Headland-bay Beach Research Articles

Equilibrium of Crenulated Bays in Thailand

The C coefficients in the now well-known parabolic bay shape equation (PBSE) are the most important parameters for verifying the bay beach stability or designing a headland bay beach in static equilibrium. These coefficients are revised specifically for bays in static and dynamic conditions in Thailand. Three techniques, namely Least Square (LS), Genetic Algorithms (GA), and Differential Evolution (DE) are used to determine the alternative coefficients. The newly derived C coefficients for static equilibrium bays (SEB) differ slightly from the original coefficients. Dynamic equilibrium bays (DEBs) with sediment within the embayment are analyzed to obtain a new set of C coefficients, which are a function not only of wave obliquity but also sediment supply ratio (SSR), which is a new parameter representing the ratio between the rate of sediment supplied from a river source to the bay and the longshore sediment transport rate. The resulting new C coefficients for DEBs vary uniformly and systematically, similar to those for the SEBs, and are expected to be applicable to DEBs elsewhere for coastal management.

Beach response due to sand nourishment on the east coast of Malaysia

The Cempedak Bay beach stability assessment was performed by comparing the spatial and temporal pattern of beach variability before and after sand nourishment. The analysis of temporal sand volume patterns shows that the beach has lost about 6% or 10 000 m3 volume of sand which is equivalent to 4 m3/m per year from the nourishment zone over the 2·5-year monitoring period. The present shoreline recession rate is established to be 1·7 m/year (valid for data set of March 2005 to July 2007). The analysis of seasonal changes is assessed through temporal beach volume patterns, which indicate that shoreline variability can be characterised by an alongshore rhythmic pattern of alternating seasonal behaviour. A simple seasonal transport pattern is proposed to account for alternating erosion and accretion. The temporal distribution pattern of beach level changes reveals the existence of a nodal point around 40 to 50 m offshore, which is influenced by the monsoonal system. The spatial distribution of the beach width indicates that the northern beach area is wider whereas the southern beach area experiences lower beach width, which is coincident with the temporal pattern of sand volume and beach profile changes. A slight beach rotation does exist attributed to a seasonal or periodic shift in wave climate, in particular wave direction. The planform stability of the beach is tricky to determine due to model uncertainties, especially the selection of the diffraction point. This baseline study is important towards the development of a process-based model in order to investigate the morphological nearshore behaviour of headland bay beaches.

An insight into headland sand bypassing and wave climate variability from shoreface bathymetric change at Byron Bay, New South Wales, Australia

Abstract The headland sand bypassing mechanisms in the Eastern Australian longshore sand transport system are investigated at Cape Byron, in response to wave climate variability. The mechanisms are interpreted from shoreface bathymetric change between surveys in 1883, 2002 and 2011 CE. They involve a split in the sand transport to follow a nearshore path along the inner bar and a cross-embayment path connecting the up-coast and down-coast outer bars. The relative magnitude of the net sand transported via the two pathways is controlled by a rotation in directional wave conditions. Two bypassing mechanisms were interpreted: (i) a predominantly cross embayment transport during unimodal east–southeast wave climate such as those interpreted for the period prior to 1883; and, (ii) a split transport between the inner nearshore and cross-embayment paths during a bimodal dominant south–south-easterly and sub-dominant east–north-easterly wave climate such as in the 2000s. The net sand transport bypassing Cape Byron was dominated by a connected outer bar system prior to 1883 and conversely, a stronger inner bar system during the 1960s to 2000s. This is manifest in the 10° rotation in seabed morphology and shoreline planforms. These changes are in accordance with decadal climate variability described by the Interdecadal Pacific Oscillation (IPO). The switching between headland sand bypassing mechanisms on interannual to decadal timescales determines the geometry of the bypass strand with the downcoast littoral zone and has important implications for understanding the shoreline rotation and the application of the headland-bay beach concept to predicting planform curvature in open compartments.

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 Sao Vicente at the south-western tip of Portugal, in combination with SW–SE wind wave climates impinging on the northern shoreline of Cadiz 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.

Wave-driven sediment transport and beach-dune dynamics in a headland bay beach

This paper presents a comprehensive study of wave refraction, wave and wind driven sediment transport, foredune development and Holocene barrier evolution over a variety of time scales at Moçambique Beach, Santa Catarina State, Southern Brazil. The motivation for this study was to examine the relationships between estimated wave driven sediment transport, medium and long term aeolian transport, foredune development, and Holocene barrier volumes and morphology. An analysis of 2years of wave rider data for the region shows two well defined peaks of frequencies: one of swell waves from the south with a period of 12s, and another peak of sea waves from east-northeast with a period of 7s. Longshore sediment transport rates were calculated using high resolution hindcast wave data for the South Atlantic Ocean, which was calibrated by the measured buoy data. The dominant southerly waves drive a longshore gradient in wave energy from south to north, and nearshore/surf zone sediment transport increases from south to north. Beach grain size is fine in both the south and north, and medium in the center. The combination of grain size and wave energy variations creates a marked alongshore variation in surf zone beach types ranging from low energy dissipative in the south, moderate energy intermediate in the central area to moderate to high energy dissipative in the north. Estimates of aeolian sediment transport, volumetric changes in foredune deposition and total Holocene dunefield volumes were also calculated. Results indicate that the morphological behavior of the foredune profiles reflects the gradients of longshore sediment transport and the exposure to wind energy and aeolian sediment delivery, with a maximum of sediment volume and transport towards, and in the central part and northern end of the barrier. Holocene (0–7000years) barrier volumes vary along the embayment, mimicking the trends in both calculated wave and wind driven sediment transport. The Short and Hesp (1982) model was more suitable in predicting the long term (Holocene) barrier evolution than the size and volume of the foredune. The combination of wide beach, high energy dissipation, maximum sediment supply, and high exposure to strong onshore winds is found in the northern end of the embayment where Holocene subaerial barrier volumes are at a maximum. Overall, this study proves that foredune development is closely related to wind exposure, wave energy and gradients of longshore sediment transport, and that dunefield development reflects the increase downdrift in potential sediment supply from the southern to the northern end of the beach, and the change alongshore from low energy dissipative, through intermediate, to high energy dissipative beach-surf zone environments. This paper significantly extends previous models of beach and dune interactions in that it (i) actually determines wave driven sediment transport for various sections of a long embayment, (ii) relates those transport patterns to surf zone/beach morphodynamic types and variations in alongshore sediment patterns, and (iii) correlates foredune volumes and Holocene barrier volumes (which reflect proxy Holocene onshore transport rates) with wave driven sediment transport rates.

Shoreline change patterns in sandy coasts. A case study in SW Spain

Coastal changes on sandy shorelines are continuous and occur at diverse spatial and temporal scales. Gaining knowledge on beach change processes increases our capability to manage risks, especially shoreline erosion, affecting the increasing population living in coastal areas. Processes and factors involved in medium- and short-term beach changes depend on the morphological and dynamic characteristics of the coast. In this work, the decadal behaviour of 58 sandy beaches along the 150km long South-Atlantic coast of Spain, between the Guadalquivir river mouth and the Strait of Gibraltar, is analysed in order to investigate the relationships between shoreline change patterns and the diverse morphological and dynamic factors controlling beach evolution in the area. For this purpose, georectified aerial photographs spanning the period 1956–2008 were compared in a GIS environment to calculate rates of shoreline change. Short-term evolution of beach profiles was also analysed in selected areas of interest.Results show that the study area exhibits a great variety of shoreline evolution trends, with erosion prevailing in the northern and central sectors and stability or even accretion in the southern sector. In general, sediment availability is the main factor determining coastal erodibility in the area, largely conditioned by the reduction in fluvial sediment supply caused by river basin regulation. Nearshore bathymetry also has a great significance, as it controls wave refraction-diffraction patterns and wave energy concentration on certain zones. Human interventions on the coast also represent a major influence on beach erodibility in the study area. Severe detrimental effects are caused at certain points by shore-normal engineering structures blocking longshore drift. Additionally extensive urban development in backbeach environments has a significant influence on the sediment budget at certain areas.On the basis of these results, a morphological and evolutionary classification of sandy beaches is proposed taking into account the way beach morphology influences erosion/accretion processes. Rectilinear beaches and enclosed beaches typically show dynamic equilibrium or even accretion trends, whereas reef-supported beaches tend to be dominated by erosion. Headland-bay beaches show complex evolution patterns greatly influenced by local conditions, such as specific shoaling processes or local winds. This classification is useful not only in forecasting general shoreline behaviour in the near future, but also in selecting the most appropriate type of intervention when managing retreating coasts.

Historical changes in the shoreline and littoral processes on a headland bay beach in central Chile

We applied parabolic and logarithmic adjustments and methods of cartographic overlay to the sandy littoral of Concón bay (Central Chile) to determine the changes associated with the shoreline and their relation with littoral processes, in a typical bay on an active continental margin and with a microtidal regime. A set of historical reference points was built by means of aerial photographs and topographies for the period 1945–2008. Given the form of the shoreline, to the southern section of the bay we applied the classical logarithmic formula of Yasso (1965) and the functions incorporated in the Coastal Modeling System (Sistema de Modelamiento Costero, SMC) of the Universidad de Cantabria. In the northern section a method of map overlay was applied. The Oluca-SP model of the SMC was used to determine the influence of waves (refraction) on the types of changes of the shoreline. Information on waves (1985–2006), mean sea level (2001–2006) and variations in the mean size of beach sediment were used to relate the changes in the plan form of the bay. There has been little spatio-temporal variability in the shoreline of the bay over the last 65 years. The southern section had a mean shoreline retreat rate of − 0.55 m/year (1945–2008) in spite of the large variability produced in an estuary dominated by waves. The best adjustment was obtained with the logarithmic function. In the northern section the mean accretion rate was 0.39 m/year (1954–2008). The plan form and the historical changes of the shoreline are closely associated with the seasonal changes of the waves and the presence of rocky thresholds in the area. The mean sea level did not produce important effects in the types of change.

Study on headland-bay sandy coast stability in South China coasts

Headland-bay beach equilibrium planform has been a crucial problem abroad to long-term sandy beach evolution and stabilization, extensively applied to forecast long-term coastal erosion evolvement and the influences of coastal engineering as well as long-term coastal management and protection. However, little concern focuses on this in China. The parabolic relationship is the most widely used empirical relationship for determining the static equilibrium shape of headland-bay beaches. This paper utilizes the relation to predict and classify 31 headland-bay beaches and concludes that these bays cannot achieve the ultimate static equilibrium planform in South China. The empirical bay equation can morphologically estimate beach stabilization state, but it is just a referential predictable means and is difficult to evaluate headland-bay shoreline movements in years and decades. By using Digital Shoreline Analysis System suggested by USGS, the rates of shoreline recession and accretion of these different headland-bay beaches are quantitatively calculated from 1990 to 2000. The conclusions of this paper include that (a) most of these 31 bays maintain relatively stable and the rates of erosion and accretion are relatively large with the impact of man-made constructions on estuarine within these bays from 1990 to 2000; (b) two bays, Haimen Bay and Hailingshan Bay, originally in the quasi-static equilibrium planform determined by the parabolic bay shape equation, have been unstable by the influence of coastal engineering; and (c) these 31 bays have different recession and accretion characters occurring in some bays and some segments. On the one hand, some bays totally exhibit accretion, but some bays show erosion on the whole. Shanwei Bay, Houmen Bay, Pinghai Bay and Yazhou Bay have the similar planforms, characterized by less accretion on the sheltering segment and bigger accretion on the transitional and tangential segments. On the other hand, different segments of some bays have two dissimilar evolvement characters. Dacheng Bay, Shenquan Bay, Hudong Bay, Wukan Bay, Fengjia Bay, Wuchang Bay, Lingshui Bay and Tufu Bay produce accretion on the tangential segment, erosion on the transitional segment and accretion on the sheltering segment. However, Guang’ao Bay, Haimen Bay, Jinghai Bay, Sanya Bay(a), Dajiao Bay, Hailingshan Bay, Hebei Bay, Fuhu Bay, Shuidong Bay, Wangcun Bay and Bomao Bay generate erosion on the tangential part, accretion on the transitional part and accretion on the sheltering part. It seems to imply some relations between headland-bay beach evolvement and controls on headland-bay beaches, which may possibly to classify headland-bay beach types and should be further studied.

A multi‐century record of linked nearshore and coastal change

ABSTRACTUsing geographic information system (GIS) and field measurements the nearshore morphological variability of a headland bay beach at Tenby, West Wales (51·66 N; –4·71 W) was assessed over historical timeframes (1748–2007). Three areas chosen for detailed analysis were the area between mean low water (MLW) and lowest astronomical tide (LAT) contours; LAT and one fathom contours; and one and two fathom contours. Estuary closurec. 1855 has been suggested as the genesis for long‐term beach evolution and did have an initial effect, with northward dune migration and reduced flushing effects. However, this research suggests nearshore bank migration and retrogradation associated with spit collapse took place prior to closure and continued throughout the assessed timeframe. Historical data revealed patterns of shoreward migration demonstrated by changes in orientation, Giltar headland acting as a pivot. Variations in sandbank position correlated with areal reduction of both Giltar spit and White Bank. Temporal offshore areal loss was contrasted against variable gains inshore as offshore banks welded to the beachface. Annual volumetric change analyses represented by profiles that extend 1 km offshore, confirmed Giltar spit and White Bank erosion rates of 91 m3 yr–1and 458 m3 yr–1respectively, and 220 m3 yr–1beachface accretion. Diminution of sediment supply observed over historical timescales was supported by decadal evidence. Here, profile analysis revealed a trend of decreasing volumes both updrift and within the study area, and increasing downdrift volumes. This explained why proximal detachment and sediment redistribution had occurred. Distinct reversal's in shoreline trend (rotation) corresponded to nearshore change; therefore, variations in seabed configuration triggered shoreface dynamic change over century timescales. Five‐year cumulative average changes in North Atlantic Oscillation were further correlated to this reversal. As comparable scenarios are likely to exist at other worldwide coastal locations, similar analyses should be incorporated into shoreline monitoring programmes. Consequently, these assessments would inform shoreline trends and support coastal management decisions. Copyright © 2011 John Wiley & Sons, Ltd.

Patterns of Sediment Transport Pathways on a Headland Bay Beach—Nanwan Beach, South China: A Case Study

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.

Mesoscale evolution of a headland bay: Beach rotation processes

The morphology change of a headland bay beach: Tenby, West Wales (GR 212200, 198599) has been analysed over a mesoscale timeframe (1830–2009). GIS, cross-shore profiles, off-shore wave climate, have been utilised to assess the role of atmospheric variability on long-term shoreline change. Previous studies have suggested that plan-form change seen in recent times has been caused by closure of Ritec valley estuary circa 1855, and whilst admittedly closure did have an initial effect with northerly dune field migration and reductions in inter-tidal and nearshore estuary flushing, this study suggests that climatic variations also contribute to evolution of this bay. Mesoscale analysis qualitatively highlights two distinct time periods of plan-form evolution characterised by total reversals in trend that take place around 1919. More recent bay rotation about a stable central sector, is shown quantitatively: the southern sector shows progressive retreat ( R 2 = 0.93), whilst the northern sector is shown to advance ( R 2 = 0.56). Points of rotation show steady migration northwards as retreat is encountered within the south sector ( R 2 = 0.79), which confirms that the bay is still evolving. On a decadal level, correlation can be found between positive NAO index values and beach level, and volume reductions based on a visually active beach profile ( R 2 = 0.44 and 0.53 respectively), whilst normalised wave height variability is also closely linked with index change ( t = 0.952, df = 82, p > 0.05) over a similar timeframe. Positive index values result in stormier south-westerly winds (180°–270°), where it is found that 54% of high winds emanate from this quadrant. Further correlation is found between these winds and NAO Index ( R 2 = 0.47). Winds from this direction produce waves that diffract and refract around Giltar headland and off-shore Caldey island, that induce a south to north movement of sediment increasing southerly shoreline retreat and, conversely, northerly advance. Qualitative observations of hind-casts produced using decadal analysis regression equations and mesoscale NAO data suggest that the atmospheric variation is a contributory factor in bay evolution. Similar scenarios are likely to exist at other locations; therefore, assessments should be repeated more widely, to develop appropriate management strategies.

Headland-bay beach planform stability of Santa Catarina State and of the Northern Coast of São Paulo State

This paper presents the results of the planform stability classification for the headland-bay beaches of the State of Santa Catarina and of the Northern Coast of São Paulo, based on the application of the Parabolic Bay-Shape Equation (PBSE) to aerial images of the beaches, using the software MEPBAY®. For this purpose, georeferenced mosaics of the QuickBird2® satellite imagery (for the State of Santa Catarina) and vertical aerial photographs (for the northern coast of São Paulo State) were used. Headland-bay beach planform stability can be classified as: (1) in static equilibrium, (2) in dynamic equilibrium, (3) unstable or (4) in a state of natural beach reshaping. Static equilibrium beaches are the most frequent along the coast of the State of Santa Catarina and the Northern Shore of São Paulo, notably along the most rugged sectors of the coast and those with experiencing lower fluvial discharge. By comparison, dynamic equilibrium beaches occur primarily on the less rugged sectors of the coast and along regions with higher fluvial discharge. Beaches in a state of natural beach reshaping have only been found in SC, associated with stabilized estuarine inlets or port breakwaters. However, it is not possible to classify any of these beaches as unstable because only one set of images was used. No clear relation was observed between a beach's planform stability and other classification factors, such as morphodynamics or orientation.

Artificial Intelligence and headland-bay beaches

Headland-bay beaches are a typical feature of many of the world's coastlines. Their curved planform has aroused much interest since the early days of Coastal Engineering. Modelling this characteristic planform is a task of great interest, not least in relation to projects of coastal structures whose effects on the shoreline must be studied from the planning stages. In this work, Artificial Intelligence is applied to this task—in particular, artificial neural networks (ANNs). Unlike conventional planform models, they are not based on a given mathematical expression of the shoreline curve. Instead, they learn from experience (from a number of training cases) how the planform of a headland-bay beach is shaped, with due regard to the obliquity of incident waves. Three artificial neural networks, with different input/output structures, are implemented and subsequently trained with a number of bays. Once trained, they are tested for validation on other headland-bay beaches. Finally, the most performing neural network is compared with a state-of-the-art planform model.

MEPBAY and SMC: Software tools to support different operational levels of headland-bay beach in coastal engineering projects

This paper presents MEPBAY and SMC software tools that allow comprehending and solving problems in headland-bay beach through a parabolic model. These tools can be employed as coastal engineering design tools (including nourishment designs) and also for academic purposes. They are oriented to different end-users, including coastal technicians, scientists and undergraduates and as coastal engineering design tools, they can be applied to different operational levels (pre-design and design). The aim of the paper is to present design guidelines, the capabilities of the tools, their potential use and applications. Both tools were applied to analyze San Lorenzo Beach and demonstrate their ability at different project levels.

The effects of a bypass dunefield on the stability of a headland bay beach: A case study

Abstract This paper presents a case study on the modelling of a headland bay beach influenced by sediment input from migrating coastal dunes. The study area is the region around the town of Ingleses on Santa Catarina Island, Santa Catarina state, South-Eastern Brazil. Ingleses has been threatened by nature at two different fronts. At the north-eastern side of the town lies Ingleses Beach, a headland bay beach which seems to be subject to persistent erosion in recent years. On the south-western side the town is threatened by a migrating dunefield, which is encroaching onto houses and infrastructure, but which has not reached the beach in the past 70 years. A second dunefield in the area does not pose a direct threat to the town, but passes it on the eastern side and forms an important influence on the development of the beach. The sediment influx rate from this dunefield to the beach is 10,000 m3/year. To investigate the effect of the dunefields on the morphodynamic system, a numerical model has been created using the software packages SWAN and UNIBEST and the static equilibrium bay shape was determined by the software package MEPBAY. The result of the long-term scenario as predicted by UNIBEST agrees rather well with the static equilibrium bay shape found with MEPBAY. This provides sounds basis for the credibility of both models. Consequently, the predicted evolutional trend of the shoreline seems plausible.

Hydrodynamics of a headland-bay beach—Nearshore current circulation

This paper is devoted to the analysis of the hydrodynamic equilibrium of a headland or semi-elliptic shaped beach. It is shown that the state of equilibrium depends not only on the in- and outgoing sediment but also on the accommodation of the sediment within the embayment. The shape and relative depth of shoals, or settling zones, also directly affect the wave and current patterns inside the bay, within which the resultant breaker line almost stops wave-induced currents at some locations, whereas the magnitude of current increases at other locations. Several numerical tests are analytically conducted in a semi-elliptic beach with two symmetrical shoals of varying relative depth where circulatory current systems are detected and analyzed. Numerical modelling for wave climate and wave-induced current estimation is also presented in order to corroborate results and provide a tool for complicated and/or physical domains. The results lead to a redefinition of the concept of equilibrium for headland-bay beaches taking into account not only the net sediment transport but also the role of the formation and disappearance of settling zones, as well as sediment interchanges between the beach and shoals.

Static bay beach concept for scientists and engineers: A review

Headland-bay beach (HBB) is one of the most prominent physiographic features on the oceanic margin of many countries in the world. Under the influence of a predominant swell, its curved periphery in natural environment may reach static equilibrium and remains stable without sediment supply from updrift and/or a riverain source within its own embayment. Coastal scientists and engineers have attempted to develop mathematical expressions to quantify this ideal bay shape since the 1940s. As the scenario with depleting sediment supply has become a common reality on many parts of the world coastline in more recent time, some coastal engineers have advocated a rational approach to mimicking the static bay shape found in nature in order to mitigate beach erosion as well as for coastal management. Nowadays, many useful applications have emerged since the publication of the parabolic bay shape equation (PBSE) developed for static equilibrium planform (SEP) in late 1980s. The advance in modern computer technologies and international collaboration has further facilitated the exchange of knowledge and applications of this static bay beach concept (SBBC). This paper reviews the progress on the research in HBB made by geographers and geologists since the 1940s, together with the involvement of coastal engineers working on shore protection and management from the 1960s. Aided by software MEPBAY developed in 2003 for the PBSE, several practical examples are demonstrated in this paper for the stability verification of natural and man-made bay beaches, shore protection, mitigating downdrift erosion of a harbour, design of recreational bay beach, as well as for environmental impact assessment. Limitations on and clarifications for engineering applications based on the SBBC are also discussed in this paper.

Headland-bay beach planform and tidal range: A neural network model

An artificial neural network model of headland-bay beach planform is presented and developed. It differs from conventional models in two fundamental respects. First, the knowledge of the problem is not input to the model in the form of a given planform equation, but is acquired by the model itself from a series of examples of headland-bay beaches in the course of a training process—in other words, the model learns. Second, the new model takes into account tidal range, a significant factor influencing sediment transport. The artificial neural network is a multilayer perceptron trained with the Bayesian regularisation algorithm. For the selection of the optimum network architecture a thorough experimental study involving 240 neural networks is carried out. The model with the selected network architecture is trained and validated on a data set comprising 29 headland-bay beaches, and shown to outperform a conventional headland-bay beach planform model. The model is then applied to investigate the relation between tidal range and headland-bay beach planform. For this purpose the non-dimensional planforms corresponding to two values of the maximum tidal range ( T r = 0.5 m and 4.5 m) under different wave obliquities ( q 0 = 40°, 50° and 60°) are simulated. For the smallest wave obliquity (40°) the shoreline curves for both tidal ranges practically overlap. For greater wave obliquities the larger tidal range is found to produce a greater bay indentation, the difference increasing with wave obliquity. These results improve our understanding of headland-bay beach morphology and, in particular, of the manner in which it varies between meso-macrotidal and microtidal conditions due to the tidal modulation of the sediment transport vectors or its absence, respectively.

Neural network modelling of planform geometry of headland-bay beaches

The shoreline of beaches in the lee of coastal salients or man-made structures, usually known as headland-bay beaches, has a distinctive curvature; wave fronts curve as a result of wave diffraction at the headland and in turn cause the shoreline to bend. The ensuing curved planform is of great interest both as a peculiar landform and in the context of engineering projects in which it is necessary to predict how a coastal structure will affect the sandy shoreline in its lee. A number of empirical models have been put forward, each based on a specific equation. A novel approach, based on the application of artificial neural networks, is presented in this work. Unlike the conventional method, no particular equation of the planform is embedded in the model. Instead, it is the model itself that learns about the problem from a series of examples of headland-bay beaches (the training set) and thereafter applies this self-acquired knowledge to other cases (the test set) for validation. Twenty-three headland-bay beaches from around the world were selected, of which sixteen and seven make up the training and test sets, respectively. As there is no well-developed theory for deciding upon the most convenient neural network architecture to deal with a particular data set, an experimental study was conducted in which ten different architectures with one and two hidden neuron layers and five training algorithms – 50 different options combining network architecture and training algorithm – were compared. Each of these options was implemented, trained and tested in order to find the best-performing approach for modelling the planform of headland-bay beaches. Finally, the selected neural network model was compared with a state-of-the-art planform model and was shown to outperform it.

Appreciation of Static Bay Beach Concept for Coastal Management and Protection

Sandy bay beach in static equilibrium is the only physiographic feature that could remain stable without sediment supply in a persistent swell environment anywhere around the world. With a continuing trend of erosion to sandy beaches worldwide, a conservative and practical hypothesis is not to consider the mobile dynamic wave parameters but to safeguard against a sandy beach under vanishing supply in the future. To achieve this, an empirical bay shape equation is strongly recommended as one of the best coastal management options. Combining with MEPBAY, software derived for implementing the static bay beach concept on a display unit, this empirical bay shape equation is readily applicable to verify the stability of numerous headland bay beaches in natural and man-made condition. It is also adequate for coastal managers to apply this empirical equation as a valuable tool to aid in the creation of headland bay beaches for shore protection, recreation, and coastal management before embarking on sophisticated numerical modeling.