共查询到20条相似文献，搜索用时 171 毫秒
1.
Alan L. Shanks Steven G. Morgan Jamie MacMahan Ad J.H.M. Reniers Marley Jarvis Jenna Brown Atsushi Fujimura Lisa Ziccarelli Chris Griesemer 《Estuaries and Coasts》2018,41(1):158-176
Surf zones, regions of breaking waves, are at the interface between the shore and coastal ocean. Surf zone hydrodynamics may affect delivery of phytoplankton subsidies to the intertidal zone. Over a month of daily sampling at an intermediate surf zone with bathymetric rip currents and a reflective surf zone, we measured surf zone hydrodynamics and compared concentrations of coastal phytoplankton taxa in the surf zones to concentrations offshore. At the intermediate surf zone, ~80% of the variability in the concentration of coastal phytoplankton taxa within the surf zone was explained by their variation offshore; however, concentrations were much higher and lower than those offshore in samples from a bathymetric rip current and over the adjacent shoal, respectively. Hydrodynamics at this intermediate surf zone did not hinder the delivery of coastal phytoplankton to the surf zone, but the bathymetric rip current system appeared to redistribute phytoplankton concentrating them within eddies. At the reflective shore, we sampled surf zones at a beach and two adjacent rocky intertidal sites. Concentrations of typical coastal phytoplankton taxa were usually an order of magnitude or more lower than those offshore, even when offshore samples were collected just 20 m beyond the breakers. The phytoplankton assemblages inside and outside the surf zone often appeared to be disconnected. Surf zone hydrodynamics at the steep, reflective shore coupled with low phytoplankton concentrations in near-surface water appeared to limit delivery of phytoplankton subsidies to the surf zone. Surf zone hydrodynamics may be a key factor in the alongshore variation in phytoplankton subsidies to coastal communities. 相似文献
2.
Many drowning and near drownings at Pensacola Beach, Florida are attributed to rip currents, the strong seaward-flowing currents that extend from the shoreline to the line of breakers and sometimes beyond. While surf forecasts assume that the rip hazard is uniform alongshore and that the (erosion) rips are ephemeral features, evidence is presented to suggest that the rip hazard at Pensacola Beach is not uniform alongshore. Rather the rip current “hotspots” develop as a consequence of an alongshore variation in the surf similarity parameter and nearshore state on the order of ~1,450 m. The variation is forced by transverse ridges on the inner shelf that force wave refraction and focusing at the ridge crests. This creates a more dissipative, rhythmic bar and beach morphology at the ridges and rougher surf. Between ridges, where wave heights and periods are smaller and the outermost bar is forced closer to the shoreline, the nearshore is in a (more reflective) bar and rip state during red flag conditions. Drownings between 2000 and 2009 are shown to be clustered between transverse ridges and in the years following a hurricane or tropical storm (2000–2003 and 2005–2008) when the bar and rip morphology first develops as the shore face recovers. This continues until the innermost bar attaches to the beach face unless the bar system is reset by another tropical storm or hurricane. It is argued that the rip hazard is dependent on the alongshore covariation of the environmental forcing with the individual and group behavior in both time and space, even on what appears to be a relatively uniform beach environment. 相似文献
3.
Perception of the rip current hazard on Galveston Island and North Padre Island,Texas, USA 总被引：1，自引：1，他引：0
Christian Brannstrom Sarah Trimble Anna Santos Heather Lee Brown Chris Houser 《Natural Hazards》2014,72(2):1123-1138
The hazard posed by a rip current depends in part on the ability of beach users to identify a rip current and to associate surf conditions with the potential for rip currents. Understanding which visual features beach users associated with rip currents is an important step in the development of appropriate programs and educational materials aimed at improving the ability of beach users to identify a rip current. A face-to-face survey (n = 392) was conducted to assess the ability of beach users to identify a rip current using five near eye-level photographs that simulate the view of the beach and surf zone as the respondent approached the beach. The survey was conducted on three heavily used public beaches in Texas (Galveston, Port Aransas, and Corpus Christi) at the height of the summer beach season in 2012. Only 13 % of respondents correctly selected the photograph showing the most hazardous conditions and correctly identified the precise location of the rip current on the photograph. The majority of beach users (87 %) incorrectly indicated that the photograph with the heaviest surf represented the most hazardous surf conditions and greatest potential for the development of rip currents, or failed to identify rip currents in photographs. Respondents who were able to correctly identify the rip current tended to recognize the breaking wave pattern, areas of darker water, or the proximity to structures as key visual characteristics of rip currents and also had higher self-reported abilities to swim in rough water and escape a rip current. 相似文献
4.
Quasi-permanent rip current hot spots at Pensacola Beach, Florida, pose a significant hazard to beach users, largely because the hot spots are located at or close to the primary access points. While an increase in the number of lifeguards has led to a decrease in the number of drownings since 2004, the number of rescues and contacts has increased to over a 30,000 year. Despite warning signs at access points along the beach, it is not clear whether beach users are able to identify a rip channel or an active rip current. To assess beach users’ knowledge of rip currents and their ability to identify rip channels and currents, 97 surveys were conducted between June and September of 2010 at Pensacola Beach. Beach users were asked to identify rip channels in oblique photographs taken on green, yellow and red flag days when the potential for rip currents is low, medium and high, respectively. A majority of participants suggested that they could identify a rip channel or current (if present), but less than 20 % of beach users were able to identify the rip channels and currents. The majority of participants identified heavy surf areas as the location of the rips versus the relatively flat water of the current or the darker color water of the channel. Results further suggest that most beach users, and particularly local participants, are overconfident in their ability to identify rip channels and currents. The focus of beach users on heavy surf as an indication of the rip current potential and the overconfidence in identifying a rip channel or current affects the spatial distribution of beach users and to some degree the location of rescues and drownings. While it can be quite difficult for the average beach user to identify rip channels and active rip currents, the results of the study suggest a need for further education efforts to reduce the rip hazard, particularly in areas where lifeguards are not permanently stationed. 相似文献
5.
6.
Evaluation of swimmer-based rip current escape strategies 总被引：2，自引：1，他引：1
R. Jak McCarroll Robert W. Brander Jamie H. MacMahan Ian L. Turner Ad J. H. M. Reniers Jenna A. Brown Anthony Bradstreet Shauna Sherker 《Natural Hazards》2014,71(3):1821-1846
Rip currents are the primary hazard on surf beaches, and early studies described them as fast, shore-normal flows that extended seaward of the surf zone. Based on this traditional view, commonly promoted safety advice was to escape a rip current by swimming parallel to the beach. However, recent studies have shown dominant rip current re-circulation within the surf zone and have endorsed floating as an appropriate escape strategy. Here, a first quantitative assessment of the efficacy of various rip current escape strategies, with a focus on the underlying physical processes, is presented. A field study was conducted at Shelly Beach, NSW, Australia, measuring three rip currents (two open beaches, one topographic) over 3 days in varying wave conditions. Floating was found to be a longer duration, more variable escape strategy ( $ \overline{t} $ = 3.8 min, σ = 2.4 min), than swimming parallel ( $ \overline{t} $ = 2.2 min, σ = 1.0 min). Neither of the scenarios is 100 % foolproof, and both fail in some scenarios, making simplified safety recommendations difficult. Swim parallel failures are related to swimming against the alongshore current of the rip circulation. Float failures related to surf zone exits, with the highest exit rate occurring in the topographic rip. Float failures also occurred due to multiple re-circulations without the person attaining safe footing on the bar. The variable spatial and temporal behaviour of rip currents suggests that a single escape strategy safety message is inappropriate. Instead, a combined approach and scenario-specific safety advice should be considered by beach safety practitioners to promote to the public. 相似文献
7.
Ménard A. Dana Houser Chris Brander Robert W. Trimble Sarah Scaman Alexandra 《Natural Hazards》2018,94(2):953-973
Natural Hazards - The rip current hazard on beaches is a global public health issue. While physical controls on rip current formation and flow behavior are relatively well understood, there has... 相似文献
8.
This study analyzes fatalities caused by rip currents in important locations along east and west coasts of India for the period 2000–2010. Results include the frequency of fatalities from rip currents, their cause, and their spatial distributions. Rip current fatalities are most common in the southeastern India, with a non-uniform spatial distribution. August and October are identified as most favorable for rip current generation. In India, rip current-related drowning is estimated as 39 per year during the last decade. East coast of India averaged 30–40 drownings, and west coast of India averaged 5–10 drownings per year. In coastal Andhra Pradesh, more than 350 people had been drowned due to rip currents and only 10 people were rescued. Visakhapatnam recorded highest drowning (293); R. K. beach is the most vulnerable potential rip current zones. From 2007 onward, rip current deaths increased at an alarming rate. The frequency of rip current drownings increased markedly during shore-normal wave incidence and mid-low tidal stages. A new empirical forecasting technique has been developed for prediction of rip current risk in India for the first time. FORTRAN-based software was developed to generate automatic rip current forecast report for any given location. The scale’s performance was tested with field data and by using different statistical methods. The new predictive scale is predicting rip current occurrences reasonably well. 相似文献
9.
Rip currents represent significant hazards to swimmers all around the world. The danger arises when a misinformed swimmer uses an inadequate strategy to escape the rip, such as fighting the current directly. This can lead to fatigue, panic, and in some cases drowning. There exists a range of strategies put forward by experts (both lifeguards and scientists) to escape rip currents. However, these recommendations are based on a limited number of scientific studies and there is still much discrepancy surrounding the best strategy to escape a rip. Thus, here we present a simple, physics-based theoretical model aimed at assessing different escape strategies in terms of their associated ‘energetic cost’ (in work and power) for any given rip current and swimmer’s proficiency level. Many combinations of swimmers and rips are considered, including both idealised and a realistic rip current. Our quantitative results back the common knowledge that swimming against the rip (which is strongly discouraged by lifeguards) is almost universally the worst possible strategy, especially when compared against strategies favoured by experts, such as floating with the current before attempting to swim back to the shore. For a realistic rip, our results suggest that swimming directly against the rip can require several times more power from the swimmer than other strategies advised by lifeguards, thus lending further scientific support to experts’ recommendations. This study may help promote education around the dangers posed by rip currents and how best to address them.
相似文献10.
Rip currents as a geological tool 总被引：2，自引：0，他引：2
MICHA&#; GRUSZCZY&#;SKI§ STANIS&#;AW RUDOWSKI† JULIA SEMIL‡ JAN S&#;OMI&#;SKI† JERZY ZROBEK‡ 《Sedimentology》1993,40(2):217-236
This paper considers the nature and sedimentary significance of rip currents. Rip currents are the main factor responsible for the transport of coarse sediments from the littoral zone to greater depths. Such sediments, deposited outside the zone of wave deformation, may be identified as storm rip current increments within sediments deposited during fair weather. Composite beds deposited during a given wave cycle by storm rip currents are closely similar to ‘turbidites’ and many so called ‘fluxo-turbidites’ described from flysch deposits. Using data gathered in studies conducted on the modern Baltic coast, supplemented by experimental work and theoretical considerations, a sedimentary model is proposed. The model may be used to interpret possible rip current deposits among shallow water ‘turbidites’, and both modern storm sediments and ancient ‘tempestites’. 相似文献
11.
Drowning accidents at beach in Japan are caused by rip currents. To reduce these accidents, a new technology that can detect rip currents and notify beachgoers by using the Internet of Things (IoT) and Artificial Intelligence (AI) was proposed. However, studies on the effect of visualizing rip currents or considering the effect of optimism bias have not been conducted. This study investigates if visualization of rip currents might help in preventing drowning accidents, while considering the effect of optimism bias. The participants were 90 Japanese beachgoers. They were asked to answer questions based on their knowledge of the beach and rip currents, their optimism bias regarding rip currents, and awareness with or without visualization. The results of the analyses suggest that despite optimism bias, the visualization of rip currents increases the tendency of beachgoers to perceive and avoid rip currents. As described above, it was found that by visualizing the rip current, beachgoers were able to perceive and avoid rip currents. In addition, an understanding of rip currents is positively related to the intent to avoid rip currents even when rip currents are visualized. Therefore, it is necessary not only to enhance the avoidance tendency by visualizing rip currents, but also to further enhance knowledge of beachgoers to deepen the understanding of rip currents including the danger associated and methods to avoid them.
相似文献12.
An examination of rip current fatalities in the United States 总被引：1，自引：1，他引：0
This study analyzes fatalities caused by rip currents in the conterminous United States for the period 1994–2007. Results
include the frequency of fatalities from rip currents, their cause, and their unique spatial distributions. An analysis of
historical hazard event data illustrate that, on average, 35 people reportedly die from rip currents each year in the United
States. Also, similar to other hazard events where unique differences in gender vulnerability have been found, men are over
six times more likely to fall victim to a deadly rip current than females. Rip current fatalities are most common in the southeastern
United States, with a nonuniform spatial distribution along other Atlantic, Pacific, and Great Lakes coastlines. Physical
vulnerabilities are suggested as the primary cause for the unique fatality distribution found. Temporally, summer season weekends
are shown to have the more fatalities than any other time of the year. A classification scheme was developed to categorize
synoptic-scale weather conditions present during deadly rip current events. More than 70% of all rip current fatalities are
associated with onshore winds. Specifically, a rip current fatality is most likely when a surface high pressure system creates
these onshore winds. The quality of the fatality reporting database available for researchers is also assessed. 相似文献
13.
为研究叠加波浪场的裂流特征,在平直沙坝海岸地形进行了叠加波浪形成的沿岸波高周期性变化的裂流试验研究。试验中叠加波浪是由波浪在垂直岸线的丁坝反射所形成的两列交叉波浪叠加产生,交叉波浪是具有等频率但入射角相反的两波列。通过对叠加波浪节腹点垂直岸线位置浪高的测量和沙坝范围内沿岸布置的声学多普勒测速仪流速测量结果来分析沙坝海岸丁坝反射波形成的裂流特性,讨论了波浪节腹点对裂流位置和裂流空间尺度的影响。对不同周期情况在x=5 m沙坝顶处的速度剖面对比,分析了不同周期对裂流的影响。 相似文献
14.
Stefania Venturi Franco Tassi Orlando Vaselli Georges E. Vougioukalakis Heba Rashed Christos Kanellopoulos Chiara Caponi Francesco Capecchiacci Jacopo Cabassi Andrea Ricci Luciano Giannini 《Natural Hazards》2018,90(2):601-621
Rip currents are fast moving, offshore flows that have the ability to move even the strongest swimmers into deeper waters. Miami Beach, Florida is one of the most visited beaches in the USA and a sought after destination for citizens and international tourists alike. It is also known to be a rip current “hot spot.” These factors greatly increase the risk of drowning; however, no previous research has focused on beachgoer perception of rip-related risks in South Florida. Over a 12-month period, 203 public surveys were collected to determine the rip current knowledge of beachgoers at Miami Beach based on factors such as swimming ability and frequency of beach visits. The responses were analyzed by constructing a normalized component factor to determine the respondent’s comprehensive knowledge of rips, and multiple regression models were used to assess the net influences of sociodemographic and behavioral characteristics on the responses. A significant proportion of the survey respondents showed insufficient knowledge, indicating they are at risk of drowning in a rip current. Frequent beachgoer’s exposure to the beach environment, maturation, and nativity is identified as the main contributors to knowledge net of other sociodemographic compositions. The most at-risk groups were determined to be young adults, foreign tourists, poor swimmers, and those who infrequently visited the beach. Miami Beach needs to initiate a rip current safety campaign to target these at-risk beachgoers, where interventions beyond familial and educational institutions should be introduced. 相似文献
15.
The quantification of groundwater flow near the freshwater–saltwater transition zone at the coast is difficult because of variable-density effects and tidal dynamics. Head measurements were collected along a transect perpendicular to the shoreline at a site south of the city of Adelaide, South Australia, to determine the transient flow pattern. This paper presents a detailed overview of the measurement procedure, data post-processing methods and uncertainty analysis in order to assess how measurement errors affect the accuracy of the inferred flow patterns. A particular difficulty encountered was that some of the piezometers were leaky, which necessitated regular measurements of the electrical conductivity and temperature of the water inside the wells to correct for density effects. Other difficulties included failure of pressure transducers, data logger clock drift and operator error. The data obtained were sufficiently accurate to show that there is net seaward horizontal flow of freshwater in the top part of the aquifer, and a net landward flow of saltwater in the lower part. The vertical flow direction alternated with the tide, but due to the large uncertainty of the head gradients and density terms, no net flow could be established with any degree of confidence. While the measurement problems were amplified under the prevailing conditions at the site, similar errors can lead to large uncertainties everywhere. The methodology outlined acknowledges the inherent uncertainty involved in measuring groundwater flow. It can also assist to establish the accuracy requirements of the experimental setup. 相似文献
16.
Lagrangian flow of two rip currents was measured using human drifters to understand how variations in surf zone circulation
affect exit positions of floating swimmers. Based on these results, two escape strategies were assessed, ‘do nothing’ and
‘swim parallel to the beach’. The drifter paths and exit positions were analysed to determine the best escape strategy for
passive swimmers in each scenario. Of the two methods, doing nothing to allow the rip current to take a swimmer is the most
effective strategy. More than 75% of rip current flow scenarios could hinder chances of escape of swimmers if the wrong direction
was chosen to swim parallel to the beach to safety. This is because in many situations a swimmer encounters not only a rip
current flowing offshore but also a longshore current flowing parallel to the beach. The best education campaign for the public,
in addition to only swimming on a patrolled beach, would be to promote the ‘do nothing’ rip current escape strategy, as it
covers all flow scenarios without reducing a swimmer’s chance of survival. 相似文献
17.
Considering the diversity of rip currents based on the classification of Castelle et al. (2016), it is crucial to study the characteristics of each individual rip current type, which are classified based on different dominant controlling forces and physical driving mechanisms. In this study, an analytical model was presented to predict the spacing of channel rip currents \((S_{\mathrm{rip}})\) in intermediate beaches using the equations of continuity and momentum. Then, the analytical model predictions were compared with the results of numerical simulations calibrated with field studies of other researchers, that showed good agreements. The main results of this study showed that rip spacing was simultaneously related to the characteristics of wave and bed in the surf zone. In addition, it was shown that due to inevitable changes of the hydrodynamic and morphological conditions of rip channel in the beach, the parameter \(H_{b0}/h_{c}\) (where \(H_{b0}\) is the wave height before approaching the sand bar and \(h_{c}\) is channel depth) is an important factor in predicting the rip current situation and the changes of the beach state with time. 相似文献
18.
为揭示潮汐流影响下珊瑚岛礁附近波浪的运动特征,通过波流水槽试验对潮汐流存在下规则波的传播变形和增水规律进行了研究,测试了一系列的潮汐流流量并对比正向流、反向流以及无流的情况。研究结果表明:反向流使波浪破碎点向远海侧移动,正向流则使其向海岸侧移动,反向流存在时破碎带内的湍流较正向流时更为剧烈;反向流时破碎点附近入射波能量由主频波向高次谐波发生转移更为显著;潮汐流的存在对波浪反射、透射和能量耗散并无明显影响;正向流造成礁坪上波浪增水减少,反向流则促进增水的增长,增水最大值与潮汐流流量间存在显著的线性关系。研究成果可望为岛礁工程的建设和维护提供一定的理论参考。 相似文献
19.
Lithofacies in the mid‐Permian Nowra Sandstone indicate a middle/upper shoreface to foreshore environment of deposition under the influence of storm‐generated waves and north‐northeasterly directed longshore currents. Palaeogeographic reconstruction for the Nowra Sandstone portrays a sand‐dominated high energy shelf and offshore shoal forming a sequence thickening seaward away from the western shore of the Sydney Basin. The shoal‐crest at the outer edge of the shelf trends north‐northeast. It is characterized by fine‐ to medium‐grained sandstone with upper flow regime structures and a high proportion of conglomerate, whereas coarser sandstone with lower energy bedforms occurs along the seaward side of the shoal. In the deeper water to the east, the lower Nowra Sandstone becomes rapidly thinner as it passes seaward, via bioturbated storm redeposited sandstone beds, into the shelf deposits of the Wandrawandian Siltstone. This sequence accumulated during a regressive event and the base of the formation becomes progressively younger eastward. The sand may have been supplied by rivers along the western coast but the major source was south of the study area. The lower Nowra Sandstone is separated from the upper part of the formation by an extensive ravinement surface overlain by the Purnoo Conglomerate Member. In contrast to the lower unit, the upper Nowra Sandstone forms a westward thickening wedge that represents a backstepping nearshore sand facies that accumulated during a transgression. The upper Nowra Sandstone passes vertically and laterally eastward into the Berry Siltstone. Thus both boundaries of the Nowra Sandstone are diachronous, first younging eastward and then westward as a response to a regressive‐transgressive episode. 相似文献
20.
P. T. Harris P. E. O'Brien P. Quilty A. McMinn D. Holdway N. F. Exon 《Australian Journal of Earth Sciences》2013,60(4):577-591
Digital echo sounding, SeaBeam swath bathymetry data and sediment cores were collected on the continental slope (1500–3700 m water depth) off southeastern Tasmania in order to study sedimentary processes in the vicinity of an ocean disposal site. The new bathymetry data show that the shallower limits of the disposal site are positioned on the seaward edge of a gently dipping (3°) mid‐slope shoulder, between 1200 and 2100 m water depth. The slope below the disposal site is relatively steep (6.5°) and is cut by submarine canyons which lead into the adjacent East Tasman Saddle. The SeaBeam bathymetry data show a small submarine canyon traversing the slope in 2400 m water depth directly downslope from the disposal site, with local slopes of up to 22°. The canyon feeds into a perched basin at 2450 m, which could be acting as a local sediment trap. Short (<90 cm) gravity cores indicate that indurated erosional surfaces characterise the slope environment. The cores contain Upper Cretaceous (upper Campanian) sandstones and siltstones, which in places crop out on the sea floor where they are locally draped by a thin (0–30 cm), modern layer of hemipelagic calcareous ooze. Five cores collected from the vicinity of the disposal site had lead and zinc concentrations in the surface 1 cm of 10.3 ± 5.0 and 39.5 ± 19.6 mg/kg, respectively, significantly greater than the background values (2.9 ± 1.4 for lead and 21.2 ± 5.4 for zinc) which characterise the underlying unit that is composed of the same hemipelagic calcareous ooze. Lead and zinc are constituents of the dumped material, jarosite, which, after mixing with slope sediments, can be used as sediment tracers. One core contains a fining‐upwards bed which is also elevated in lead and zinc. This is interpreted as evidence for dispersal of the jarosite from the disposal site downslope to depths >3000 m via turbidity flows sometime during the past 24 years. Current meter data collected from 30 m above the sea floor over one year at the disposal site show that bottom currents attain speeds of up to 0.46 m/s. The current events are attributed to eddies shed by the East Australia Current. The measured bottom currents are capable of transporting fine‐grained hemipelagic muds and could provide a trigger mechanism for turbidity flows. 相似文献