Beach Surface Research Articles

ASSESSMENT OF METAL POLLUTION IN INTER TIDAL AND BEACH SEDIMENTS ALONG NORTH EAST COAST OF TAMILNADU, INDIA

The concentrations of major (Al, Fe, Mg, Mn, Na, K and Ca) and trace (Cr, Cu, Ni, Pb and Zn) elements have been determined in inter tidal and beach surface sediments samples collected from North east coast of Tamilnadu, India. Major element analysis showed that the sediments had low concentrations when compared with crustal average and upper continental crust. Using sediment quality guidelines and different types of indexes, current trace elements pollution status in the study area were assessed. Sediment quality guidelines suggest that nickel and lead must be considered as a chemically potential concern in the study area. The indexes used in this study were enrichment factor, geo-accumulation index and modified degree of contamination. Different indexes gave diverse status of inter tidal and beach sediment quality. The results are discussed in the context of the sources and pathways of trace elements in the North east coast of Tamilnadu, India.

Utility of an inexpensive near-infrared camera to quantify beach surface moisture

Surface moisture content is an essential factor that must be considered when studying aeolian sediment transport on a sandy beach. In recent years, near-infrared (NIR) remote sensing sensors have shown promise for obtaining accurate surface moisture data; however, prior studies utilized instruments with extreme costs. This study assesses the capability of an inexpensive NIR digital camera to measure surface moisture at two sandy beach environments – Tybee Island, Georgia and Pensacola Beach, Florida – that exhibit varying sediment hue characteristics. To account for temporal variations in solar atmospheric conditions, we normalized the raw sediment surface reflectance data against a white reflectance card and a sample of oven dry sand representative of each study site. This is a necessary step to account for solar atmospheric conditions. Calibration results illustrate that the NIR camera is capable of producing accurate representations of beach surface moisture; analyses from both study sites produced R2 values greater than 0.76 with error estimates at ±1–2% moisture. No statistical difference in calibration relationships were observed for data collected over multiple days and times of day. Calibration data for the reflectance card produced more robust relationships with smaller prediction errors than the oven dry sand analyses; however. Overall, this study illustrates that an inexpensive digital camera modified to record NIR radiation is capable of producing robust and accurate measurements of beach surface moisture.

Support vector regression for high-resolution beach surface moisture estimation from terrestrial LiDAR intensity data

Beach Surface Moisture (BSM) is a key attribute in the coastal investigations of land-atmospheric water and energy fluxes, groundwater resource budgets and coastal beach/dune development. In this study, an attempt has been made for the first time to estimate BSM from terrestrial LiDAR intensity data based on the Support Vector Regression (SVR). A long-range static terrestrial LiDAR (Riegl VZ-2000) was adopted to collect point cloud data of high spatiotemporal resolution on the Ostend-Mariakerke beach, Belgium. Based on the field moisture samples, SVR models were developed to retrieve BSM, using the backscattered intensity, scanning ranges and incidence angles as input features. The impacts of the training samples’ size and density on the predictive accuracy and generalization capability of the SVR models were fully investigated based on simulated BSM-intensity samples. Additionally, we compared the performance of the SVR models for BSM estimation with the traditional Stepwise Regression (SR) method and the Artificial Neural Network (ANN). Results show that SVR could accurately retrieve the BSM from the backscattered intensity with high reproducibility (average test RMSE of 0.71% ± 0.02% and R2 of 0.98% ± 0.002%). The Radial Basis Function (RBF) was the most suitable kernel for SVR model development in this study. The impacts of scanning geometry on the intensity could also be accurately corrected in the process of estimating BSM by the SVR models. However, compared to the SR method, the predictive accuracy and generalization performance of SVR models were significantly dependent on the training samples’ coverage, size and distribution, suggesting the need for the training samples of uniform distribution and representativeness. The minimum size of training samples required for SVR model development was 54. Under this condition, SVR performed similarly to ANN with a test RMSE of 1.06%, but SVR still performed acceptably (with an RMSE of 1.83%) even using extremely few training samples (only 16 field samples of uniform distribution), far better than the ANN (with an RMSE of 4.02%).

MORFOMETRI GISIK KAWASAN PANTAI WISATA BAHARI SARIO KOTA MANADO

Beach formation has an important role in protecting land from the action of the sea and it is useful for recreation, conservation and other uses. In “Wisata Bahari Sario” Kota Manado coastal area there is still a particular area of beach that is used for various purposes, so it is important to study its morphology. This research was conducted with the aim of describing morphology and analyzing oceanographic factors that affected the dynamic process of beach morphology. The results showed that the beach had an area of 422.69 m2, with the criteria for short slopes in the Northeast and long slopes in the Southwest. The shapes of the beach surface were in the form of gutters and shoots, their appearance was more visible towards the Southwest. In general, the deposition process took place more intensively in the Southwestern part of the beach. Keywords: Beach, Morphology, Slope, Deposition

Lithological and geochemical analyses of sandy beach sediments of different geological frameworks: the south-eastern Baltic Sea (Lithuania)

This study aims to analyse the spatial lithological and geochemical composition of beach sediments from two sites representing coastal areas with different geological and geomorphological frameworks, sediment availability and sediment transport pathways. The sandy beach surface sediments were sampled in spring 2018, the magnetic susceptibility was measured on-site and the grain size analysis was carried out and the geochemical composition of the samples determined in the laboratory (ICP-MS/ES). The results indicated that even though the sites differed in term of geology and geomorphology, the mean magnetic susceptibly and grain size did not differ significantly. On the contrary, the two sites showed significant differences in elemental composition. The factorial analysis revealed that there were two main groups of elements; the first was composed of Fe–V–Cr–Pb–As–K–Co–P–Ni–Al–Ga, mostly represented in the sediments of the Curonian Spit, and the second group was composed of Mn–Ca–Mg–Sr–Ti–Ba which defined the composition of the sandy beach sediments of the mainland coast. We interpreted the geochemical anomalies as having different causes. On the mainland coast, geochemical and lithological anomalies tend to form where the coastal erosive processes are active, while on the Curonian Spit, these anomalies are located where relict coarse sand dominates and the main unloading of sediments from the alongshore northward current occurs. These results allow the sediment transport process to be better understood and the sediments’ provenance to be identified. In the future, they could also be used for coastal sediment transport modelling exercises.

Monitoring spatiotemporal variation in beach surface moisture using a long-range terrestrial laser scanner

The measurement of surface moisture on beaches is vital for studying aeolian sand transport mechanisms, but existing techniques are not adequate for monitoring the surface moisture dynamics over a substantial beach section. In this study, we investigated the suitability of a new remote sensing method to monitor the spatiotemporal variation in surface moisture on a sandy beach using a long-range static terrestrial laser scanner (TLS). The TLS was permanently deployed on top of a 42 m high building overlooking the study site at Ostend-Mariakerke, Belgium. Considering the effect of target surface roughness on the intensity and the laboratory’s length limitation, a new intensity correction method is proposed which only uses the field point cloud data measured on a homogenous beach surface (without time-consuming indoor experiments). Based on the corrected intensity data, the relation of the beach surface moisture to the corrected intensity was modeled by an exponential model with a correlation-coefficient squared of 0.92. A moisture estimation model was developed which can directly derive the beach surface moisture from the original intensity data of the TLS with a standard error of 2.27%. The hourly surface moisture dynamics across two tidal cycles on the beach were investigated as a case study, in which the point clouds derived from corresponding unmanned aerial vehicle (UAV) imagery are utilized to improve the calculation accuracy of the incidence angles of TLS point clouds at long distances. Results reveal that, after the intensity correction, the long-range static TLS is an extremely suitable technique to monitor the surface moisture dynamics (daytime and nighttime) over a substantial beach section (hundreds of meters) at a high scanning frequency (minutes to hours).

Groundwater Flow and Moisture Dynamics in the Swash Zone: Effects of Heterogeneous Hydraulic Conductivity and Capillarity

AbstractA density‐dependent, variably saturated groundwater flow and solute transport model was used to investigate the influence of swash motions on subsurface flow and moisture dynamics in beach aquifers with heterogeneous distributions of hydraulic conductivity (K) and capillarity. The numerical simulations were performed within a Monte Carlo framework using field measurements conducted in the swash zone of a sandy beach. Our results show that heterogeneous capillarity causes spatially variable capillary rise above the groundwater table. In response to swash motions, heterogeneity creates capillary barriers that result in pockets of elevated moisture content beneath the swash zone. These moisture hotspots persist within the unsaturated zone even at ebb tide when the swash motions recede seaward. Heterogeneous capillarity also results in highly tortuous preferential flow paths and alters the flow rates from the sand surface to the water table. Heterogeneous K greatly enhances the seawater infiltration into the swash zone and modulates its spatial distribution along the beach surface. Due to heterogeneous K and capillarity, complex mixing patterns emerge. Both strain‐dominated and vorticity‐dominated flow regions develop and dissipate as tides and waves move across the beach surface. Complex mixing patterns of seawater percolating from the swash zone surface to the water table, with localized areas of high and low mixing intensities, are further demonstrated by analysis of dilution index. Our findings reveal the influence of geologic heterogeneity on swash zone moisture and flow dynamics, which may have important implications for sediment transport and chemical processing in beach aquifers.

The effect of porous zigzag-type breakwaters on the coastline changes in Neuheun village, Aceh

The process of changing the coastline has always been a challenge for coastal communities. Beach erosion has been a threat with the coastline withdrawing from its previous position. Coastal protection buildings are needed to overcome coastal erosion problems, and alternative construction also needs to be developed. The zig-zag type porous breakwater is quite effective in reducing erosion based on several small-scale physical models that have been developed. Therefore a prototype was built and tested to observe its usefulness, and how it was applied in the field. This study aims to assess the effect of installing zigzag type porous breakwaters on coastline changes. This research began with the installation of construction and continued with observing changes in the coastline. Observations are carried out periodically at any time, to see changes in the contour of the beach that occurs. Observations were made by leveling the beach surface against several transverse profiles. Changes in coastline due to construction will be analyzed by looking at the relation to the wind direction. The results obtained from several observations show that the construction of a zig-zag type porous breakwater has a positive effect in reducing erosion, as long as the breakwater distance with the coastline does not exceed the breakwater length.

Study on the Coastline Evolution in Sopot (2008–2018) Based on Landsat Satellite Imagery

The coastline is the boundary between the water surface in a reservoir or watercourse and the land, which is characterised by high instability and functional diversity. For these reasons, research on coastal monitoring has been conducted for several decades. Currently, satellite images performed with synthetic aperture radars (SARs) are used to determine its course and variability together with high-resolution multispectral imagery from satellites such as IKONOS, QuickBird, and WorldView, or moderate-resolution multispectral images from Landsat satellites. This paper analysed the coastline variability in Sopot (2008–2018) based on Landsat satellite imagery. Furthermore, based on multispectral images obtained, it was determined how the beach surface in Sopot changed. Research has shown that the coastline keeps moving away from the land every year. This was particularly noticeable between 2008 and 2018 when the coastline moved on average 19.1 m towards the Baltic Sea. Moreover, it was observed that the area of the sandy beach in Sopot increased by 14 170.6 m2, which translates into an increase of 24.7% compared to 2008. The probable cause of the continuous coastline shift towards the sea and the increase of the beach surface is the oceanographic phenomenon called tombolo, which occurred in this area as a result of the construction of a yacht marina near the coast.

Density and composition of surface and buried plastic debris in beaches of Senegal

Debris poses a series of problems to marine life and human well-being. However, estimates of density and characteristics of debris found on beach surfaces and buried in the sand are patchy on a global scale and absent for West Africa. Here we investigate the density of surface and buried debris accumulated in two beaches with contrasting levels of urbanisation in Senegal, West Africa. We also describe type, colour, weight, size, and possible source of the 1766 items collected. The average density of debris buried at a depth of 10 cm (48.75 items/m2) was 25 times higher than that observed at the surface (1.92 items/m2). Plastics accounted for 97.62% of the items. Plastic bags and clothing plastic were the most common types, whereas white and transparent were the most common colours. Most items originated from mixed sources, i.e. beach users and land-based sources (51.30%). Debris density in the urbanised site was 20 times higher than that in the non-urbanised site. Debris density can, therefore, be largely underestimated when sampling only on the beach surface. Our study provides the first findings for future research on beach debris in Senegal.

Study of the Ponta Negra Beach Surface in Manaus / AM: Evidence and Causes of Mass Movement of the Artificial Beach Landfill

Ponta Negra Beach is located on the banks of the Rio Negro, in the city of Manaus, state of Amazonas, Brazil. In 2012, a revitalization of the beach was carried out, with emphasis on the construction of an artificial beach landfill, in order to perpetuate the population's access to the beach throughout the hydrological year. This work resulted in the formation of several irregularities throughout the terrain, such as cavities, plumbing and pipes exposed on the surface, and sudden cavities between shallower and deeper parts of the bed. These problems have resulted in several fatalities since the opening of the landfill. Given these questions, this study aimed to assess the changes that occur on the beach surface, through analysis of sediments, topography and space, as a result of the construction work, for a period of two to three years, and thus, to identify the cause of these problems to understand what failures occurred in the construction of the landfill that led to the formation of these irregularities. The results showed that the grounded sediments from the artificial beach are being transported more easily by the force of the river and the rains because they are finer sediments than those of the natural beach, intensifying the erosion rates and resulting in the generation of ravines and depressions along the entire beach, being responsible for the movement of sandy mass of the ladfill and in the formation of the irregularities found. This study proves that the anthropic relationships interfered in the natural processes that act on the beach's morphology, warning the importance of serious previous studies in the execution of works with landfills and their continuous maintenance

High-frequency in situ measurements of beach responses to Tropical Storm Bebinca at Qing’an Bay, Guangdong Province, China

Tropical cyclones are one of the primary driving forces that cause beach evolution in South China. Because of the harsh working conditions, few high-frequency in situ observations of beach responses to tropical storms have been reported. In this study, high-frequency in situ measurements were conducted over six and a half days at Qing’an Bay beach, Xuwen County, Guangdong Province, China, during the strong tropical storm Bebinca in 2018. The measured parameters included overall hydrodynamics, hourly variations of beach surface elevations, and daily sediment sampling. Four main analysis results were identified. (1) Dominated by the spatial distribution of Hainan Island and the Leizhou Peninsula and the long-lasting and changeable characteristics of Bebinca, the hydrodynamic processes of Qing’an Bay were complex, but the variation range was not large. (2) In each tidal cycle, both erosion and accretion occurred in different parts of the beach profile. (3) During Bebinca, there were two main erosion patterns: first vertical and then horizontal. First, the response processes of the spring tidal berm comprised three stages: rapid erosion, slow erosion, and oscillatory recovery. The oscillatory recovery rate during the storm could reach one-quarter of the maximum erosion depth. Thereafter, the storm berm gradually receded laterally after the rapid erosion of the spring tidal berm. A sandbar appeared at the breaking point of the high tide, formed by gradual sand transportation from the beach berm to the sea, and its position was relatively stable. (4) Changes in grain size parameters of beach surface sediments were complex and were significantly influenced by the vertical distribution of grain size components, sediment confluence, and wave sorting.

Measuring Surface Moisture on a Sandy Beach based on Corrected Intensity Data of a Mobile Terrestrial LiDAR

Surface moisture plays a key role in limiting the aeolian transport on sandy beaches. However, the existing measurement techniques cannot adequately characterize the spatial and temporal distribution of the beach surface moisture. In this study, a mobile terrestrial LiDAR (MTL) is demonstrated as a promising method to detect the beach surface moisture using a phase-based Z&F/Leica HDS6100 laser scanner mounted on an all-terrain vehicle. Firstly, two sets of indoor calibration experiments were conducted so as to comprehensively investigate the effect of distance, incidence angle and sand moisture contents on the backscattered intensity by means of sand samples with an average grain diameter of 0.12 mm. A moisture estimation model was developed which eliminated the effects of the incidence angle and distance (it only relates to the target surface reflectance). The experimental results reveal both the distance and incidence angle influencing the backscattered intensity of the sand samples. The standard error of the moisture model amounts to 2.0% moisture, which is considerably lower than the results of the photographic method. Moreover, a field measurement was conducted using the MTL system on a sandy beach in Belgium. The accuracy and robustness of the beach surface moisture derived from the MTL data was evaluated. The results show that the MTL is a highly suitable technique to accurately and robustly measure the surface moisture variations on a sandy beach with an ultra-high spatial resolution (centimeter-level) in a short time span (12 × 200 m per minute).

Community understanding and attitude levels on the implementation of illegal sand mining on the Induk Beach, West Lombok

Taman Ayu Village in Gerung, West Lombok District, has a prospect as an up-coming tourist area. It is unfortunate if the coastal sand mining activities damage the coastal regions. The research conducted aims to describe the level of understanding and attitude of the community towards the impact of mining illegally. This research method is descriptive, with a qualitative approach by using observation, in-depth interviews. The results of the study show that mining is carried out by the community, because of the need for beach sand for building materials, especially as the final content for making ornaments or home decorations. Coastal sand mining caused a decrease in the beach surface, potential disasters, and coastal abrasion. The positive impact of these activities is increasing the income of the mining community. The community has understood that sand mining activities cause damage to coastal areas, but due to economic demands, the community continues to carry out these activities. In tackling illegal mining on the central coast, the role and responsibility of the Government is integral. Banning and giving warnings in the form of installing warning boards around the mining site as well as providing specialized training for mining officials to provide an understanding to stop the mining activities.

Beach surface lost historically: The case of the eastern coast of Las Palmas de Gran Canaria (Canary Islands, Spain)

Land use changes cause significant loss of natural and cultural elements. This is the case of the eastern coast of Las Palmas de Gran Canaria (LPGC) (Canary Islands), which was heavily transformed between the late XIX century and the 1960s by increased urban sprawl. Most of the beaches were covered by the city and, therefore, disappeared. The aim of the study is to identify and describe the natural characteristics of the beaches lost between 1879 and 2017 along the eastern coastline of LPGC, as well as to quantify the lost surface area. The changes in land uses that have taken place around these beaches are also addressed. For these purposes, historical sources (documentary, graphic, cartographic and oral) and geographic information systems (GIS) have been used. The results show that, since 1879, eleven beaches, with an extension of 13.19 ha, have disappeared and, with them, their natural and cultural features. Eight land uses were identified: fishing, defensive, agriculture, port, industrial, commercial, residential and recreational. It was also found that beaches from the northern and central sectors had more varied uses than those of the southern sector, which tended to be mainly used for fishing. The results are analyzed at both global and local scale. At global scale, different effects of globalization on coastal urban areas are discussed. At local scale, a discussion is undertaken on how the knowledge acquired can be used to improve future urban planning and to rebuild the memory of the city's coast for its inhabitants and visitors.

Identification and Characterization of Critical Sites for Small Pelagic Fish in the Coastal Marine Area of Senegal, West Africa

Better management of coastal marine resources generally requires good knowledge of habitats and resources. This need led to the performance of an identification and bioecological characterization study of critical sites for small pelagics in the Senegalese coastal marine zone. Biological and ecological data were collected using beach seines (12 to 28 mm mesh) and surface drifting gillnets (28 to 36 mm mesh) at sites identified by fishermen on the basis of surveys. The results of the study highlight the bioecological characteristics of these sites: (i) the Port-Baie Hann site - a nursery and spawning site with a high diversity for the target species; it is under marine pollution threat; (ii) the Mbodiène-Ngazobil site, with high diversity for target species and the Kafountine-Cap site are nursery and spawning sites under high fishing pressure, (iii) the Diakhanor-Sangomar site - a spawning site under the potential threat of exploration of offshore Sangomar oil in addition to the high fishing pressure. This work is a first flagship contribution to a process that should lead to the development and control of new tools for the effective and sustainable management of small pelagics at national and regional scales.

Numerical Study of Tide-Induced Airflow and Salt-Fresh Water Dynamics in Unconfined Aquifers.

This study employed a coupled water-air two-phase flow and salt water transport model to analyze the behaviors of generated airflow in unsaturated zones and the fluctuations of salinity at the salt-fresh water interface in a two-layered unconfined aquifer with a sloping beach surface subjected to tidal oscillations. The simulation results show that as the new dynamic steady state including effects of tidal fluctuations is reached through multiple tidal cycles, the dispersion zone in the lower salt water wedge is broadened because fresh water/salt water therein flows continuously landward or seaward during tidal cycles. The upper salt-fresh water interface exhibits more vulnerable to the tidal fluctuations, and the variation of salinity therein is periodic, which is irrelevant to the hydraulic head but is influenced by the direction and velocity of surrounding water-flow. With the tidal level fluctuating, airflow is mainly concentrated in the lower permeable layer due to the restraint of the upper semi-permeable layer, and the time-lag between the pore-air pressure and the tidal level increases with distance from the coastline. The effect of airflow in unsaturated zones can be transmitted downward, causing both the magnitude of salinity and its amplitude in the upper salt-fresh water interface to be smaller for the case with airflow than without airflow due to the resistance of airflow to water-flow. Sensitivity analysis reveal that distributions of airflow in unsaturated zones are affected by the permeability of the upper/lower layer and the van Genuchten parameter of the lower layer, not by the van Genuchten parameter of the upper layer, whereas the salinity fluctuations in the salt-fresh water interface are affected only by soil parameters of the lower layer.

A Case Study: Determination of the Optimal Tailings Beach Distance as a Guideline for Safe Water Management in an Upstream TSF

Most tailings storage facility (TSF) failures occur in active, upstream-type TSFs, often due to extreme and unexpected weather conditions—specifically, heavy rainfall and strong winds. This case study of a TSF in southern Arizona examines the use of the optimum safe beach distance (Doptimal, the optimum distance between the crest and decant pond) as a tool for monitoring geotechnical stability and reducing catastrophic failures. A digital model of the TSF was used to determine the critical beach distance (Dcritical) under normal weather conditions, and Doptimal was then determined by adding incremental distances to account for the effects of heavy rainfall (Drainfall) and strong winds (Dwind). To overcome accessibility issues, a drone was used to map the TSF geometry and create a digital model. This model served as the basis for conducting a coupled stress-seepage, finite-element (FEM) analysis with a safety factor of 2.0 to assess geotechnical stability (Dcritical). The safe beach distance increments were determined using the PMP (probable maximum precipitation) and possible maximum wind speed. Based on this analysis, the optimal safe beach distance at the study site was identified as 202.2 m. Since the current beach distance (371 m) exceeds this value, the TSF was considered to be stable and satisfied the design safety factor of 2.0. However, this distance should be reassessed periodically to account for changes in the TSF geometry and other conditions. Furthermore, it applies only TSFs that are well-managed and feature a smooth, non-undulating beach surface with a consistent slope.

Decomposition of sediment-oil-agglomerates in a Gulf of Mexico sandy beach

Sediment-oil-agglomerates (SOA) are one of the most common forms of contamination impacting shores after a major oil spill; and following the Deepwater Horizon (DWH) accident, large numbers of SOAs were buried in the sandy beaches of the northeastern Gulf of Mexico. SOAs provide a source of toxic oil compounds, and although SOAs can persist for many years, their long-term fate was unknown. Here we report the results of a 3-year in-situ experiment that quantified the degradation of standardized SOAs buried in the upper 50 cm of a North Florida sandy beach. Time series of hydrocarbon mass, carbon content, n-alkanes, PAHs, and fluorescence indicate that the decomposition of golf-ball-size DWH-SOAs embedded in beach sand takes at least 32 years, while SOA degradation without sediment contact would require more than 100 years. SOA alkane and PAH decay rates within the sediment were similar to those at the beach surface. The porous structure of the SOAs kept their cores oxygen-replete. The results reveal that SOAs buried deep in beach sands can be decomposed through relatively rapid aerobic microbial oil degradation in the tidally ventilated permeable beach sand, emphasizing the role of the sandy beach as an aerobic biocatalytical reactor at the land-ocean interface.

Timescales of beach cusp evolution on a steep, megatidal, mixed sand-gravel beach

Field observations are presented of the morphological evolution of beach cusps on a 1:10 slope, megatidal (8–12 m range), mixed sand-gravel beach at the head of the Bay of Fundy, Nova Scotia. Cusps had mean wavelengths of 3–6 m and displayed pronounced horn/bay sediment size segregation, with sand-sized material in the bays and gravel-sized material in the horns. Cusp occurrence was limited to the upper third of the beach face. Shoreline position during the tidal cycle was estimated at three minute intervals from time-averaged video imagery. Three cusp events are examined in detail, two exhibiting pronounced topographic relief, and the third demonstrating sensitivity of the rate of cusp evolution to the beach surface grain size distribution. Forcing conditions were weak, with significant offshore wave heights of 10–20 cm and peak periods of 4–7 s. Relict cusp morphology was inundated with the rising tide and destroyed or reworked during high tide. New cusps formed during the falling tide through a combination of accretion at the horns and erosion in the embayments. Timescales of growth and decay were short, ranging from 10 to 30 min. The location and dynamics of cusp horns appeared to depend on the high water line and its location relative to any pre-existing cusp morphology. The apparent sensitivity of cusp formation timescales to the local grain size distribution suggests that size segregation is intrinsic to the process of mixed sand-gravel cusp evolution.