Beach Cusp Formation Research Articles

Observations of beach cusp morphodynamics on a composite beach

Substantial volumes of sediment are moved on coarse grained beaches through the formation and destruction of beach cusps, yet the processes governing cusp behaviour remain poorly understood. Here, we combine continuous 2D LiDAR scan data with daily UAV topographic surveys and RGB imagery to provide detailed morphological measurements of beach cusps on a composite beach with the aim to investigate the role of sediment size and tidal stage on cusp behaviour. Rapid changes in cusp height and prominence were observed when storm-eroded gravels were readily transported over relatively impermeable sandy substratum, showing the high-order control that mixed matrix sediments have on this process. Post storm, gravels armoured the swash zone overlaying the sand and were rapidly reworked into horns, with the incipient bays simultaneously experiencing erosion. We provide some of the first field observations to show divergent behaviours occurring simultaneously along the beach as cusps adjust to the new dominant hydrodynamic regime, with some areas experiencing a shortening of cusp wavelength through new horn growth, whilst others contemporaneously experienced wavelength growth through the removal of intermediate horns. Cusp formation was generally more pronounced on the falling tide, but some evidence indicates horns can also be consolidated and grow in relief at some stages of individual rising tides. This research demonstrates how feedback between sediments, morphology and hydrodynamics are key to determining cusp form, with these insights only made possible through the novel combination of LiDAR, UAV, and camera methods to provide sufficient temporal and spatial resolution to resolve key processes.

Beyond The Tertiary Institutional Classroom: How I use mobile technology for field data gathering

Originally focused on the scientific study and documenting of sea wave patterns and the phenomena of beach cusps off the coast of New Zealand, this poster presentation will focus on how I use digital mobile technology in the field and how it is documented. The focus of this paper lies with pedagogy going beyond the tertiary institutional classroom. As an educator and artist using mobile digital technology within the environment, this paper will explore the connection between research, field data gathering, mobile technology and how these ideas can be transferred back into the digital graphic design classroom. In doing so it will also show examples of the findings and how they are translated into digital artworks in the form of motion graphics and poetic artworks such as the poem film. Taken from the inspiration of the findings it will further explore what is real and what is virtual and how inspiration is taken from nature and explored in the digital environment. In the creative processing of this research, I employ the methodology of heuristic inquiry. This is referred to by Moustakas as, “internal search through which one discovers the nature and meaning of experience and develops methods and procedures for further investigation and analysis” (Moustakas, 1990). It will further investigate the poetic and artistic patterns created from these natural events seen through a poetic moving image piece. These creative visualizations and scientific study of water wave energy patterns and the formation of beach cusps has shaped an artistic observation of these energy patterns created from their movements. It will show examples of the creations of the artistic works and explore the digital environment of the poem film and how this is explored within pedagogy.

Morphodynamic modelling of beach cusp formation: The role of wave forcing and sediment composition

A field of beach cusps formed during a field experiment at Nha Trang Beach, Vietnam, under accretive conditions. The measured data was used to set-up morphodynamic simulations in XBeach, which was able to simulate cusp formation from an initially long-shore uniform beach profile. Several types of simulations were run in order to observe the resulting variation in mean cusp dimensions (length, depth and height), swash flow patterns, and sediment sorting. Both time-constant (JONSWAP) and time-varying (measured) wave forcing conditions were superimposed on the measured tide. In the former, four wave parameters were varied (wave height, period, direction, and spreading), while in the latter, the median sediment size and sediment composition were varied. The wave period was found to primarily influence long-shore length scales, the wave height cross-shore length scales, and obliquely incident waves enhance all these dimensions particularly under narrow-banded conditions. Cusps are not prominent if the wave energy is too low to effect significant onshore transport, if the wave angle of incidence and spreading are too large (effectively smoothing out swash perturbations), or if the sediment is too fine in relation to the wave conditions (dissipative beaches or highly erosive wave conditions). Coarse sediment generally tends to be located on cusp horns above the waterline, but is otherwise variable depending on cross-shore location and tide levels. As the XBeach model results show large agreement with well-established norms, it may therefore be used to more rigorously study processes that help to initiate cusps in future work.

Grand Circulation Process of Beach Cusp and its Seasonal Variation at the Mang-Bang Beach from the Perspective of Trapped Mode Edge Waves as the Driving Mechanism of Beach Cusp Formation

Grand Circulation Process of Beach Cusp and its Seasonal Variation at the Mang-Bang Beach from the Perspective of Trapped Mode Edge Waves as the Driving Mechanism of Beach Cusp Formation

Morphometric and sediment analysis of beach cusp in correlation to rip currents: a case study from tropical coast, West coast of India

The presence of rhythmic beach cusps in foreshore regions are of persistent research interest to coastal researchers, engineers with respect to their formation in beaches. Morphometric and sediment analysis were used to study beach cusp morphology at Vengurla beach, a gentle slope beach characterized by medium sand. The cusp dimensions such as spacing, elevation, amplitude and depth were measured for detailed analysis. The distinctive sediment characteristics between the horn and the bays of the cusp are different and cusp measurements show a high level of irregularity. Horns and bays have medium sand, but sorting is varying. Sorting variations clearly demonstrated the difference in energy condition between horns and bay. Negative skewness of few horn samples has been correlated with erosional trend. Based on the grain size analysis result, it was observed that Vengurla beach cusps follow the regular grain size distribution pattern. Additionally, the low-intensity rip currents were also noticed in the study area. The rate of occurrence and strength of rip currents are decided by the nearshore bathymetry and play an imperative role in rip current formation. The present study is based upon the field measurements along Vengurla coast and contributes to morphometric analysis of beach cusps. Regarding beach cusps, there are no documented databases along the Indian coast. Understanding the beach cusp formation and its seasonal changes along the beaches will be useful for effective coastal management.

Cusp morphodynamics in a micro-tidal exposed beach

Beach cusps have attracted the focus of several studies due to their effect on sediment transport and their rhythmic presence in the midst of complex nearshore interactions among waves, currents and sediment. In this paper, cusp evolution is investigated to determine the factors which influence them within Maracas Bay, Trinidad, in the micro-tidal environment of the southern Caribbean. Data on beach profiles, beach sediment, coastal processes, and cusp dimensions were collected using standard geomorphological techniques across daily, weekly and seasonal time-scales. Results indicate that beach cusp dimensions are predominantly determined by beach volume and beach angle. These two parameters in turn are influenced by wave energy. In both the wet and dry seasons, periods of lower wave energy promote accretion, leading to the formation of smaller beach cusps; conversely, periods of higher wave energy and the associated increase in erosion result in the formation of larger beach cusps. There was agreement with the self-organization theory since cusps were always present along the beach, constantly changing morphologically but never completely being erased and recreated anew. Beach cusps form an integral part of the total sediment deposited and retained on beaches over tidal and seasonal cycles, with implications for nearshore currents and beach safety. As such, a proper understanding of their dynamics will help support planning and management of beaches as they go through cyclic phases annually.

Mapping of coastal landforms and volumetric change analysis in the south west coast of Kanyakumari, South India using remote sensing and GIS techniques

The coastal landforms along the south west coast of Kanyakumari have undergone remarkable change in terms of shape and disposition due to both natural and anthropogenic interference. An attempt is made here to map the coastal landforms along the coast using remote sensing and GIS techniques. Spatial data sources, such as, topographical map published by Survey of India, Landsat ETM+ (30m) image, IKONOS image (0.82m), SRTM and ASTER DEM datasets have been comprehensively analyzed for extracting coastal landforms. Change detection methods, such as, (i) topographical change detection, (ii) cross-shore profile analysis, (iii) Geomorphic Change Detection (GCD) using DEM of Difference (DoD) were adopted for assessment of volumetric changes of coastal landforms for the period between 2000 and 2011. The GCD analysis uses ASTER and SRTM DEM datasets by resampling them into common scale (pixel size) using pixel-by-pixel based Wavelet Transform and Pan-Sharpening techniques in ERDAS Imagine software. Volumetric changes of coastal landforms were validated with data derived from GPS-based field survey. Coastal landform units were mapped based on process of their evolution such as beach landforms including sandy beach, cusp, berm, scarp, beach terrace, upland, rockyshore, cliffs, wave-cut notches and wave-cut platforms; and the fluvial landforms. Comprising of alluvial plain, flood plains, and other shallow marshes in estuaries. The topographical change analysis reveals that the beach landforms have reduced their elevation ranging from 1 to 3m probably due to sediment removal or flattening. Analysis of cross-shore profiles for twelve locations indicate varying degrees of loss or gain of coastal landforms. For example, the K3-K3′ profile across the Kovalam coast has shown significant erosion (−0.26 to −0.76m) of the sandy beaches resulting in the formation of beach cusps and beach scarps within a distance of 300m from the shoreline. The volumetric change of sediment load estimated based on DoD model depict a loss of 241.69m3/km2 for 62.82km2 of the area and land gain of 6.96m3/km2 for 202.80km2 of the area during 2000–2011. However, an area of 26.38km2 unchanged by maintaining equilibrium in sediment budgeting along the coastal stretch. The study apart from providing insight into the decadal change of coastal settings also supplements a database on the vulnerability of the coast, which would help the coastal managers in future.

Erosion/accretion patterns and multiple beach cusp systems on a meso-tidal, steeply-sloping beach

This study examines daily variations in intertidal topography and beach cusps on a meso-tidal, steeply sloping beach during a five-month period. The observations are based on coastal imagery and frequent topographic surveys and are extracted from patterns of contours positioned 1 and 3m above MSL (lower/higher beach-face, respectively). The intertidal topography was very sensitive to variations in the wave regime, triggering rapid transitions from erosive to accretive states and vice versa, as well as transformations of the cusp systems, often involving severe horn erosion and beach-face scarping. Distinct beach cusp systems were observed at different levels of the beach, with their evolution being controlled by: (i) wave forcing; (ii) tidal modulation of the wave power at different levels of the beach; and (iii) interactions between the existing beach cusp systems. The lower beach-face rhythmical patterns changed constantly and merged with the upper beach-face cuspate features, typically when the significant wave height exceeded Ho>1.5m. The upper beach-face pattern was persistent during the monitoring period, re-emerging with similar spacing and alignment, despite being eroded during energetic events; this persistence is also maintained by the interactions between swash and irregularities (e.g. embayments) in the dune/backshore morphology. The spacing of the observed beach cusps ranged from λc,min=8m to λc,max=67m; these values were underestimated by the edge wave and self-organization theories and were better predicted by the Sunamura (2004) formula. Beach cusp growth was linked to breaker angles of near-normal incidence and narrow-banded frequency wave conditions. Bay infilling was found to be the most dominant cusp reduction mechanism for larger features (λc>30m), while smaller features vanished during erosive conditions. The most intense cusp growth episodes were linked to accretive conditions, while larger features were shown to emerge during more energetic, erosion events. These findings highlight the need for more longer-term observations of diverse beach morphologies to formulate a global theory regarding beach cusp formation and evolution.

Radio Frequency Identification (RFID) technology applied to the definition of underwater and subaerial coarse sediment movement

In this paper, Radio Frequency Identification technology has been applied to track both underwater and subaerial displacement of pebbles along an artificial coarse beach at Marina di Pisa, Italy. Several preliminary laboratory tests have been performed to adapt the RFID technique for underwater use, which has been the primary impediment to this promising approach to the study of coarse sediment transport and movement. Tests showed the reliability of low frequencies for this kind of work, since they enable good signal transmission and reception through water. Passive ABS plastic transponders were inserted into about 100 pebbles and released onto the beach in March, 2009. A CORE-125 reader was chosen as the operating antenna to continuously transmit low frequency (125 kHz) signals. An acoustic signal toned whenever a pebble was detected while the unambiguous identification code of the pebble is shown immediately on the screen of a laptop connected to the reader. The positions of the pebbles were recorded with a total station. After two months (May, 2009), 74 marked pebbles were retrieved, 77% of the total. The positions of the retrieved pebbles were also recorded with the total station, thus allowing calculation of the coarse sediment transport tendency. About 60% of the recovered pebbles (44 out of 74) were found on the upper shoreface. The analysis of the marked pebble trajectories revealed a divergent transport movement in the northernmost sector of the beach. This movement was probably triggered by an irregularity of the submerged breakwater fronting the shoreline. The southern sector is characterised by chaotic pathways related to the formation and evolution of beach cusps. This outcome highlights and confirms the importance of a complete definition of the beach system, with no separation between the underwater and the subaerial portion of the shore when it comes to sediment transport and movement. This successful application of RFID technology to the underwater environment provides a chance to broaden understanding of a topic in need of further study.

Shoreline Evolution around a River Entrance

The shoreline position in alongshore direction around the Nanakita River mouth was measured from aerial photograph which have been taken every 2 months in 20 years. Empirical Orthogonal Function analysis was used to decompose the data into the dominant mode of shoreline variability for left and right side of river mouth. The results were also examined in relation with wave parameter and river discharge. The first mode shows the same shoreline movement between left and right side which reveals cross-shore process. The analysis of second mode and its correlation with river discharge reflects the influence of long-shore process. This mode also reveals the influence of river mouth in interrupting the long-shore sediment transport. The higher modes reflect the formation of beach cusps in relation with wave parameter.

Video observations of beach cusp morphodynamics

Beach cusps are a common feature of steep reflective and intermediate beaches. Although many observations of beach cusp spacing exist, there are few observations quantifying the incipient formation, evolution and eventual destruction of these features. Beach cusp morphodynamics were analyzed using a 3-year dataset of video images collected at Tairua Beach (New Zealand). Twenty-four beach cusp episodes were selected to monitor the cycle of beach face changes, from planar to the appearance of the cusp patterns and back to planar again. Observations show that beach cusp disappearance can be ascribed not only to the erosive influence of storms but also to the persistence of accretionary conditions leading to the infilling of beach cusp bays and the development of an alongshore continuous berm. We also report observations of changes in beach cusp spacing over time which can be attributed to the merging of adjacent cusps within the cusp field, with the overall cusp spacing re-adjusting to accommodate the disappearance of a horn. Although the self-organization theory provides a better fit to the data and theory, we were unable to conclusively refute any of the mechanisms causing beach cusp formation since both existing theories, subharmonic standing edge wave and self-organization, can predict the trend in the observed beach cusp spacing. These observations show that initial beach cusp formation primarily occurs (around 70% of the episodes analyzed) under mildly accretionary conditions and, when accretion persists, the pattern disappearance is likely to occur as a result of bay infilling to form a featureless berm.

Test of edge wave forcing during formation of rhythmic beach morphology

This paper reports on concurrent measurements of evolving rhythmic beach morphology and the associated water motion on a macrotidal, coarse sandy beach. Beach cusps with a spacing of 19 m developed over a 3‐day period of low‐energy swell after which they were destroyed by energetic wind waves. The beach cusps were clearly accretionary features and developed mainly during the rising tide. Detailed hydrodynamic measurements were conducted at three locations in the swash and inner surf zone in the vicinity of a developing cusp horn and revealed that energetic standing, mode‐zero, subharmonic edge waves were not present during the initiation of the beach cusps. Specifically, analysis of the hydrodynamic data indicated that: (1) the amount of subharmonic energy was limited (<10% of the total energy); (2) none of the computed energy spectra exhibited a significant peak at the subharmonic frequency; (3) the cross‐shore velocity amplitude at the subharmonic frequency was 2–3 times larger than the longshore velocity amplitude; (4) the longshore current motion at the subharmonic frequency was barely coherent between adjacent locations in the surf zone; and (5) the time series of pressure and cross‐shore current were in phase at either side of the developing cusp horn. It is concluded that, at least during this event of beach cusp formation, energetic standing edge waves are not a prerequisite to initiate the development of rhythmic beach morphology.

The role of tides in beach cusp development

Field measurements of morphology and swash flow during three episodes of beach cusp development indicate that tides modulate the height and cross‐shore position of beach cusps. During rising tide, beach cusp height decreases as embayments accrete more than horns and the cross‐shore extent of beach cusps decreases. During falling tide, beach cusp height increases as embayments erode more than horns and cross‐shore extent increases. A numerical model for beach cusp formation based on self‐organization, extended to include the effects of morphological smoothing seaward of the swash front and infiltration into the beach, reproduces the observed spacing, position, and tidal modulation. During rising tide, water particles simulating swash infiltrate, preferentially in embayments, causing enhanced deposition. During falling tide, exfiltration of water particles combined with diversion of swash from horns causes enhanced erosion in embayments. Smoothing of beach morphology in the swash zone seaward of the swash front and in the shallow surf zone accounts for most of the observed tidal modulation, even in the absence of infiltration and exfiltration. Despite the qualitative, and in some cases quantitative, agreement of the model and measurements, the model fails to reproduce observed large deviations of horn orientation from shore normal, some aspects of beach cusp shape, and deviations from the basic tidal modulation, possibly because of the simplified parameterization of cross‐shore sediment transport and the neglect of the effects of sea surface gradients on flow.

Test of self‐organization in beach cusp formation

Field observations of swash flow patterns and morphology change are consistent with the hypothesis that beach cusps form by self‐organization, wherein positive feedback between swash flow and developing morphology causes initial development of the pattern and negative feedback owing to circulation of flow within beach cusp bays causes pattern stabilization. The self‐organization hypothesis is tested using measurements from three experiments on a barrier island beach in North Carolina. Beach cusps developed after the beach was smoothed by a storm and after existing beach cusps were smoothed by a bulldozer. Swash front motions were recorded on video during daylight hours, and morphology was measured by surveying at 3–4 hour intervals. Three signatures of self‐organization were observed in all experiments. First, time lags between swash front motions in beach cusp bays and horns increase with increasing relief, representing the effect of morphology on flow. Second, differential erosion between bays and horns initially increases with increasing time lag, representing the effect of flow on morphology change because positive feedback causes growth of beach cusps. Third, after initial growth, differential erosion decreases with increasing time lag, representing the onset of negative feedback that stabilizes beach cusps. A numerical model based on self‐organization, initialized with measured morphology and alongshore‐uniform distributions of initial velocities and positions of the swash front at the beginning of a swash cycle, reproduces the measurements, except for parts of one experiment, where limited surveys and a significant low‐frequency component to swash motions might have caused errors in model initialization.

Regularity and randomness in the formation of beach cusps

Controversy still exists on whether rhythmic features such as beach cusps are the result of the presence of standing edge wave motions in the hydrodynamics or if they are the result of self-organising processes. The compatibility between the two mechanisms is here investigated through the use of a numerical model simulating the formation and development of beach cusps. Simulations characterised by different forcing conditions have been performed. A series of ‘random’ simulations, each individual run simply differing from the others in the seed used in the random number generator, showed the typical self-organisation behaviour with the features appearing at different locations and even with slightly different spacing. ‘Regular’ series of simulations have been run by changing the wavelength of the template superimposed by the hydrodynamic forcing and the number of cycles when the template was present. Results surprisingly indicate that even a minimum number of cycles with a regular forcing can deterministically induce the final shoreline configuration. Furthermore, if the forcing template has the same wavelength as the one resulting from purely random simulations, growth rates are much faster than those obtained with random conditions. Implications for the kind of field measurements necessary to discern which of the two mechanisms is responsible for beach cusp formation have also been considered.

Investigation of a self‐organization model for beach cusp formation and development

A recent numerical investigation of “self‐organization” [Werner and Fink, 1993] suggests that the feedback process between currents and sediment response can result in “self‐organized” patterns and can be used to predict beach cusp formation and spacing. A similar model based on self‐organization is tested here in order to understand the processes occurring during beach cusp formation and development, to evaluate the sensitivity toward the parameters used, and to examine how the model might relate to field observations. Results obtained confirm the validity of the self‐organization approach and its capacity to predict beach cusp spacing, with values in fair agreement with the available field measurements, with most of the input parameters primarily affecting the rate of the process rather than the final spacing. However, changes in the random seed and runs for large numbers of swash cycles reveal a dynamical system with significant unpredictable behavior. Cusp spacing tends to change with time, and cusp regularity shows large long‐term variations. Cusps are found to be accretionary in the swash zone, and in agreement with most observations, mean flows are horn divergent over developed topography. Simulations over nonplanar slopes characterized by the presence of preexisting nonrhythmic or cuspate features have been performed. Results indicate that preexisting large‐amplitude cusps are destroyed if their spacing is substantially different from that expected under self‐organization and that the final spacing is consistent with that predicted by the model for an equivalent plane beach. These findings support the hypothesis that self‐organization is a robust mechanism for beach cusp formation.

Alongshore variation in beach cusp morphology in a coastal embayment

The variation in beach cusp characteristics was examined along a 1 km long embayed beach (Pearl Beach, New South Wales, Australia). The beach cusp morphology had formed during the previous day and/or night and displayed a marked alongshore variation in cusp spacing. The edge wave mechanism of beach cusp formation could not account for the observed trend in cusp spacing, because no relationship could be established between the spacing of the cusps and the gradient of the beachface. On the other hand, the cusp spacing was strongly related to the horizontal swash excursion, providing some support for the self-organization model of beach cusp formation. Copyright © 1999 John Wiley & Sons, Ltd.

Alongshore variation in beach cusp morphology in a coastal embayment

The variation in beach cusp characteristics was examined along a 1 km long embayed beach (Pearl Beach, New South Wales, Australia). The beach cusp morphology had formed during the previous day and/or night and displayed a marked alongshore variation in cusp spacing. The edge wave mechanism of beach cusp formation could not account for the observed trend in cusp spacing, because no relationship could be established between the spacing of the cusps and the gradient of the beachface. On the other hand, the cusp spacing was strongly related to the horizontal swash excursion, providing some support for the self-organization model of beach cusp formation. Copyright © 1999 John Wiley & Sons, Ltd.

Beach cusp formation and spacings at Duck, USA

Aproximately nine years of daily video images from Duck, NC, USA, were analyzed to determine the timing of cusp formation in relation to environmental forcing and the distances separating consecutive cusp horns. 57 independent cusp events (defined as transitions from visibly smooth to cuspate topography) were observed with most of the cusps forming after storms. The temporal lag between the peak in storm intensity and cusp development was typically 3 days. Approximately half of the cusp events had formations predicted by an empirical threshold relating storm presence, breaker angle, and beach reflectivity. This threshold and other statistical observations suggest that Duck cusps form as energy conditions become more reflective, as the offshore wave angle approaches normal incidence and as the directional spread of the incident wave field becomes narrower. The standard deviation of the observed spacings relative to the mean spacing for each event was around 15% with the range in spacings for each event being typically less than half the event’s mean cusp width. There were no strong statistical relationships between mean cusp spacings and environmental parameters (such as swash excursion lengths).

Variations of Spacings between Beach Cusps discussed in relation to Edge Wave Theory

Rasch, Morten, Jørgen Nielsen & Niels Nielsen: Variations of Spacings between Beach Cusps discussed in relation to Edge Wave Theory. Geografisk Tidsskrift 93:49–55. Copenhagen 1993. Variations in cusp spacings of beach cusp systems have been examined, and the conclusion is that the apparent regularity of the spacings is not always real. Established edge wave theory predicts equal cusp spacings, and accordingly, the theory needs to be improved or alternative theories accepted. Field measurements of beach cusp formation under reflective morphodynamic conditions confirmed that established edge wave theory was not always capable of explaining beach cusp formation. The beach cusps grew from small irregularly spaced mounds, and the regularity of the cusp spacings seemed to increase during beach cusp development. Correlation between observed average cusp spacing and the average cusp spacing predicted on the basis of edge wave theory might suggest that edge waves were the initiating mechanism causing beach cusp development. However, the observed water circulation pattern and the variations of the individual spacings between the beach cusps were both contradictory to existing edge wave theory.