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The phenomenon of rhythmic patterns of the coastal-zone morphology (beach cusps, longshore sand waves, spits, and nearshore bars) is considered the result of self-organization of the relief when a positive feedback is established between sediment transport and morphology. It is shown that the dynamics of the contour and profile of the coast can be described in terms of the diffusion equation, which allows for both attenuation and growth of relief perturbations. The conditions are determined under which the self-organization mechanism is activated and the resulting perturbations grow over time. Rhythmic structures of the coastal contour are traditionally associated with waves propagating at a large angle relative to the coastal normal. However, it has been shown that the self-organization of beach cusps and megacusps also occurs in normal coast waves due to the development of circulation cells in the surf zone. The conclusion is substantiated that the formation of nearshore bars under certain conditions is also determined by the self-organization mechanism. The results obtained help to interpret the available observational data regarding the evolution of multiple bar systems. [ABSTRACT FROM AUTHOR]

The study is aimed at investigating the problem of in what conditions could the morphodynamic self-organizational mechanism controlling the growth of small perturbations that have arisen on bed be responsible for the development of nearshore bars. A simplified sediment transport model is used in which the sediment discharge is directly proportional to the local bed slope. This model reduces the problem to analytical solution of the diffusion equation, which gives the base to predict the evolution of a perturbation that has arisen on bed. The conclusion is argued that favorable preconditions for nearshore bar formation can exist in the case of onshore sediment transport associated with the dominant contribution of wave asymmetry in the transport process. However, under conditions of steep storm waves, undertow develops, resulting in offshore sediment flux from the beach. In this case, a breaker bar is formed by two mechanisms: self-organization and convergence of opposite sediment fluxes. The results agree with available data and also help to explain some properties of multiple bar systems revealed from observations. [ABSTRACT FROM AUTHOR]

Some solutions are proposed to problems of designing an artificial sandy beach that protects the sea shore and ensures its recreational capacity. The subaqueous part of the artificial profile is approximated by Dean's [13] equilibrium profile, while the subaerial beach segment is determined taking into account storm surge and runup heights. The parameters for constructing the berm are determined under the condition that initially the all of the structural material is concentrated on the subaerial beach. The subaqueous profile is formed by the waves themselves, what is confirmed by numerical simulation. When the computed beach width differs from the designed value, it can be corrected by shifting the entire artificial profile by an appropriate distance. However, in the case of a too large difference, the only option is to use a different particle size. Beach material losses depend on the longshore diffusion coefficient, which has been determined by the author as the function of the annual total of longshore sediment fluxes. Sediment losses are plotted as a function of wave activity, sediment fluxes, and beach length. Background losses due to sea-level rise are also taken into consideration. The proposed calculating algorithm is applied to design the artificial beach in the Western Crimean coastal segment. It is shown that the designed beach profile would not change significantly under severe storm impact. [ABSTRACT FROM AUTHOR]

The depth of closure limits the area of significant morphological changes in a beach profile on an annual time scale, and the prediction of is important for coastal engineering practice. The previously proposed analytical formulation is inconsistent with observed data; possible reasons for this are discussed. In an attempt to determine the mass conservation principle is applied connecting bed deformations with sediment transport gradients. Two essential mechanisms of cross-shore sediment transport in the nearshore zone are taken into account: asymmetry of wave orbital velocities and undertow. The derived formula establishes the proportionality between the depth of closure and wave height , which is exceeded only 12 h per year. The factor of proportionality depends on both the wave steepness and the threshold of bed deformations associated with the measurement accuracy of profile surveys. For typical values of varying from 0.1 to 0.3 m, the depth varies from to . Comparison with field observation data shows that predicted value of is a representative estimate of the depth of closure on a microtidal wave-dominated sandy coast. [ABSTRACT FROM AUTHOR]

Abrasion of coasts is considered, the destruction of which is accompanied by extraction of sediments capable of forming a beach (sand, gravel, pebble). The behavior of such a type of coast is controlled by the feedback between the abrasion rate and volume of growing beach. The suggested evolutionary model leads to conclusion that abrasion should decay exponentially with time. The duration of the process may be measured in decades, centuries, or millennia depending on the fraction of beach-forming material incoming from the cliff. A rise in relative sea level contributes to an increased duration of abrasion. To predict the yearly volume of cliff abrasion, the approach by Larson et al. [15] is applied, taking into account the difference between the elevation of the beach and height of wave runup. The computational formula includes an empirical coefficient, which is estimated from data on the coasts of the Kama water-storage basin and Sea of Okhotsk (where the tide plays a significant role in cliff abrasion). It is shown that a comparatively small-scale beach fosters a substantial decrease in the abrasion volume. Abrasion of a submerged coastal slope is determined by both the cliff abrasion rate and "closure depth" concept. [ABSTRACT FROM AUTHOR]

A criterion or index for assessing the hazard of storm-induced coastal erosion is suggested. It is based on comparison of actual beach volume and its optimal value sufficient to avoid irreversible beach changes due to severest storm attack over the year. The erosion hazard level is determined taking into account the difference of and ; it reaches the maximum (3 points) when the actual beach volume becomes less than a half the optimal value (0 points corresponds to > ). To calculate the erosion index, a representative beach profile is required, as well as the data on the mean sand size and wind/wave regime. The erosion index is tested on the coasts of the Anapa bay-bar (Black Sea) and southern part of the Vistula Spit (Baltic Sea). The index makes it possible distinguish vulnerable sections of the coast, and at the same time it reflects the sediment deficit volume that could be used in shore protection designs. [ABSTRACT FROM AUTHOR]

A model is developed to simulate the morphodynamics of a barred shore profile on the scale of a storm cycle, comprising the phases of high and low wave activity. In the CROSS-PB model, the main mechanisms governing sediment transport in wave shoaling and surf zones are taken into consideration, in particular, skewness and asymmetry of the wave orbital velocities, undertow, and infragravity oscillations associated with wave groups. By comparing calculations with observed data, it is concluded that the model correctly reproduces seaward displacement of bars during a storm and shoreward under moderate or weak wave conditions. The first process is shown to be provided by balance of transport mechanisms when the peak offshore transport is located at the front slope of bar. The second process is conditioned by dominant shoreward transport and its sharp decay over the bar crest. Testing of the model yields estimates for the calibration coefficients, and it is concluded that shoreward sediment flux is mainly controlled by wave asymmetry. [ABSTRACT FROM AUTHOR]

Abstract—A model has been developed that explains sediment accumulation within a groin field from the aspect of mass conservation. The model revealed that intergroin sedimentation is related to the gradient of the adjacent longshore sediment transport. An important model parameter is the length Λ of the structure's zone of influence. It is shown that the accumulation rate reaches its maximum when the intergroin distance is close to Λ, while material accretion terminates when the distance is close to 2Λ. The optimal relationships between the intergroin distance, groin length, and width of the sediment flux have been obtained. This allows operational forecasting of the accumulation volume and distance the beach advances within time periods from hours to decades. The model can calculating the optimal groin field parameters to achieve the required performance and avoid unnecessary impacts. The calculations reasonably agreement with published observations. [ABSTRACT FROM AUTHOR]

Abstract—The trend of the recent development of the Anapa bay-bar is considered based on modeling of sediment transport and morphodynamic processes. It is shown that longshore sediment transport does not have a crucial influence on the coastal dynamics. Most coastlines undergo degradation despite accumulation due to unloading of the longshore sediment flux. The probable reason is the relative sea level rise due mainly to tectonic processes. The proposed model of the coastal barrier following the sea level movement explains to a certain extent the observed trends. [ABSTRACT FROM AUTHOR]

The paper considers the results of long-term observations of megacusp (large-scale shoreline cusps) on the coast of the Gulf of Terpenya (Gulf of Patience), Sakhalin Island. The typical spatial step of the rhythmic forms is about 800 m, and the amplitude of shoreline undulations is 40–50 m. Despite significant changes on time scales of seasons, years, and decades, the main morphological features of the megacusps are preserved for more than 60 years. A model is proposed that explains the evolution of rhythmic shoreline patterns by self-organization of the bottom relief under wave impact. Development of megacusps is shown to be related to the generation of nearshore circulation cells; due to flows within the cells, a small initial perturbation to the shoreline contour can increase over time. A positive feedback between the coastal morphology and hydrodynamics arises when a certain relation is established between the length of the perturbation, the width of the surf zone, and the speeds of nearshore currents. It is concluded that the megacusp system in the Gulf of Terpenya is mainly supported by moderate waves with a significant wave height of ~1.6 m. [ABSTRACT FROM AUTHOR]

A model of an artificial beach is proposed for protecting a seacoast subjected to erosion under significant storm surge impact. The beach profile properties are based on the Dean equilibrium profile. It is shown that coarser sand yields a greater total beach width, but requires a greater volume of berm material. At the same time, this results in decreased loss of material to longshore sediment transport. The results of applying the model to three sectors of eroded coast in the Kurortny District of St. Petersburg (eastern Gulf of Finland) recommend the use of medium-grained 0.3–0.5 mm sand to construct the artificial beach. In this case, the width of the dry beach section would be about 80–140 m, while the volume of berm material would be (1.3–3.2) × 102 m3 per one meter of coast length depending on the sediment deficit for a given coastal sector. To minimize the relative loss of material, it is suggested to construct a beach no less than 1 km in length; in this case, more than half the initial beach volume would be retained even after 30 years. Modeling of extreme storm impact leads to the conclusion that the designed beach profiles are only slightly deformed and can retain their resources for many years. [ABSTRACT FROM AUTHOR]

It is shown that behavior of a multiple-bar system during a storm can be described with a model assuming that bars move toward the sea at almost the same mean rate, while the depths over the bars increase in accordance with the local bed slope. Analysis of the suspended-sediment balance over the bar crest yields an expression for the bar movement rate, which demonstrates a very strong dependence on the ratio of wave height to depth above the bar crest. When the empirical criterion of bar activity [11] is used, the proposed model can assess bar displacement during storm impact and predict the poststorm bed profile. Comparison with published field data leads to the conclusion that the computed and observed storm-induced deformations of barred beach slopes are satisfactorily consistent. [ABSTRACT FROM AUTHOR]