Beach Planform Research Articles

NEW PROCESS BASED EQUATION FOR A STATIC EQUILIBRIUM BEACH PLANFORM

Equilibrium planform formulations of beaches are engineering tools for providing solutions for beach erosion problems. They aim at defining the final orientation of the beach on a scale of years and thus they are used for evaluating the shoreline response due to human interference (ports, breakwaters, protection works…etc). These formulations create engineering solution to numerous coastal stability problems. The Parabolic Bay Shape Equation (PBSE) proposed by Hsu and Evans (1989) is the most used equation and allow to solve problems. However, these shape equations are valid under certain simplifications. Therefore, they are unable to determine the beach planform when the bathymetry is complex, with rocky areas or/and islands. The aim of this study is to present a new equilibrium beach planform equation (Gainza et al. 2018) that overcomes the problem previously mentioned. What is more, an extension of the model is presented in order to modeled the shape of a shoreline on a given day.

Equilibrium planform of pocket beaches behind breakwater gaps: On the shape of the equilibrium shoreline.

Bay beaches are common coastal landforms along the world's coastlines and have frequently been used as equilibrium coastal systems to mitigate erosion problems and stabilize coasts. Throughout the literature, several formulae can be found to obtain the static equilibrium planform (SEP) of such beaches on the leeward sides of single protruding headland structures. However, equations used to define SEP behind breakwater gaps are rare and based on a limited number of studies, especially when the obliquity angle ( β ) is large. This paper proposes a new formula for modelling the SEP of bay beaches that includes cases with planform shapes characterized by large obliquity angles ( β > 75°) for which the SEP is almost quasi-semicircular. The formula represents a general form of the parabolic bay shape equation (PBSE) with modified coefficients to alter the planform's curvature to be quasi-semicircular, mimicking the behavior of such bays in nature. The coefficients are expressed as functions of both the obliquity angle ( β ) and the curvature-adjustment angle ( φ ), which was determined based on field observations of the best-fitting SEP of 26 bay beaches with ( β > 75°) along the coasts of Spain, Portugal and Brazil. Additionally, 32 beach cases characterized by smaller obliquity angles ( β < 70°) were included in the derivation of the curvature adjustment angle, which was expressed as a function of ( β ). The model showed good results in modelling the SEP, with an RMSE of 0.90° obtained when estimating the planform's curvature-adjustment angle ( φ ) to obtain quasi-semicircular planform shapes for the prototype cases, confirming its utility as a valuable tool for engineering applications. • Static equilibrium planforms (SEPs) characterized by large obliquity angles are modelled. • A new formula was derived to plot the (SEP) of bay beaches behind gaps when (β > 75°). • A curvature-adjustment angle is used to alter the SEP's curvature based on field cases. • The SEP is quasi-semicircular for pocket beaches behind breakwater gaps when (β > 75°). • The curvature-adjustment angle is directly proportional to the obliquity angle (β).

Equilibrium planform of pocket beaches behind breakwater gaps: On the location of the intersection point

Pocket beaches bounded by coastal structures are widely used as coastal systems that are in equilibrium for shoreline stabilization. Throughout the literature, several equations can be found to obtain the static equilibrium planform (SEP) of these embayed beaches, such as the parabolic bay shape equation (PBSE). The literature has already addressed some methodologies used to determine the location of the down-coast control point from which the parabolic shoreline is applicable for pocket beaches to the leeward side of a single headland structure. However, a methodology for locating this down-drift limit for double-curvature pocket beaches behind breakwater gaps is still lacking. This paper explores a methodology for locating this down-drift limit, hereafter called the intersection point (P i ), and investigates the role of the breakwater gap configuration as well as the directional wave climate close to the gap by employing 32 prototype beach cases along the Spanish coast. Moreover, an extensive series of numerical simulations using a spectral wave model was carried out to model the wave refraction-diffraction conditions on the leeward side of a breakwater gap under different wave conditions and various gap configurations. The results show the importance of the gap width and its orientation ( θ gap ) with relation to the direction of the mean wave energy flux ( θ EF ) at the gap as well as the ratio of the widths of the two parts of the bay beach that are affected by the breakwaters, denoted as the breakwater influence ratio (BIR), on the location of the intersection point (P i ). The results also indicated that a symmetrical pocket beach with a gap orientation ( θ gap ) parallel to the θ EF direction has an intersection point (P i ) around the mid-width point of the breakwater gap. On the other hand, the larger the difference angle (Δ θ gap ) between θ gap and θ EF is, resulting in asymmetrical beach cases, the wider the eccentricity of the location of the intersection point (P i ) from the gap centerline towards the shallower landward breakwater of the gap is. New formulae were derived for calculating the angles used to locate the intersection point (P i ) from the two diffraction points of the gap as a function of the gap width, BIR and the offshore distances of the diffraction points. The model showed good results, with R 2 = 0.9571 and an RMSE value of 0.9731° in estimating the location of the intersection point (P i ) in various prototype beach cases, confirming its utility for coastal engineering practices. Accordingly, a design procedure was proposed for the design of new equilibrium pocket beaches behind breakwater gaps. • Wave refraction-diffraction behind breakwater gaps is simulated with a spectral model. • The Best fit static equilibrium planform (SEP) is obtained for pocket beaches behind gaps. • Gap's configuration affects the SEP of double-curvature bay beaches. • The location of the intersection point (P i ) point depends on the breakwater influence ratio. • Presence of eccentricity of (P i )'s location from the gap centerline for asymmetrical bays.

Beach narrowing on prograding coasts: Examples from the tropics to subtropics of eastern Australia

Subtropical to tropical sandy beaches are subject to a wide variety of processes that influence shoreline position, though they receive little research attention compared to temperate coastlines. This presents challenges to understanding the drivers of long-term coastal change, particularly in places like the sub/tropical margins of Australia, where there are significant differences in local to regional geologic, oceanographic, and climatic conditions. Here, we investigate changes in beach planform morphology for a number of beaches in Queensland, Australia, over a period of up to 90 years using high resolution (0.5–5 m pixel size) aerial photographs. In total, 945 images were orthorectified and bounding features for the subaerial beach (high water and dune vegetation lines) were digitised to extract shoreline change statistics for 15 beaches ranging from the tropics to subtropics, between 15°S and 28°S. Three beach types were identified, defined based on lateral boundary features and the scale of shoreline/beach width variability. These include low variability beaches with two bounding rocky headlands (type 1); beaches with one headland and one river boundary, with the most significant shoreline adjustment away from the headland (type 2); and highly variable beaches with two river boundaries (type 3). Our change analysis demonstrates overall seaward displacement of the high water and vegetation lines, but also net losses in beach width due to fast rates of seaward vegetation advance in a tropical setting. These changes are largely consistent along this coastline, despite differences in exposure to deep-water waves and large variation in tidal ranges. Long-term accretion persists here despite rising sea levels over the past century. This result suggests a long-term net positive sediment budget along this section of the coast that is likely a reflection of global adjustments to tropical climate, and associated increases in terrestrial sediment generation and dune vegetation growth rates. Overall, this study provides insights into a variety of coastal settings through the subtropics and tropics and highlights the importance of tracking change along both the landward and seaward edges of the subaerial beach, regardless of exposure and associated wave regimes.

BEACH PLANFORM EQUILIBRIUM, APPLICATION AND METHODOLOGIES FOR CLIMATE CHANGE RESILIENCY CONSIDERATION

Climate change and sea level rise (SLR) present a challenge and added uncertainty for managing coastal areas. Many coastal cities and developed coastal areas are assessing future vulnerabilities to SLR and developing adaptation plans for improved resiliency. Equilibrium conditions for beach planform can be critical to the long-term stability of beaches and dunes fronting coastal cities. In many cases, resiliency and adaptation programs for beachfront areas are based on assumptions of evaluating scenarios of higher water elevations and hydrodynamic forcing under present time topographic and bathymetric conditions. These evaluation parameters suggest that the coastline and existing morphological features are near equilibrium condition and are expected to remain near similar equilibrium over the SLR scenarios under consideration. Such assumptions may be limited to open coast conditions where the beach and the developed coastal planform follows theoretical open coast conditions or constant equilibrium planform. This paper discusses factors influencing beach planform along the Florida Atlantic and Gulf of Mexico coastlines and proposes conceptual methodologies in various applications.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/gWsbmi6VIo0

Modelling of embayed beach equilibrium planform and rotation signal

Embayed beaches are highly attractive sandy beaches bounded laterally by rigid boundaries, which deeply affect equilibrium beach planform and shoreline dynamics. We use LX-Shore, a state-of-the-art shoreline change model coupled with a spectral wave model to address embayed beach shoreline dynamics driven by longshore sediment transport processes. The model is applied to different idealized embayed beach configurations including variations in headland lengths. The model simulates a large range of equilibrium embayed beach planforms and associated spatial and temporal modes of shoreline variability. For short headlands enabling occasional headland sand bypassing, both embayed beach curvature and maximum erosion at the upwave side of the embayment increases with increasing headland length. Beach curvature also increases with increasing headland length for headlands long enough to prevent any headland sand bypassing. In contrast, at the same time, embayed beach becomes increasingly curved and symmetric, with maximum localised erosion within the embayment decreasing in intensity. When there is no headland sand bypassing, rotation signal decreases in amplitude and becomes increasingly symmetric with increasing headland length. The modal (time-invariant) directional spreading of incident waves is critical to embayed beach behaviour, with the envelope and variance of cross-shore shoreline change and time-averaged shoreline curvature all increasing with decreasing modal directional spreading. Embayed beach rotation characteristic timescale increases with increasing embayed beach length, while the narrower the embayment the smaller the cross-shore amplitude of shoreline variability. Our simulations provide new insight into the influence of embayment characteristics and incident wave conditions on equilibrium planform and shoreline dynamics of embayed beaches. This work also implies that the degree of potential headland sand bypassing should be taken into account for modelling of beach rotational dynamics and embayed beach dynamic planform configuration.

The Microbiomes of Sea Turtle Nests in Venice Beach, Florida

Sea turtles nest throughout the world’s beaches and the fate of their clutches depends on many factors including the biotic and abiotic properties of the sand.It is well documented how a multitude of sand properties can impact the nest microenvironment and consequentially have a positive or negative effect on incubation. The present study looks at the microbiotic diversity in the sand of four beach areas of varying human traffic on Venice Beach, Florida. Our goal was to document bacterial species presence, relate them to human usage and extrapolate the potential role these bacteria species have on their respective sea turtle nest nest microbiomes.This study was conducted during the sea turtle summer nesting season and samples were collected at four locations in Venice Beach every week from July until October. The locations were a pubic beach, a private beach, a dog beach and an isolated beach. This study design documents changes within the same beach and nesting site. Samples were also collected along the dune and high tide line and at three different depths in the same location to document microbiotic differences across and at different depths of the beach planform, respectively. Sargassum and other macroalgae were collected at random locations and its bacterial fauna identified to see if they could serve as possible bacterial sources for beach sand.Sand samples were incubated in trypic soy broth and then plated in agar that selected for gram positive and negative bacteria. After individual bacterial colonies were isolated, DNA was extracted using standard procedures. The 16s ribosome was target with a primer, DNA was amplified using a PCR, and the DNA was sent for Sanger sequencing.Bacteria species were identified by comparing their DNA sequences against several online databases such as BLAST. Data collected from several biochemical tests (oxidase test, glucose/fructose/lactose fermentation, anaerobic test, MacConkey and Mannitol Salt media, etc) done prior to DNA isolation were used to confirm the bacteria species identified by the database.Our results show that there is diversity in bacterial fauna in the sand samples from the different sea turtle nesting areas of Venice Beach. Although some bacteria species (i.e. Pseudomonas), were found more prevalent in sand from hatched than unhatched clutches we cannot, at this time, state they played a significant role in the fate of the clutch. However, species diversity could not be explained in relation to sand properties and we believe it to be correlated to the level of anthropogenic impact. Further research is needed to test the direct influence these bacterial species have on the incubation of sea turtle eggs.Support or Funding InformationStudy was funded by National University’s Undergraduate Research Opportunity Program

Open access Bayesian Belief Networks for estimating the hydrodynamics and shoreline response behind fringing reefs subject to climate changes and reef degradation

Reef-protected beaches are vulnerable to the effects of sea level rise and degradation of their associated fringing reefs. The SWAN hydrodynamic wave model is combined with classical theory describing the planform of beaches in equilibrium with the wave forcing to estimate the reef top hydrodynamics and the shoreline configuration in the lee of the reefs. Open access Bayesian Belief Networks with high accuracy and simple user interfaces have been built to communicate the results. The BBN enable end users to access all the model results and to compare different scenario to determine how changes in the wave climate or reef elevation change the shoreline configuration. The results show that recession of the shoreline in the lee of fringing reefs due to sea level rise may be much greater than that expected on open coast beaches. Loss of reef flat elevation can also lead to severe shoreline erosion.

A method to nourished beach stability assessment: The case of China

Beach nourishment is an effective method for maintaining shoreline position, and it has been preferred to restore beaches in China. However, in the post-nourishment assessment, there are only some single-indicator models (e.g. beach durability, sediment loss rate) which could not fully reflect the actual performance of a nourished beach. This study presents a multiple-indicator model of nourished beach stability assessment, aiming at quantitatively assessing the physical performance of nourished beaches. Geomorphic factors affecting the physical performance of nourished beaches were analyzed and summarized through critical review of literature. An indicator system for assessing the stability of nourished beaches was established by integrating oceanographic parameter (i.e. wave energy, storm intensity, and storm frequency), design parameter (i.e. beach length, grain size, volume density, beach planform, and beach protection structure) and adaptability parameter (i.e. intertidal width, dry beach width, and erosional hot spot). Based on data collecting, each indicator was graded into five classes from 1 to 5, and the associated weight of each indicator was given by the method of variation coefficient. Finally, a multi-indicator and indicator-weighted assessment model for the stability of nourished beaches was established and a new index called Nourished Beach Stability Index (NBSI) was proposed. The physical performances of sixteen nourished beaches representative of China were then quantitatively assessed. The results showed this assessment model could better assess the physical performance of nourished beaches than the single-indicator assessment models for taking beach's characteristics into account. The results can help scientists and managers make appropriate management strategies. This multiple-indicator assessment model can be used to both quantitatively assess the actually physical performance of the beach nourishment projects and to choose the design scheme from multiple alternatives for beach nourishment project.

Dynamic equilibrium planform of embayed beaches: Part 2. Design procedure and engineering applications

The design of equilibrium beach systems employing beach nourishment techniques in conjunction with coastal support structures has received increased interest from coastal engineers in recent years. One such solution to remedy coastal erosion problems is to design an equilibrium pocket beach in order to stabilize the shoreline. Such coastal landforms may exist in nature in static or dynamic equilibrium states. The concept of the Static Equilibrium Planform (SEP) has received much more attention from coastal engineers than that paid to the Dynamic Equilibrium Planform (DEP). This paper presents a design procedure for embayed beaches in dynamic equilibrium which have a specific net littoral drift rate. The proposed methodology employs the net sediment transport rate passing through the bay, together with the time series of the wave climate impinging on the beach, in order to compute the angle (γd). This angle represents the difference in degrees between the direction of the mean wave energy flux at the diffraction point (θEF) and the orientation of the dynamic equilibrium beach (θDB), to be utilized in a newly derived DEP formula to predict the shoreline shape in the long term. The procedure was applied and validated using prototype bays in dynamic equilibrium with different net sediment transport rates along the Brazilian coast, producing good results. Furthermore, it was employed as a tool to investigate the influence of changes in the net annual littoral drift rate on the (DEP) shape in a case study along the Spanish coast. Taken together, these confirm its utility as a valuable tool for coastal management and engineering practice.

A process based shape equation for a static equilibrium beach planform

Coastal erosion is a major problem for shorelines everywhere in the world. In order to mitigate beach stability problems it is necessary to determine the equilibrium shape of the beach planform. Current equilibrium planform shape equations are only valid under certain simplifications; for instance, they are unable to predict the effect of nearshore islands and/or rocky bottoms, as well as the effect of several diffraction points. The aim of this paper is to present a new process-based shape equation that is able to overcome those limitations and estimate the static equilibrium shoreline of complex bathymetry beaches. The equation is based on the hypothesis that a pocket beach gets its static equilibrium planform when the mean surf-zone longshore velocity averaged over a period of time is null (V¯=0) in every point along the beach. Based on this hypothesis, the direction of the shoreline that nulls the mean surf zone longshore velocity along the beach is evaluated. Therefore, the shape equation is based on the longshore current velocity formula. The new equilibrium shape equation is applied to two Spanish beaches, namely Milagro beach and Cala Millor beach. Milagro beach has a very smooth bathymetry and the parabolic shape equation developed by Hsu and Evans (1989) is able to predict the equilibrium shoreline. Cala Millor is more complex: it has some rock outcrops along the beach and the parabolic shape equation does not work. The equilibrium shape equation presented in this paper simulates the equilibrium shoreline of both beaches successfully with a high R2 (around 0.96) between the modelled shoreline and the real shoreline in both case studies.

Dynamic equilibrium planform of embayed beaches: Part 1. A new model and its verification

Equilibrium beach formulations are useful tools for diagnosing and managing coastal engineering problems, providing solutions for beach erosion problems. Headland Bay Beaches (HBBs) can be used as equilibrium coastal systems for stabilizing coastlines and mitigating erosion problems. These embayed beaches may exist in a state of static or dynamic equilibrium. Throughout the literature, several equations can be found for obtaining the Static Equilibrium Planform (SEP) of Headland Bay Beaches (HBBs) with almost negligible net littoral drift rates. However, the formulations used to define the Dynamic Equilibrium Planform (DEP) of embayed beaches with specific net sediment transport rates are scarce, and based on a limited number of studies. This paper proposes a new derived formula for obtaining the planform shape of HBBs in dynamic equilibrium conditions. The formula represents a general form of the Parabolic Bay Shape Equation (PBSE) with modified coefficients as a function of both the wave obliquity (β) and the net littoral drift rate passing through the bay (Q). The angular difference (γd) between the direction of the mean wave energy flux at the diffraction point of the headland and the beach orientation down-coast is also incorporated in the proposed formula. The model was verified against natural HBBs in dynamic equilibrium with different net littoral drift rates along the Brazilian coast, producing good results.

On the influence of wave directional spreading on the equilibrium planform of embayed beaches

Equilibrium beach formulations are engineering tools for estimating a response of beaches in the long term. They aim at defining the final orientation of a beach on a scale of years and thus they are used for evaluating the shoreline response due to human interference (ports, breakwaters, protection works, etc). Several equations can be found in the literature for obtaining the Static Equilibrium Planform (SEP) of Headland Bay Beaches (HBBs), one such being the Parabolic Bay Shape Equation (PBSE). The SEP is strongly dependent on the location of the down-coast control point (Po) which is the downdrift limit from which the PBSE is applicable. The literature recommends the determination of the (Po) point by means of the direction of the mean wave energy flux at the diffraction point. However, when this is applied to equilibrium embayed beaches in zones with a wide variability of wave climate directionality and/or in cases where the diffraction point is located far from the equilibrium shoreline, this approach is no longer valid and thus the resulting planform shape does not properly fit the SEP for such conditions. This paper investigates the methodology for locating the (Po) point of the SEP for such cases, exploring the role of wave climate directional spreading, employing 44 HBBs in Spain and Latin America. It correlates the planform shape in the long term with the directional variability of the wave climate at the diffraction point. Additionally, an extensive series of numerical simulations using a spectral wave model was carried out to model the combined effects of refraction-diffraction in the lee of a breakwater, defining the part affected by the coastal structure under different wave conditions. The results clarify the importance of wave directional spreading in locating the (Po), indicating that the wider the directional spreading the farther the (Po) point on the shoreline. Moreover, the farther the diffraction point from the coast, the smaller the part of the beach affected by the coastal barrier. A new formula has been derived to locate the down-coast control point (Po) of the parabolic part of the shoreline corresponding to the PBSE as a function of the directional variance of the wave climate and the location of the diffraction point. The model produced good results with (R2 = 0.9117 and a RMSE = 1.8297°) in estimating the location of the (Po) point in various natural and man-made beaches with different degrees of wave directionality.

On the relation between the direction of the wave energy flux and the orientation of equilibrium beaches

The Equilibrium beach planform concept has been widely used in recent years as an engineering tool for modeling shoreline changes, designing new beaches and for stability studies of existing ones. It defines the final shape of a beach on a scale of years, which is important for solving erosion problems and for the design of nourishment projects. Throughout the literature, the planform final shape, hereinafter denoted as the Static Equilibrium Beach Orientation (SEBO), is obtained based on the direction of the mean wave energy flux of whole waves impinging on the coast. This paper investigates the effect of beach sediment size and the Shape of the Directional Distribution (SDD) of the energy flux of the wave climate on the direction that dictates the (SEBO). The study employs field data from 32 beaches along the Spanish coast and available long-term databases of directional wave climates. Initiation of sediment motion due to wave action is taken into account in order to filter the directional wave climate to consider only waves that are capable of moving the sediment. The results indicate that the direction of the mean energy flux of filtered waves is more appropriate for the determination of the (SEBO) than that of whole waves. Additionally, the results confirm the importance of both the filtration process of the local directional wave climate and the usage of the whole directional spectra in stability studies and coastal engineering practice.

Early Stage Evolution of Nourished Beach under High-energy, Macro-tidal Environment

Beach planform evolution, profile equilibration and sediment grain size change have been studied during the first 4 months from 4th September to 24th December 2011 after the construction of beach nourishment project at Longfengtou Beach, Haitan Bay. Monthly beach profiles, shoreline surveys, sediment sampling and nearshore wave measurements were carried out after implementation of the 1.3km long nourishment project which was completed on 20th August 2011. This study indicates that: (1) rapid beach profile equilibration occurred in the early stage after the construction of the project. A null point was observed, which is equal to the height of mean high tide, basically kept dynamic stable during the process of profile evolution. Shoreface sediment accumulated beneath the height of this point while erosion happened above it, the slope between the beach berm and the landward edge of low tidal zone became more gradual accompanied with seaward transportation of beach sediment. The velocity of beach slope adjustment in earlier period is faster than later. (2) Beach planform adjustment initiated simultaneously with the combination of the process of profile equilibration and longshore sediment transport. Shoreline retreated with an average distance of 11.1m and maximum of 31.02m from 4th September to 24th December, erosion in the south part was more serious than in the north, and 3 erosion hot spots were found along the coast. (3) Sediment redistributed with cross-shore profile equilibration, it showed a pattern across beach profile as medium sand (0.4-0.5mm) in beach berm, smaller (0.3-0.4mm) in high and middle tidal zone, coarse sand(0.6-1mm) in beach slope transitional zone, fine sand(0.1-0.25mm) in low tidal zone. The sediment grain size change of foreshore was rapidly response to the passage of storm surge.

A free software for sand and gravel embayed beach modelling: PhoEbuS- parabolic equation shape

An in-depth knowledge of the littoral system is essential for its conservation and for an accurate planning of due interventions. The parabolic bay shape equation, used to study the embayed beach planform, is a qualitatively assessed instrument to obtain information about beach equilibrium conditions. Nowadays the equation has been extended in order to be applicable not only to sand beaches but also to gravel beaches. In this paper Phoebus user-friendly software for an automatic use of the extended parabolic bay shape equation is presented. The software enables both technical experts and non-professionals to conduct expeditious analysis in order to evaluate the evolution and equilibrium conditions of embayed littoral beaches lying between natural headlands or man-made structures, as well as to artificially recreate stable embayed beaches by building new artificial structures on open beaches. The software can be also used for coastal planning, to anticipate beach modifications in response to new building or to changes in pre-existing structures.

Storm-induced readjustment of an embayed beach after modification by protection works

This paper examines storm-induced morphological and hydrodynamic changes after a submerged and a detached breakwater were constructed at La Barceloneta beach (Barcelona, NW Mediterranean) in 2006–2007. The shoreline configurations before and after beach nourishment and the construction of the protective structures were compared using a video dataset comprising 29 storm events spanning the pre- (2001 to 2005, n = 17) and the post-breakwater situation (2006 to 2011, n = 12), and hydrodynamic modelling based on the SMC coastal modelling system. As a result of the protection works, La Barceloneta was subdivided into two beaches separated by an artificial salient. The analysis of shoreline response to storms has been improved by using the shoreline hyperbolic tangent fit to represent the beach planform. Comparing the pre- and post-breakwater situations on the basis of these shoreline fits facilitated the identification of beach rotation processes because interference by smaller-scale morphological features was eliminated (e.g. the formation, changes in shape or migration of mega-cusps). In the current post-breakwater situation, there is evidence for a change in the behaviour of the north-eastern beach triggered by the submerged breakwater built in 2007. Furthermore, a counter-clockwise beach rotation has occurred at the north-eastern beach, whereas the south-western beach has experienced a clockwise beach rotation. This morphodynamic behaviour is caused by a new, complex wave-induced circulation system comprising two dominant alongshore currents flowing in opposite directions. In contrast to the pre-breakwater situation, the alongshore component of the radiation stress does not accomplish beach rotation in the post-breakwater situation.

BEACH MEMORY

A new concept of beach memory is investigated in this research. Using a Beach Evolution Model developed for beach rotation, we define a function of beach memory able to describe the weight of the preceding wave conditions and their contribution in the current beach response. The time beach memory time is also defined as the period of time required for the beach memory function to be dissipated in the previous time to negligible values. The Beach Memory Function and the Beach Memory Time can be used to determine the influence of the preceding energy in the current coastal changes. Both new concepts were applied to quantify the Weighted Energy Flux Direction required for the beach planform to be estimated based on the parabolic approximations. Modeled results reproduce successfully observed planform positions.

A LONG-TERM EQUILIBRIUM BEACH PLANFORM MODEL FOR COASTAL WORK DESIGN

Traditional models usually allow fitting the equilibrium beach planform of crenulated beaches knowing wave climate characteristics at a control point. However, sometimes there are shoals or bars in the surf zone which affect surf zone dynamics and longshore sediment distribution, and it is difficult to take into account these elements using those traditional models. A long-term equilibrium beach planform model is proposed here based on sediment transport equations. This model takes into account the sediment transport due to oblique wave incidence and that due to wave height gradient. Two case studies have been studied: a simple pocket beach and a beach which is sheltered by a sandstone bar. Results show the model fits reasonably well the equilibrium beach planform to the shorelines of those beaches. This model is more suitable than traditional models when there are elements affecting surf zone dynamics.

Decadal-scale gravel beach evolution on a tectonically-uplifting coast: Wellington, New Zealand

Uplift of the shoreline in tectonically-active areas can have a profound influence on geomorphology changing the entire process dynamics of the coast as the landforms are removed from the influence of the sea. Over decadal timescales it is possible for the landforms to return to their pre-earthquake condition and this paper examines the re-establishment of mixed sand and gravel beaches on the coast of Wellington, New Zealand, subsequent to an uplift event in 1855. Over 60 topographic profiles were surveyed, seven sets of aerial photographs from a 67 year period were mapped and sediment size analyses conducted in order to quantify the nature of beach change following uplift, and associated relative sea level fall. These data were supported by surveys using ground penetrating radar. It is found that uplift raised the gravel beaches out of the swash zone thereby removing them from the littoral zone. Intertidal rocky reefs which occur between each embayment were also uplifted during the same event and completely interrupted the longshore transport system. Continued input of gravel material to the littoral zone allowed beaches to re-establish sequentially along the coast as each embayment was infilled with sediment. This reconnection of the embayments with the longshore drift system is associated with the beach planform being initially drift dominated during infill but then switching to swash alignment once the embayment becomes infilled. This has resulted in shoreline accretion of over 100 m in some places, at rates of up to 4 m/yr, covering shore protection works built in the past few decades. The ability of the shore to adjust back to its pre-uplift condition appears to be a function of the accommodation space created during uplift and the rate of sediment supply. Copyright © 2012 John Wiley & Sons, Ltd.