Equilibrium Beach Profile Research Articles

Beach Profile Model with Size-Selective Sediment Transport. II: Numerical Modeling

AbstractBeach profile evolution is a dynamic phenomenon that often leads to threatening consequences such as severe beach erosion and shoreline retreat. A new comprehensive morphodynamic model is introduced in this study that includes representation of bedload and suspended size-selective sediment transport and cross-shore sediment grain-sorting models. The model is capable of simulating the changes in cross-shore bathymetry and sediment grain size composition observed under laboratory conditions for both erosive- and accretive-type equilibrium beach profiles. The new model is most advantageous for scenarios with poorly sorted sediments or sites with strong cross-shore variability in sediment grain sizes. Information on sediment size composition in the domain and its history is also provided by the new model, which can be useful for engineering, recreational, or biological considerations.

Post-monsoon equilibrium beach profiles and longshore sediment transport rates at Candolim, Miramar and Keri beaches of Goa, India

Equilibrium profile is one of the conce pts in coastal geomorphology which is a result of the balance of destructive versus constructive forces. Two e quilibrium be ach profile models, viz. Bruun/Dean’s twothirds power mode l and modified Bodge expone ntial model were used to analyse the measured post-monsoon (winter) beach profiles from three beaches in Goa having varying coastal morphology settings. The major factors that affect the equilibrium beach profile, viz. the me dian grain size (D50) and the profile shape factor m, which are inve rsely proportional to each othe r, have been analysed for their application to the study site. Also, the variation of these two parameters with beach slope and grain size is studie d. Longshore sedime nt transport rates (LSTRs) are estimate d at these three beaches from the littoral environme ntal observations. LSTRs show that during winte r months, the net transport is of the orde r of 10.83  10 6 m 3 /year (southe rly transport) and 9.02  10 6 m 3 /year (southerly transport) respectively, at Candolim and Ke ri beaches, whe reas it is about 0.62  10 6 m 3 /year (northerly transport) at Miramar. This article discusses the methods used and results of measure me nts of beach morphology, LSTRs, analysis of equilibrium profiles and influe nce of various paramete rs relate d to equilibrium profiles.

長期地形観測データに対する非線形混合モデルの適用による平衡断面の不確実性評価

長期地形観測データに対する非線形混合モデルの適用による平衡断面の不確実性評価

Equilibrium shoreline modelling of a high-energy meso-macrotidal multiple-barred beach

Abstract 8-year time series of incident wave energy and monthly alongshore-averaged beach surveys at the high-energy meso-macrotidal multiple-barred Truc Vert beach are analysed. We apply two behaviour-oriented equilibrium shoreline models that relate the rate of cross-shore shoreline displacement to the wave energy and the wave energy disequilibrium between the wave energy and the equilibrium wave energy that would cause no change to the present shoreline location. The two models show similar skill. Results show that the equilibrium shoreline model concept works on meso-macrotidal multiple-barred beaches, with similar skill when applied to non-barred and/or micro-mesotidal beaches, provided that a relevant shoreline proxy is used. Simulations show that Truc Vert beach responds predominantly at seasonal timescales rather than at individual storm frequency. The first winter storms drive the most pronounced erosion events because both the wave energy disequilibrium and erosion change potential are large. The best shoreline proxy at Truc Vert beach is the mean high water level, where the inner-bar and berm dynamics have little influence on the shoreline cross-shore displacement. Implications for shoreline monitoring through video imagery on this type of beach are discussed. Results also reveal that the equilibrium shoreline concept can be extended to an equilibrium beach profile concept pending further improvements.

The modified Bruun Rule extended for landward transport

article i nfo The Bruun Rule (Bruun, 1954, 1962) provides a relationship between sea level rise and shoreline retreat, and has been widely applied by the engineering and scientific communities to interpret shoreline changes and to plan for possible future increases in sea level rise rates. The Bruun Rule assumes that all sand removed from the upper profile is deposited offshore as sea level rises, although overwash during storms and landward Aeolian transport clearly indicate otherwise. Herein, we examine processes associated with sandy beach evolution in response to relative sea level rise and propose a modified form of the Bruun Rule that considers the full range of parsing cross-shore transport, from completely seaward to completely landward depending on the prevailing storm and surge conditions and whether there is a surplus or deficit of sand in the profile with respect to the equilibrium beach profile. A methodology is proposed that more appropriately represents the long-term processes and beach response. However, an improved quantitative understanding of landward transport is required for optimal application of the proposed method. Published by Elsevier B.V.

DEVELOPMENT OF DYNAMIC SEDIMENT BUDGET TO PREDICT FUTURE SHORELINE POSITIONS ON A SAND LIMITED SHORELINE IN LOUISIANA

A shoreline change analysis was performed along the shoreline of the chenier plain in southwestern Louisiana in an attempt to forecast future shoreline position and to determine the performance of a proposed sand beach nourishment project along the shoreline which extends 14 km west of the western jetty of Calcasieu Pass, Louisiana and runs through the community of Holly Beach, Louisiana. Observations of shoreline morphology revealed a solitary sediment wave traversing the project site from east to west since the 1960’s. The genesis of the sediment wave is unknown and is unexplored in this work. The presence of the sediment wave masked the long-term shoreline change rates along the project site and therefore biased the predictions of future shoreline positions due to the transient nature of the sediment wave morphology. Standard coastal engineering methods used to predict future shoreline positions include simple translation of the shoreline based on measured shoreline change rates (referred to herein as historical linear progression or HLP) and one-line numerical models. For the project site, due to the presence of this sediment wave the HLP approach to predict future shoreline positions is not applicable. One-line shoreline morphology models such as the US Army Corps of Engineer's GENESIS model require the assumption that the beach profile can be represented by an equilibrium beach profile which was developed for sand rich shorelines. The project site profile composition of a sandy veneer extending to a depth of approximately -1.2 to -2 m over a muddy bottom violates this assumption, and therefore the traditional one-line model cannot be applied. Therefore, a dynamic sediment budget (DSB) method was developed to predict future shoreline positions based on available historical data, longshore transport rates, known morphological processes, statistical estimates of storm events, beach nourishment diffusion, and a relationship between volume change and shoreline change based on existing profile composition. This method was validated with existing data and was able to predict 20 years of morphology within ±15 m of measured shoreline positions.

INFLUENCES OF CLIMATE CHANGE ON BEACH PROFILE

The influences of climate change due to global warming have been estimated on not only sea level rise but also wave characteristics such as height or energy flux. In this study, the characteristics of medium and long term beach profile change is investigated based on the observed beach profile data at HORS for past 24 years and the relationship between the wave characteristics observed at Kashima port and the climate indexes. In order to estimate the influences of the medium and long term wave characteristic change, a theory is introduced based on equilibrium beach profile with wave parameter, which is theoretically based on sediment characteristic. Moreover, the validation of the theory is evaluated based on the observed beach profile data and wave data.

Beach profiles characteristics along Giao Thuy and Hai Hau coasts, Vietnam: A field study

Giao Thuy and Hai Hau coasts are located in Nam Dinh province, Vietnam, with a total coastline of 54.42 km in length. The sea-dike system has been seriously damaged and there have been many dike breaches which caused floods and losses. This situation is considered of a general representative for coastal area in the northern part of Vietnam. A variety of studies have shown that the gradient in the longshore sediment transport rate and the offshore fine sediment lost are the main mechanisms causing the beach erosion. This study presents a field investigation of the beach profiles at Giao Thuy and Hai Hau beaches. Three types of empirical functions for the equilibrium beach profile are applied and compared with the observations. Results show that all observed beach profiles can be described by a single function. However, one specific equilibrium profile equation is not sufficient to assess all beach profiles. In Section 1 of Giao Thuy and Section 3 of Hai Thinh beaches, beach profiles are consistent with the logarithmic function, while the exponential function fits well in Section 2. This difference is explained with respect to coastal morphology, sediment characteristics and hydrodynamic conditions which vary in site. An analysis of the validity of the beach profile functions is recommended for the numerical modeling and engineering designs in this area.

Modelling the effect of bottom sediment transport on beach profiles and wave set-up

In this paper we augment the wave-averaged mean field equations commonly used to describe wave set-up and wave-induced mean currents in the near-shore zone, with an empirical sediment flux law depending only on the wave-induced mean current and mean total depth. This model allows the bottom to evolve slowly in time, and is used to examine how sediment transport affects the beach profile and wave set-up in the surf zone. We show that the mean bottom depth in the surf zone evolves according to a simple wave equation, whose solution predicts that the mean bottom depth decreases and the beach is replenished. Further, we show that if the sediment flux law also allows for a diffusive dependence on the beach slope then the simple wave equation is replaced by a nonlinear diffusion equation which allows a steady-state solution, the equilibrium beach profile.

平衡海浜断面に対する中長期的な波浪変化の影響について

平衡海浜断面に対する中長期的な波浪変化の影響について

Topographic Change near the Shoreline during High Waves

Relationships between the topographic changes near the shoreline and the waves both offshore and just outside the swash zone are studied for some twenty storm events observed during years of 2003 to 2004 at Hasaki. All the storms which lasted long enough produced a kind of equilibrium beach profile of mildly sloping uniform one near the shoreline, irrespective of the initial profiles. It is shown that the slope may be predicted by the parameter by Sunamura(1984), employing either the offshore data of significant waves or the long wave properties near the shoreline.

A flume test on erosion mechanism for an abandoned section of the Huanghe (Yellow) River Delta

The erosion mechanisms of abandoned coastal section are understood detailedly by flume experiment, which play an important role to the offshore engineering facilities. A movable-bed physical model has been used to investigate the coastal erosion of an abandoned section of the Huanghe (Yellow) River Delta. The theory of physical scale models is discussed and a method for constructing the representative seabed section is developed. The results indicate that during the period initially after the abandonment of the delta the entire bed experienced rapid erosion because the seabed was steep and prone to liquefaction that resulted from storm wave action. After this initial period, a balance of erosion and accretion was established, and the beach profile equilibrated with a point of balance present on the profile. The experimental results indicate that the volume of deposition was about half that of the erosion. Wave action may also induce significant stratal changes through its interaction with the soft seabed. The major morphological features developed in the model delta section were found to be qualitatively comparable with those observed in the prototype. A distorted modeling law that maintains the similarity of the modeled and prototype equilibrium beach profiles is proposed. Experimental results show that the distorted modeling is able to reproduce the beach-face slope in nature, and the model also successfully reproduced three historical evolutionary stages of erosion.

Physical modeling of intermediate cross‐shore beach morphology: Transients and equilibrium states

Laboratory experiments on cross‐shore beach morphodynamics are presented. A lightweight sediment (density ρs = 1.19 g cm−3) model is used in order to fulfill a Shields number and Rouse number scaling. This choice aims at correctly reproducing bed load transport as well as suspension dynamics. Terraces and barred beach profiles obtained in the experiments also present close similarities with profiles observed in the field. In order to question the concept of equilibrium beach profile, wave forcings conforming to a JONSWAP spectrum were imposed over long periods (up to more than a hundred hours). An average bottom evolution velocity is defined and used to determine when the profile reaches equilibrium. Usually, beach profiles are characterized according to the Wright and Short (1984) classification based on the Dean number Ω. This well‐known classification is investigated and refined in the intermediate range, that is, for 1 ≤ Ω < 5. For Ω close to 1, a typical reflective profile is obtained. Terraces are obtained for the Ω = 2.5 cases. For Ω ≈ 3.7, the profiles exhibit two parts: a mild dissipative offshore slope producing low reflection and a steeper beach face with slightly higher reflection. The wave dissipation, velocity skewness, and acceleration skewness are computed from the free surface elevation time series. The dissipation and wave nonlinearities patterns are similar for similar equilibrium beach profiles, that is, with the same Dean number. Dissipation peaks coincide with bottom slope transitions as higher energy dissipation occurs with milder bottom slope sections. Besides, the uniformity of volumetric wave energy dissipation seems to concern only a limited zone of beaches with a widely developed surf zone.

Validity of the equilibrium beach profiles: Nile Delta Coastal Zone, Egypt

Beach profile equilibrium is the principal concept assumed by most numerical modelling. The response of beach profile configuration to natural and anthropogenic changes could be predicted to help in selecting the most appropriate engineering design required to mitigate coastal erosion and accretion alongshore. Thus, in order to apply coastal engineering projects, the predicted profile of equilibrium should be close enough to the measured profile. Therefore, before application of numerical modelling techniques, equilibrium expressions have to be validated at the study site. This research aims to assess the validity of the equilibrium profile concept on the Nile Delta coast based on beach profiles surveyed in 1990 from the main promontories; Abu-Quir Bay, the Rosetta promontory and the El-Burullus promontory. The results indicate that the equilibrium beach profile is consistent with the measured profiles at the study sites beyond 200 m distance offshore at − 4 m depth. In contrast, the equilibrium status is not valid along the beach face at − 1 m depth. Accreted beaches at Abu-Quir bay and Burullus promontory are characterized by wide berms and gentle beach face whereas eroded stretches at Rosetta promontory have a narrow berm and steep beach faces. The measured profiles are also compared with the exponential beach profile concept. An exponential hypothesis is not valid along the Nile Delta coast. Profiles measured at Abu-Quir, Rosetta and El-Burullus depart significantly from the exponential equation. Despite the fact that equilibrium expression can describe beach profiles along the Nile Delta, one equilibrium profile equation is not sufficient to assess all beach profiles. This can be explained as the morphology of beach profiles is subjected to some factors including; sediment characteristics, wave parameters and closure depth, which vary alongshore. Analysis of the validity of the equilibrium beach profile is recommended to get accurate results in modelling simulations and design the most appropriate engineering projects required for shore protection.

Modelling of wave climate and sediment transport patterns at a tideless embayed beach, Pirita Beach, Estonia

Nearshore sand transport patterns along the tideless, embayed Pirita beach, Tallinn, Estonia, have been investigated utilizing high-resolution modelling of wave processes combined with bathymetric surveys and sediment textural analyses of the nearshore sea floor. Textural analysis showed the mean grain size is about 0.12 mm. Fine sand (0.063–0.125 mm) accounts for about 77% of the sediments. Coarser-grained sand (0.28 mm) dominates along the waterline. Based upon the spatial distribution of the mean grain size and basic features of the local wave activity, properties of the Dean Equilibrium Beach Profile were determined. Alongshore sediment transport was calculated based upon a long-term time series of wave properties along the beach, and the CERC formula applied to about 500 m long beach sectors. The time series of wave fields and the properties of the local wave climate were modelled using a triple nested WAM wave model with an extended spectral range for short waves. The model is forced by open sea wind data from Kalbådagrund for the years 1981–2002. Results indicate that typical closure depth at Pirita is 2.5 m. The width and mean slope of the equilibrium profile are 250 m and 1:100, respectively. Southward transport dominates in the northern sections of the beach whereas no prevailing transport direction exists in the southern sections. This pattern has several nontrivial implications for the planning of beach protection activities.

Long-Term Equilibrium Beach Profile Based on Maximum Information Entropy Concept

This paper presents an application of the maximum information entropy concept to formulate an equilibrium beach profile (EBP) associated with the long-term beach evolution. The model assumes the beach profile is monotonic from a maximum depth at an offshore location to the runup limit or the berm level at the shoreline. The derived equilibrium beach profile has a logarithmic shape in terms of the cross-shore distance and can be either concave or convex depending on the profile shape parameters. If only the underwater portion of the profile is considered, the new EBP in nondimensional form matches the well known 2/3 power profile with the shape parameter S being between 1 and 1.5. The dimensional form of the profile is controlled by parameter S together with three other parameters which are the beach levels at the two boundaries of the profile and horizontal extent of the profile. These parameters are either directly measurable from the given initial profile and the calculated equilibrium profile or could ...

Hydrodynamic Modeling of St. Joseph Bay for Stability Analysis of Coastal Barrier Breaching

A hydrodynamic model of St. Joseph Bay, FL has been developed based on a finite-element circulation model. We have tested the model against predicted astronomical tides and field measurements of water levels at three locations inside and outside the bay. Good agreement has been found, including the correct prediction of the change of the tidal regime from diurnal to mixed tides and the high-frequency oscillations in St. Joseph Bay excited by meteorological forcing. The validated hydrodynamic model was employed to partition the tidal prism of St. Joseph Bay in the event of a breach at Stump Hole north of Cape San Blas and to estimate the flushing through a new inlet at Stump Hole, or the portion of tidal prism controlled by a breach. The existing methodology for inlet stability analysis of a single-inlet system is extended to this two-inlet system if stump Hole is breached by a tropical cyclone. A ten-step procedure has been developed for the breach stability analysis, which has three major components. First, the empirical relationships of inlet geometric parameters were employed to develop a series of possible breach configurations. Second, the validated hydrodynamic model was modified to accommodate the new inlet and numerical simulations were carried out to determine the hydraulic conditions corresponding to each inlet configuration. Third, the computer model results of this two-inlet system were combined with the empirical relationship of tidal prism and inlet cross-sectional area for equilibrium inlets to predict the stable inlet configuration and the fate of a breach using the maximum velocity curve in an Escoffier-type diagram. Similar to the use of an equilibrium beach profile in the design of beach nourishment projects, the concept of an equilibrium inlet and the empirical relationship for stable inlets provide a useful tool to predict the fate of a breach in a multi-inlet, multi-tidal-regime system.

Temporal and Spatial Change in Equilibrium Beach Profiles from the Florida Panhandle

Guidance regarding equilibrium beach profiles has been well established, although limited knowledge exists regarding the spatial and temporal variability of the equilibrium beach profile parameter for engineering usage, and limited data have been published regarding such changes. Additionally, the controlling parameter in the equilibrium beach profile theory depends on assumed depth of profile closure. Equilibrium beach profile theory is utilized herein to assess the spatial and temporal variability of beach profiles along the Florida Panhandle Coast to provide added empirical guidance on this subject.

Equilibrium Beach Profile Concept for Delaware Beaches

We utilize beach profile data from 37 profile locations on the Atlantic coast of Delaware that were surveyed an average of 12 times between 1964 and 1993 to assess the validity of several equilibrium beach profile (EBP) formulations. Under consideration are (1) a power law formulation; (2) a formulation including the effects of downslope transport; and (3) a modified form of the latter model suggested herein. We perform a least-square fit of these models to the individual observed profiles, the mean profiles at the 37 locations, as well as regionally averaged profiles over eight geographically distinct regions. The analysis results in best-fit values for the model coefficients. The results indicate that the first model is robust and predicts observed mean and regionally averaged profiles with an estimated normalized error of 26 and 15%, respectively. However, the predicted beach slopes near the shoreline are infinite and, hence, unphysical. The second model includes the effects of downslope transport and ...

A Study on the Dependence of the Migration Rate of Bottom Sediment on Different Equilibrium Beach Profiles

The relation between the migration rate of sand and water particle velocities in the two phase flow of a solid-liquid involving suspended sediments in the surf zone has not been satisfactorily understood yet. This study presents the effects of the different equilibrium beach profiles on the temporal and spatial distribution of migration rate of suspended sediments in the two phase flow of a solid-liquid, where sediments at the flow bottom are suspended under breaking waves. As a result, we have found that the migration rate of sediments averaged over a wave period between Type I and Type II of the beach profiles change. Type I has showed larger flow velocities than Type II in the entire region, particularly under wave crests. The migration direction of sand particles in Type I is the same as that in Type II. Specially, the migration direction is shoreward near the wave crests and seaward near the wave troughs in both types.