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Alcántara-Carrió, J.; Caicedo, A.; Hernández, J.C.; Jaramillo-Vélez, A., and Manzolli, R.P., 2019. Sediment bypassing from the new human-induced lobe to the ancient lobe of the Turbo Delta (Gulf of Urabá, Southern Caribbean Sea). Journal of Coastal Research, 35(1), 196–209. Coconut Creek (Florida), ISSN 0749-0208. Artificial river diversions cause intense and unpredictable changes in the geomorphological evolution and sedimentary dynamics of deltas. This study analyzes the effects of the 1958 course diversion of the Turbo River delta, Gulf of Urabá, southern Caribbean Sea. Recent satellite images were analyzed and beach topography was monitored to obtain the shoreline migration and sediment budget; surface sediments were seasonally sampled, and their grain size parameters were determined; and seasonal sediment transport directions were deduced according to grain size trends. It was concluded that the bimodal wave regime controls the seasonal sedimentary patterns associated with southward longshore transport during both the dry and rainy seasons, and the northward longshore transport occurs in the midsummer drought. Beach morphodynamics of Yarumal Point, close to the present-day river mouth, show that this is the most exposed sector to waves, whereas fluvial sediment inputs are evidenced by a decrease in mean grain size and by poorly sorted sediments in the rainy season. A new spit is forming in Yarumal Point, with an intense increase in area and a westward progradation related to high fluvial sediment inputs from the La Niña event of 2010–12 and low erosion from the El Niño events of 2009–10 and 2015–16. In the central sector, longshore drift has formed the Yarumal barrier spit with a southeastward progradation that recently closed the interdistributary El Uno Bay. Consequently, a humaninduced sand barrier–lagoon system resulted with a stable or slightly regressive shoreline. Moreover, the Yarumal barrier spit has generated a new sediment bypass to Barajas Beach in the northern limit of the Las Vacas spit (i.e. the ancient delta lobe). Therefore, there is an unusual accretion of the abandoned delta lobe by sediment supply from the new lobe. [ABSTRACT FROM AUTHOR]

Fellowes, T.E.; Gacutan, J.; Harris, D.L.; Vila-Concejo, A.; Webster, J.M., and Byrne, M., 2017. Patterns of sediment transport using foraminifera tracers across sand aprons on the Great Barrier Reef. Sediment dynamics exert large control over coral reef geomorphological evolution and are vital to understanding past and present geomorphic responses. Large benthic foraminifera (LBF) live in the algal reef flats, and their tests (shells) are transported post-mortem by waves and currents onto back-reef environments, including sand aprons. This study investigated the patterns of transport linking surficial and downcore sediments in samples from three sand aprons with different wave exposures at One Tree Reef on the southern Great Barrier Reef (Australia). Six LBF genera represented up to 32% of the sediments analysed. Lagoonward transport increased LBF test abrasion and sediment bulk density. Sediment grain size and LBF abundance in sediments also decreased with lagoonward transport. Sediment transport patterns indicated by LBF species used as tracer were consistent with the prominent E-SE wave environment. A novel taphofacies approach was used to describe stratigraphic layers in downcore sediments based on LBF test abrasion and abundance. Varied sediment deposition rates did not affect the LBF test abrasion signature downcore. It appears that Baculogypsina sphaerulata has been the dominant species for at least 3 ka. Tests that were deposited slowly exhibited less or the same levels of abrasion than those that were rapidly deposited. It appears that test abrasion is primarily determined by the distance travelled rather than the influence of increased age or chemical dissolution. [ABSTRACT FROM AUTHOR]

Jeon, H.S.; Obana, M.; Kim, K.H., and Tsujimoto, T., 2017. Flow and sediment transport with non-submerged riparian vegetation in 1D scheme. In: Lee, J.L.; Griffiths, T.; Lotan, A.; Suh, K.-S., and Lee, J. (eds.), The 2nd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 79, pp. 329-333. Coconut Creek (Florida), ISSN 0749-0208. Recently depth averaged analysis has become popular and powerful even in a stream with vegetation by taking account of form drag due to vegetation. A number of studies about the drag force related with various vegetation configuration were also carried out and focus on determining the drag coefficients and empirical formulas. However, there must be some restriction for application in depth averaged model for flow with vegetation. When it is applied to a stream with vegetation, form drag due to vegetation is taken into account, but the shear stress is not properly described because the frictional resistance law due to bed roughness is not modified in vegetated area. Therefore, friction factor in depth-averaged scheme must be modified by the flow with vegetation. In this paper, the concept of 'bed roughness boundary layer' is proposed and analytically formulated against the vegetation density. Sensitivity analysis were also conducted under several parameters and vegetation densities. The calculated results bring the reasonable evaluation of shear stress and proposed concept will affect other many kinds aspect in fluvial process, which will be clarified successively. Resultantly we are able to apply the depth-averaged analysis reasonably to flow and fluvial process in a stream with various density of vegetation. [ABSTRACT FROM AUTHOR]

Collin, A., Etienne, S. and Jeanson, M., 2016. Three-dimensional structure of coral reef boulders transported by stormy waves using the very high resolution WorldView-2 satellite. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 572-576. Coconut Creek (Florida), ISSN 0749-0208. Coral reef boulders have been showed to reliably characterize the amount of wave energy related to cyclone, storm or tsunami events. The wave height and current velocity have been successfully explained by the variability in the boulder individual (morphology) and population (distribution) spatial patterns. Even if a single boulder may include a substantial amount of information, it may be highly challenging to characterize it given the access difficulty at the local and regional scales. Moreover, a boulder population is meaningful to robustly and continuously depict the energetic event that drove the sediment transportation. Recently the very high resolution satellite remote sensing has been demonstrated to help classify and measure the horizontal patterns (A- and B-axes) of the boulders at the submeter scale. Here we focus on the vertical dimension (C-axis) of the boulders. Based on boulder fieldwork measurements of the three axes and geographic locations, we constrain various spectral parameters of the remotely-sensed datasets (WorldView-2) to retrieve the three axes of the boulders, reaching a very satisfactory agreements (R2) of 0.95, 0.88 and 0.75, respectively. The innovative C extraction combined with the A and B information will allow geomorphologists to rapidly and extensively collect boulder data so that the underlying energy can be computed in a more expanded and accurate way, at the population scale. [ABSTRACT FROM AUTHOR]

Haghshenas, S.A.; Razavi A., A.; Bakhtiari, A., Jedari Attari, M., and Risk, M.J., 2016. Decadal Evolution of Mond River Delta, the Persian Gulf. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 805-809. Coconut Creek (Florida), ISSN 0749-0208. This paper studies the results of multi-disciplinary investigations on different features of evolution of the Mond River delta during the past five decades. Considering the high importance of Mond River and corresponding sediment discharge, physiography and watershed analysis of Mond River is investigated and sediment discharge from the river and its sand content are estimated in the first step. A numerical model has been utilized to investigate cases of flow and sediment transport behaviour in the coastal Mond area and annual rates of longshore sediment transport are estimated. The shoreline changes are investigated by analysing thirty four sets of aerial photos and satellite imagery taken between 1967 and 2014 to investigate decadal evolution of Mond River Delta during the past three decades. Eventually, numerical results are compared with field observations and comprehensive GIS based analysis of historic shoreline changes from aerial photos and satellite imagery. [ABSTRACT FROM AUTHOR]

Tõnisson, H.; Suursaar, Ü.; Alari, V.; Muru, M.; Rivis, R.; Kont, A.; and Viitak, M., 2016. Measurement and model simulations of hydrodynamic parameters, observations of coastal changes and experiments with indicator sediments to analyse the impact of storm St. Jude in October, 2013. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 1257 - 1261. Coconut Creek (Florida), ISSN 0749-0208. The aim of the study is to analyse the meteorological parameters, hydrodynamic conditions and coastal changes caused by a severe European storm referred to as St. Jude (Christian). It crossed the Baltic Sea on 27-29 October 2013. At Cape Kelba in the west Estonian archipelago, wave parameters were measured by RDCP and simulated by two wave models. Shoreline and topographic changes were recorded before and after the storm by RTK-GPS device. Simultaneous experiments with painted sediments were carried out to analyse sediment transport patterns and wave impact on the nearshore sea bed. It was the most significant storm in Estonia since 2007 with wind gusts up to 33 m/s and local storm surge height 1.5 m. The measured significant wave height reached 3.4 m at the 5.5 m deep point near the geomorphic study site. Modelling study indicated some wave-current-surge interaction effects. The distal section of the Kelba Spit elongated by about 12 m, but only minor changes were registered in the proximal part of the spit. The painted sediments placed on the sea bed at depths from 2-6 m were swept up to 20 m towards the shore. [ABSTRACT FROM AUTHOR]

Sedigh, M.; Tomlinson, R.; Cartright, N., and Etemad-Shahidi, A., 2016. Morphological evolution of the Nerang River Entrance ebb-tidal delta. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 238-242. Coconut Creek (Florida), ISSN 0749-0208. The Nerang River entrance is a tidal inlet that connects the Pacific Ocean to the extensive Gold Coast estuarine system known as the Broadwater. Due to relatively fast northward migration of the inlet from 1920 to 1985 and the importance of having a safe navigable channel, the inlet was stabilized with two training walls in 1986. A sand bypassing system was implemented upstream with an average sand bypassing rate equal to the estimated net northward lonshore sediment transport in the area to prevent the formation of a bar across the entrance. However, historical analysis of survey data has shown an ongoing growth of the ebb-tidal delta at the river mouth. Thus, despite the sand bypassing system, costly dredging of the ebb-tidal delta is required to maintain safe navigation through the entrance. A number of studies have been undertaken to investigate sediment transport and hence morphological evolution. However, despite all the previous efforts, the cause of the ongoing ebb-tidal delta accretion is still not known with any degree of certainty. According to recent numerical modeling efforts, there is a considerable amount of longshore sediment transport leakage past the sand bypassing system, particularly during storm events. This paper will present a brief history of the dynamics of the Nerang River entrance since the early 1820s before reviewing historical sand volume analysis based on available survey data. An updated conceptual model will then be developed in order to better understand the morphological change in and around the Nerang River entrance area. [ABSTRACT FROM AUTHOR]

Hein, C.J.; Fitzsimons, G.G., FitzGerald, D.M., and Fallon, A.R., 2016. Records of Migration and Ebb-Delta Breaching at Historic and Ancient Tidal Inlets along a River-Fed Paraglacial Barrier Island. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 228-232. Coconut Creek (Florida), ISSN 0749-0208. Tidal inlets link backbarrier environments to the coastal ocean and play a dominant role in both longshore and cross-shore sediment transport. Additionally, inlet-fill sequences comprise up to 50% of barrier lithosomes in wave-dominated settings. This study uses historic records to investigate centennial-scale cycles of inlet dynamics and barrier shoreline adjustment at Merrimack River Inlet (Plum Island, Gulf of Maine). Geophysical and sedimentological data reveal geometric and stratigraphic signatures of these recent changes, and allow for comparison to similar records preserved within a nearby 3600-year-old inlet-fill sequence. Driven by processes of longshore transport, spit elongation and ebb-delta breaching, the Merrimack River Inlet once actively migrated across a 2.5-km long section of Plum Island. An ebb-delta breaching event in the mid-1800s caused abandonment of the former inlet channel and the onshore welding of a large sand bar, which developed into the northern 1.5 km of the island. The inlet stabilized by jetties in the late 1800s. Ground-penetrating radar profiles and sediment cores across this former inlet channel capture the details of changes prior to breaching, including the seaward deflection of the otherwise southerly and landward-migrating channel, in response to onshore bar migration and welding. Similar details of inlet migration, bar welding, and ebb-delta breaching are observed stratigraphic records of an ancient inlet in central PI, located 7 km to the south. Comparison between the ancient and historical sequences provides clues to decipher the complex inlet dynamics preserved in the stratigraphic and sedimentologic record. [ABSTRACT FROM AUTHOR]

Dai, H.; Ye, M., and Niedoroda, A.W., 2015. A model for simulating barrier island geomorphologic responses to future storm and sea-level rise impacts. This paper presents the Barrier Island Profile (BIP) model, a new computer code developed to simulate barrier island morphological evolution over periods ranging between years and decades under the impacts of accelerated sea-level rise and long-term changes in the storm climate. The BIP model is a multiline model that represents the time-averaged dynamics of major barrier island features from front beach to backshore. Unique contributions of BIP to coastal modeling include a dynamic linking of interacting barrier island features and consideration of both future sea-level rise and storm climate impacts. The BIP model has the built-in capability of conducting Monte Carlo (MC) simulations to quantify predictive uncertainty caused by uncertainty in sea-level rise scenarios and storm parameters. For a series of barrier island cross-sections derived from the characteristics of Santa Rosa Island, Florida, BIP was used to evaluate their responses to random storm events and five potential accelerated rates of sea-level rise projected over a century. The MC simulations using BIP provide multiple realizations of possible barrier island morphologic responses and their statistics, such as mean and variance. The modeling results demonstrate that BIP is capable of simulating realistic patterns of barrier island profile evolution over the span of a century using relatively simple representations of time- and space-averaged processes with consideration of uncertainty of future climate impacts. [ABSTRACT FROM AUTHOR]

Cohn, N., Ruggiero, P., Ortiz, J., D.J. Walstra, 2014. Investigating the role of complex sandbar morphology on nearshore hydrodynamics. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 053-058, ISSN 0749-0208. Coastal environments are characterized by complex feedbacks between flow, sediment transport, and morphology, often resulting in the formation of nearshore sandbars. In many locations, such as Hasaki (Japan), the Netherlands, and the Columbia River Littoral Cell (CRLC, USA), these sandbars exhibit a net offshore migration (NOM) cycle whereby these features form in the inner surf zone, migrate seaward and decay offshore on interannual cycles. Depending on the stage of the cycle, the number and configuration of the bars may differ widely. It has long been recognized that sandbars act as natural barriers during storm events by dissipating wave energy through breaking far from the beach face. Thus, dependent on the stage of the NOM cycle, one might expect significant variability in nearshore hydrodynamics. Using a non-linear wave model we demonstrate that inter-annual variability in sandbar configuration can significantly alter inner surf zone and swash zone processes. The model indicates that under different end-member NOM stages the same wave conditions can result in up to a 36% variance in the vertical extent of infragravity runup and can alter both the rate and direction of net cross shore sediment transport. [ABSTRACT FROM AUTHOR]

Li, B., Ellis, J. T., Sherman, D. J., 2014. Estimating the Impact Threshold for Wind-Blown Sand. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 627-632, ISSN 0749-0208. In many aeolian studies, it is commonplace to use Bagnold's (1936) equation to calculate threshold shear velocity ( u*t), which includes an empirical constant, A, typically set at about 0.082 for maintaining saltation (the dynamic, or impact, threshold). Here, we present data from a pilot study to assess the variability of A to improve estimations of u*t, which in turn, should improve transport rate predictions. Using field data from three coastal environments, we measured or calculated all parameters within the Lettau and Lettau (1978) model and u*t equation. In Jericoacoara, Brazil (BRA), Inch, Ireland (IRE), and Esposende, Portugal (POR) wind velocities were measured with cup anemometer towers and transport rates were measured using traps for 31 data runs lasting 120 to 1020 seconds each. Mean grain sizes were 0.17 mm (IRE), 0.31 mm (POR), and 0.30 mm (BRA), and mean shear velocities were 0.38 m s−1 (IRE), 0.40 m s−1 (POR), and 0.49 m s−1 (BRA). Empirically determined, adjusted A values ranged from 0.02 to 0.21 with a mean and standard deviation of 0.11 and 0.04. No relationship exists between estimates of A and grain Reynolds number. A statistically significant (p < 0.001), negative relationship was found between A and mass transport rate, leading to substantial over-prediction of transport rates near the threshold and under-prediction during fast winds if a constant of 0.082 is used. [ABSTRACT FROM AUTHOR]

Bouchette, F., Manna, M., Montalvo, P., Nutz, A., Schuster, M.,Ghienne, J.-F., 2014. Growth of cuspate spits. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70 pp. 047-052, ISSN 0749-0208. The present work concerns cuspate spits: slightly symmetrical geomorphic features growing along the shoreline in shallow waters. We develop a new formulation for the dynamics of cuspate spits. Our approach relies on classical paradigms such as a conservation law to the shoreface scale and an explicit formula for alongshore sediment transport. We derive a non-linear diffusion equation and a fully explicit solution for the growth of cuspate spits. From this general expression, we found interesting applications to quantify shoreline dynamics in the presence of cuspate spits. In particular, we point out a simple method for the datation of a cuspate spit given a limited number of input parameters. Furthermore, we develop a method to quantify the mean alongshore diffusivity along a shoreline perturbed by well-defined cuspate spits of known sizes. Finally, we introduce a formal relationship between the geometric characteristics (amplitude, length) of cuspate spits, which reproduce the self-similarity of these geomorphic features. [ABSTRACT FROM AUTHOR]

Thomas, T., Lynch, S.K., Phillips, M.R., Williams, A.T., Duck, R.W. 2014. Relationships between sand spit evolution, environmental forcing and inland inundation. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium(Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 072-077, ISSN 0749-0208. Topographic field data and environmental forcing agents were used to assess morphological changes (1995-2010) at Ginst Spit, Pendine Sands, West Wales and flood potential at Laugharne, a town in the lee of the spit. Areal change between annual surveys showed variable distal end migration eastward extending into the channel of the Towy, Taf and Gwendreath estuaries. Dominant waves emanate from south toward southwest and suggest that the longshore sediment drift is from west toward east. However, sub-dominant waves from southeast are limited by fetch but engender a counter drift back toward the west at the distal end forming the customary northward hook.Wave model results showed significant modifications occurred between the inshore model boundary and the nearshore zone and overall results suggest that spit evolution is dependent on sediment movement that occurs during high spring tidal conditions within this macrotidal environment. Precipitation and flood events were correlated to spit evolution, which suggested that a combination of fluvial and coastal processes in combination contribute to the flooding of Laugharne town. [ABSTRACT FROM AUTHOR]

Burningham, H., French, J.R., 2014. Travelling forelands: complexities in drift and migration patterns. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 102-108, ISSN 0749-0208. Cuspate forelands have been described from a range of shorelines around the world, but in the majority of cases, the foreland maintains a constant position relative to the neighbouring shoreline. Here, we describe the contemporary geomorphology and historical evolution of a small cuspate foreland on the Suffolk coast, UK, which has been migrating northward for several centuries. Benacre Ness, a mixed sand and gravel sedimentary accumulation, is currently located at Kessingland, 5 km to the north of Benacre, from which it gained its name when adjacent to it in the 19th century. The foreland was previously called Covehithe Ness, having been adjacent to Covehithe (3 km south of Benacre) early in the 19th century. Previous sediment transport experiments and modelling studies have demonstrated a net southerly transport direction on this coastline, yet the foreland has continued to migrate northward over several centuries. Local reversals in sediment transport direction and rates are likely responsible for the northward migration of the foreland, but substantial changes in behaviour over the last 400 years suggest a close relationship between foreland dynamics and coastal configuration. [ABSTRACT FROM AUTHOR]

Healy, T. and de Lange, W., 2014. Reliability of geomorphic indicators of littoral drift: Examples from the Bay of Plenty, New Zealand. The net direction of littoral drift can be evaluated by multiple lines of evidence, including a range of geomorphic indicators and trends in sediment characteristics. In this article, the processes that influence the longshore transport of sediment are reviewed and assessed by the types of geomorphic indicators and sediment trends that can be expected. Various proxies for measured littoral drift are used to evaluate the littoral drift in the Bay of Plenty, New Zealand. Previous studies, utilising geomorphic indicators and, to a lesser extent, sediment characteristics and simple models of longshore sediment transport, developed a conceptual model of two main littoral drift systems starting at the western and eastern margins of the Bay of Plenty and converging in the vicinity of Ohiwa Harbour, an estuary enclosed by two opposing spits within the bay. Comparison of geomorphic indicators of littoral drift with the results of 30 years of monitoring and investigation demonstrate that geomorphic indicators can be misleading or misinterpreted. Overall, they do not appear to have been reliable for the Bay of Plenty, whereas sediment characteristics have performed better. The published rates of net littoral drift, and also the directions, appear to be too high and are inconsistent with observed patterns of erosion and accretion. Further, the exchange of sediment between the beach and the inner shelf has not been considered. Within the Bay of Plenty the net littoral drift magnitude and direction varies in response to changes in the wave climate associated with climatic variability, particularly the magnitude, frequency, and duration of the La Niña and El Niño extremes of the El Niño-Southern Oscillation. Decadal-scale fluctuations in the patterns of erosion and accretion along the Bay of Plenty coast have also been recognised. Finally, the influence of tectonic effects on geomorphic indicators of littoral drift needs further investigation. [ABSTRACT FROM AUTHOR]

The efficiency of a rocky headland in delimiting littoral cells and preventing sediment bypass was investigated in a coastal area of Liguria (Italy, NW Mediterranean). This area harbours two contiguous pocket beaches separated by a headland that can be considered as a geomorphic and hydrodynamic limit of two littoral cells. Surveys using a single- beam echo sounder were carried out in order to update historical data on the morphology and hydrodynamics of the area. Sediment samples were collected from the foreshore and the nearshore in two pocket beaches, and sediment (including gravel) transport patterns around the headland were described. Distribution and state of health of the endemic seagrass Posidonia oceanica were assessed in order to explore potential links among sediment transport, hydrodynamics, and meadow development. A rip current transporting sediments with an updrift origin to the downdrift beach was evidenced, causing gravel sediment bypass between the two contiguous littoral cells. The direction followed by the rip current was largely influenced by the P. oceanica meadow, which hindered its flow towards the open sea. The shape of sediments and their grain size have been shown to play a significant role in the sediment transport patterns around the rocky headland. [ABSTRACT FROM AUTHOR]

Traditionally, an edge wave is measured along a long and straight coast with pressure-gauge arrays to acquire the frequency-wavenumber for dispersion relationships. Ideal measurement locations are limited, and the cost of purchasing and operating some 20 instruments emerges as a threshold requirement. In the present study, one instrument measuring both the bottom pressure and the flow velocity was used to retrieve edge-wave information on the east coast of Taiwan outside the Hua-Lien Harbor. Using the progressive linear-wave assumption for irrotational and inviscid shallow water provided the pressure-flow relationships for both the infragravity edge and leaky waves. The relationship for edge waves was helpful in identifying the edge-wave mode, whereas the relationship for the leaky waves eliminated the possibility of incorrectly interpreting a leaky wave as an edge wave. Applying this approach to field measurements on the east coast of Taiwan shows that a Stokes edge wave is a significant component in the band of period 70-120 seconds before the landfall of a typhoon coming from the southeast but still hundreds of kilometers from Hua-Lien Harbor. This result suggests that the approach being presented can be applied in the real ocean, and a unique method for taking into account edge waves may need to be considered for the resonance problem that occurs in Hua-Lien Harbor during passing storms. [ABSTRACT FROM AUTHOR]

The short-term dynamics of a dredged tidal sandbank (the Kwinte Bank, southern North Sea) are examined, on the basis of field measurements and ID sediment transport modelling. The field measurements include current data from shipborne Acoustic Doppler Current Profiler (ADCP) and from moorings (ADCP and electromagnetic S4), collected across the bank during a nominal (spring) tidal cycle, and during 7 tidal cycles, respectively. The dynamics of the bank are described in terms of tidally-averaged (residual) currents and (net) bedload transport. The results indicate a predominance of ebb flow during the period of study. Convergence of (net) bedload transport is predicted, from both flanks towards the crest of the bank. The exact location of the sand transport convergence zone varies, in the short-term, according to the prevailing tidal currents. The observation of clockwise veering of the peak ebb and flood currents over the bank indicates that this sediment transport pattern relates, at least partially, to tidal rectification of the flow. In relation to dredging, the present study suggests that the presence of a (dredged) depression at the crest of the bank influences locally the short-term hydrodynamics. The currents are channelised, and the across-bank peak (near-bed) flow is enhanced towards the crest. Net erosion of the depression is predicted, over the tidal cycle considered. More data are needed to evaluate the morphological evolution of the trough over the long-term. [ABSTRACT FROM AUTHOR]

Embayed beaches bounded by headlands, headland bay beaches, are a common feature along the coast of southern China. The patterns of sediment transport pathways in these beaches are important for understanding changes in beach and nearshore geomorphology that are a response to different wave energy conditions. Nanwan Beach in southern China is characterized by a large seasonal variation of incident waves. In this study, sediment samples and a series of beach profiles from Nanwan Beach are examined to determine spatial changes in sediment transport pathways. Empirical orthogonal function analysis of the profile data indicates that the variation of sediment transport occurs in two distinct modes. The first mode is related to seasonal changes in cross-shore sediment transport with associated alongshore sediment transport. The trend of sediment transport is seaward in winter and landward in summer. The second mode is onshore-offshore sediment exchange, which occurs in the intertidal zone in summer and in the swash zone in winter. Moreover, grain size trend analysis of sediment samples suggests that sediment transport in the nearshore zone is predominantly in the northwesterly direction because of southeast incidence waves in winter, with Nanwan Bay opening to the south. The sediment transport pathways are to the north in summer from the influence of typhoons. [ABSTRACT FROM AUTHOR]

Predicting the morphological impacts and associated hazards of extreme storms on barrier islands is facilitated by examining historical poststorm images and identifying the predominant alongshore and cross-shore patterns of erosion and deposition for different island segments. Morphological changes on the Mississippi-Alabama barrier-island chain produced by 12 Category 3 and stronger hurricanes since 1852 were analyzed to investigate whether barrier-island responses to extreme storms are controlled primarily by local geomorphic conditions or primarily by storm characteristics. Results of those analyses demonstrate that (1) antecedent topography and geomorphic conditions (island width, land elevations, nearshore bathymetry, subaqueous-boundary conditions) tend to exert greater control on local barrierisland impacts than storm parameters (path, intensity, wind speeds, water levels, shelf duration), and (2) types and alongshore patterns of storm overwash and island breaching are commonly repeated for the same island segments. Even when impact patterns are identical, magnitudes of sequential impacts, such as the inland distance of sediment transport, are unequal and are controlled by storm parameters (water levels, wind speeds) that influence wave heights, overwash-flow depths, and current velocities. [ABSTRACT FROM AUTHOR]

Long-term studies (1989-2007) of the gravel beaches in Prince William Sound, Alaska, conducted as part of the Exxon Valdez oil spill monitoring programs, provide the basis for understanding the geomorphology and sediment dynamics of these intermittently exposed, coarse-grained gravel beaches. There are key differences between these beaches and open-ocean gravel beaches, including bermlike ridges that occur at different levels on the beach as a result of the diurnal inequality of the tides. The 1964 earthquake, with up to 3.5 m of uplift, provided information on sediment transport patterns and rates. In less than 25 years, a stable cobble/boulder armor formed on the upper and lower platforms, and the beaches reached a steady-state or graded condition. Eighteen years after the spill, oiled sediments were still present at depths greater than about 25 cm on beaches with a stable armor in the middle and lower intertidal zones. Cleanup efforts to remove the deep oil penetration into the porous gravel of the upper intertidal zone provided an indicator of short-term rates of sediment erosion and deposition. Where the high-tide berms were pushed onto the middle intertidal zone, they quickly reformed, usually after a few storms. However, the storm berm that was relocated for 2000 m along one of the most exposed shorelines in Prince William Sound took 6 years to recover. Data on the occurrence of gravel beaches in North America show that they are most common (comprise 48% of the shoreline) on paraglacial, leading-edge coasts and least common on nonparaglacial, trailing-edge coasts (~2% of the shoreline). [ABSTRACT FROM AUTHOR]

The coastline of Hai Hau District, located on the northeast coast of Vietnam with about 30 km of shoreline, is chronically eroding. Previous studies have tried to highlight the main causes of the erosion along this coastline, and several hypotheses exist. To examine the hypothesis that gradients in the longshore sediment transport rate and cross-shore fine sediment lost offshore are the main causes generating the serius erosion at Hai Hau Beach, a newly developed numerical model of shoreline change based on the one-line theory was applied and compared with data. Sea dike segments, reinforced by stones and mortar, were modeled using a seawall boundary condition, and the sediment continuity equation was modified to take into account the offshore transport of fine-grained sediment. The simulated shorelines agreed well with the measured shorelines, both for the calibration and validation periods. The calculated sediment budget shows that the net sediment transport is in the southward direction and that a large amount of finegrained sediment is lost into deep water. These two sinks of sediment are believed to be the main causes of the serious erosion at Hai Hau Beach. [ABSTRACT FROM AUTHOR]

Field measurements of tidal current velocities are used to infer sediment transport characteristics in the lower section of a large, tidally dominated estuarine system at Whangarei Harbour, New Zealand. Recent (2002) developments at the harbour entrance included a 32.6 ha intertidal reclamation and a 31.8 ha dredged turning basin. Residual distance vectors indicate that the postdevelopment, large-scale pattern of sediment transport dynamics remains consistent. Minor, localised modification of transport potentials has been observed immediately adjacent to the developments, however. These modifications include a slight realignment of current flows near the reclamation wall and some leakage from a previously identified transport loop near the dredged basin. The potential for scour is identified along the eastern margin of the dredged basin, which could act to remove material moving downslope into the basin from its western edge. These data are consistent with numerical model results that predicted minimal consequences resulting from the developments. Lower harbour sediment dynamics are consistent with established patterns for tide-dominated inlets, with separation of the channel into areas of ebb and flood dominance, and typical transport patterns over the flood tidal delta. Broad-scale inlet geomorphology has been maintained, which is consistent with other dredged tide-dominated inlets. [ABSTRACT FROM AUTHOR]

Marsh surface deposition, suspended sediment concentrations, tidal hydrodynamics, and marsh surface characteristics were measured within a tidal creek system of a west-central Florida, microtidal, open marine Juncus roemerianus marsh to examine the depositional relationship between a creek system and the surrounding marsh during nonstorm conditions. Results suggest that short-term marsh deposition is highly episodic with deposition showing an inverse relationship with marsh surface inundation. Deposition was greatest at marsh sites adjacent to secondary creek segments over all examined timescales. Variations in hydroperiod, time-velocity asymmetry, vegetation density, and sediment availability could not explain the observed differences in short-term deposition. [ABSTRACT FROM AUTHOR]

A coherent approach to structuring reference units for coastal vulnerability analysis is often required for large-scale analyses of the coastal system. However, a review of existing spatial reference frameworks within vulnerability analyses demonstrates that our use of coastal space within large-scale models remains relatively poor. This paper examines a series of challenges to spatial modeling that have emerged from the development of a national to global impact tool, DIVA (Dynamic Interactive Vulnerability Assessment). The paper addresses how best to utilize the limited data to develop a reference framework for modeling vulnerability within the global coastal environment. It outlines the approach to spatial modeling that has been developed for use within the DIVA tool: segmenting the coastal zone into a series of relatively homogenous reference units at the scale of DIVA, based on the behavior of the physical, social, and economic systems within the zone. The importance of effective spatially defined models is emphasized within the paper. Encouraging greater spatial recognition and definition of the behavioral environment of the coast is critical to modeling space within the coastal system. By decreasing spatial uncertainties in the creation of reference units for vulnerability analysis, the accuracy of modeling within large-scale coastal environments can be further improved. [ABSTRACT FROM AUTHOR]

Grain-bed collision is a key component of saltation, but substantial uncertainty remains regarding many aspects of this process. Previous empirical work is used to develop a conceptual model of this process that accounts for the partitioning of impact energy between rebounding grains and the bed. The model envisions two distinct collision regimes: (i) a quasi-elastic regime at low impact speeds and (ii) an inelastic regime at high impact speeds. In the quasi-elastic regime, colliding grains retain a constant proportion of their kinetic energy, and thus rebound at speeds that are proportional to the impact speed and shear velocity. In the inelastic regime, colliding grains retain a fixed and limited amount of kinetic energy, transferring any excess above this limit to the bed. Rebound speeds are thus constant and independent of both impact speed and shear velocity. Impact energy transferred to the bed is expended in ‘deformation’ (i.e., ejection, rearrangement, etc. of bed grains). These two collision regimes are separated by a critical impact speed/kinetic energy level that is controlled by bed texture (more directly, by the inertia or resistance to motion of the bed grains). Field measurements under near-threshold conditions are found to correspond to the higher speed inelastic regime, suggesting that inelastic collisions predominate in aeolian saltation on loose, unconsolidated sand beds. The quasi-elastic regime might therefore only be pertinent for reptating grains, or in situations in which interparticle bonding (from crusts, surface moisture, etc.) increases the ‘effective’ inertia of bed grains and thus the critical impact speed separating the two regimes. It is also shown that rebound speed in the inelastic regime varies in inverse proportion to grain size (mass), so that particles rebound with an approximately constant level of kinetic energy regardless of size. Thus, larger grains will rebound at smaller speeds and follow lower, shorter trajectories, providing a mechanism that accounts for the commonly observed size sorting of grains subjected to aeolian saltation. [ABSTRACT FROM AUTHOR]

High-frequency measurements of airflow from ultrasonic anemometers and time-averaged cup anemometer profiles were taken during an oblique alongshore sand-transporting event (6.7 m/s) over a vegetated foredune in May 2002 as part of a larger study on the sedimentary dynamics of a beach-dune complex in Greenwich Dunes, Prince Edward Island National Park, Canada. Local flow and sand transport pathways deviated significantly from the regional wind because of topographic steering of oblique alongshore airflow on the beach back toward the foredune in the backshore. Flow decelerated on the lower seaward slope of the foredune because of flow stagnation and vegetation-induced roughness effects. On the upper seaward slope, flow veered crest-parallel because of secondary flow effects, including potential flow reversal, acceleration, and interaction with faster regional flow. An inflection point in velocity profiles indicates a momentum sink at plant canopy height, and above this height exists a distinct shear layer. Flow acceleration occurs only on the upper slope above the plant canopy as the shear layer intensifies. Flow steadiness, as indicated by the coefficient of variation in horizontal (U) and vertical (W) velocity, also declines up the seaward slope, in contrast to measurements of flow over unvegetated dunes, perhaps because of increasing vegetation-induced drag and turbulence. Gusting and vertical bursting was evident as honami motion in the beachgrass and was responsible for maintaining intermittent saltation into the foredune. Temporal correlations exist between U, W, and flow angle. As flow shifted onshore, both U and W increased because of enhanced topographic forcing and increased vertical lift on the lower seaward slope, whereas when flow shifted alongshore, U and W declined because of reduced forcing and acceleration effects because the dune is effectively less steep to flow. Although these dunes align well with the vector of the regional resultant sediment drift potential, sand transport pathways followed local flow vectors of varying magnitude and direction. Offshore to oblique alongshore winds are typical of the summer wind regime, and, although frequently incompetent, they contribute to dune maintenance by cycling sand to the backshore for incipient foredune growth, scarp infilling, or both. To date, the role of secondary flows under alongshore winds in foredune morphodynamics has not been well documented. [ABSTRACT FROM AUTHOR]

Sediment transport across a foredune and beach at Ocean City, New Jersey, was examined to identify the effect of houses, dune topography, sand fences, vegetation, and wrack lines during an offshore wind. Houses are as close as 18 m from the crest of the 2- to 3-m-high foredune and are up to 9.0 m high and 12.8 m wide and spaced 4.0 to 5.0 m apart. Data were gathered during a 1-day study on 3 March 2003 with the use of 15 vertical sand traps, 13 erosion pins, and eight sets of anemometers placed 0.3, 0.6, and 0.9 m above the ground surface. Wind speeds 0.9 m above the ground ranged from 1.61 to 3.75 m/s. Trapping rates were negligible on the vegetated dune crest and up to 2.03 kg m-1 h-1 near mid foreshore. The highest rate of trapping was 2.4 kg m-1 h-1 at a <10-m-wide unvegetated area in the dune. Houses shelter the dune from offshore winds and might contribute to dune stability. Increases in wind speed in the offshore direction cause greater rates of transport on the seaward side of the dune where vegetation has not had time to become established. Dune vegetation, remnant sand fences, wrack lines, and the sheltered area in the lee of the seaward dune ridge can trap sediment moving offshore during relatively low wind speeds. Sediment deposited at these obstacles could contribute to deflation of the backshore, which is the primary source of sediment moved to the inter-tidal foreshore. Losses of sediment from unvegetated portions of the dune to the beach can be overcome by replacing sand fences and suspending beach raking until the calmer summer months. [ABSTRACT FROM AUTHOR]

A cross-shore profile evolution model, Uniform Beach Sediment Transport-Time-Averaged Cross-Shore (UNIBEST-TC), is used in the present study. The model was developed at WL/Delft hydraulic laboratory in the Netherlands and comprises a conglomerate of submodels representing identified processes of cross-shore sediment transport. Validation of UNIBEST-TC was carried out using the collected field data at the Egmond site in the Netherlands and at the Duck site in the US. The model is capable of predicting wave height and wave direction for both sites (Egmond site and Duck site). The prediction of long-shore current is reasonable for the Egmond site, but it is unsatisfactory for the Duck site. The difference between the measured and the predicted values for long-shore current and cross-shore current is partly due to the difference between the measured values, which are at a certain depth, and the predicted values that are depth-averaged velocity. Beside that, the turbulence in the breaker zone leads to errors in the measurements, which could be another factor. It is shown in the present study that on relative small scales, opposite morphological behavior is present. Therefore, morphodynamic profile modeling requires a representative characteristic bottom profile. To achieve a qualitative data for the calibration of the model, it is suggested that field measurements should include error ranges. Furthermore, the effect of small variations of the water depth on the processing of the signals should also be taken into account. [ABSTRACT FROM AUTHOR]

The greatest change in particle roundness, sphericity, and size in most fluvial systems generally occurs in the initial first few kilometers of sediment transport. Observations in natural settings and laboratory experiments have shown that changes, such as increased grain rounding and decreased size due to particle breakage, wear, and attrition, tend to be progressive along the dispersal path. In marked contrast, this study records highly variable and poorly developed particle-texture trends downslope along short (<5 km) channels that extend directly from a high-relief carbonate source area down to the shore of Lake Annecy in the western Alps, SE France. The observed inconsistent patterns are measured in both a region-wide analysis using all collected samples and also in a more specific survey of samples in six different channels incised on the steep, topographically irregular mountain flanks that border the lake. The major factor responsible for the irregular downslope patterns of roundness, sphericity, and size in the Annecy study area is the lateral introduction of sediment into the fluvial channels along dispersal paths. Episodic failure of mechanically unstable sediments and their transport down steep valley walls bring less-abraded sediment of variable shape and size along the dispersal paths. The valley wall sediment influx factor warrants further examination to better interpret sedimentation processes in dissected, high-gradient terrains that border coastal areas. [ABSTRACT FROM AUTHOR]

Sorting of sediment on a beach occurs when the cross-shore profile consists of graded sediments. Each grain-size fraction within a mixture responds differently to the same hydrodynamic regime. Sorting of sediment under wave action takes several forms. Stratified layers of finer and coarser sediment are formed, depending on wave climate, grain size, and beach slope. Grain size and sorting studies are of great importance in characterizing the dynamic beach environment. Some field data have been reported in the literature. In the present study, the cross-shore distribution of sediments, as well as the corresponding beach profiles, were measured in a wave basin on 1:5 beach slope for regular waves. Eighteen sets of experiments were performed on cross-shore sorting mechanisms using two different sand beds. The sorting of bed material and the formation of armor coats along beach profiles were defined by grain-size distribution and dimensionless parameters in this study. The experiments showed that finer material was deposited on the crest of bar-type beach profiles, but coarser grains accumulated on the foreshore, trough, ridge, and toe sections. Finer materials settled on the foreshore and crest of step-type profiles while coarser grains were deposited on the ridge and toe sections. The effect of the movement of a particular fraction on the sediment transport rate was also studied. Calculated sediment transport, modified to include the effects of sorting, was compared with transport rates measured in the wave basin. This suggested that the results under the experimental conditions were satisfactory for the description of sediment transport in the surf zone using the partial sediment transport mechanism over the beach profiles. [ABSTRACT FROM AUTHOR]

A port complex was implanted in the coast region of Suape, PE-Brasil, in 1979–80, which altered the geomorphological and hydrodynamic conditions of the area, mainly in the estuary of the Ipojuca River. Water samples were collected from the surface and the deep layer to determine the salinity, pH, dissolved oxygen, transparency, and temperature from three fixed stations in the estuary of the Ipojuca River during the summer and winter before (1978) and after (1986–87) the port's construction, in order to evaluate the effects of the port-induced changes. The data were subjected to a principal component analysis and to individual t tests. The first principal component, the axis of maximum information, alone explained 50% of the total variance, being associated with the generalized increase of the chemical parameters after the port's construction, mainly the salinity. Despite the fact that the results of the t tests presented significant differences only for the dissolved oxygen, pH, and temperature, the increased salinity produced the greatest ecological effects in the estuary. The water flow of the Ipojuca River was diverted toward the ocean, decreasing the river-flow velocity at the mouth. This decrease in flow caused a sedimentation in the area, a decrease in the circulation and depth, and a transformation of the mouth of the river into a coastal lagoon with an increase in evaporation and salinity. A delay of more than 2 hours was observed in the dynamic tide in relation to the normal 6-hour cycles. Despite an increase in the concentration of dissolved oxygen and transparency values, effects that theoretically improve environmental conditions, a morphological transformation occurred that caused drastic changes in the estuary's circulation and in the tidal currents. [ABSTRACT FROM AUTHOR]

The decrease in longshore sediment volumes from north to south, calculated for littoral cells between inlets, indicates significant loss from the littoral drift system along the Florida east coast or localized deposition. The decrease in littoral drift volume from about 490,000 m³ of sediment over a distance of about 550 km (average diminution rate of about 890 m³ km-1) was traditionally accounted for in terms of alongshore deposition and some unknown degree of speculated offshore transport. With the application of laser airborne depth sounding (LADS) technology to bathymetric survey in southeast Florida (2001–2003), recognition of detailed bottom topography became possible for the first time. Significant in this regard was the bathymetric display of macro- and mesoscale morphological features that showed areal continuity of sandy bottoms and the prominent but disjunctive occurrence of relict barrier coral reef tracts that line the shelf edge. Identification of gaps in the line of barrier reefs showed pathways of cross-shore sediment transport from the inner shelf to offshore beyond the shelf edge. Diabathic sediment transport through these reef gaps robs the littoral sediment package by allowing the chuting of sediments during high energy events or when the backreef flats over fill with sand. The reef gaps are thus leaky valves where littoral sediments are periodically chuted offshore and lost from the littoral drift system. [ABSTRACT FROM AUTHOR]

Although, a variety of methods have been employed to determine sediment transport along Goa coast, the results differ in some sections. Fifteen studies have been reviewed, compared, re-assessed and a corrected shore drift map of the Goa coast is prepared and presented. Advantages and limitations of these methods are discussed. The present review and re-assessment confirms that, though sediment transport is bi-directional, the long-term net shore drift direction along Calangute and Colva beaches is southward. The overall net shore drift direction along Goa coast is also towards south. It is qualitatively determined that except for 3 short drift cells, shore zone has long-term stability. Finally, it is concluded that landform indicator study using remote sensing can be an effective method for determining tong-term net shore drift along the coast. [ABSTRACT FROM AUTHOR]

The inlet of the Lagoa dos Patos lagoon is located in the southwest sector of the exceptionally long barrier-lagoon system of Rio Grande do Sul, Brazil. Historical morphological changes resulting from the interaction between waves and lagoonal flow at the lagoonal mouth were evaluated using data from 26 bathymetric charts made from 1883 to 1909. Before the 3 km long jetty was constructed in 1911, the inlet was fronted by a well developed ebb-tidal delta with a half-moon shape. Here because of wave action swash bars formed and migrated towards the shoreline over the swash platform of the ebb delta. The time between formation and attachment to the mainland of a swash bar here was about 5 years. During this five year period the swash bar has enlarged significantly and migrated 600 m across the swash platform at an average rate of migration of 120 m/year. [ABSTRACT FROM AUTHOR]

Microtidal estuaries are common on the world's coastline and a variety of forms have been described from different environmental settings. Studies around the South African coast indicate the presence of two main categories of microtidal estuary (river- and tide-dominated) with near-permanent surface water connections with the sea. Inlets of tide-dominated microtidal estuaries are maintained by tidal currents and contain a distinctive tripartite facies variation along the estuary axis. Inlets of river-dominated estuaries are maintained by river discharge and contain river-dominated back-barrier sediments adjacent to the estuarine barrier. The development of each of the types of system depends on fluvial sediment supply, fluvial discharge, coastal gradient and nearshore sediment dynamics. While a broad spatial pattern exists in the development of these types of estuary, evolutionary pathways are described that link the two types of system (and other estuary forms) in a space-time continuum. The management implications of these findings are discussed. [ABSTRACT FROM AUTHOR]

Duxbury Beach is a retrograding barrier system located along the South Shore of Massachusetts Bay. The barrier fronts a large embayment consisting of a broad supratidal marsh in the northern sector grading to intertidal flats and open water to the south. Radiocarbon dates indicate that the barrier began forming sometime prior to 3,700 14C years BP. The paucity of sediment combined with rising sea level have produced a relatively low barrier ranging in width from 95 to 285 m. The foredune is discontinuous and storm washovers are common. Historical maps and coastal charts indicate the presence of several former tidal inlets along the length of the barrier, although none exist today. Ground-Penetrating Radar (GPR) surveys suggest a minimum of 18 paleo-inlets along the barrier as indicated by large-scale channel cutand- fill structures. Former inlet channels range from 60 to 285 m in width and are typically 3 to 6 m deep. The ephemeral character of the inlets and their diminutive size are a product of their inability to capture a significant portion of the bay tidal prism. Seven channel fill patterns were documented in the GPR records; the three major types include prograded, conformable, and complex. The patterns of subsurface reflectors reveal that former inlet channels infilled by a variety of processes including simple spit extension from one or both sides and channel aggradation through landward sediment transport. Statistical analyses indicate that generally the position and geometry of former tidal inlets are unrelated to present barrier dimensions or offshore bathymetry, however, there are correlations with bay morphology and hydraulics as well as barrier stratigraphy. In one instance, a relatively wide paleo-inlet coincides with a moderately large bay tidal channel. Deepening of another inlet appears to be related to migration of its channel toward a resistant till headland. This study demonstrates that tidal inlet fill deposits can comprise a significant portion of the coastal lithosome along retrograding barriers (>25% at Duxbury Beach). [ABSTRACT FROM AUTHOR]

An unusual longshore grain size 'variation series' is examined on North Beach, Kaikoura, for two related reasons: To identify the processes that have been responsible for creating the sediment pattern and; to establish whether there is a relationship between these processes and an erosion problem on the Kaikoura township foreshore. A study of North Beach over 30 years ago revealed an unusual curvilinear grain size pattern that phased in a regular fashion from gravel to sand alongshore, but how such a pattern formed was unknown. Research conducted by the author over three decades later reveals that this same pattern still exists in the beach. Sixty-four surface sediment samples were analysed and modeled by a range of techniques that enabled a thorough examination of the sediment characteristics of the beach. The distinctive longshore variation series is explained fundamentally as two linear grain size series occurring one after the other, and is a combination of modern and relict features. Previously it has been assumed that the Hapuku River has supplied all the sediments to North Beach by a simple southward drift of gravels and sands. Whilst this is partly true, it was determined that a second source, the Kowhai River was also active in the past, contributing materials to the southern part of the shoreline. Sediments from this old source are still present in the beach, preserved by a unique combination of local geomorphological features, and are in effect relict. The Kowhai River has since migrated further south, and this in combination with a recent period of tectonic uplift has caused sediment starvation and subsequent erosion of the township foreshore. Essentially, this links the processes responsible for the longshore sediment grain size pattern with the erosion problem. These findings highlight the importance of source area characteristics and challenge a common assumption that because beaches are dynamic systems, sediment patterns on them must reflect contemporary hydrodynamic processes. [ABSTRACT FROM AUTHOR]

Ridge and runnel beach topographies have been extensively studied in the literature of beach dynamics. Empirical and numerical approaches have attempted to explain the formation and evolution of such morphological features. This paper reports on an investigation conducted at Dundrum Bay, Northern Ireland, to study the morphodynamics of a ridge and runnel topography set in a low energy fetch limited macrotidal coastal environment of the Irish Sea. The study focussed on the potential effects of wave action as interpreted from deep water records and numerical modelling of shoaling across the extensive surf zone. Extensive wave propagation simulations were conducted over a highly detailed topographic representation of the ridge and runnel system acquired by Differential Global Position System survey (accuracy sub-centimetre). Simulations showed that energy levels on incoming waves decreased progressively as water depth decreased and slopes increased. The first (most seaward) bar acts as a buffer for incoming waves and the patterns of wave energy dissipation suggest that onshore sediment transport may occur from the seaward face of the bar towards the top of the feature. Wave energy is subsequently lower on more landward bars. A conceptual behavioural model for the morphodynamics of ridge and runnel topography is presented based on the wave analyses. [ABSTRACT FROM AUTHOR]