Beach Morphological Changes Research Articles

Planview Geometry and morphological characteristics of pocket beaches on the Catalan coast (Spain)

Coastal planform studies are a relevant initial stage before launching detailed dynamic field experiments. The aim of this study is to define the planform characteristics of 72 Catalan pocket beaches, natural and man-made, and to determine their sheltering effect, embaymentization and their status of equilibrium. Planform measurements were performed on SIGPAC, 1:5000 orthophoto sets and wave climate was provided by Puertos del Estado (Wana model). Planform parameters were applied and coastal planview indexes were determined. The study shows that the Catalan pocket beaches display a wide range of indentation, suggesting that no single structural, tectonic or morphological control dominates their planform. The man-made pocket beaches typically display indentations which are smaller than those shown by natural pocket beaches. Headland spacing and beach area are positively correlated. The more indented bays are, the shorter their beaches become. Low-indented pocket beaches are the widest and the longest ones. Deep indentation contributes towards beach protection and energy dissipation which counteracts rip efficiency and inhibits the formation of mega-rips. Pocket beaches often show gradual and moderate alongshore changes in texture and beach morphology. One third of the Catalan pocket beaches are “sediment starved”, i.e., 60% and more of their embayed shorelines are deprived of beach sediments. Examination of the status of equilibrium demonstrates that most of the Catalan pocket beaches are in an unstable mode, with indentation ratios that are unrelated to the wave obliquity.

Dune Retreat and Shoreline Change on the Outer Banks of North Carolina

Barrier islands are popular recreational areas of economic importance and are constantly undergoing change. Costly efforts are made to maintain beaches and stabilize dunes within this dynamic environment. Light detection and ranging data collected in September 1997 and 1998 along a 175-km stretch of the Atlantic coast of the Outer Banks, North Carolina, provide the basis for quantitative determination of the changes in beach morphology. The 1998 survey was conducted just after the passage of Hurricane Bonnie. During the 1-year study interval, beach widths throughout the study region tended to decrease. Maximum dune retreat was determined for each 1-m bin of 1997 beach width. For comparable beach widths, maximum dune retreat increased from south to north. The maximum dune retreat was greatest for supratidal beaches with widths of ∼20 m. For wider supratidal beaches, from 20 to 60 m, the associated maximum dune retreat gradually decreased. There was no further decrease in maximum dune retreat for beaches wider than ∼60 m. Relatively little change in beach width, dune height, and dune base position occurred along the less developed beaches of the Core Banks. The greatest morphological changes occurred on Ocracoke Island and Hatteras Island. Of the geomorphic parameters examined, preexisting beach width and the dune base elevation were the best indicators of vulnerability to dune retreat.

Alternation of beach erosion/accretion cycles related to wave action off Rosarito, Baja California, Mexico

A total of 1860 beach profiles were surveyed monthly from October 1995 to December 2003 at 29 control points along the coast of Rosarito (Baja California, Mexico). Sand volumes were estimated for the subaerial beach and related to deep-water wave records off California and nearshore waters at two localities off Rosarito. The spectral analysis of the sand volume time series revealed two main spectral peaks of 12- and 36-month periods. The latter cycle was identified for the first time along Rosarito beaches, showing a slightly larger amplitude on the beaches near the Federal Electricity Commission´ s breakwater and in the southern part of the study area. The contribution to sand movement produced by the annual cycle was 80 m3 m–1, while the transport induced by the 36-month cycle was 50 m3 m–1. The erosion and accretion cycle corresponded to winter and summer, respectively, but this pattern was inverted at two localities. The annual or seasonal cycle of sand volume change, defined in terms of the Dean number (Ω = Hs/wsT), is controlled by the seasonal wave pattern, while the inverted cycle is due to local changes in beach morphology and approach angle of breaking waves. The factor that accounted for this cycle is associated with interannual wave pattern variations and this, in turn, with ENSO events.

Depth of Closure and Shoreline Indicators: Empirical Formulae for Beach Management

In 1997, the effects of severe erosion along the Penarth, Wales, UK, foreshore became apparent when the beach surface fell to critical levels. A 240 m length of beach, bounded by a slipway, sea wall, and pier, was surveyed each September and April between 1997 and 2002 to assess summer and winter changes. Results in September 1997 showed that sediment transport was southerly in direction, whilst by September 2002, there had been a consistent return to the traditionally accepted south-to-north longshore drift, verified by significant differences in longshore gradients (t = 2.664; degrees of freedom [DF] = 6; p < 0.05). Analysis of changes in beach morphology has shown that erosion induced a southerly movement of beach contours, and a northerly movement was produced by accretion. Foreshore analysis has resulted in important regression models representing the variation of the shoreline indicator mean high water (MHW) with both shoreline position (mean beach level) and gain/loss of beach material. The cross-shore position of the depth of closure (DoC) was 50 m seaward of the survey line, at a water depth of 5.5 m. Results from analyses of cross-shore profiles verified temporal variations in back beach level with little variation beyond the DoC. Furthermore, there was significant correlation between the two shoreline indicators, MHW and DoC (84%). This correlation, combined with a derived equation for a management response parameter (MRP = 17.035 tan−1 (x14 − x6)/240[°]), produced simple tools to rapidly assess beach health. Results were compared with past data for interpretation of significance, and management strategies based on tabulated MRP values are suggested. A general form of this equation has been developed for testing at other beach locations, which should have significance for worldwide beach management.

Beach Morphological Dynamics: A Case Study of Nyali and Bamburi Beaches in Mombasa, Kenya

This study evaluated the spatial and temporal changes in beach morphology by analyzing the grain size distribution and the effect of the hydrodynamic conditions on the beach showing shoreline instability. Ten transects, from which morphological and hydrodynamic parameters were measured, were selected along the Nyali-Bamburi shoreline perpendicular to the shore. Morphological parameters such as beach orientation, beach width, and beach slopes were determined and sediment samples obtained during low tide. Wave energy was calculated from wave heights measured at the breaker point using a graduated staff, whereas swash and backwash velocities were determined at midbeach during high tide. Sediment samples were dried and sieved using an automatic shaker for grain size analysis using the graphical method. The study showed that beach morphology was rapidly changing with time along the shoreline. The changes were mostly attributed to wave and sediment characteristics. It was also established that steep-sloping beaches were associated with strong wave energy and coarse sediments, whereas gently-sloping beaches were of fine, well-sorted, and positively-skewed sediments, with relatively less strong waves. Steep beaches seem to be relatively short in width. There was a remarkable retreat of the shoreline.

Beach Morphology Change Caused by Overwash on Yokosuka Coast

At the beginning of October 2006, an extreme Typhoon 18th hit Yokosuka coast of Japan. There is a big amount of sediment transported and deposited inland after the typhoon. This study is to evaluate of this overwashed sediment volume and the prediction of overwash occurrence. These estimation are significant for coastal authorities and local managers to give evacuation warnings to people who live near the coast, it is useful for planners and engineers to mobilise equipment for cleaning up sediment after a storm. Profile change estimations are useful for planners creating “buffer zones” indicating where it is safe to build houses. And this calculation is also important for evaluating sediment budgets of sand beach or barrier islands, especially where these sand beach or islands are migrating due to overwash.

CHARACTERISTICS OF TURBULENT BOUNDARY LAYER OVER A ROUGH BED UNDER CNOIDAL WAVES MOTION

Ocean waves in reality often have a strong non-linear shape when propagating to shallow water, and the gap from the sinusoidal wave become remarkable. Therefore, it is generally believed that wave boundary layers, bottom shear stress and sediment transport behaviors actualizing the effect of non-linearity are different from sinusoidal wave. However, the example of research treating such turbulent boundary layer and sediment transport characteristic is very few. Therefore, the accuracy of bottom shear stress and amount of sediment transport used to evaluate the beach morphological change obtained from the wave motion model of sinusoidal is necessary to be clarified by that of non-linear. In this present study, turbulent boundary layer characteristics for asymmetric or non -linear waves according to the non-linearity effect is examined through both experimental and BSL turbulence model. Moreover, a new calculation method of botto m shear stress based on incorporating acceleration and velocity terms is used to examine both the experimental and BSL model results of bottom shear stress.

Variação morfodinâmica diária da praia do Cassino, RS, durante os verões de 2002/2003 no setor do terminal turístico

High frequency morphodynamic surveys permit to analyze, in detail, beach morphology changes. With the purpose to investigate daily beach profiles variability, surveys were carried during the summers of 2002 and 2003 at Cassino beach. Bar migration rate of 4,8m per day was found and berm development in 3 days, as well as high erosion in the first days of a storm followed by accretion in the final days of the event. This accretion was verified in other points toward the south of the monitored point; nevertheless, the material deposited was in form of fluid mud, highlighting the importance of a specific wave power band in the reworking of the mud deposits. The results found here show the existence of small changes in the sediment stock, not detected in previous works, which only related erosion episodes to meteorological systems.

Nest Placement of the Giant Amazon River Turtle, Podocnemis expansa, in the Araguaia River, Goiás State, Brazil

The giant Amazon river turtle (Podocnemis expansa) nests on extensive sand bars on the margins and interior of the channel during the dry season. The high concentration of nests in specific points of certain beaches indicates that the selection of nest placement is not random but is related to some geological aspects, such as bar margin inclination and presence of a high, sandy platform. The presence of access channels to high platform points or ramp morphology are decisive factors in the choice of nesting areas. The eroded and escarped margins of the beaches hinder the Amazon river turtle arriving at the most suitable places for nesting. Through the years, changes in beach morphology can alter nest distribution.

The influence of Amazon-derived mud banks on the morphology of sandy headland-bound beaches in Cayenne, French Guiana: a short- to long-term perspective

The 1600-km-long South American coast between the Amazon and the Orinoco Deltas has a prograded muddy shoreline comprised of sandy cheniers. The 15-km-long bedrock coast of Cayenne, French Guiana, differs from the rest of this fluctuating alluvial coast in that it comprises several headland-bound fringing sandy barriers that have experienced limited progradation and do not behave as cheniers that migrate landward over a muddy base. The limited progradation of these barriers is probably due to blanketing of fluvial sand by the cover of Amazon mud on the inner shelf, which precludes shoreward reworking to supply the beach and barrier systems. Aerial photographs, satellite images and recent field observations show that alternations between ‘mud bank’ phases, when Amazon-derived mud banks migrating northwestwards attain the Cayenne area, and ‘interbank’ phases, characterised by relative scarcity of mud, result in marked spatial and temporal variations in beach dynamics and morphology. These include periodic alternations in longshore drift that lead to a rare form of total or partial beach rotation that does not result, as is generally reported for nonmud bank-affected beaches, from seasonal variations in deepwater wave approach directions. These beach morphological changes have been defined in terms of a simple, four-stage conceptual model comprising ‘bank’, ‘interbank’ and transitional phases. In extreme ‘bank’ phases, the mud banks responsible for muddy coastal progradation on the Amazon–Orinoco coast may directly weld onto the beaches for periods ranging from months to years, leading to a rare example at the world scale wherein the dynamics of ocean-facing beaches are completely muted under the protective cover of mud that may become rapidly colonised by mangroves. The observations also suggest that these changes do not affect the medium-term (order of tens of years) beach sand budgets. Mud welding onto the beaches may, however, sequester at short time scales (order of months to years) sand eroded from the beaches. Subsequent mud erosion leads to release of this sand and its restitution to the beach sand budget.

Automatic cluster detection of lumber spine 3D CT images

This study discusses the morphological changes and evolution of Agadir Bay beach (Morocco) in response to eight storms between January 2014 and March 2014. A comparison is carried out of the evolution and variability of the beach in a sector of the bay protected by the commercial harbour of Agadir relative to a sector down drift of the harbour that is more exposed to waves, and changes affecting the beach following these storms are examined. Wave influence is evaluated using numerical simulations. The results show that despite being of relatively low intensity, the two first storm events, and especially storm 1, are responsible for major beach morphological changes. Three zones were identified as a function of the beach sediment dynamics: (i) a northern zone, representing the sector of the beach protected by Agadir harbour, with a net loss of about 21% of the total sediment, (ii) a southern zone, corresponding to the exposed sector with a net loss reaching74% of the total sediment, and (iii) a sector of residual dune that recorded no significant change during the storms.

Coastal and nearshore morphology, bedforms and sediment transport pathways at Teignmouth (UK)

The beach and nearshore area of Teignmouth (UK) has been the object of a multidisciplinary research project, COAST3D, carried out by 11 European institutions. This paper emphasises the sedimentological and morphological investigations of the intertidal and nearshore area using a variety of techniques. From the results presented, it is clear that the Teignmouth site is very dynamic. Sediment mobility is high during fair-weather conditions owing to the strong jet-like current flows associated with the presence of the narrow estuary mouth. The beach at Teignmouth can be categorised as composite with a dissipative low-tide terrace and a reflective upper beach. From surficial sediment sampling, selective transport processes were identified, imposed by the high current velocities at the estuary mouth. This process also leads to the formation of characteristic depositional lobes with poorly sorted sediment. From digital side-scan sonar mosaicing, cross-shore and longshore-oriented bedforms could be observed, with their characteristics being dependent on the pre-survey hydro-meteo conditions. Although the nearshore system is dominated by the jet-outflow, littoral drift processes can also be important. They proved to be important for beach morphological changes leading to a rythmic alongshore beach behaviour which was attributed to a reversal of the littoral drift imposed by a period of larger waves. Moreover, the influence of waves and associated longshore currents cannot be neglected as they form the link between different sedimentary environments. From combined side-scan sonar imagery and sediment trend analysis, residual sediment transport directions were identified. These showed that fair-weather and storm-dominated processes are needed to explain the textural and morphological differentiation at this site. Further analysis will be required to identify the different time-scales involved in producing these changes.

Lake Waves, Coarse Clastic Beach Variability and Management Implications, Loch Lomond, Scotland, UK

Abstract The variability of two lake gravel beaches (Loch Lomond, Scotland) is described in the context of changing environmental conditions. Waves, water levels and wind orientation and velocity were recorded for 1 year. The wave climate comprises small amplitude, high frequency, short-period waves and periods of calm (mean frequency = 0.92 secs; mean significant wave height = 0.08 m). Incident wind-wave direction was an important influence on beach morphology. Water levels fluctuate and there is a general increase in level. Wave activity combined with high water levels affects the upper beach and backshore although here, the highest waves were recorded at low water levels which minimised wave damage. Cliff erosion rates were recorded. Beach morphological changes showed highly variable profile types which were closely related to beach elevation, exposure and sediment supply. Sections of beach represented by individual profile types showed re-occurring profile types and different sections of beach respond...

Seasonal changes in beach morphology along the sheltered coastline of Perth, Western Australia

Abstract Seasonal change in beach morphology is traditionally ascribed to a variation in the incident wave energy level with calm conditions in summer resulting in wide beaches with pronounced subaerial berms and energetic conditions in winter causing narrow beaches with nearshore bar morphology. The coastline of Perth, Western Australia, is characterised by a large seasonal variation in the incident wave height and local beaches exhibit a distinct seasonal change in morphology. However, these morphological changes are better explained by a seasonal reversal in the littoral drift direction than by variations in the incident wave energy conditions. In summer, when northward sediment transport prevails due to sea breeze activity, beaches located south of coastal structures, headlands or rocky outcrops become wider due to the accumulation of sediment against the obstacle. These beaches will subsequently erode in winter during storms when the longshore sediment transport is toward the south. In contrast, beaches located north of obstacles will become narrower during summer and wider during winter. The usefulness of the dimensionless fall velocity Ω=H b /w s T (where Hb is the breaker height, ws is the sediment fall velocity and T is the wave period) as a predictor of presence/absence of bar morphology and beach type was investigated. It was found that Ω fluctuates around the threshold of bar formation (Ω≈1.5–2) over a variety of time scales (daily, weekly, and seasonally). These temporal variations in Ω in conjunction with the relatively low wave energy level that characterises the coast negates the development of beach and nearshore morphology that is in equilibrium with the hydrodynamic conditions. As a result, bar occurrence and beach type can not be readily predicted using Ω along the Perth coast.

Monitoring Beach Morphology Changes Using Small-Format Aerial Photography and Digital Softcopy Photogrammetry

Current methods of monitoring beach morphology changes commonly involve the establishment of Global Positioning System profiles that are surveyed on a regular basis. Although this method produces precise measurements of coastal topography, it is costly in time and effort and may result in large data gaps between profiles. Much of our understanding of coastal dynamics is thus limited by profile spacing and survey frequency. Softcopy photogrammetry is increasingly being used as an alternative to assess shoreline change and study beach morphodynamics. This method of producing three-dimensional topographic models and orthophotographs from digitized aerial photography can aid in filling in the gaps between established profiles. A limiting factor to this technology is the cost of obtaining high-resolution aerial photography. We have developed an aerial mapping system designed to collect data in an efficient and cost-effective way. We use a small-format aerial photography system that can be mounted on a variety of small aircraft on short notice. After a flight, the photographs are scanned, and softcopy photogrammetry software is used to create both DTMs (Digital Terrain Models) and orthophotographs. The DTMs can be compared with existing profiles for accuracy, and volumetric changes can be computed. The orthophotos are used to make precise measurements of the position and morphology of shoreline features. This aerial mapping system is advantageous over previous methods of beach morphology change monitoring because it allows for rapid response to storm events and provides a cost-effective method of establishing a continual monitoring program in erosion hazard areas.

Steep beach morphology changes due to energetic wave forcing

The three-dimensional variability of the sub-aerial beach is examined for Waimea Bay, Hawaii, a steep-slope pocket beach subject to energetic winter swell events. The beach is mapped using 32 Real-Time Kinematic Global Positioning System (RTK-GPS) surveys collected from March 1996 to July 1997. The survey method provides 4 m horizontal spacing and 2–3 cm vertical accuracy. The primary morphology change is the episodic removal and re-establishment of a foreshore dune during the winter swell season. The average sand volume flux between surveys reaches −8 and 4 m 2/day during peak erosion and accretion periods. The sand volume of the sub-aerial beach is found to be highly correlated (0.96) with the position of the shoreline. Longshore variations in morphology include beach cusps with typical peak to trough amplitudes of 0.5–1.5 m and longshore wavelengths of 30–70 m. The relationships between the energetic swell forcing and the volume and flux of sand on the sub-aerial beach are examined. The highest correlation (−0.88) is found between the total sand volume and the wave energy flux after the latter is filtered following Wright et al. [Wright, L.D., Short, A.D., Green, M.O., 1985. Short-term changes in the morphodynamic states of beaches and surf zones: an empirical predictive model. Mar. Geol. 62, 339–364]. The filter is effective at capturing slow accretion phases following energetic erosion events.

Evaluation of Changes in Beach Morphology along Louisiana Barrier Island Coast: ABSTRACT

Evaluation of Changes in Beach Morphology along Louisiana Barrier Island Coast: ABSTRACT

Short-Term Changes in Beach Morphology on Louisiana Coast: ABSTRACT

Short-Term Changes in Beach Morphology on Louisiana Coast: ABSTRACT

BEACH NOURISHMENT AS A MANAGEMENT TECHNIQUE

Beach nourishment is considered an environmentally safe management technique, since an unsuccessful nourishment project would simply result in the redistribution of borrow material by wave action into environments more in keeping with a state of equilibrium. No permanent modifications of the beach and nearshore environment need result, and since no permanent structures are required for beach nourishment, the management commitment allows rapid project abortion if necessary. Beach nourishment monitoring has usually been concerned with evaluating changes in the extent of subaerial beach and/or retention of fill volume. These parameters are important, but it is also necessary to consider the way in which nourishment sand is taken up by the beach system since relationships between volume change, change in extent of subaerial beach, and changes in beach morphology are complex. This paper is concerned with evaluating beach nourishment on the Gold Coast (Figure 1), Australia's major resort, where 2.A million cubic metres of fill were applied in the largest beach nourishment project attempted in this country at the time of writing. Methodology, reported in Chapman &amp; Smith (1977) and Chapman (1978a) included repetitive profile survey from backshore to point of zero change in inshore zone (over 4.00 profiles) using highly accurate techniques, and use of 38 tonnes of tracer, which was injected into the dredge line at a controlled rate.

Beach Sedimentology of Mustang and Padre Islands: A Time-Series Approach

Systematic profiling and sampling of 11 beach sites along more than 90 miles of Mustang and Padre Islands shows seasonal as well as geographic trends. On the basis of sediment characteristics and beach morphology, three geographic areas can be delineated; the northern, convergence, and southern provinces. Mean grain size and sorting values in both the northern and southern provinces show little seasonal variation; in the convergence province they display great temporal variation. Skewness shows a wide temporal variation throughout the entire study area. Foreshore sediments in the convergence province are generally coarser, less sorted, and less skewed than those of the other two provinces. Beach morphology also varies throughout the area. The northern and southern provinces have rather flat profiles without a pronounced berm and with a gently sloping foreshore. The convergence province contains beaches with a steep foreshore, well developed berm, and a landward sloping backshore. Although there is a general tendency for each beach to retain its own general morphology, there are seasonal modifications and geographic variations. Changes in beach morphology, as shown by monthly surveys, indicate that the 11 sites tend to respond as a single group or that the changes may be associated with a single province. There is a general tendency for beach morphology to conform to seasonal trends. Long after the termination of the systematic study, each of the sites was resurveyed and the profiles obtained were not significantly different than those surveyed in the same month two years previously.