Long-term shoreline response of a nontidal,barred coast

Long-term variations of shoreline positions along the southern Baltic coast were investigated using multichannel singular spectrum analysis (MSSA) to determine the most dominant long-term response patterns. The investigated beach is located at Lubiatowo on the Polish Coast and is mildly sloping with multiple bars. Data on coastal morphology have been collected at Lubiatowo including (1) bathymetric surveys since 1987 twice a year, and (2) beach topography surveys since 1983 every 4 weeks on the average, extending from the shoreline to the dune foot. Furthermore, several dedicated field campaigns have been carried out at Lubiatowo, as well as measurements of deep-water wave properties since 1998. MSSA was employed to the whole data set of shoreline position from all survey lines. In summary, three patterns emerged reproducing alongshore standing waves with different periods 7 to 8, 20+ and several decades. They represent long-term shoreline response, such that at some locations the longest wave is most predominant, at other locations the medium cycle predominates, whereas the shortest is the most prominent at yet other locations. However, all three can be detected at every location monitored, eliminating the confusion resulting from ordinary singular spectrum analysis (SSA) analysis, done previously for the same data set.     

Rip currents, mega-cusps, and eroding dunes

Dune erosion is shown to occur at the embayment of beach mega-cusps O(200 m alongshore) that are associated with rip currents. The beach is the narrowest at the embayment of the mega-cusps allowing the swash of large storm waves coincident with high tides to reach the toe of the dune, to undercut the dune and to cause dune erosion. Field measurements of dune, beach, and rip current morphology are acquired along an 18 km shoreline in southern Monterey Bay, California. This section of the bay consists of a sandy shoreline backed by extensive dunes, rising to heights exceeding 40 m. There is a large increase in wave height going from small wave heights in the shadow of a headland, to the center of the bay where convergence of waves owing to refraction over the Monterey Bay submarine canyon results in larger wave heights. The large alongshore gradient in wave height results in a concomitant alongshore gradient in morphodynamic scale. The strongly refracted waves and narrow bay aperture result in near normal wave incidence, resulting in well-developed, persistent rip currents along the entire shoreline.

The alongshore variations of the cuspate shoreline are found significantly correlated with the alongshore variations in rip spacing at 95% confidence. The alongshore variations of the volume of dune erosion are found significantly correlated with alongshore variations of the cuspate shoreline at 95% confidence. Therefore, it is concluded the mega-cusps are associated with rip currents and that the location of dune erosion is associated with the embayment of the mega-cusp.     

Identifying storm impacts on an embayed, high-energy coastline: examples from western Ireland

Large sections of the western Irish coast are characterised by a highly compartmentalised series of headland-embayment cells in which sand and gravel beaches are backed by large vegetated dune systems. Exposure to modally high-energy swell renders most of these beaches dissipative in character. A mesotidal range (c. 3.5–4.5 m) exists along much of the coast. Analysis of instrumental wind records from three locations permitted the identification of a variety of storm types and the construction of storm catalogues. Few individual storms were recorded at all three stations indicating a lack of regional consistency in storm record. Of the total storms recorded, only a small percentage are potentially damaging (onshore directed) and even fewer span a high tide and thus potentially induce a measurable morphological response at the coast.

Through a combination of historical records, meteorological records, field observations and wave modelling we attempt to assess the impact of storms. Quantifiable records of coastal morphology (maps, air photos and beach profiles) are few in number and do not generally record responses that may be definitely attributed to specific storms. Numerical wave simulations and observations at a variety of sites on the west Irish coast, however, provide insights into instantaneous and medium term (decadal) storm responses in such systems.

We argue that beaches and dunes that are attuned to modally high-energy regimes require extreme storms to cause significant morphological impact. The varying orientation of beaches, a spatially nonuniform storm catalogue and the need for a storm to occur at high water to produce measurable change, impart site-specific storm susceptibility to these embayments. Furthermore, we argue that long-period wave energy attenuation across dissipative shorefaces and beaches reduces coastal response to distant storms whereas short-period, locally generated wind waves are more likely to cause major dune and beach erosion as they arrive at the shoreline unrefracted.

This apparently variable response of beach and dune systems to storm forcing at a decadal scale over a coastline length of 200 km urges caution in generalising regarding regional-scale coastal responses to climatic change.     

Drones as tools for monitoring beach topography changes in the Ligurian Sea (NW Mediterranean)

The aim of this study was to evaluate topographic changes along a stretch of coastline in the Municipality of Borghetto Santo Spirito (Region of Liguria, Italy, north-western Mediterranean) by means of a remotely piloted aircraft system coupled with structure from motion and multi-view stereo techniques. This sector was surveyed three times over 5 months in the fall–winter of 2013–2014 (1 November 2013, 4 December 2013, 17 March 2014) to obtain digital elevation models and orthophotos of the beach. Changes in beach topography associated with storm action and human activities were assessed in terms of gain/loss of sediments and shifting of the wet–dry boundary defining the shoreline. Between the first and second surveys, the study area was hit by two storms (10–11 November 2013 and 21–22 November 2013) with waves approaching from the E–NNE, causing a shoreline retreat which, in some sectors, reached 7 m. Between the second and third surveys, by contrast, four storms (25–27 December 2013, 5–6 January 2014, 17–18 January 2014 and 6–10 February 2014) with waves propagating from the SE produced a general advancement of the shoreline (up to ~5 m) by deposition of sediments along some parts of the beach. The data also reflect changes in beach topography due to human activity during the 2013 fall season, when private beach managers quarried ~178 m³ of sediments on the emerged beach near the shoreline to accumulate them landwards. The results show that drones can be used for regular beach monitoring activities, and that they can provide new insights into the processes related to natural and/or human-related topographic beach changes.     

Reduction of sand demand for shore protection

Beach nourishment is an environmentally preferred method of shore protection, but the annual sand requirement may lead to substantial maintenance costs. The shoreline processes, involving the surf zone, beach and dune, are reviewed with the aim of reducing the annual sand requirement of eroding shorelines. It is shown that surf zones with equilibrium profiles, on which the wave energy conversion is evenly distributed across the surf zone, from experience for given conditions indicate least loss of sand. On steep, eroding shorelines it may be difficult to establish an equilibrium profile. For such cases, the use of perched surf zones is recommended, which are supported at the seaward limit by an underwater sill. For reduction of littoral transport, the use of pervious pile groynes is recommended. These are arguably more efficient than impervious groynes. The sand loss from a usually dry beach by raised water levels is shown to be a function of the beach slope and is least when the storm waves at raised water levels do not cut an erosion escarpment. The loss of sand from a dune by infrequent severe storm tides can be prevented with the aid of a built-in membrane. These sand losses are usually large and constitute an uneconomic use of this sand resource. The proposed concepts and measures are linked to existing knowledge, augmented by data from the large wave flume (LWF) in Germany and field data from the North and Baltic Sea coasts.     

深圳大鹏半岛南岸西冲海滩的沉积物来源、平面形态稳定性及横向变化

The coast of the Dapeng Peninsula has been honored as one of "the eight most beautiful coasts in China". The most precious tourism resource for the peninsula is headland bay beaches, among which the beach at Xichong on the southern coast of the peninsula is the longest and the most important one. The information of the stability, sedimentary source and shape change of the beach is very important for maintaining the beach in terms of sustainable development of the peninsula. Heavy minerals in the sand of the beach and the inland stream at Xichong are compared with those of a nearby beach on the same coast to determine the beach sand source; with help of a computer software, MEPBAY, the equilibrium planforms of the beaches on the peninsula are compared with those of an island without rivers to evaluate the stream’s effects on the beach stability; cross shore profiles along the Xichong beach are also surveyed in different seasons of a year to assess the annual shore normal beach changes affected by the stream input, and the relation between the equilibrium planform state and cross shore changes of the beach. It is shown that(1) stream is the main sedimentary source of the beach and the weathering materials of the rocky headlands on both sides of the bay transported by waves are the second source for the beach but it is limited, sand from an inner shelf is not the sedimentary source for the beach at present and was not even during the Holocene transgression;(2) the Xichong beach cannot reach static equilibrium around the entire bay shoreline, the segment of the shoreline where a stream outlet is located is in dynamic equilibrium, and the unstable section occurs in the wave shadow region in the lee of an offshore island;(3) no matter whether the section of the beach shoreline at Xichong is in an equilibrium state or not, it is eroded in the typhoon season and recovered after the season, the maximum change in erosion and accretion occurs in the unstable segment;(4) the Xichong beach can only have small sand body since it is supplied with sand mainly form inland streams, resulting in a possible danger in which sand loss induced by human activities or huge storms cannot be replenished naturally.     

台风"艾利"对福建沙质海滩影响过程研究

通过对福建沙质海滩地形地貌现场调查,对比分析0418号台风“艾利”登陆福建前后各沙滩剖面的蚀淤变化,探讨了福建沙滩对台风“艾利”响应规律。研究结果表明,2004年8月底台风“艾利”过境期间,福建沿海砂质海岸显出了较强烈的地貌响应。沙滩剖面地形变化,冲淤相间,以冲蚀为主;后滨沙丘蚀退、滩肩蚀低、岸线向陆迁移是地貌响应的主要特征;沙滩沉积物的总收支趋于亏损。不同海岸类型的沙滩剖面对台风“艾利”的响应特征不同。岬湾型沙滩剖面地貌响应以前滨滩面侵蚀为主要特征。夷直型的长乐江田下沙剖面,对“艾利”台风的主要地貌响应特征为后滨沙丘、高潮带侵蚀,岸线后退超过16m,出现高度近1 m的直立侵蚀陡坎。沙坝-泻湖型沙滩剖面冲淤变化的主要特征是中潮带形成次一级沙坝。各沙滩的地貌风暴效应有自北往南依次减弱的趋势。     

The coast between Cabo de Santa Maria (Portugal) and Rabat (Morocco): a mega-size headland-bay shoreline under control of the North Atlantic swell?

Equilibrium headland-bay beach systems have been mathematically described by logarithmic, parabolic and hyperbolic curve functions. The largest system of this type reported to date has a shoreline length of about 62 km. In the present study, an apparent headland-bay system is presented which has a shoreline length of about 500 km. It was discovered on satellite images, and is located between Cabo de Santa Maria in Portugal and the coastal city of Rabat in Morocco. It appears to be controlled by long-period North Atlantic swells diffracting around Cabo São Vicente at the south-western tip of Portugal, in combination with SW–SE wind wave climates impinging on the northern shoreline of Cádiz Bay. The coast shows two marked departures from the equilibrium shoreline along its central section north and south of the Strait of Gibraltar, which are easily explained. Thus, the promontories to the north of the strait still exist because there has not been sufficient time to erode these back to the equilibrium shoreline since postglacial sea-level recovery. The coastal indentation to the south is explained by an insufficient sediment supply from terrestrial sources to facilitate the required beach accretion. Perfectly adjusted planimetric headland-bay shoreline shapes represent situations where wave orthogonals approach the coast at right angles everywhere, i.e. there is no longer any alongshore sediment transport. Equilibrium shorelines form independently of the grain size of the beach sediment, whereas morphodynamic beach states are indirectly affected by the shoreline shapes because the latter are modulated by wave period and breaker height which also control the morphodynamic response of the beach in combination with the local grain size.     

Long-term evolution of Baltic Sea wave climate near a coastal segment in Poland; its drivers and impacts

The paper analyses long-term variability of wave climate near Poland for the 1958–2002 period. With spectral and cross-spectral analysis, linear regression and singular spectrum analysis the modes of long-term variability were quantified for the most energetic months (November–February). For monthly indices of North Atlantic Oscillation from 1950 until 2006, it was established that the long-term trends of NAO and significant wave height demonstrate a gentle coupling. For Januaries this relationship is strongest and dates back to 1960, for Februaries a certain consistency appears since 1975. For Novembers and Decembers no statistically discernible coupling was found. Thus, the Baltic Sea appears to be the easternmost NAO-affected region, despite its separation from the Atlantic. The hydrodynamic variability also includes a non-trivial oscillation in the January wave energy records with T=8 years. The same periodicity was identified with the multi-channel SSA technique in the long-term shoreline data of a neighboring beach. The study shows that even almost entirely isolated water bodies are becoming exposed to global climatic phenomena and accelerated erosion of sandy beaches, typical for the South Baltic region. On the other hand, the 8-year hydrodynamic cycle can be viewed as the driver of long-term shoreline evolution.     

Shoreline changes and beach-sand sorting along the northern Sinai coast of Egypt

 Changing shoreline positions along the Sinai coast of Egypt were determined by comparing aerial photographs and historical charts with present-day conditions. The analyses identify longshore patterns wherein erosion along a protruding stretch of the coast gives way to accretion in an adjacent major embayment. This pattern defines two coastal subcells consisting of source/sink couplets. There is a general correspondence between the mineral variation, grain sizes of beach sand, and the patterns of shoreline changes. Associated with erosion/ accretion shoreline change is a selective transport of different minerals according to their densities and grain sizes. Two heavy-mineral groups were obtained by applying Q-mode factor analysis on the heavy-mineral data. These two groups are influenced by transport processes, including sediment provenance from different sources: eroded Nile delta west of Sinai, relict sediments from the former Nile distributaries, and sediment supply by land valleys and from wind-blown sand. Received: 2 June 1995 / Revision received: 29 May 1996     

Calculation of beach change under interacting cross-shore and longshore processes

This paper presents a mathematical approach and numerical model that simulates beach and dune change in response to cross-shore processes of dune growth by wind and dune erosion by storms, and by gradients in longshore sand transport that will alter shoreline position. Sub-aerial transport processes are represented, whereas sub-aqueous transport is neglected. The system is tightly coupled morphologically, with the berm playing a central role. For example, the potential for sand to be transported to the dune by wind depends on berm width, and sand lost in erosion of the dune during storms can widen the berm. Morphologic equilibrium considerations are introduced to improve reliability of predictions and stability of the non-linear model. An analytical solution is given under simplification to illustrate properties of the model. Sensitivity tests with the numerical solution of the coupled equations demonstrate model performance, with one test exploring beach and dune response to potential increase in storm-wave height with global warming. Finally, the numerical model is applied to examine the consequences of groin shortening at Westhampton Beach, Long Island, New York, as an alternative for providing a sand supply to the down-drift beach. Results indicate that the sand will be released over several decades as the shoreline and dune move landward in adjustment to the new equilibrium condition with the shortened groins.     

A simple new shoreline change model

A simple new shoreline change model has been developed and calibrated/evaluated with several sets of high quality field data. The model is based upon the general observation that the shoreline tends to approach an equilibrium position exponentially with time when subjected to constant forcing. The model represents the shoreline response to cross-shore processes only and is extremely efficient, requiring only readily obtainable wave and water-level data as input. Shoreline changes are forced by changes in the local water surface elevation due to a combination of local tide, storm surge and wave-induced setup. The model contains three adjustable parameters, representing a baseline condition from which equilibrium shoreline displacements are calculated, and two rate constants, all of which are evaluated by minimizing the error between model hindcasts and several historical shoreline data sets. Several possible forms for the rate parameters, incorporating local wave and sediment properties, were considered and evaluated. At most sites, the model has proven successful in predicting large-scale shoreline response to local water level and wave forcing. The combination of model accuracy and efficiency, along with the minimal data required to drive the model, make it a potentially useful tool in many coastal engineering applications. As more high-quality shoreline, wave and water-level data sets become available, significant improvements can be made in the determination of the rate parameter governing the time scale of the beach response.     

The infralittoral prograding wedge: a new large-scale progradational sedimentary body in shallow marine environments

A progradational sedimentary body, the infralittoral prograding wedge (IPW), has been developing from the mean fair-weather wave-base level to the storm wave-base level between the onshore (beach) and the offshore (inner continental shelf) depositional zones along the Spanish coast during the Late Holocene. The main sedimentary body is composed of large inclined master beds which prograde seawards parallel to the shoreline, formed by sediments swept offshore by waves from shallow-water littoral environments. The inclined beds downlap onto finer-grained offshore sediments and, in turn, are overlain by shoreface deposits. The IPW is generated by downwelling storm currents and associated seaward transport of sediment. It represents a new depositional model for clastic wave-dominated coasts, and its identification requires a new subdivision of the nearshore environment. Received: 10 June 1999 / Revision accepted: 15 February 2000     

Evidence for storm-dominated early progradation of Castle Neck barrier, Massachusetts, USA

Washovers, dune scarps and flattened beach profiles with concentrations of coarse-grained sediment or heavy minerals are the diagnostic geological signatures of large storms on barriers today. It is clear that storms are a major force driving transgressive barriers onshore, but what is not as well understood is the role these powerful erosive events play in the evolution of prograding barriers. Application of ground-penetrating radar (GPR) and a combination of coring techniques have significantly improved our ability to image barrier architecture. Results of these studies reveal a more complex evolution than previously recognized. It is now possible to precisely locate and map storm deposits within prograded barrier lithosomes.

A comprehensive study of northern Castle Neck, Massachusetts was performed using 15 km of GPR surveys, a 120-m-long seismic line, 11 cores, and several radiocarbon dates. Storm-related layers are the most prominent horizons contained in the barrier stratigraphy. The geometry and sedimentology of these layers closely resembles those of a present-day post-storm beach. Twenty closely spaced, curvilinear heavy mineral layers imaged in the landward portion of the barrier suggest that the Castle Neck barrier was heavily influenced by storms during its initial phase of progradation beginning 4000 years BP. Approximately 1800 years BP, two intense storms impacted the coast depositing two extensive coarse-grained units. These layers mimic the flat-lying sand and gravel deposits that occur in front of a nearby eroding till outcrop following major storms. The great number of storm deposits in the early history of Castle Neck is related to either a period of greater storm activity and/or a slow rate of barrier progradation. The occurrence and preservation of these earlier storm layers are likely a product of the exposure of nearby drumlins resulting in greater availability of iron oxide and ferromagnesian sands. The supply of heavy-mineral sands has gradually diminished as the barrier prograded and the proximal drumlin source was buried by beach and dune sands.     

Monitoring and comparison to predictive models of the Perdido Key beach nourishment project, Florida, USA

This paper summarizes the results of over 8 years of data describing the performance of a large beach nourishment project on Perdido Key, immediately adjacent to Pensacola Pass in Escambia County, FL, USA. As a result of a major excavation of the entrance channel to Pensacola Bay, over 7 million m³ of beach-quality sand were placed along the easternmost 7.5 km of Perdido Key, adjoining the entrance channel at Pensacola Pass. The project included the placement of 4.1 million m³ of sand directly upon the shoreline in 1989–1990, followed by the placement of an additional 3 million m³ as an underwater berm just offshore of the beach nourishment project in water depths of roughly 6 m. Monitoring of the performance of the beach nourishment project and the offshore berm has been conducted since 1989, beginning with a pre-construction survey of the project area. Monitoring surveys have been conducted on an annual or biennial basis since that time, with the most recent survey occurring in July/August, 1998. Over 8 years of monitoring data indicate that the beach nourishment project has retained approximately 56% of the original volume placed within the 7.5-km project length. In addition, according to the latest monitoring survey, the dry beach width of the project, initially constructed as 135 m on average, is still 53 m wider than pre-project conditions. Approximately 41% of the originally placed dry planform area remains as of July 1998. The most recent monitoring surveys in 1995, 1997, and 1998 encompass the effects of two major storm systems, Hurricanes Erin (August 1995) and Opal (October 1995). Monitoring of the offshore berm area indicates only a slight landward migration of the berm, accompanied by a minor decrease in volume, over the entire monitoring period. The performance of both the beach nourishment project and the offshore berm appear to be significantly related to the two storm events, particularly Hurricane Opal, and the proximity of the project to the tidal entrance at Pensacola Pass. Comparison of the documented performance of the beach nourishment project to simple existing analytical models of beach-fill evolution have yielded encouraging results in terms of preliminary design aids for future beach nourishment projects in the vicinity of deep tidal entrances.     

Sub-weekly to interannual variability of a high-energy shoreline

Sixty-one Global Positioning System (GPS), sub-aerial beach surveys were completed at 7 km long Ocean Beach, San Francisco, CA (USA), between April 2004 and March 2009. The five-year time series contains over 1 million beach elevation measurements and documents detailed changes in beach morphology over a variety of spatial, temporal, and physical forcing scales. Results show that seasonal processes dominate at Ocean Beach, with the seasonal increase and decrease in wave height being the primary driver of shoreline change. Storm events, while capable of causing large short-term changes in the shoreline, did not singularly account for a large percentage of the overall observed change. Empirical orthogonal function (EOF) analysis shows that the first two modes account for approximately three-quarters of the variance in the data set and are represented by the seasonal onshore/offshore movement of sediment (60%) and the multi-year trend of shoreline rotation (14%). The longer-term trend of shoreline rotation appears to be related to larger-scale bathymetric change. An EOF-based decomposition technique is developed that is capable of estimating the shoreline position to within one standard deviation of the range of shoreline positions observed at most locations along the beach. The foundation of the model is the observed relationship between the temporal amplitudes of the first EOF mode and seasonally-averaged offshore wave height as well as the linear trend of shoreline rotation. This technique, while not truly predictive because of the requirement of real-time wave data, is useful because it can predict shoreline position to within reasonable confidence given the absence of field data once the model is developed at a particular site.     

Immediate profile and planform evolution of a beach nourishment project with hurricane influences

In this study, planform adjustment began during a period of calm weather immediately after nourishment and then the passage of one strong storm caused a substantial portion of the total profile equilibration. Weekly beach profiles, shoreline surveys, and nearshore wave measurements were conducted before, during, and immediately after construction of the 1100-m long Upham Beach nourishment project on the low-energy, west coast of Florida. This project was constructed in three segments: the wide north segment, the central segment, and the narrow south segment. With the exception of the relatively distant passage of Hurricane Charley, calm weather prevailed for 45 days following completion of the south and central segments. Construction of the wide north segment was completed on August 27, 2004. Substantial planform diffusion occurred prior to construction completion via formation of a 300-m long spit extending from the wide north segment. The shoreline orientation was changed abruptly due to this diffusion spit formation, as opposed to the gradual adjustment predicted by most long-term models. Planform adjustment was initiated prior to profile equilibration, and it did not require high-energy conditions. A simple vector sum model for determining the orientation of a potential diffusion spit was developed. This study recommends designing end transitions at the predicted diffusion spit orientation to avoid post-nourishment spit formation during future projects.     

Beach and shoreface response to sea-level rise: Ocean City, Maryland, U.S.A.

Sea-level is one of the principal determinants of shoreline position. Sea-level rise induces or accelerates on-going shore retreat since deeper water decreases wave refraction, thus increasing littoral drift, and also allowing waves to arrive closer to shore before breaking. Tidal records from the US East and Gulf coasts indicate a relative sea-level rise of approximately 0.3m has occurred during the past century. Concomitantly, erosion has been prevalent almost everywhere along these sandy shorelines. Ocean City, Maryland, was selected as a case study site to determine historical shoreline changes and to project future beach erosion based on accelerated rates of sea-level rise. During the past 130 years (1850–1980), this shore has retreated approximately 75m and many highrise buildings at Ocean City are now threatened during storm conditions. Accelerated sea-level rise is expected to increase the rate of retreat by a factor of 2 to 5 based on analysis of present trends. This significantly reduces the planning time available for mitigating the hazard and increases the vulnerability of this urbanised barrier through time.     

基于Argus图像的舟山东沙海滩对连续风暴的响应研究

海滩对风暴的响应是一个复杂的过程,尤其在连续风暴发生时。本研究利用Argus视频监测系统拍摄的连续图像,从海滩地貌、剖面、海滩滨线、海滩宽度等方面,定量分析了舟山东沙海滩对连续风暴"马勒卡"和"暹芭"的响应特征,并初步探讨了影响海滩地形地貌变化对连续风暴响应的因素。结果表明:(1)风暴"马勒卡"发生后海滩单宽体积变化量平均值为?73.75m3/m,风暴"暹芭"发生后海滩单宽体积变化量的平均值为?54.56m3/m,风暴"马勒卡"使整个海滩滨线平均后退14.75m,风暴"暹芭"使得海滩滨线相对于两次风暴前后退10.91m;(2)在海滩自身因素、外部动力因素以及人类活动等共同作用下海滩对连续风暴产生了复杂的响应。     

The distribution and behaviour of tar balls along the Israeli coast

A fortnightly sampling of tar balls on six beaches along the Israeli coastline between 14 April 1975 and 25 June 1976 showed that the mean content of tar during that period was 3625 g m^?1 of beach front. The northern and central parts of the coast were significantly more polluted than the southern part. Between July 1975 and February 1976 the mean tar quantity decreased continuously from 5635 to 1344 g m^?1.A comparison of tar quantities on the Israeli beaches with those of other beaches in the world showed that the Israeli beaches are more polluted than those of the west Atlantic coast, are as polluted as other beaches on the eastern coast of the Mediterranean Sea, and are less polluted than the beaches of Alexandria, Egypt, and Paphos, Cyprus. It is suggested that the tar content on the beach is related to the degree of oil pollution in the sea. The closer a beach is to an oil shipping lane or an oil dumping site, the heavier it is polluted.During storms, beach tar balls are pushed by the waves to the back of the beach or, in the case of a cliffed coast, are carried along the shore by the longshore current. When the tar balls reach a gap in the cliff (such as an estuary), they are carried inland by the storm waves. There the tar may become buried or dry, shrink and break into small particles which are then dispersed by the wind.