Beach Slope Research Articles

Importance of Pre-Storm Morphological Factors in Determination of Coastal Highway Vulnerability

This work considers a database of pre-storm morphological factors and documented impacts along a coastal roadway. Impacts from seven storms, including sand overwash and pavement damage, were documented via aerial photography. Pre-storm topography was examined to parameterize the pre-storm morphological factors likely to control whether stormwater levels and waves impact the road. Two machine learning techniques, K-nearest neighbors (KNN) and ensemble of decision trees (EDT), were employed to identify the most critical pre-storm morphological factors in determining the road vulnerability, expressed as a binary variable to impact storms. Pre-processing analysis was conducted with a correlation analysis of the predictors’ data set and feature selection subroutine for the KNN classifier. The EDTs were built directly from the data set, and feature importance estimates were reported for all storm events. Both classifiers report the distances from roadway edge-of-pavement to the dune toe and ocean as the most important predictors of most storms. For storms approaching from the bayside, the width of the barrier island was the second most important factor. Other factors of importance included elevation of the dune toe, distance from the edge of pavement to the ocean shoreline, shoreline orientation (relative to predominant wave angle), and beach slope. Compared to previously reported optimization techniques, both machine learning methods improved using pre-storm morphological data to classify highway vulnerability based on storm impacts.

Subaqueous and Subaerial Beach Changes after Implementation of a Mega Nourishment in Front of a Sea Dike

Sandy nourishments can provide additional sediment to the coastal system to maintain its recreational or safety function under rising sea levels. These nourishments can be implemented at sandy beach systems, but can also be used to reinforce gray coastal infrastructure (e.g., dams, dikes, seawalls). The Hondsbossche Dunes project is a combined shoreface, beach, and dune nourishment of 35 million m3 sand. The nourishment was built to replace the flood protection function of an old sea-dike while creating additional space for nature and recreation. This paper presents the evolution of this newly created sandy beach system in the first 5 years after implementation based on bathymetric and topographic surveys, acquired every three to six months. A significant coastline curvature is created by the nourishment leading to erosion in the central 7 km bordered by zones with accretion. However, over the five-year period, net volume losses from the project area were less than 5% of the initial nourished sand volume. The man-made cross-shore beach profile rapidly mimics the characteristics of adjacent beaches. The slope of the surfzone is adjusted within two winters to a similar slope. The initially wide beaches (i.e., up to 225 m) are reduced to about 100 m-wide. Simultaneously, the dune volume has increased and the dune foot migrated seaward at the entire nourished site, regardless of whether the subaqueous profile gained or lost sediment. Our results show that the Hondsbossche Dunes nourishment, built with a natural slope and wide beach, created a positive sediment balance in the dune for a prolonged period after placement. As such, natural forces in the years after implementation provided a significant contribution to the growth in dune volume and related safety against flooding.

Surf-zone dynamics derived from basin-scale experiments

Surf-zone hydrodynamics forced by oblique wave shoaling and breaking on beach slopes were investigated. The results showed that in wave-basin experiments with incident angles in the range of 15°–30°, wave breaking was initiated at a breaker coefficient of around 0.67, which was significantly less than that predicted from empirical relations based on normally incident waves for a given beach slope and deep-water wave steepness. The measurements also showed that subsequent saturated breaking occurred at a breaker coefficient of around 0.47 that was independent of beach slope in the range of 1:10 to 1:100. This result is likely applicable to both oblique and normally incident waves. It is shown that the measured wave heights and longshore velocity profiles in wave-basin studies can be reasonably well predicted by theory with proper adjustments to the process parameters. Best-match formulations were identified for quantifying bottom friction, eddy viscosity, and energy loss due to surface rollers.

A comprehensive analysis of solitary wave run-up at sloping beaches using an extended experimental dataset

In this work, the phenomenon of wave run-up induced by solitary waves in breaking and nonbreaking conditions has been investigated. Despite several studies have been carried out to study this kind of physical process, a robust determination of solitary wave run-up on plane beaches over a wide range of wave conditions and beach slopes is still lacking. In this context, 99 laboratory tests were undertaken in the wave channel of the University of Calabria by adopting three beach slopes and three water depths. The experimental set-up was made up of four wave gauges, a pressure transducer, a velocimeter and an adjustable waterproof ramp to reproduce the plane sloping beach. Using graduated markers along the beach and a video camera, the run-up was deduced. The present experiments cover a range not extensively analyzed in literature, and specifically related to wave run-up comparable or greater than the water depth. The laboratory run-up, velocity and pressure data were validated using the IH-2VOF numerical model. Two different approaches, both for breaking and nonbreaking conditions, were used to obtain semi-analytical formulas for the wave run-up. The first approach is conventional, being based on wave non-linearity and beach slope, while the second is based on the wave energy.

Runup characteristics of a tsunami-like wave on a slope beach

Solitary waves (SWs) are often applied to the investigation of the hydraulic characteristics of tsunamis. However, SWs not only have a considerably narrower distribution than an actual tsunami but also have a smaller volume. By examining the 2011 Tohoku tsunami, we found that the volume ratio (V/V0) of the tsunami observed from the GPS buoy to the SW ranged from 2.54 to 14.76. This study proposes a tsunami-like wave (TLW) generation method which improves the shortcomings of existing SWs and has characteristic similar to an actual tsunami to better represent such wide-waveform tsunamis. Numerical analysis was performed by considering the TLW with various waveforms. In SWs, the maximum runup on the slope and the beginning of the rundown at the shoreline occur almost simultaneously. In a TLW, in contrast, rundown starts first under the influence of gravity before reaching the maximum runup height on the slope. As the waveform distribution becomes wider, the time difference between the beginning of the rundown and the maximum runup increases. The runup height increases as V/V0 increases within a certain range, but the rise slows beyond this range. Correlation of newly proposed friction parameters with the TLW breaking conditions, breaking wave types, and non-dimensional runup was also analyzed.

Characteristics Nesting Ground of Turtle (Lepidochelys olivaceae) in Gampong Gelumpang Sulu Timur Dewantara Sub-district, North Aceh Regency

One of the reptiles whose natural habitat is in the sea and has the ability to migrate very far is the turtle. Threats that endanger the turtle population, both directly and indirectly, come from natural sources and from human activities. The factors that influence turtle nesting ground were predators, sand grain size, substrate humidity, substrate temperature, beach width, coastal vegetation and beach slope. Humans as one of the predators of the availability of turtles in nature by taking turtle eggs. The aim of the study was to determine the nesting habitat characteristics of the Lekang turtle (Lepidochelys Olivaceae) in the coastal area of Gampong Geulumpang, East Sulu, Dewantara District, North Aceh Regency. This research was carried out in November 2021, which took place on the coast of the village of Gelumpang, East Sulu, Dewantara District, North Aceh Regency. In this study, observational data collection and biophysical measurements were set at 3 stations. Station 1 (Dusun Cot U Sibak), station 2 (Dusun Pasie Kuala), and station 3 (Dusun Teupin). The distance between stations in this study was ± 2 km. Data analysis was carried out by weight body and scoring methods. Based on the results of data analysis from three observation stations at turtle nesting locations from several parameters such as beach slope is 4.5-9.3%, beach width is 10.20 -22 meters, the sand temperature is 29-32 0C, humidity is 21-28%, the size of the sand grains is 0.15322-0.31601 mm, while the coastal vegetation is 16.7-49.4%, it is concluded that the three observation stations are in the very suitable category for turtle nesting locations

Wind-induced changes to shoaling surface gravity wave shape

Unforced shoaling waves experience growth and changes to wave shape. Similarly, wind-forced waves on a flat-bottom likewise experience growth/decay and changes to wave shape. However, the combined effect of shoaling and wind-forcing on wave shape, particularly relevant in the near-shore environment, has not yet been investigated theoretically. Here, we consider small-amplitude, shallow-water solitary waves propagating up a gentle, planar bathymetry forced by a weak, Jeffreys-type wind-induced surface pressure. We derive a variable-coefficient Korteweg-de Vries-Burgers (vKdV-B) equation governing the wave profile's evolution and solve it numerically using a Runge-Kutta third-order finite difference solver. The simulations run until convective prebreaking -- a Froude number limit appropriate to the order of the vKdV-B equation. Offshore winds weakly enhance the ratio of prebreaking height to depth as well as prebreaking wave slope. Onshore winds have a strong impact on narrowing the wave peak, and wind also modulates the rear shelf formed behind the wave. Furthermore, wind strongly affects the width of the prebreaking zone, with larger effects for smaller beach slopes. After converting our pressure magnitudes to physically realistic wind speeds, we observe qualitative agreement with prior laboratory and numerical experiments on breakpoint location. Additionally, our numerical results have qualitatively similar temporal wave shape to shoaling and wind-forced laboratory observations, suggesting that the vKdV-B equation captures the essential aspects of wind-induced effects on shoaling wave shape. Finally, we isolate the wind's effect by comparing the wave profiles to the unforced case. This reveals that the numerical results are approximately a superposition of a solitary wave, a shoaling-induced shelf, and a wind-induced, bound, dispersive, and decaying tail.

A Database of Topo-Bathy Cross-Shore Profiles and Characteristics for U.S. Atlantic and Gulf of Mexico Sandy Coastlines

A database of seamless topographic and bathymetric cross-shore profiles along with metrics of the associated morphological characteristics based on the latest available lidar data ranging from 2011–2020 and bathymetry from the Continuously Updated Digital Elevation Model was developed for U.S. Atlantic and Gulf of Mexico open-ocean sandy coastlines. Cross-shore resolution ranges from 2.5 m for topographic and nearshore portions to 10 m for offshore portions. Topographic morphological characteristics include: foredune crest elevation, foredune toe elevation, foredune width, foredune volume, foredune relative height, beach width, beach volume, beach slope, and nearshore slope. This database was developed to serve as inputs for current and future morphological modeling studies aimed at providing real-time estimates of coastal change magnitudes resulting from imminent tropical storm and hurricane landfall. Beyond this need for model inputs, the database of cross-shore profiles and characteristic metrics could serve as a tool for coastal scientists to visualize and to analyze varying local, regional, and national variations in coastal morphology for varying types of studies and projects related to Atlantic and Gulf of Mexico sandy coastline environments.

A nonlinear, non-dispersive energy balance for surfzone waves: infragravity wave dynamics on a sloping beach

A fully nonlinear non-dispersive energy balance for surfzone waves is derived based on the nonlinear shallow water equations to study the nearshore dynamics of infragravity (IG) waves. Based on simulations of waves on a relatively moderate and mild beach slope with a non-hydrostatic wave-flow model (SWASH), the new theory shows that spatial gradients in IG energy flux are nearly completely balanced by the combined effect of bottom stresses and predominantly nonlinear triad interactions. The new balance confirms many features of existing weakly nonlinear theories, and yields an improved description in the inner surfzone where waves become highly nonlinear. A gain of IG energy flux throughout the shoaling and outer surfzones is driven by triad interactions between IG waves and pairs of sea-swell (SS) waves. The IG energy flux decreased in the inner surfzone, primarily through an energy cascade to the swell-band and superharmonic frequencies where wave energy is ultimately dissipated. Dissipation by bottom friction was weak on both slopes. The IG wave breaking, characterized by triads between three IG or two IG waves and one SS wave, was significant only deep inside the surfzone of the mild slope. Even though IG waves broke on the mild slope, nonlinear interactions between IG waves and pairs of SS waves were responsible for at least half of the net IG flux loss.

Combined influence of human disturbance and beach geomorphology on Ghost Crab, Ocypode cursor, burrow density and size in the eastern Mediterranean

Ghost Crabs, Ocypode cursor (Linnaeus, 1758), are used as a bioindicator species to evaluate the ecological condition of sandy beaches. Studies using Ghost Crabs as bio-indicator have often focused on the influence of human disturbance and beach geomorphology, separately. However, the relative importance of these variables should be assessed to maintain community structure. Here, I used an indirect burrow examination technique to understand whether Ghost Crabs respond to human disturbance stronger than to geomorphological properties of the sites. I analysed sand compaction rate, sand grain size, beach width, and beach slope as geomorphological features and urbanization index as a measure of human disturbance on each site. I further examined Ghost Crab burrows by counting and measuring the openings. Ghost Crabs showed lower population density and individual body sizes as a response to human disturbance, and the level of this response was partly related to the geomorphological features of the sites. However, human disturbance explained approximately 72% of the variation in the Ghost Crab burrow density and about 70% of the variation in the burrow size, alone. The findings of this study corroborate the use of Ghost Crabs as an efficient bioindicator species of human disturbance on sandy shores to achieve efficient beach management, yet suggest that managers and scientists should combine the influences of geomorphological features of the beaches and the degree of human disturbances in their ecological assessments.

Characteristics of turtle laying habitat on vemara beach, Banyuwangi Regency, East Java

Turtles have a unique behavior, namely laying eggs on the same beach where they hatched. Turtles as protected animals continue to experience a decline in population caused by various factors including the degradation of nesting habitats. This study aims to determine the condition of the Cemara Beach habitat as a turtle nesting habitat. The research was conducted during September-November 2020 with a survey method by measuring the parameters of the Cemara Beach habitat which include sand temperature, air temperature, air humidity, beach width, beach slope, vegetation types and predators. The data collected was then analyzed descriptively qualitatively. The average air temperature is 28.07oC, the average sand temperature at a depth of 50 cm is 29.95oC, the average air humidity is 71.53%, the average beach width is 40 m and the average beach slope is 11.80 which shows the sloping beach category. The types of vegetation that grow along the coast are ketapang (Terminalia catappa), sea pine (Casuarina equisetifolia), horse tread (Ipomoea pes-caprae), cikumpai cikarao (Lepturus repens). As for the presence of predators identified during the observation, namely ghost crabs (Ocypode cursor).

An estimate of the value of the beachfront with respect to the hotel room rates in Thailand

An economic assessment for a non-market resource like sandy beaches is always a challenge for Thailand's coastal policy planners due to the lack of data availability, especially on the national scale. While beach tourism in Thailand has been an essential part of the Thai economy, the sandy beaches are probably exposed to the future sea-level rise. Therefore, the need for tourism benefits of the beaches should be conducted. The research attempted to measure the effect of sandy beach characteristics and hotel location on hotel room rates. A sample of 3319 hotel rooms across Thailand's coastal sub-districts, covering the entire sandy beaches in Thailand, was collected through a hotel-booking online database during the country's peak season. The considered variables include hotel room attributes, sandy beach characteristics, hotel locations, and coastal infrastructures. Through a hedonic price model based on geographically weighted regression analysis, the relationship between the dependent variables (hotel room rate) and the independent variables (selected beach variable) was estimated to evaluate the marginal effect and its spatial variations. The tourism benefit was calculated assuming the marginal effect of the hotel's beachfront locations on hotel price. The study suggested that the location in front of the beach raised the average hotel room rates by 13–41%. The results emphasized the significant spatial variability of the effect of beachfront location on the hotel price. In addition, the effect of beach protection structures (i.e., seawall, breakwaters, groins) on the hotel price was also investigated and implied a slight drop by 8–15% of the average price. The other sandy beach variables (such as beach length, width, and slope) effects on hotel price were also investigated. The finding of this study aims to help policymakers select and design proper adaptations to coastal erosion on tourist beaches in Thailand.

Numerical Simulation of Solitary Waves Propagating on Stepped Slopes Beaches

The objective of the current paper is to study the propagating and breaking of solitary waves on stepped slopes beaches, to simulate the shoaling and breaking, specifically the location of breaking point Xb, and solitary wave height at breaking Hb of solitary waves on the different stepped slopes. Ansys Fluent is used to implement the simulation, a two-dimensional volume of fluid (VOF) which is based on the Reynolds-Averaged Navier–Stokes (RANS) equations and the k–ε turbulence closure solver. The obtained results were firstly validated with existing empirical formulas for solitary wave run-up on the slope without stepped structure and are compared with the experimental and numerical results. The numerical computation has been carried out for several, configurations of beach slopes with tan ß= 1:15, 1:20, 1:25, wave height H0= 0.04, 0.06, 0.08m, water depth h0= 0.15, 0.2, 0.25m, and step height Sh= 0.025, 0.05, 0.075m. A set of numerical simulations were implemented to analyze shoaling and breaking of solitary waves, wave reflection, wave transmission, and wave run-up with various parameters wave heights, water depth, beach slopes, and Sh step height.

Karakteristik dan Preferensi Habitat Penyu dalam Membuat Sarang Alami untuk Peneluran

This study aims to examine the characteristics and environmental factors of turtles' preferences in making their natural nests. The method used is the descriptive quantitative method. The results showed that there were two types of turtles found during the observation, namely the green turtle (Chelonia mydas) and the hawksbill turtle (Eretmochelys imbricata). Measurements and observations of the characteristics of the 14 nesting points showed that the diameter and depth of the green turtle's nest were larger than those of the hawksbill turtle. Both types of turtles have a preference for nesting areas on sloping beaches with temperatures of 28-30ºC and humidity of 76-89%, as well as being around vegetation in the form of sea pine (Casuarina equisetifolia), sea oyster (Gynura sp), sea pandanus (Pandanus odorifer), sea kangkung (Ipomea peltate) and sea hibiscus (Thespesia populnea). In conclusion, temperature, humidity and types of vegetation around the nest determine the turtle's preference in making natural nests for laying eggs.
 Keywords: Nest Characteristics, Conservation, Turtle, Habitat Preference

Sloshing, Steklov and corners: Asymptotics of Steklov eigenvalues for curvilinear polygons

We obtain asymptotic formulae for the Steklov eigenvalues and eigenfunctions of curvilinear polygons in terms of their side lengths and angles. These formulae are quite precise: the errors tend to zero as the spectral parameter tends to infinity. The Steklov problem on planar domains with corners is closely linked to the classical sloshing and sloping beach problems in hydrodynamics; as we show it is also related to quantum graphs. Somewhat surprisingly, the arithmetic properties of the angles of a curvilinear polygon have a significant effect on the boundary behaviour of the Steklov eigenfunctions. Our proofs are based on an explicit construction of quasimodes. We use a variety of methods, including ideas from spectral geometry, layer potential analysis, and some new techniques tailored to our problem.

Performance Evaluation of Seawalls in Mitigating a Real-World Tsunami Wave Using a Nonhydrostatic Numerical Wave Model

In the past few decades, huge surges and waves generated during tsunami events have caused devastating destruction to both onshore and offshore infrastructures, seriously threatening the safety and intactness of coastal communities around the world. As one of the most important coastal protection infrastructures, a seawall can effectively reduce the impact intensity of surges and waves, thus playing a vital role in protecting coastal regions. Most previous studies have systematically investigated the hydrodynamic characteristics of seawalls under the action of regular and irregular waves. Meanwhile, solitary wave models are often used as the wave model for tsunamis. However, vast hydrodynamic differences exist between solitary wave models and real-world tsunamis in terms of both wave profile and wave period. Hence, our understanding of the performance of seawalls in mitigating the damaging power of real-world tsunamis is still insufficient. Hence, it is of great significance to systematically study the performance of seawalls in mitigating the huge surges and waves generated during real-world tsunamis. In comparison to previous research, where the wave profiles of solitary waves were used as tsunami wave models, a parameterized tsunami-like wave based on the recorded wave profile of the 2011 Japan tsunami is applied in this study to evaluate the performance of different seawalls in mitigating tsunami surges and waves by using a nonhydrostatic numerical wave model (NHWAVE). The effects of the prominent factors, such as incident wave height, still water depth, beach slope, and the side slope of the seawall, on the hydrodynamics of the seawall are systematically discussed. It is believed that the research findings drawn from this study can further broaden our understanding of the performance of seawalls in mitigating tsunamis.

Effects of the bed roughness and beach slope on the non-breaking solitary wave runup height

In this study, a series of laboratory experiments were carried out to investigate the effects of bed roughness and beach slope on the non-breaking solitary wave runup height. Experimental measurements reveal that the bottom friction plays different roles in the solitary wave runup process for different beach slopes. Under the same incident wave condition, the maximum runup height on a smooth steel bed was found to be larger than that on a rough sandpaper bed over a 10° beach slope, whereas the same runup heights were observed for the smooth and rough beds over a 45° beach slope. By introducing the runup similarity parameter, quantitative relationships between the maximum runup height and the bed roughness, as well as the beach slope, were analyzed. On the basis of Synolakis (1987), a new empirical model for estimating the non-breaking solitary wave induced runup height was proposed, after incorporating a slope-related enhancement coefficient and a friction-related reduction coefficient. It is found that both the enhancement coefficient (being always larger than unity) and the reduction coefficient (being always smaller than unity) are large under the small relative incident wave height and steep beach slope condition. Influence of the bed roughness is more significant under the small runup similarity parameter condition, under which the runup height monotonically decreases with the increase of the runup similarity parameter for the small bed roughness, whereas it first increases then decreases with the increase of the runup similarity parameter for the large bed roughness. Nevertheless, influence of the bed roughness could be neglected for the large runup similarity parameter condition. These results are consistent with experimental observations. Finally, the present model was validated using a large amount of existing solitary wave runup data with different bed frictions and beach slopes. The good agreement between the model predictions and measured data indicates the reliability and accuracy of the present model.

Prediction of landslide tsunami run-up on a plane beach through feature selected MLP-based model

We proposed new prediction models based on multilayer perceptron (MLP) which successfully predict the maximum run-up of landslide-generated tsunami waves and assess the role of parameters affecting it. The input is approximately 55,000 rows of data generated through an analytical solution employing slide’s cross section, initial submergence, vertical thickness, horizontal length, beach slope angle and the maximum run-up itself, along with its occurrence time. The parameters are first ranked through a feature selection algorithm and six models are constructed for a 9,000-row randomly sampled dataset. These MLP-based models led predictions with a minimum Mean Absolute Percentage Error of 1.1% and revealed that vertical slide thickness has the largest impact on the maximum tsunami run-up, whereas beach slope angle has minimal effect. Comparison with existing literature showed the reliability and applicability of the offered models. The methodology introduced here can be suggested as fast and flexible method for prediction of landslide-induced tsunami run-up.

Near‐Bed Sediment Transport During Offshore Bar Migration in Large‐Scale Experiments

AbstractThis study presents novel insights into hydrodynamics and sediment fluxes in large‐scale laboratory experiments with bichromatic wave groups on a relatively steep initial beach slope (1:15). An Acoustic Concentration and Velocity Profiler provided detailed information of velocity and sand concentration near the bed from shoaling up to the outer breaking zone including suspended sediment and sheet flow transport. The morphological evolution was characterized by offshore migration of the outer breaker bar. Decomposition of the total net transport revealed a balance of onshore‐directed, short wave‐related and offshore‐directed, current‐related net transport. The short wave‐related transport mainly occurred as bedload over small vertical extents. It was linked to characteristic intrawave sheet flow layer expansions during short wave crests. The current‐related transport rate featured lower maximum flux magnitudes but occurred over larger vertical extents. As a result, it was larger than the short wave‐related transport rate in all but one cross‐shore position, driving the bar’s offshore migration. Net flux magnitudes of the infragravity component were comparatively low but played a nonnegligible role for total net transport rate in certain cross‐shore positions. Net infragravity flux profiles sometimes featured opposing directions over the vertical. The fluxes were linked to a standing infragravity wave pattern and to the correlation of the short wave envelope, controlling suspension, with the infragravity wave velocity.

Two-Phase Smoothed Particle Hydrodynamics Modelling of Hydrodynamic-Aerodynamic and Wave-Structure Interaction

A two-phase (air and water) smoothed particle hydrodynamics (SPH) method is employed to study the hydrodynamic-aerodynamic and wave interaction with fixed and floating structures in a wave basin. The method is first verified for a classical two-phase dam-breaking. A mirror-open boundary is implemented at the top and left sides of a two-phase wave basin with a piston to generate a second-order regular wave. It is observed that, compared to the single-phase simulation, the two-phase one obtains a smoother water surface and prevents the non-physical water splash when interacting with the sloped dissipative beach. This wave basin is also used to investigate wave-structure problems such as wave interaction with a rigid cantilever beam fixed to the basin bottom and downstream of the wave-maker mechanism and the dynamics of a single floating box and two floating boxes in the waves. A typical wave-structure interaction period is captured and described using pressure contours and velocity vectors at three selected instants for the wave-rigid cantilever beam case. With the increase of the structure’s height, the wave height after the structure decreases, but no evident variation is found when changing its thickness. Besides the hydrodynamics interaction, a periodical collision is observed between the two floating boxes on the wave surface.