Open Ocean Beach Research Articles

Drivers of seasonal and decadal change on an estuarine beach in a fetch-limited temperate embayment

Beaches in estuaries and bays (BEBs) are critical landforms along many coastlines, providing vital protection to human infrastructure and ecosystem services. Like open-ocean beaches, their morphodynamics are driven by the interaction of waves and tides with the boundary conditions determined by sediment supply and geology. However, as estuaries and bays tend to be lower energy than the open ocean, and are often fetch limited, BEB behaviour is typically controlled by high magnitude events rather than modal conditions. In this study, we assess the dynamics of a BEB in a semi-enclosed bay (Port Phillip Bay, Victoria, Australia). We analyse shoreline and subaerial cross sectional beach change across a range of time scales, including in response to storm events, using a combination of aerial photography, satellite imagery and UAV-based surveys spanning multiple decades. The study assesses the impact of geological controls on beach dynamics in this estuarine/embayed setting, investigating the impact of an intertidal rocky reef and the role of sediment budgets. The rocky outcrops throughout the compartment appear to exert little long-term control on beach morphology. We find that the location of the beach with respect to the sediment compartment boundaries is fundamental to determining long-term shoreline evolution. St Leonards Beach is located near the boundary between two longshore transport systems flowing in opposite directions. This results in low sediment flux across the compartment and therefore a paucity of sand supply for beach and dune development. As a consequence, the beach is relatively stable on a seasonal scale, but has a net erosional trend over the 75-year aerial photographic record. Erosion appears to be event driven as sand is transported out of the sediment compartment during storms. This work shows the importance of understanding local boundary conditions especially local sediment budgets in estuarine environments when analysing beach dynamics.

Seasonal Morphological Variability on Estuarine Beaches and Implications for Low-Energy Beach Management

Mercaldi, B.; Brideau, L.E.; Tait, J.F., and Griggs, G., 2022. Seasonal morphological variability on estuarine beaches and implications for low-energy beach management. Journal of Coastal Research, 38(6), 1135–1147. Coconut Creek (Florida), ISSN 0749-0208. Estuarine beaches and other low-energy shorelines are critical for habitats and coastal infrastructure protection. Many different species inhabit estuaries because of the water bodies' unique characteristics, such as their mixed seawater and freshwater and variable tidal ranges. Estuarine beaches also have the important role of buffering storm wave energy. Yet, their natural physical processes are understudied. This research focuses on seasonal morphological variability of estuarine, low-energy beaches and evaluates the implications for beach management practices. Five sandy beaches were studied along the northern shoreline of Long Island Sound in the northeastern region of the United States. The studied beaches vary in location, width, length, and orientation within Long Island Sound to represent different exposures to wave energy. Three seasonal profiles were measured at each beach approximately every four months from late 2015 to early 2019 to document topographic changes. The results revealed minimal sediment movement throughout the study period and there was no evidence of significant cyclic cross-shore sediment transport to indicate patterns of seasonal profile changes. These findings reveal important implications for beach management practices on low-energy shorelines. Specifically, estuarine and other low-energy beaches should be studied on decadal time scales to document any long-term variability and post-storm recovery rather than the monthly or yearly time scales on which open-ocean beaches are typically evaluated. Additionally, estuarine beaches and other low-energy shorelines require specialized management practices that cater to their stagnancy to ensure adequate protection of coastal structures and infrastructure in the face of intensifying hurricanes and sea level rise.

Shallow lacustrine versus open ocean coastal clastic deposits: Morphosedimentary diagnostic indicators and interpretation

Lacustrine coasts, especially those associated with shallow highly fluctuating lakes, do not evolve in exactly the same way as marine coasts. Climate variability can significantly modify the morphology of the water body, affecting the lake surface area, the available fetch, and the water depth, resulting in possible changes to wave generation and propagation. To look more closely at the nature of coastal sediments generated under such specific environments, we selected examples of both shallow lacustrine and open ocean beach deposits. The first location was Gallocanta Lake, a shallow body of water in the Iberian Chain in central Spain; and the second was Mazagón Beach, in the Gulf of Cádiz, a mesotidal sandy beach exposed to Atlantic waves and tides. Both deposits are formed by beach and ridge and runnel systems. The sedimentary structures of the two deposits were compared, together with a genetic scheme for these. In both cases, applying wave propagation models facilitated the interpretation of the sedimentary processes responsible for their genesis. Although the general morphosedimentary characteristics of the two deposits are roughly similar, a more detailed analysis revealed significant differences, some of which could be used as diagnostic indicators of shallow lacustrine environments in geoarchives. Effective fetch seemed not to be a determining factor for explaining the textural differences between the two deposits. Local factors such as wind strength and direction, and approaching wave refraction patterns are important in controlling the final energy reaching both types of coasts, and, hence, the resulting geometry of the clastic coastal deposits. The type and maturity of the available sediment also influence the final textural properties of the deposits. Open ocean beaches receive sporadic high energetic storms; these partially erode the sedimentary record and reduce the preservation potential of coastal deposits compared with those from shallow lake beaches. Comparing lacustrine deposits with marine analogues and identifying similarities and differences between the two coastal environments may help to infer the main factors underlying the formation and development of coastal deposits in non-tidal, fetch-limited environments.

Citizen science for monitoring seasonal-scale beach erosion and behaviour with aerial drones

Sandy beaches are highly dynamic systems which provide natural protection from the impact of waves to coastal communities. With coastal erosion hazards predicted to increase globally, data to inform decision making on erosion mitigation and adaptation strategies is becoming critical. However, multi-temporal topographic data over wide geographical areas is expensive and time consuming and often requires highly trained professionals. In this study we demonstrate a novel approach combining citizen science with low-cost unmanned aerial vehicles that reliably produces survey-grade morphological data able to model sediment dynamics from event to annual scales. The high-energy wave-dominated coast of south-eastern Australia, in Victoria, is used as a field laboratory to test the reliability of our protocol and develop a set of indices to study multi-scale erosional dynamics. We found that citizen scientists provide unbiased data as accurate as professional researchers. We then observed that open-ocean beaches mobilise three times as much sediment as embayed beaches and distinguished between slowed and accelerated erosional modes. The data was also able to assess the efficiency of sand nourishment for shore protection. Our citizen science protocol provides high quality monitoring capabilities, which although subject to important legislative preconditions, it is applicable in other parts of the world and transferable to other landscape systems where the understanding of sediment dynamics is critical for management of natural or anthropogenic processes.

Differences in perception and reaction of tourist groups to beach marine debris that can influence a loss of tourism revenue in coastal areas

Marine debris is the most conspicuous pollutant that makes beaches aesthetically unappealing to users. The perceptions and reactions of beach users to stranded litter were compared between second-home owners and users (SHOU) and non-recurrent tourists (T). A questionnaire was applied to obtain socio-economic characteristics; assessment of the overall beach quality and perception of beach litter pollution (perception); hypothetical scenarios of marine litter pollution and deterrence (reaction); and potential alternative destinations in the case of deterrence (economic effect). Questionnaires (n = 319) were applied at two Brazilian subtropical beaches, with different physiographical settings (Pontal do Sul, PS, estuarine beach; Ipanema, I, open-ocean beach). Beach users’ groups differed regarding daily expenses (T > SHOU), period of permanence per trip (SHOU > T) and trip frequency (SHOU > T). The open-ocean beach (I) was rated the worst regarding overall beach quality. Marine debris generation was mainly attributed to local “beach users”, in the open-ocean beach (I). “Marine” (or non-local) sources were four times more frequently cited in the estuarine beach (PS). Perception on actual litter pollution and litter deterrence scenarios, did not vary between beaches or groups. More than 85% of beachgoers would avoid a beach visit if a worst scenario (> 15items/m2) occurred and most users would choose a neighboring state beach destination. Stranded litter may potentially reduce local tourism income by 39.1%, representing losses of up to US$ 8.5 million per year. These figures are proxies to support the trade-off local authority's make between investments to prevent/remove beach litter and the potential reduction in income from a tourist destination change.

A morphological modeling study to compare different methods of wave climate schematization and evaluate strategies to reduce erosion losses from a beach nourishment project

Beach nourishment on open ocean beaches not bounded by headlands or other structures suffers from high rates of lateral losses of fill volume as the nourished shoreline equilibrates with its surroundings. Estimates of lateral losses are essential for beach nourishment design, these predictions have been made in the last decade utilizing empirical formulations, one line models or lately, process-based coastal morphology models. Coastal morphology models are, however, complex and computationally intensive and in order to maintain a balance between model complexities, computational effort and processing capacity, schematization of model input (input reduction) is necessary. This paper is divided into two main sections. In the first section techniques of wave input reduction for morphological models are evaluated with focus on open ocean wave-dominated coasts. Subsequently, the optimized morphological model is applied to evaluate coastal engineering interventions aimed at reducing volume losses from the Delray Beach nourishment project. Wave input reduction is defined here as the process of reducing the full wave climate of a given coastal region to a set of representative wave-wind conditions, ‘running’ a model with these representative wave conditions in sequence for a smaller time period (i.e. a few tide cycles) and multiplying its effect on the morphology by a Morfac value, that is related to the frequency of occurrence of that wave condition in nature, or its weight in the overall wave climate. Five different techniques of wave input reduction were tested. Of all the methods of wave climate schematization tested the methods defined as ‘Energy Flux Method’ and ‘Opti Method’ showed best results in terms of representing accurately the sediment transport patterns of the study area. The tests conducted indicate that a number around 12 representative wave cases was enough to represent an annual wave climate compared to a very detailed wave climate used as benchmark. The optimized model was used to evaluate alternative engineering solutions to reduce volumetric losses from the beach nourishment project. Engineering solutions evaluated included a construction of a breakwater field, backfilling all dredge pits located offshore of the project site, construction of a groin field at the downdrift end of the project, and backfilling the deepest dredge pit. These engineering interventions caused a reduction in beach volume losses within the project limits with varying levels of effect on the downdrift beaches. Reduction of the volume loss from the project site is technically feasible and may be economically feasible pending further economic feasibility evaluation.

OBSERVATIONS OF NEARSHORE AND SURF ZONE WIND STRESS

Field data of the wind stress over surf zone waves is presented from an open ocean beach on the East Australian Coast. Two ultrasonic anemometers were deployed at nominal heights of 5 and 10 m above the water surface in the intertidal and inner surf zones, with concurrent measurements of water levels and offshore wave param- eters. Considering near-neutral conditions only, the wind drag coefficients were found to systematically change with the wind angle of approach relative to the shoreline, and are much smaller for longshore wind than during onshore wind. The concept of an apparent wave steepness changing with wind direction is suggested to explain this behaviour. The drag coefficients over the surf zone during onshore wind and near-neutral conditions were determined to be almost twice the values expected at the same wind speed and open ocean conditions. The ob- served Charnock coefficient was similarly an order of magnitude larger than open ocean values. A wave celerity of the order of that expected in the inner surf zone is required to explain the observed large roughness and drag coefficients using existing wave-age dependent parameterisations. This suggests that the slower wave celerity in the surf zone is an important contributor to the increased wind stress, in addition to the sawtooth wave shape.

Direct measurements of wind stress over the surf zone

Field data of the wind stress over surf zone waves are presented from an open ocean beach on the East Australian Coast. Two ultrasonic anemometers were deployed at nominal heights of 5 and 10 m above the water surface in the intertidal and inner surf zones, with concurrent measurements of water levels and offshore wave parameters. Following a rigorous quality control procedure, the wind stress was determined by the eddy correlation technique. A constant stress layer was observed between 5 and 10 m elevation. Considering near-neutral conditions only, the wind drag coefficients were found to systematically change with the wind angle of approach relative to the shoreline and are much smaller for longshore wind than during onshore wind. The concept of an apparent wave steepness changing with wind direction is suggested to explain this behavior. The drag coefficients over the surf zone during onshore wind and near-neutral conditions were determined to be almost twice the values expected at the same wind speed and open ocean conditions. The observed Charnock coefficient was similarly an order of magnitude larger than open ocean values. A wave celerity of the order of that expected in the inner surf zone is required to explain the observed large roughness and drag coefficients using existing wave age-dependent parameterizations. This suggests that the slower wave celerity in the surf zone is an important contributor to the increased wind stress, in addition to the sawtooth wave shape. Key Points A new field data set of the wind stress over surf zone waves is presented Concept of an apparent wave steepness is proposed to explain drag observations Surf zone drag coefficients were almost twice the values outside the surf

Phytoplankton Productivity and Photophysiology in the Surf Zone of Sandy Beaches in North Carolina, USA

Measurements of primary production in surf-zone habitats are relatively rare and often utilize simulation approaches, owing to the physical challenges of working in surf. The study reported here examined primary production in situ at two open ocean sandy beaches in southeastern North Carolina during relatively calm summer conditions. In situ bottle incubations using 14C uptake methods were complemented by simultaneous measures of phytoplankton photo-physiology assessed by Fast Repetition Rate Fluorometry (FRRF) in flow-through mode at the two sites across a spring-neap tidal cycle in July, 2010. The surf-zone phytoplankton was dominated by small centric and pennate diatoms as well as cyanobacteria and chlorophytes with biomass concentrations of 3.63–9.23 mg chl a m−3. Primary productivity was relatively high, ranging from 31.5–88.0 mg C m−3 h−1 by 14C. Biomass-specific productivity averaged ∼9.4 mg C (mg chl a)−1 h−1 by 14C, indicating healthy phytoplankton populations. Measurements of the functional absorption cross section of photosystem II, σPSII, via FRRF were 327–380, comparable to values reported by other investigators of open ocean phytoplankton. Averaged values of the maximum effective quantum yield, Fv/Fm, corresponded to proportions of photochemically competent PSII reaction centers of 62.6 % to 72 %, indicating that the phytoplankton were nutrient-replete. These data suggest that the surf zone, although a spatially confined habitat, is a productive one that plays a significant role in coastal ocean ecology. Further investigation is needed to better understand primary productivity of phytoplankton in the surf zone and the effect of the dynamic environment on their physiological responses.

Benthic Microalgal Biomass on Ocean Beaches: Effects of Sediment Grain Size and Beach Renourishment

Cahoon, L.B.; Carey, E.S., and Blum, J.E., 2012. Benthic microalgal biomass on ocean beaches: effects of sediment grain size and beach renourishment. Benthic microalgal biomass was measured as sediment chlorophyll a at two open ocean beaches in southeastern North Carolina between December 2003 and December 2004, spanning beach renourishment projects in spring 2004 at both beaches. Sampling design included replicate sampling (n = 6) at three elevations in the surf zone along paired transects at paired renourished and unnourished (control) sites at each beach 17 times during the study period. Grain-size analyses of beach sediments and measurements of water temperature were also conducted. Sediment grain size, expressed as mean grain size and percentage of total sediments <500 µm diameter, significantly affected sediment chlorophyll a values. Renourishment drove a small and temporary but significant increase in sediment chlorophyll a at one beach, which was interpreted as an effect of source material but otherwise had no detectable negative effects. The grain-size effects reinforce the importance of efforts to match material used for renourishment with existing beach sediments because benthic microalgae likely form a significant portion of the base of the food chain in surf-zone communities.

Onshore Bar Migration in a Fetch/Limited Strong Wind Bay

WONG, H and STEPHENSON, W., 2011. Onshore Bar Migration in a Fetch/Limited Strong Wing Bay. In: Micallef, A. (ed.), MCRR3-2010 Conference Proceedings, Journal of Coastal Research, Special Issue, No. 61, pp. 458-469. Grosseto, Tuscany, Italy, ISSN 0749-0208.This paper investigates bar migration in a fetch limited strong wind bay (Seaford Beach SE Australia). Onshore bar migration on open ocean beaches is dependant on long period swell wave and occurs during low energy conditions. However, in a fetch limited environment such waves are absent and most studies suggest that during low energy conditions the beach remains in an arrested state (Jackson et al. 2002). This paper spans a three month study period (15th March – 8th June 2008). Measurement of near shore morphology and wind data were collected. The two bars at Seaford behaved very differently; both onshore and offshore migration was detected during the three recorded storm events. The paper found that, firstly, wave breaking was incomplete in the middle bar during event 1 — the inner bar migrated offshore. Secondly wave breaking in the middle bar was almost complete during event 2 and the inner bar migrated onshore. Thirdly when wave breaking was complete in the middle bar during event 3 — the inner bar remained arrested on some profiles but bar height increased on others. The wave steepness threshold for onshore migration of the inner bar was parameterized s 0.041 – 0.042. Beach sediment modeling in fetch limited strong wind bays remains understudied. Our results should help to improve the predictive capability of beach sediment budgets in fetch limited strong wind bays.

Radon as an indicator of limited cross-shelf mixing of submarine groundwater discharge along an open ocean beach in the South Atlantic Bight during observed hypoxia

Hypoxic conditions (dissolved oxygen (DO)<2 mg l −1) have been documented in the nearshore coastal waters of Long Bay, South Carolina, United States of America, during summer months over the past several years. Hypoxia was documented in August 2009 in the nearshore (<500 m offshore) for ten consecutive days and four days in September 2009 corresponding with spring tides. This study measured radon activities of shallow beachface groundwater and nearshore bottom waters to estimate mixing rates and submarine groundwater discharge (SGD) in the nearshore waters of central Long Bay. Statistical analyses demonstrate significant correlations between high bottom water radon activities, low DO, and cooler bottom water temperatures during hypoxic conditions. Elevated radon activities during hypoxia were significantly influenced by upwelling favorable conditions which severely limited cross-shelf mixing. Model results indicate mixing of nearshore and offshore waters was limited by up to 93% (range: 43–100%) relative to non-hypoxic conditions. Data suggests previously overlooked natural phenomena including limited cross-shelf mixing and SGD can significantly influence nearshore water quality.

FIELD MEASUREMENT OF AEOLIAN SAND FLUX USING CERAMIC SAND FLUX SENSOR UD-101 AT A SAND DUNE

This study conducted field observations in terms of the number of blown sand impacts and wind velocity at an open ocean beach in Japan, in order to investigate characteristics of the aeolian sand transport flux over a sand dune slope. Charnock constant of a roughness length equation calculated from wind velocity data had a larger value over the slope compared to over a flat. Furthermore, the aeolian flux over the slope tended to be larger than that over the flat. Characteristics of the Charnock constant and the aeolian flux over the flat and the slope were demonstrated from the field measurements.

砂丘斜面上の飛砂に関する現地観測

This study conducted field observations in terms of the number of blown sand impacts and wind velocity for two hours on 21 February 2009 at an open ocean beach in Japan in order to investigate characteristics of the aeolian sand transport flux over a sand dune slope. The Charnock constant related to wind shear on the sand bed surface calculated from the wind velocity data on the slope had a larger value over a flat. Furthermore the aeolian flux on the slope tended to be larger than that on the flat. Knowledge of the Charnock constant and the aeolian flux on the flat and slope was obtained from the field measurements which will become a great help for further investigation of the aeolian sand transport mechanisms.

Effect of Beach Grass Cover on Beach Thermal Environment in Summer

This study conducted field observations in terms of beach surface temperature ground cover ratio of beach grass water content and grain size of beach sand in August 2003 at an open ocean beach in Japan in order to investigate the effect of the ground cover on thermal environment at beach. The temperatures of sandy area and grass area had strong proportional relationships with solar radiation. In addition the proportional coefficient of the grass area was one-tenth of that of the sandy area indicating that beach grass was effective in moderating the thermal environment in summer. Clear effects of the water content on the thermal environment could not be observed. These results obtained from high temporospatial resolution data will contribute to beach management.

Aminostratigraphy and thermoluminescence dating of coastal aeolianites and the later Quaternary history of a failed delta: The River Murray mouth region, South Australia

A geochronological framework for the sequential development of coastal barrier aeolianite complexes in the mouth region of the River Murray, Australia's largest river system is presented based on amino acid racemization and thermoluminescence dating. The sedimentary successions represent a foreshortened and condensed sequence of coastal barriers compared with those of the Coorong Coastal Plain in southern South Australia where the barrier complexes are more widely separated in response to tectonic uplift. The barriers have formed during interglacial sea-level highstands and are correlatives of genetically equivalent landforms of the Coorong Coastal Plain. Thermoluminescence dating and the extent of amino acid racemization in aeolianite ‘whole-rock’ sediment samples, reveal a general increase in age of the barriers landwards from the modern coastline. In detail, however, the individual barriers represent composite structures having formed in more than one interglaciation, due to the reoccupation of Pleistocene shoreline positions during sea-level highstands of similar amplitude, in a zone of gradual basin subsidence. The most seaward Pleistocene aeolianite at Surfer Beach is of interstadial age (Marine Isotope Stage 5c, 105 ± 5 ka; MIS 5c), and correlates with the Robe Range of the Coorong Coastal Plain. The last interglacial shoreline (130 ± 15 ka; MIS 5e) is particularly well-defined in the River Murray mouth region. It is represented by a complex association of coastal parabolic dunes superimposed on a transverse dune system, which runs parallel with the former coastline, and also includes associated estuarine, lagoonal and open ocean beach facies. Landward of the last interglacial succession are distinct barriers relating to the penultimate interglaciation (215 ± 35 ka; MIS 7), as well as earlier interglaciations (350 ± 65 ka; MIS 9 or 11 and 470 ± 70 ka; MIS 11 or 13). The coastal barriers have been successively breached by the ancestral River Murray at times of lower sea level during glacial cycles. Former mouths of the River Murray during interglacial sea-level highstands are likely to have existed near Tauwitchere Island during MIS 7, and between Goolwa and Hindmarsh Island and near the southern-most part of Lake Albert during the last interglacial (MIS 5e). The River Murray mouth region represents a failed delta as the limited sediment brought to this area since late middle Pleistocene time has been either rapidly incorporated within aeolian deposits during sea-level highstands, or transported to the edge of the Lacepede Shelf during glacial maxima. The Holocene and modern River Murray has not established a marine delta, but deposits its load in the settling basins of the terminal lakes. Only a small digitate delta has formed where the river enters Lake Alexandrina.

Coastline sand waves on a low‐energy beach at El Puntal spit, Spain: Linear stability analysis

Shoreline sand waves of approximately 125–150 m of wavelength and ≈15 m of amplitude in the offshore direction (reached in a few days) are often observed at the west end of El Puntal spit, Santander, Spain. They tend to last for about 2 months and do not show an evident alongshore propagation during that time. Since wave incidence on that beach is typically very oblique, a shoreline linear stability analysis is performed to test whether those sand waves could be generated by shoreline instability. Because of the low‐energy wave climate and the steep mean bathymetric profile, the predicted wavelength (100–150 m) and growth time (4–8 days) are much smaller than is typical on open ocean beaches. This provides a unique opportunity to test high‐angle wave instability. Thus, the role of the instability on the growth, evolution, and subsequent destruction of the sand waves is examined. A remarkable agreement between predictions and observations regarding the wavelength and growth time is found. Furthermore, by analyzing shoreline instability for a 2 year period where sand waves sometimes occur and sometimes do not, a clear correlation is found between sand wave occurrence and predicted instability growth rate. Intriguingly, results are less satisfactory regarding alongshore migration since the model predicts some migration that is not supported by observations. However, it becomes clear that the instability caused by high‐angle waves is crucial for shoreline sand wave formation at El Puntal and should be considered for any future research.

High-frequency Field Measurements of Aeolian Sand Transport Rate at a Beach

This study conducted field observations in terms of the number of wind-blown sand impacts and wind velocity in the period of 22 September - 2 December 2005 at an open ocean beach in Japan, in order to investigate variation of the wind-blown sand transport rate. Measured transport rate was calculated using the number of wind-blown sand impacts and compared to the rate estimated from the wind velocity using Bagnold's, Kawamura's, and Owen's equations. During the measurement period, the rate estimated using Owen's equation was relatively good agreement with the measured rate and the other equations overestimate the measured rate. The rate estimated using Kawamura's equation from hourly wind data obtained at off-site significantly overestimates the measured rate more than one order. Further knowledge about the actual aeolian sand transport should be accumulated in the field.

Observations of wind‐blown sand under various meteorological conditions at a beach

Field observations were conducted on a natural, open ocean beach system in Japan to investigate characteristics of wind‐blown sand transport under various weather conditions including a storm event. Data sets over periods of several hours included blown sand impact counts, three‐dimensional wind conditions, hourly precipitation, and moisture content of the sediment surface. The intermittent blown sand impact data shifted by 1 s ahead of the wind velocity correlated with the wind velocity during a no‐rainfall period (for an assumed dry surface) and in the longshore wind direction (for sufficiently long fetch length). The 5‐min mean wind velocity/impact counts relationship was well constrained by both second‐ and third‐order polynomial fitting of velocity under similar weather conditions. During a no‐rainfall period and in the longshore wind direction, the relationship between the wind velocity and sand flux estimated from the counts coincides with existing studies in wind tunnel experiments. The sand flux, however, decreased by 1 order of magnitude because of a change in the wind direction from longshore to cross‐shore and then by more than 1 order of magnitude because of an increase in the moisture content. Threshold wind velocity calculated using the time fraction equivalence method with the impact counts and the horizontal wind velocity in 5‐min sampling periods was approximately equal to the value predicted using Bagnold's equation during the no‐rainfall period and increased significantly during the rainfall phase. The sand flux sensor has several limitations for complex conditions in the field; however, it provides a number of characteristics of sand transport under various meteorological conditions.

Low-Energy Beach Morphology with Respect to Physical Setting: A Case Study from Cockburn Sound, Southwestern Australia

Low-energy beaches are omnipresent coastal features. In total, their overall length greatly exceeds that of ocean shorelines throughout the world. However, a comprehensive understanding of low-energy beaches is lacking, with their dynamics generally considered under existing principles governing open ocean beaches. This study investigates the morphodynamic characteristics of very low energy beaches on which wave heights can be less than 0.15 m under nonstorm conditions, as distinguished from the characteristic of high-energy environments in which low energy states commonly have modal wave heights of 0.5–1 m. This investigation is achieved through an analysis of a 30-year profile data set for Cockburn Sound, a fetch-limited, low-energy basin in southwestern Australia. The Sound experiences the full ranging of microtides and surges of the region, together with locally generated wind waves. Recurring patterns in cross-shore geometries and their distribution were identified through regression analysis of mean profile shapes. The spatial variability in the wind-wave regime was established by hindcasting conditions for key fetch directions. Cluster analysis of profile and environmental variables identified four morphotypes. Each morphotype can be explained in terms of a simple exposure factor, Ef = log(Fl/Ms), which is the proportion of fetch length (Fl) to marginal shoal width (Ms), such that Ef < 1 was characteristic of exponential profiles, Ef = 1–1.5 of segmented profiles, Ef = 1.5–2 of concave-curvilinear profiles, and Ef > 2 of convex-curvilinear profiles. Thus, the exposure factor is identified as a useful nondimensional parameter for the delineation of low-energy profile morphotypes within the study area. The utility of this approach in widespread classifications of low-energy beach morphology requires further research. This should take place in a variety of environments with varying degrees of protection and shelter from swell and subject to different tidal ranges and fluctuations in sea level.