly better sorted with a higher negative skew after Rammasun. The sediment grain size pattern shifted from a high content (39%) of very fine sand in the lower intertidal zone pre-Rammasun to a high content (76%) of fine sand in the swash zone post-Rammasun. During Rammasun, wave action was responsible for the main transition of grain size pattern in the lower intertidal and mid-tidal zones, and tidal level and beach morphology could affect the grain size distribution of the sandbar and trough in the swash zone. In addition, the increase in the coarse-grained fraction in the upper beach and berm was primarily due to wind action.

Observations of surface cobbles at two southern California beaches

Southern California beaches are often sandy, but with largely undocumented cobble patches and berms. We describe the first multi-year, spatially extensive observations of surface cobbles at southern California beaches. The variation (spatial and temporal) of surface cobble distribution and backshore (e.g. upper foreshore) cobble morphology (slope, vertical extent, and elevation) are characterized using 11 years (2008–2018) of observations spanning 4.8 km of shoreline at Cardiff and Torrey Pines State beaches. Quarterly Global Positioning System surveys of beach elevation and visually identified sediment type (either sand or cobble) are used to create 1076 cross-shore profiles. Cobbles were not exposed continuously at either of these predominantly sandy beaches. The 202 cross-shore profiles with backshore cobbles and sandy foreshores are used for morphology analysis. Consistent with previous studies, cobble and sandy morphologies varied seasonally, and cobbles were most exposed during winter when wave energy increased. Extensive (vertical extent ≥ 2 m) backshore cobbles were usually fronted by low elevation, low slope sandy foreshores. At Torrey Pines cobble patches were occasionally exposed mid-profile on primarily sandy summer beaches. Persistent (2008–2015) backshore cobbles at Cardiff were apparently buried in 2016 by effects of a 2012 sand nourishment. Formation of year-round cobble piles on these seasonally sandy beaches may result from chronically reduced sand input owing to anthropogenic controls on river flooding and coastal cliff erosion (e.g. dams and seawalls).

Analysis of coastal vulnerability of Rangsang Island due to climate changes

Rangsang Island is home to more than 48,000 residents. Climate change has been a critical issue to the Island and threatened the existence of the inhabitants. This study is proposed to identify the zone of the coastal area of Rangsang Island which is vulnerable to climate change. By mapping coastal vulnerability index (CVI) of the island, it is expected to be a reference of local government in planning their spatial management. The method of this study was by a direct survey for collecting data of geomorphology, beach elevation, sea level rise, tidal fluctuation, significant wave height, and changes in the coastline. To determine CVI, each parameter is divided into 5 categories and given a value level: 1 for very not vulnerable, 2 for not vulnerable, 3 for moderate, 4 for vulnerable, and 5 for very vulnerable. The results show that most villages on the island are classified as highly vulnerable to climate change, namely 9 villages. Even 2 villages are threatened very high risk because the village has CVI more than 12.5. Only 6 villages whose territory has moderate vulnerability index. Vulnerability level of coastal Rangsang Island is strongly influenced by geomorphological variable and coastal elevation. In addition, the variable coastline changes and sea level rise also contributed to the vulnerability index of the Island.

Storm response of a mixed sand gravel beach ridge plain under falling relative sea levels: A stratigraphic investigation using ground penetrating radar

AbstractBeach ridge stratigraphy can provide an important record of both sustained coastal progradation and responses to events such as extreme storms, as well as evidence of earthquake induced sediment pulses. This study is a stratigraphic investigation of the late Holocene mixed sand gravel (MSG) beach ridge plain on the Canterbury coast, New Zealand. The subsurface was imaged along a 370 m shore‐normal transect using 100 and 200 MHz ground penetrating radar (GPR) antennae, and cored to sample sediment textures. Results show that, seaward of a back‐barrier lagoon, the Pegasus Bay beach ridge plain prograded almost uniformly, under conditions of relatively stable sea level. Nearshore sediment supply appears to have created a sustained sediment surplus, perhaps as a result of post‐seismic sediment pulses, resulting in a flat, morphologically featureless beach ridge plain. Evidence of a high magnitude storm provides an exception, with an estimated event return period in excess of 100 years. Evidence from the GPR sequence combined with modern process observations from MSG beaches indicates that a palaeo‐storm initially created a washover fan into the back‐barrier lagoon, with a large amount of sediment simultaneously moved off the beach face into the nearshore. This erosion event resulted in a topographic depression still evident today. In the subsequent recovery period, sediment was reworked by swash onto the beach as a sequence of berm deposit laminations, creating an elevated beach ridge that also has a modern‐day topographic signature. As sediment supply returned to normal, and under conditions of falling sea level, a beach ridge progradation sequence accumulated seaward of the storm feature out to the modern‐day beach as a large flat, uniform progradation plain. This study highlights the importance of extreme storm events and earthquake pulses on MSG coastlines in triggering high volume beach ridge formation during the subsequent recovery period. © 2019 John Wiley & Sons, Ltd.

IMPLICATIONS OF CONSOLIDATION ON BARRIER BEACH STABILITY

Barrier beaches often overlie backbarrier deposits composed of poorly consolidated sediments. Hence, they can consolidate significantly if loaded. A retreating barrier beach provides such a load. In the static situation of beach nourishment, the increased load of the raised beach volume will also cause increased consolidation. These can lower beach elevation promoting wave overtopping, overwashing and retreat. However, there is limited research concerning the role of consolidation on the stability of barrier beaches worldwide. This paper focuses on this issue using Hurst Spit on the UK south coast as a study site where consolidation is a known significant process (Nicholls, 1985; Burt et al., 2018). It is a storm beach composed of shingle (pebble and cobble) sediments and formerly retreated at 2 to 3 m/yr, Since the later 1990s it has been more stabilized by a major nourishment (Bradbury and Kidd, 1998), but continues to retreat slowly (Figure 1). A second nourishment phase is now being actively assessed following major damage in the large storm of 14 February 2014. In this context, the role of consolidation has been analyzed via new data collection, consolidation modelling and morphodynamic modelling. This paper presents these results and their implications.

A Bayesian Approach to Predict Sub-Annual Beach Change and Recovery

The upper beach, between the astronomical high tide and the dune-toe, supports habitat and recreation along many beaches, making predictions of upper beach change valuable to coastal managers and the public. We developed and tested a Bayesian network (BN) to predict the cross-shore position of an upper beach elevation contour (ZlD) following 1 month to 1-year intervals at Fire Island, New York. We combine hydrodynamic data with series of island-wide topographic data and spatially limited cross-shore profiles. First, we predicted beach configuration of ZlD positions at high spatial resolution (50 m) over intervals spanning 2005–2014. Compared to untrained model predictions, in which all six outcomes are equally likely (prior likelihood = 0.16), our prediction metrics (skill = 0.52; log likelihood ratio = 0.14; accuracy = 0.56) indicate the BN confidently predicts upper beach dynamics. Next, the BN forecasted three intervals of beach recovery following Hurricane Sandy. Results suggest the pre-Sandy training data is sufficiently robust to require only periodic updates to beach slope observations to maintain confidence for forecasts. Finally, we varied input data, using observations collected at a range of temporal (1–12 months) and spatial (50 m to > 1 km) resolutions to evaluate model skill. This experiment shows that data collection techniques with different spatial and temporal frequencies can be used to inform a single modeling framework and can provide insight to BN training requirements. Overall, results indicate that BNs and inputs can be developed for broad coastal change assessment or tailored to a set of predictive requirements, making this methodology applicable to a variety of coastal prediction scenarios.

Nesting Patterns of Loggerhead Sea Turtles (Caretta caretta): Development of a Multiple Regression Model Tested in North Carolina, USA

Numerous environmental conditions may influence when a female Loggerhead sea turtle (Caretta caretta) selects a nesting site. Limited research has used Geographic Information Systems (GIS) and statistical analysis to study sea turtle spatial patterns and temporal trends. Therefore, the goals of this research were to identify areas that were most prevalent for nesting and to test social and environmental variables to create a nesting suitability predictive model. Data were analyzed at all barrier island beaches in North Carolina, USA (515 km) and several variables were statistically significant: distance to hardened structures, beach nourishment, house density, distance to inlets, and beach elevation, slope, and width. Interestingly, variables that were not significant were population density, proximity to the Gulf Stream, and beach aspect. Several statistical techniques were tested and Negative Binomial Distribution produced good regional results while Geographically Weighted Regression models successfully predicted the number of nests with an average of 75% of the variance explained. Therefore, the combination of traditional and spatial statistics provided insightful predictive modeling results that may be incorporated into management strategies and may have important implications for the designation of critical Loggerhead nesting habitats.

Variability of Wave-induced Current Analyzed with Intensive Field Measurements in the Coastal Waters of Anmok

ABSTRACT Lim, H.S.; Kim, M.; Do, J.-D.; Kim, S.-S.; Lee, H.J., and Kim, D.H., 2018. Variation of nearshore currents induced by seasonal waves in Haeundae. 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. 686–690. Coconut Creek (Florida), ISSN 0749-0208. Wave-induced currents at Anmok, located on the eastern coast of the Korean Peninsula, are one of the main causes of beach erosion related to high waves. Coastline changes induced by beach erosion and deposition are predominantly caused by sediment transport in the surf zone. This sediment transport is generated by wave-induced currents and depends on the wave height and direction. To understand beach erosion processes and the sediment transport mechanisms, field measurements of beach elevation and water depth were conducted for one month in winter 2015–2016. Using AWAC, ADP, VECTOR, and Aquadopp Profiler with OB...

Modelling coastal erosion: A case study of Yarada beach near Visakhapatnam, east coast of India

Prediction of coastal erosion is a challenging field of research with immense application potential in coastal management plans. In the present study, we simulated coastal morphological changes that occurred under normal and extreme wave conditions during a four-month winter monsoon period along a pocket beach at Yarada near Visakhapatnam city. We used Xbeach, a process-based numerical model to simulate the morphological changes by forcing the model with buoy observed wave parameters. Initial beach topography was generated from DGPS profiles surveyed in November 2014 at regular spatial intervals. Model simulated changes in the beach elevation due to accretion and erosion are validated by DGPS profiles re-surveyed in March 2015. During the four-month period, the net sediment transport at Yarada is generally southerly and becomes strong during high wave activity inducing erosion at the northern sector and accretion at the southern sector. The model has simulated the changes in elevation with a high degree of accuracy for the eroded northern sector, and with some disparity along the accreted southern sector. The swash and nearshore processes responsible for the coastal erosion were found to exist throughout the simulation period and intensified during the high wave condition. The paper highlights the importance of modelling studies for conceptual understanding of the beach response to normal and extreme conditions, and for identifying vulnerable sectors of a beach so that appropriate measures can be taken to prevent coastal erosion and loss of land.

Numerical investigation of the impacts of extreme storm waves on coastal erosion in Hujeong Beach using XBeach model

The east coast of Korea occasionally suffers from the extreme storms developed by the winter time extratropical cyclones in the East/Japan Sea. The damages from these storms are not only due to strong winds but also due to high waves that cause severe coastal erosions. In October, 2006, storm waves were observed higher than 6 meters, the highest record in the past 15 years. In this study, we performed a numerical experiment to predict possible erosion rates by simulating the 2006 storm condition in Hujeong Beach as this area is listed as one of the sites that have highest waves among the beaches along the east coast of Korea. For this we employed XBeach nearshore process model because it is specifically designed for the computation of coastal response during time-varying storm conditions. For XBeach modeling conditions, we also used SWAN model to calculate wave parameters based on the observations during the 2006 storm event. The grid spacing is set as fine as 5 m to resolve the minute changes in the nearshore region where seabed topography is complex due to sand bars. We ran XBeach for 48 hours during which the wave height at Hujeong Beach increased from ~1 to ~7m in the first 20 hours. The results show that the shoreline is retreated ~10m on average during the storm period. However, the erosion becomes more severe with maximum retreat of ~30m at the mouth of a stream where the original beach elevation was relatively lower. The eroded sediments are then cumulated outside the swash zone, which shows that the sand is conserved in the shallow region between the coastline and the sand bars. However, some of the crests of the sand bars are lost to offshore, indicating that total sand in the whole nearshore region may not be conserved under this high wave conditions.

LIDAR-based detection of the post-typhoon recovery of a meso-macro-tidal beach in the Beibu Gulf, China

Because of global sea-level rising with frequent storm activities, most beaches in the world experience widespread erosion, which poses a significant hazard to beach management. The morphodynamic process of the evolution of a beach in response to storm activities is of increasing concern. Using a terrestrial laser scanner, the topography of Yintan beach was continuously observed for 33days with a 25cm spatial resolution digital elevation model (DEM) of that covered an area of 15ha before and after typhoon Rammasun. The short-term beach recovery was explored using a comprehensive approach, which included grey relational analysis, terrain analysis, Gaussian fitting, Gamma fitting, and Delft3D wave simulation methods. The results show that the Yintan beach recovery process can be divided into three stages with two transition points. Stage one began at the end of Rammasun, which indicated a weakly stable state with an average daily net erosion of −588m3, a mean beach slope that ranged from 0.96° to 1.28°, and a landform with no obvious alterations. After the vast accretion of 6874m3 of first transition, stage two, which was characterized by oscillations, occurred in the region with an average daily net erosion of −396m3 and a conspicuous beach slope reconstruction in the range of 0.94°–2.16°. During this stage, sandbar reconstruction played a key role. The second transition event arose at the end of stage two with a vast accretion of 5762m3. Afterwards, the daily net accretion of 200m3 and the beach slope range of 0.93°–1.74° dominated the region during stage three, and the beach surface became similar to that of the pre-Rammasun. Within the entire observation period, intense beach elevation changes that ranged from −15cm to −6cm and 6cm to 15cm mainly occurred in the sandbar and foreshore zones, respectively. Additionally, slight elevation changes (ranging from −4cm to 4cm) were densely distributed in the backshore and dunes, and moderate elevation changes (ranging from −6cm to −4cm and 4cm to 6cm) emerged along the entire beachface. It was concluded that the spatial distribution of the bottom shear stress that was induced by wave action was responsible for the reconstruction of the foreshore and sandbar after Rammasun, whereas the short-term beach recovery process was affected by the beach states in various wave breaking conditions.

Application of marine radar to monitoring seasonal and event-based changes in intertidal morphology

This paper demonstrates the application of marine radar and a newly developed waterline mapping technique to the continued surveillance and monitoring of inter- and intra-annual intertidal morphological change, thus capturing new detail on coastal system behaviours. Marine radar data from 2006 to 2009 are used to create a sequence of waterline elevation surveys that show clear morphological evolution of two different sites in the Dee estuary, UK. An estimate of volumetric change was made at two locations: West Hoyle sandbank and the NW Wirral beach. Both sites exhibited a similar cyclic pattern of volumetric change, with lowest volumes in autumn and winter, respectively. The average beach elevations above Admiralty Chart Datum clearly reflect the observed change in sediment volume, with reduced elevations in winter and increased elevations in summer, suggesting a trend of high-energy storm waves in autumn and winter that remove sediment and simultaneously moderate the vertical dimension of bedforms in the intertidal area. Data at this temporal and spatial scale are not easily obtainable by other current remote sensing techniques. The use of marine radar as a tool for quantifying coastal change over seasonal and event timescales in complex hydrodynamic settings is illustrated. Specifically, its unique application to monitoring areas with dynamic morphology or that is vulnerable to erosion and/or degradation by storm events is exemplified.

Sedimentological records of the C.E. 1707 Hōei Nankai Trough tsunami in the Bungo Channel, southwestern Japan

A tsunami generated by the C.E. 1707 Hōei earthquake is largely thought to be the flood event of record for southwestern Japan, yet historical documentation of the event is scarce. This is particularly true within the Bungo Channel, where significant inconsistencies exist between historical records and model-derived tsunami heights. To independently assess flooding from the Hōei tsunami in this region, we present complementary reconstructions of extreme coastal inundation from three back-barrier lakes in the northern Bungo Channel: Lake Ryuuoo, Lake Amida, and Lake Kamega. At all sites, the age of the most recent prominent marine overwash deposit is consistent with the timing of the 1707 tsunami. When combined with historical documentation of the event, these sedimentological records provide strong evidence that the 1707 tsunami is the most significant flood of recent centuries and one of the most significant floods over the last millennium in the region. At Lake Ryuuoo, modern barrier beach elevations and grain sizes in the tsunami’s resultant deposit provide ~4 m as the first physically based height constraint for the 1707 tsunami in the northern Bungo Channel. A concurrent transition in lithology that is consistent with regional geomorphic change is also observed at all three sites around 1000 years ago, although the precise timing and nature of the transition remain unclear.

Multiscale impacts of armoring on Salish Sea shorelines: Evidence for cumulative and threshold effects

Shoreline armoring is widespread in many parts of the protected inland waters of the Pacific Northwest, U.S.A, but impacts on physical and biological features of local nearshore ecosystems have only recently begun to be documented. Armoring marine shorelines can alter natural processes at multiple spatial and temporal scales; some, such as starving the beach of sediments by blocking input from upland bluffs may take decades to become visible, while others such as placement loss of armoring construction are immediate. We quantified a range of geomorphic and biological parameters at paired, nearby armored and unarmored beaches throughout the inland waters of Washington State to test what conditions and parameters are associated with armoring. We gathered identical datasets at a total of 65 pairs of beaches: 6 in South Puget Sound, 23 in Central Puget Sound, and 36 pairs North of Puget Sound proper. At this broad scale, demonstrating differences attributable to armoring is challenging given the high natural variability in measured parameters among beaches and regions. However, we found that armoring was consistently associated with reductions in beach width, riparian vegetation, numbers of accumulated logs, and amounts and types of beach wrack and associated invertebrates. Armoring-related patterns at lower beach elevations (further vertically from armoring) were progressively harder to detect. For some parameters, such as accumulated logs, there was a distinct threshold in armoring elevation that was associated with increased impacts. This large dataset for the first time allowed us to identify cumulative impacts that appear when increasing proportions of shorelines are armored. At large spatial and temporal scales, armoring much of a sediment drift cell may result in reduction of the finer grain-size fractions on beaches, including those used by spawning forage fish. Overall we have shown that local impacts of shoreline armoring can scale-up to have cumulative and threshold effects -- these should be considered when managing impacts to public resources along the coast.

Nest site selection minimizes environmental stressor exposure in the American horseshoe crab, Limulus polyphemus (L.)

The American horseshoe crab, Limulus polyphemus, migrates to beaches at Seahorse Key, FL, on the highest-high tides to mate and deposit clutches of fertilized eggs. By nesting at high beach elevations, females may increase hatching success by minimizing exposure of the developing eggs to hypoxia and hydrogen sulfide, although at the potential added cost of increased exposure to harmful high temperatures. To test this, we took a two-fold approach: 1) we determined microclimate conditions experienced by developing horseshoe crab eggs at a nesting site on the Gulf Coast of Florida, and 2) in laboratory-rearing experiments we determined whether developmental success was affected by exposure to temperature, ambient O2 and sulfide conditions modeled on values from potential nesting sites. We found that most horseshoe crabs nested in the high and extreme-high tidal height zones above the high tide line. These high-tidal areas were characterized by normoxia, temperatures exceeding 35°C, and minimal exposure to hydrogen sulfide. When fertilized eggs and larvae were exposed to similar “control” conditions in the laboratory, eggs and larvae exhibited 80–90% developmental success. The mid-tidal height zone was characterized by temperatures exceeding 35°C, 21–17% ambient O2, and minimal exposure to hydrogen sulfide. When exposed to similar mid-tidal conditions in the laboratory, development success was equivalent to eggs exposed to control conditions. In contrast, the low tidal height zone was characterized by temperatures never exceeding 35°C, ambient O2 as low as 5.9%, and significantly greater exposure to hydrogen sulfide. In the laboratory, exposure to conditions similar to low-tidal zone resulted in developmental success that was reduced by up to 25% compared to the eggs and larvae exposed to control conditions. We conclude that horseshoe crabs choose nesting sites that maximize developmental success by avoiding sites containing hypoxia and hydrogen sulfide, although this increases exposure to high temperature.

The late Nordic Iron Age and Viking Age royal burial site of Borre in Norway: ALS- and GPR-based landscape reconstruction and harbour location at an uplifting coastal area

The Nordic Iron Age and Viking Age royal burial site of Borre on the western coast of the Oslofjord in Norway is an exceptional archaeological site in Northern Europe. The burial mounds, associated archaeological structures as well as geomorphological features have been analysed by a 1 × 1 m digital terrain model derived from airborne laser scanning. The interpretation of this data used different derivates of the digital elevation model including hillshade, slope map, local relief model and their combination. Additionally, ground penetrating radar profiles have been measured to investigate the internal structure of selected micro-topographic features. Based on the high-resolution topographic data, four smaller burial mounds were added to those previously known. Scandinavia is strongly affected by ongoing post-glacial isostatic recovery and, consequently, a sequence of elevated beach ridges were documented within the burial site down to the present shoreline. Local sea-level reconstructions in the Oslofjord indicate that the burial site of Borre was located close to the shoreline in the period of its use when the local sea-level was 3.5–5 m higher than today. Two prominent ridges between 4.5 and 0 m above present day sea-level are interpreted as Viking Age jetties facilitating safe landing on an otherwise unprotected coast.

A simplified approach for simulating changes in beach habitat due to the combined effects of long-term sea level rise, storm erosion, and nourishment

Better understanding of the vulnerability of coastal habitats to sea level rise and major storm events are aided by the use of simulation models. Since coastal habitats also undergo frequent nourishment restoration works in order to maintain their viability, vulnerability models must be able to assess the combined effects of sea level rise, storm surge, and beach nourishment. The Sea Level Affecting Marshes Model (SLAMM) was modified and applied to quantify the changes in the beach area in a 5-km stretch of beach in Santa Rosa Island, Florida due to these combined effects. A new methodology to estimate spatial erosion patterns was developed based on measured erosion during three historic storm events representing a wide range of storm intensities over the study area (named storms Ivan (H5), Dennis (H4), and Katrina (TS)). Future major storms over the 2012-2100 period were generated based on the frequency distribution of historic storms using 4000 simulations to account for uncertainty in the storms temporal distribution. Potential effects of individual, successive, and random storms occurring over the area under 0-1.5 m nourishment schemes were evaluated. The risk of losing the beach habitat in 90 years for different scenarios is studied based on probability distribution contours constructed with the model results. Simulation results suggest that without nourishment, a major storm with a category of tropical storm or higher will reduce the beach at the end of the period by 97-100%. This loss can be reduced to 60% by maintaining a 1-m beach elevation and can further be reduced to 34% with 1.5 m beach nourishment.

Morphodynamics of a Nontidal Embayed Beach: The Case Study of Is Arutas (Western Mediterranean)

Simeone, S.; Palombo, L., and De Falco, G., 2013. Morphodynamics of a nontidal embayed beach: the case study of Is Arutas (western Mediterranean).This study evaluates the reliability of the Short morphodynamic model by using experimental data on the wave climate, sediment budget, and topographic beach profiles of an embayed beach located in western Sardinia, Mediterranean Sea. Wave parameters, measured by an offshore buoy located to the NW of Sardinia were downloaded daily, from the Rete Ondamentrica Nazionale Web site. Beach elevation data were collected in 2005 and 2010, using a Differential Global Positioning System, to determine the volume of beach sediments. Three beach profiles were measured in the northern, central, and southern areas of the beach from September 2010 to May 2011 to investigate morphological variability. Grain-size and composition of beach sediments were determined.From 2005 to 2010, the sediment volume did not show any significant changes (14,200 m3 and 13,800 m3, respectively). Sediments were sandy to gravelly, whereas the composition was siliciclastic. Morphological variability occurred in the swash zone, where the northern and southern profiles showed an opposite trend, in terms of changes in elevation. This was related to the longshore redistribution of sediments and occurred mainly during the autumn–winter season. The Short model revealed that, for 98% of the available data, Is Arutas assumed a “normal” or “transitional” morphodynamic state. The sediment remained constrained between the headlands, in accordance with the results of the Short model, which showed the assumed morphodynamic states did not implicate the transport of sediment outside the system.Experimental data confirmed that the Short morphodynamic model can be applied to studies on sediment exchange on embayed Mediterranean beaches.

A comparison of the post-storm recovery of two sandy beaches on Hong Kong Island, southern China

Typhoon Hagupit was one of six tropical cyclones that affected Hong Kong in 2008. When the typhoon made landfall, the combined effect of the waves, storm surge and seasonal high tides resulted in a maximum sea level of 3.53 m at the nearest tide gauge to the study site, the highest since 1962. The event caused considerable damage to coastal infrastructure and large-scale erosion on many sandy beaches in Hong Kong. To study the degree of erosion and recovery of Hong Kong beaches, we surveyed two sandy beaches: Tai Long Wan (TLW), a relatively high-energy exposed beach system, and To Tei Wan (TTW), a relatively low-energy Sheltered beach system. We examined the two beaches for changes in their beach profiles and sediment properties. TLW recovered quickly, with significant post-storm accretion of fine- to medium-grained sand. Within four months after the typhoon, TLW regained >700 m3 sand, forming a new, ∼1.0 m high, berm, with the beach face prograding approximately 5.0 m seaward. In contrast, within the same four months after the typhoon, TTW showed little evidence of sand accretion or recovery, with only minor changes in the beach profile. In fact, instead of post-storm sand accretion, the landward migration of the high tide mark shown in the pre- and post-storm satellite images suggested that the post-storm beach elevation at TTW decreased. The results, which reflect the different background energy regimes of each beach, indicate that different coastal management strategies should be applied. In the case of relatively high-energy beaches of Hong Kong, we suggest not interfering with their natural state. In contrast, in the case of relatively low-energy beaches of Hong Kong, which appear unlikely to recover rapidly from erosion during storms, we suggest further investigation before applying any long- to medium-term management strategies.

Coastal geomorphic conditions and styles of storm surge washover deposits from Southern Thailand

The characteristics of tropical storm washover deposits laid down during the years 2007 to 2011 along the southern peninsular coast of the Gulf of Thailand (GOT) were described in relation to their different geomorphic conditions, including perched fan, washover terrace and sheetwash lineations preserved behind the beach zone within 100m of the shoreline. As a result, washover terrace and sheetwash lineations were found where the beach configuration was uniform and promoted an unconfined flow. Non-uniform beach configurations that promoted a confined flow resulted in a perched fan deposit. Washover sediments were differentiated into two types based on sedimentary characteristics, including (i) a thick-bedded sand of multiple reverse grading layers and (ii) a medium-bedded sand of multiple normal grading layers. In the case of thick-bedded washover deposits, the internal sedimentary structures were characterized by the presence of sub-horizontal bedding, reverse grading, lamination, foreset bedding and wavy bedding, whereas, horizontal bedding, normal grading, and dunes were the dominant structures in the medium-bedded washover sand. Rip-up clasts were rare and recognized only in the washover deposits in the bottom unit, which reflects the condition when a mud supply was available. All washover successions were found in the landward inclined-bedding with a basal sharp contact. A high elevated beach ridge associated with a large swale at the backshore proved suitable for a thick-bedded washover type, whereas a small beach ridge with uniformly flat backshore topography promoted a medium-bedded washover sediment.