A morphological stability analysis for a long straight barred coast

A morphological stability analysis is carried out for a long straight coast with a longshore bar. The situation with oblique wave incidence and a wave-driven longshore current is considered. The flow and sediment transport are described by a numerical modelling system. The models comprise: (i) a wave model with depth refraction, shoaling and wave breaking, (ii) a depth integrated model for wave driven currents and (iii) a sediment transport model for the bed load transport and the suspended load transport in combined waves and current. The direction of the sediment transport is taken to be parallel to the depth integrated mean current velocity, neglecting the effects of a bed slope and secondary currents. An instability is found to develop around the bar crest. The instability is periodic in the alongshore direction, and tends to form rip channels and to steepen the offshore face of the bar between the rip channels. The alongshore wave length of the most unstable perturbation is determined for different combinations of the wave conditions and the geometry of the profile.     

堆积海岸平衡岸线轮廓的解析

对堆积海岸平衡岸线轮廓的三个表达式进行了分析和对比,其中平衡岸线轮廓表达式在一定程度上包含了潮流作用对岸线塑造的影响,适用于对凹岸和沙质海岸岸线轮廓的分析,同时也适用于对凸岸和淤泥质海岸岸线轮廓的分析,因而较基本平衡岸线形态方程和B.A.保保夫堆积岸弧方程适用范围更广。利用平衡岸线轮廓表达式,对舟山群岛金塘山和册子山附近水道的两段岸线轮廓进行了分析,结果表明:两岸段均为堆积岸弧,且理论弧长与实测弧长、理论半径与实测半径的值接近,说明理论岸线与实际岸线形态吻合得较好,同时,金塘山西部岸段较册子山西部岸段岸线形态更趋稳定,但两岸线均未达到稳定状态,目前仍处于演变过程中。     

Waves, currents, sediment flux and morphological response in a barred nearshore system

A shore-normal array of seven, bi-directional electromagnetic flowmeters and nine surface piercing, continuous resistance wave staffs were deployed across a multiple barred nearshore at Wendake Beach, Georgian Bay, Canada, and monitored for a complete storm cycle. Time-integrated estimates of total (ITVF) and net (INVF) sediment volume flux together with bed elevation changes were determined using depth-of-activity rods.

The three bars, ranging in height from 0.10 to 0.40 m accreted during the storm (0.03 m), and the troughs were scoured (0.05 m). Sediment reactivation depths reached 0.14 m and 12% of the nearshore control volume was mobilized. However, the INVF value for the storm was less than 1% of the control volume revealing a near balance in sediment volume in the bar system. Landward migration of the inner, crescentic and second, sinuous bars occurred in association with an alongshore migration of the bar form itself; the outermost, straight, shore-parallel bar remained fixed in location.

The surf zone was highly dissipative throughout the storm (ε = 3.8 × 10²–192 × 10²) and the wave spectrum was dominated by energy at the incident frequency. Spectral peaks at frequencies of the first harmonic and at one quarter that of the incident wave were associated with secondary wave generation just prior to breaking and a standing edge wave, respectively. The former spectral peak was within the 95% confidence band for the spectrum while the latter contributed not more than 10% to the total energy in the surface elevation spectrum even near the shoreline.

During the storm wave height exceeded 2 m (H_s) and periods reached 5 s (T_{p k}): orbital velocities exceeded 0.5 m s⁻¹ (u_{rm s}) and were above the threshold of motion for the medium-to-fine sands throughout the storm. Shore-parallel flows in excess of 0.4 m s⁻¹ were recorded with maxima in the troughs and minima just landward of the bar crest.

The rate and direction of sediment flux is best explained by the interaction of antecedent bed slopes with spatial gradients in the mean and asymmetry of the shore-normal velocity field. These hydrodynamic parameters represent “steady” flows superimposed on the dominantly oscillatory motion and assumed a characteristic spatial pattern from the storm peak through the decay period. Increases spatially in the magnitudes of both the mean flows and flow asymmetries cause an increasing net transport potential (erosion); decreases in these values spatially cause a decreasing net transport potential and thus deposition. These transport potentials are increased or decreased through the gravity potential induced by the local bed slope. Shore-parallel flow was important in explaining sediment flux and morphological change where orbital velocities, mean flows and flow asymmetries were at a minimum.     

Modeling regional sediment transport and shoreline response in the vicinity of tidal inlets on the Long Island coast,United States

A new numerical model was developed to simulate regional sediment transport and shoreline response in the vicinity of tidal inlets based on the one-line theory combined with the reservoir analogy approach for volumetric evolution of inlet shoals. Sand bypassing onshore and sheltering effects on wave action from the inlet bar and shoals were taken into account. The model was applied to unique field data from the south coast of Long Island, United States, including inlet opening and closure. The simulation area extended from Montauk Point to Fire Island Inlet, including Shinnecock and Moriches Inlets. A 20-year long time series of hindcast wave data at three stations along the coast were used as input data to the model. The capacity of the inlet shoals and bars to store sand was estimated based on measured cross-sectional areas of the inlets as well as on comprehensive bathymetric surveys of the areas around the inlet. Several types of sediment sources and sinks were represented, including beach fills, groin systems, jetty blocking, inlet bypassing, and flood shoal and ebb shoal feeding. The model simulations were validated against annual net longshore transport rates reported in the literature, measured shorelines, and recorded sediment volumes in the flood and ebb shoal complexes. Overall, the model simulations were in good agreement with the measured data.     

Effects of shoreline and bedrock irregularities on the morphodynamics of the Alexandria coast littoral cell,Egypt

Beach-nearshore profiles combined with beach and surficial sediment samples were analyzed in conjunction with wave, current, littoral drift and sea-level data to determine the effect of bedrock on morphodynamic processes within the littoral zone of Alexandria on the Mediterranean coast of Egypt. This 14.5-km-long littoral cell is bounded by pronounced embayments and pocket beaches separated by headlands which prevent bypassing of beach sands, in effect making this cell a large, semi-closed basin. The compartmented nature of this cell acts together with the rough irregularity of the rocky seafloor to trap a thin veneer of sediment (<3 m thick), showing proportional mixing between two sedimentary provinces. A modern fine-grained sediment facies consisting of mixed carbonate/siliciclastic sand flanks most of the nearshore zone down to a depth of 8–10 m. Beyond this depth, considered to be the depth of closure, a relict late Pleistocene to mid-Holocene coarse-grained facies composed of biogenic carbonate sand is found. Along a short section of the coastline (km 3–6), the coarser sediment also occupies the nearshore zone. Over most of the study area the two sediment types are mixed in various proportions, largest mixing coinciding with poorest sorting. Profile analyses revealed seasonal changes in sediment volume along the coast which closely follow the cyclicity of seasonal changes in wave climate. The present shoreline orientation, headlands and rough, irregular rocky seabed are reflected in the erosion/accretion pattern, sediment characteristics, and the reversibility of longshore currents and littoral drift. Although there is a marked deficiency in the sediment balance, the sand budget for this cell, including artificial material (2.339*10⁶ m³) has increased slightly by 0.041*10⁶ m³ year^–1 as a result of engineering works carried out to widen the coastal road (Corniche). In addition to the physical properties of the bedrock (degree of induration), the accelerating sea-level rise during the Holocene and human influences, the modern morphology of the coast, the erosional seabed features in the nearshore zone, and the texture of seabed sediments are all controlled by the original geometry of the coast which consisted of an elevated subaerial ridge.     

辽宁省黄海沿岸人工岸线潮间带大型海藻调查与分析研究

为调查辽宁省黄海沿岸人工岸线上潮间带大型海藻多样性情况, 于2011 年10 月至2012 年6 月在大连湾、獐子岛、旅顺及丹东进行采样, 并与其附近天然岸线上海藻进行对比。调查结果显示, 在人工岸线上共发现17 种海藻, 以红藻与绿藻为主, 其中11 种可在相邻天然岸线发现。海藻多样性天然岸线＞混合岸线＞人工岸线, 但人工岸线上绿藻种类与天然岸线上的基本相同。在大连湾及獐子岛地区, 无机氮低的海域, 海藻多样性高; pH 高的海域, 海藻多样性高。调查中发现有人工岸线与天然岸线共存的混合岸线, 此岸线可看作是生境岸线(living shoreline)的一个变形, 为生物保护及生态恢复提供了新思路。     

Assessment and prediction of shoreline change using multi-temporal satellite images and statistics: Case study of Damietta coast,Egypt

The shoreline trajectory of Damietta city, locates at the Northern coast of Egypt, is dramatically subjected to kinematic changes. These variations mainly occur based on the incessant duel hydrodynamic impacts of both wave action and coastal currents. Several types of coastal measures have been applied substantially along the coastal stretch of Damietta to protect shoreline such as detached breakwaters, Jetties, groins, and seawalls. This study is essentially focused on the assessment of shoreline kinematics response due to the existence of these structures during the period from 1990 to 2015. In addition, the future changes of the shoreline at 2020, 2025 and 2035 are predicted using satellite images, Geo-spatial tools and Digital Shoreline Analysis System (DSAS) by the meaning of End Point Rate (EPR) and Linear Regression Rate (LRR) methods. Four Landsat images at different periods; TM1990, TM 1999, ETM 2003 and ETM 2015 are used to detect shoreline changes. Three semi-automatic extraction techniques are initially tempted for Landsat ETM 2003 imagery namely; Iso cluster technique, threshold method, and onscreen digitizing method to select the optimal one. Iso cluster technique is used as the optimal technique which achieves the least errors with the corresponding field data in 2003 by value of 0.34. Furthermore, the extraction shoreline change for Damietta coast is extensively measured for three zones: zone (1) the western sector encompassing Damietta port with two jetties; zone (2) the central sector including detached breakwaters; zone (3) the eastern portion of Damietta estuary passing through a seawall. Verification analysis shows that the EPR is the optimum method for shoreline detection with a value of RMSE by 0.27. The results show that, for zone (1), the western shoreline of Damietta port is progressed by a rate of +10.0 m/year. On the other hand, the shoreline on the down drift side at zone (2) has retreated by a rate of -5.0 m/year. While the shoreline behind the detached breakwaters in the central sector has advanced by +12.0 m/year from 1999 to 2003, then decreased gradually until become stable in 2015. For zone (3), alongshore currents have derived the disassembled sandy soil from west to east leaving a highly eroded area by average rate of -78m/year. The results of this study give indication to shoreline trend of near future which should be under consideration in planning of Damietta coastal zone.     

Geostrophic response near the coast

Geostrophic response of a two-layer fluid near a straight coast is investigated for a successive disturbance by the use of the inviscid, reduced gravity model. Poincare waves, coastal motion (which is trapped by the coast) and a geostrophic eddy are created. The energy of these motions is obtained. The manner in which the ocean responds is found to depend considerably on the way the disturbance is applied. When the water is supplied continuously to a calm upper layer adjacent to the coast, a quasi-steady geostrophic eddy is formed and its energy increases in proportion toT ² (T is the duration for which water is supplied). The energy of the coastal motion increases in proportion toT. When the water is supplied continuously into the upper layer from a certain portion of the coast, a geostrophic eddy is not formed. The coastal motion has the same structure as in the former case and its energy increases in proportion toT.     

辽河口岸线变化对潮不对称影响的研究

受河口地形等因素的影响,潮汐潮流会出现涨落潮不对称现象,这种不对称对河口物质输运过程具有重要的影响.本研究采用流通量偏度和水位不对称度的统计方法研究辽河口岸线变化对潮波变形的影响.结果表明,辽河口潮汐潮流不对称性表现为涨潮主导型,岸线变化导致涨潮历时延长,落潮历时减小,不对称度缩减了0.007~0.071;岸线变化导致涨潮流速减小,落潮流速增大,流通量偏度缩减了0.000~0.248,岸线变化对潮流不对称的影响程度比对潮汐影响的程度大.     

Morphodynamic zone variability on a microtidal barred beach

This paper builds on the work of Masselink [Masselink, G., 1993. Simulating the effects of tides on beach morphodynamics. J. Coast. Res. SI 15, 180–197.] on the use of the residence times of shoaling waves, breaking waves and swash/backwash motions across a cross-shore profile to qualitatively understand temporal beach behaviour. We use a data set of in-situ measurements of wave parameters (height and period) and water depth, and time-exposure video images overlooking our single-barred intertidal measurement array at Egmond aan Zee (Netherlands) to derive boundaries between the shoaling zone, the surf zone and the swash zone. We find that the boundaries are functional dependencies of the local relative wave height on the local wave steepness. This contrasts with the use of constant relative wave heights or water levels in earlier work. We use the obtained boundaries and a standard cross-shore wave transformation model coupled to an inner surf zone bore model to show that large (> 5) relative tide ranges (RTR, defined as the ratio tide range–wave height) indicate shoaling wave processes across almost the entire intertidal profile, with surf processes dominating on the beach face. When the RTR is between 2 and 5, surf processes dominate over the intertidal bar and the lower part of the beach face, while swash has the largest residence times on the upper beach face. Such conditions, associated with surf zone bores propagating across the bar around low tide, were observed to cause the intertidal bar to migrate onshore slowly and the upper beach face to steepen. For RTR values less than about 2, surf zone processes dominate across the intertidal bar, while the dominance of swash processes now extends across most of the beach face. The surf zone processes were now observed to lead to offshore bar migration, while the swash eroded the upper beach face.     

Model study of a shoreline wave-power system

A wave-power system which combines the concept of a breakwater and a harbor resonance chamber was developed in this study. In the caisson chamber, a multi-resonant oscillating water column (MOWC) was formed to push or suck air through the air turbine and thus continuously generated the power. The proposed wave-power system has two aims in mind: one is shore protection and the other is to extract energy from the ocean. To achieve an optimal effect of harbor resonance when excited by incident waves of various periods, a 60° opening of the cylindrical chamber with an entrance section and an arc-shaped curve board in front of the caisson was designed. In order to assess the energy-conversion efficiency and the hydraulic performance, a 1/20 model of this system was constructed and tested in the wave tank under various wave conditions. Our experimental data for the amplification factor of the MOWC agree well with previous theoretical results [Lee, J.J., 1971. Journal of Fluid Mechanics 45, 375–394]. The curve board proves to be useful: it not only broadens the resonant period but also increases the energy-extraction rate. The reflection coefficient was found to be generally low and to decrease with increasing wave height. However, due to the relatively high energy loss of the MOWC, only 28.5% of the incident-wave energy was converted into air energy, indicating that there are still areas for further improvement. In any event, the experimental results provided a clear picture of the energy-transformation process, and demonstrated the preliminary feasibility of this wave-energy device.     

1973 年以来射阳河口附近海岸蚀淤变化遥感分析

以射阳河口北部扁担港口和射阳河口南部斗龙港口之间的海岸作为研究区,基于1973,1987,2000和2013年四期Landsat影像提取了该岸段岸线,并进行了时空变化分析。结果表明,射阳河口以北的扁担港口—射阳河口岸段仍处于侵蚀状态,呈现侵蚀—淤积—缓慢侵蚀的变化格局,40 a间侵蚀面积为12.6 km2,淤积面积为1.0 km2;射阳河口以南的射阳河口—斗龙港口岸段处于淤积的态势,呈现淤积—快速淤积—缓慢淤积的格局,40 a间淤积的面积为223.1 km2,仅在2000~2013年间该岸段北部出现了侵蚀。结论是虽然射阳河口以南岸段仍总体处于淤积的过程中,但是近年来江苏海岸的侵蚀范围已经扩展到了射阳河口以南,这证明了江苏海岸侵蚀岸段有进一步扩大的趋势。     

Beach morphology and shoreline evolution: Monitoring and modelling medium-term responses (Portuguese NW coast study site)

Numerical models for shoreline evolution have been used for coastal management planning for several decades. The model calibration is a start point to project shoreline scenarios and in this aim the use of data acquired within the scope of monitoring programmes provides the opportunity to assess the models' capabilities under real condition. This work applies calibration data (retrieved from field surveys) to numerical models to predict medium-term shoreline evolution using, as a case study, a beach stretch named AC, about 3.5 km long and located downdrift of a groin on the northwest Portuguese coast. A smaller stretch AB (2.4 km long), included in the total one, which exhibits a pronounced erosive tendency usually better reproduced in shoreline evolution models, was also analysed. Based on topographic surveys, associated wave climate conditions registered between 2003 and 2008 and typical wave conditions registered over a longer wave climate time period, this work compares the calibration of two different shoreline evolution models, Long-term Configuration (LTC) and GENESIS for this period. Then, considering the 2003 topographic conditions for the models' calibration, the results of both models are discussed with respect to simulation scenarios after 10, 15 and 20 years of evolution. The 10-year evolution projections of the models are also compared to the results of a survey performed in February 2012. For the wave data calibration period (2003–2008), the average shoreline retreat of the analysed coastal stretch was reproduced with small differences (around 1% and 10% for LTC and 15% and 14% for GENESIS, considering stretches AB or AC, respectively), though local differences along the AB coastal stretch represent root mean square errors reaching up to 52% and 88% for GENESIS and LTC, respectively, and were above 118% for both models along the AC coastal stretch.     

Bedforms and depositional sedimentary structures of a barred nearshore system, eastern Long Island, New York

The depositional sedimentary structures and textures of a single-barred nearshore system on the Atlantic coast of eastern Long Island, New York, were studied along seven shore-normal transects. Data along these transects consisted of textural analysis of 160 sediment samples, temporal bedform observations, and 42 can cores for the analysis of sedimentary structures.

Six sedimentary subenvironments were observed, based on distinct combinations of sediment color and texture, bedforms, physical, and biogenic sedimentary structures, and benthic infaunal communities. The shoreface environment is divided into the upper shoreface, the longshore trough, and the longshore bar. The divisions of the inner shelf environment are the shoreface-inner shelf transition, the offshore, and the coarse-grained deposit. The first five subenvironments are arranged in bands parallel to the shoreline, whereas the coarse-grained deposit occurs in patches across the inner shelf.

The location of fair-weather wave base, coinciding with a reduction in slope (3.0–0.3°) from the shoreface to the inner shelf, is characterized by the cessation of debris surge in the troughs of ripples, the formation of a “rust layer” of microorganisms over the bedform surface, and a sediment color change caused by an increase in organic detritus. The sequence of bedforms and physical sedimentary structures observed in this system fits well with existing wave-generated (oscillatory) flow regime models. These models explain the observed sequences as a response to the degree of asymmetric flow created by shoaling waves. Distribution of biogenic structures and assemblages of infaunal organisms is influenced by the distance landward or seaward of fair-weather wave base.

The overall relationships of this nearshore system can then be summarized as a hypothetical prograding stratigraphic sequence. The entire sequence is underlain by organic-rich, bioturbated, offshore deposits. Overlying the offshore is the planar-laminated sediments of the transition. Grading upward from the transition are the cleaner, planar-laminated, seaward slope deposits of the longshore bar. Above this, is a distinct erosional surface indicating the base of the massive to cross-laminated coarse sediments of the longshore trough. Capping the sequence are the cross- to planar-laminated, clean sands of the upper shoreface and foreshore.     

Sediment flux and equilibrium slopes in a barred nearshore

Estimates of time-integrated values of total (ITVF) and net (INVF) sediment volume flux and the associated changes in bed elevation and local slope were determined for a crescentic outer nearshore bar in Kouchibouguac Bay, New Brunswick, Canada, for eight discrete storm events. A 100 × 150 m grid of depth-of-activity rods spaced at 10 m intervals was used to monitor sediment behaviour on the seaward slope, bar crest and landward slope during the storms, at which time winds, incident waves and near-bed oscillatory currents were measured. Comparisons between storm events and between these events and a longer-term synthetic wave climatology were facilitated using hindcast wave parameters. Strong positive correlations between storm-wave conditions (significant height and total cumulative energy) and total volume flux contrasted strongly with the zero correlation between storm-wave conditions and net volume flux. ITVF values ranged up to 1646 m³ for the experimental grid and were found to have power function relations with significant wave height (exponent 2) and cumulative wave wave energy (exponent 0.4); values of INVF ranged from 0 up to 100 m³ for the same grid indicating a balance of sediment volume in the bar form through time. Sediment reactivation increased linearly with decreasing depth across the seaward slope and bar crest reaching maxima of 20 cm for the two largest storms; bed elevation, and thus slope, changes were restricted to the bar crest and upper landward slope with near zero morphological change on the seaward slope. The latter represents a steady-state equilibrium with null net transport of sediment under shoaling waves. Measurements of the asymmetry of orbital velocities close to the bed show that the energetics approach to predicting beach slope of Inman and Bagnold (1963) is sound. Gradients predicted vary from 0.01 to 0.03 for a range of angles of internal friction appropriate to the local sediment (tan ø = 0.3–0.6). These compare favorably with the measured seaward slope of 0.015 formed under average maximum orbital velocities of 1.12 m s⁻¹ (landward) and 1.09 m s⁻¹ (seaward) recorded during the period of the largest storm waves.     

Holocene sedimentation of a wave-dominated barrierisland shoreline: Cape Lookout, North Carolina

The sedimentary record of 130 km of microtidal (0.9 m tidal range) high wave energy (1.5 m average wave height) barrier island shoreline of the Cape Lookout cuspate foreland has been evaluated through examination of 3136 m of subsurface samples from closely spaced drill holes. Holocene sedimentation and coastal evolution has been a function of five major depositional processes: (1) eustatic sea-level rise and barrier-shoreline transgression; (2) lateral tidal inlet migration and reworking of barrier island deposits; (3) shoreface sedimentation and local barrier progradation; (4) storm washover deposition with infilling of shallow lagoons; and (5) flood-tidal delta sedimentation in back-barrier environments.

Twenty-five radiocarbon dates of subsurface peat and shell material from the Cape Lookout area are the basis for a late Holocene sea-level curve. From 9000 to 4000 B.P. eustatic sea level rose rapidly, resulting in landward migration of both barrier limbs of the cuspate foreland. A decline in the rate of sea-level rise since 4000 B.P. resulted in relative shoreline stabilization and deposition of contrasting coastal sedimentary sequences. The higher energy, storm-dominated northeast barrier limb (Core and Portsmouth Banks) has migrated landward producing a transgressive sequence of coarse-grained, horizontally bedded washover sands overlying burrowed to laminated back-barrier and lagoonal silty sands. Locally, ephemeral tidal inlets have reworked the transgressive barrier sequence depositing fining-upward spit platform and channel-fill sequences of cross-bedded, pebble gravel to fine sand and shell. Shoreface sedimentation along a portion of the lower energy, northwest barrier limb (Bogue Banks) has resulted in shoreline progradation and deposition of a coarsening-up sequence of burrowed to cross-bedded and laminated, fine-grained shoreface and foreshore sands. In contrast, the adjacent barrier island (Shackleford Banks) consists almost totally of inlet-fill sediments deposited by lateral tidal inlet migration. Holocene sediments in the shallow lagoons behind the barriers are 5–8 m thick fining-up sequences of interbedded burrowed, rooted and laminated flood-tidal delta, salt marsh, and washover sands, silts and clays.

While barrier island sequences are generally 10 m in thickness, inlet-fill sequences may be as much as 25 m thick and comprise an average of 35% of the Holocene sedimentary deposits. Tidal inlet-fill, back-barrier (including flood-tidal delta) and shoreface deposits are the most highly preservable facies in the wave-dominated barrier-shoreline setting. In the Cape Lookout cuspate foreland, these three facies account for over 80% of the sedimentary deposits preserved beneath the barriers. Foreshore, spit platform and overwash facies account for the remaining 20%.     

Sub-weekly to interannual variability of a high-energy shoreline

Sixty-one Global Positioning System (GPS), sub-aerial beach surveys were completed at 7 km long Ocean Beach, San Francisco, CA (USA), between April 2004 and March 2009. The five-year time series contains over 1 million beach elevation measurements and documents detailed changes in beach morphology over a variety of spatial, temporal, and physical forcing scales. Results show that seasonal processes dominate at Ocean Beach, with the seasonal increase and decrease in wave height being the primary driver of shoreline change. Storm events, while capable of causing large short-term changes in the shoreline, did not singularly account for a large percentage of the overall observed change. Empirical orthogonal function (EOF) analysis shows that the first two modes account for approximately three-quarters of the variance in the data set and are represented by the seasonal onshore/offshore movement of sediment (60%) and the multi-year trend of shoreline rotation (14%). The longer-term trend of shoreline rotation appears to be related to larger-scale bathymetric change. An EOF-based decomposition technique is developed that is capable of estimating the shoreline position to within one standard deviation of the range of shoreline positions observed at most locations along the beach. The foundation of the model is the observed relationship between the temporal amplitudes of the first EOF mode and seasonally-averaged offshore wave height as well as the linear trend of shoreline rotation. This technique, while not truly predictive because of the requirement of real-time wave data, is useful because it can predict shoreline position to within reasonable confidence given the absence of field data once the model is developed at a particular site.     

Visualisation of flow conditions inside a shoreline wave power-station

The particle flow inside an oscillating water column type wave power-station varies with time and changes direction. In order to establish flow patterns and energy dissipating mechanisms, and to assess the influence of geometry changes on the hydraulic performance, flow visualisation experiments were conducted on a 1/36 two-dimensional model of the Islay prototype wave power-station. It was found that large vortices develop around the comparatively thin front wall for in- and outflow and that internal sloshing occurs during the inflow period. From the observations it could be deduced that the front lip curvature and thickness have to be increased. Previous suggestions to structure the front wall surface in order to reduce wave loads had to be revised as these obstacles would interfere with the inflow. An internal breaker was observed, indicating that the loads on the back wall might be considerably higher than assumed.     

Forced and self-organized shoreline response for a beach in the southern Baltic Sea determined through singular spectrum analysis

Temporal and spatial variations in shoreline position along the southern Baltic coast were investigated using singular spectrum analysis (SSA) with the overall aim to determine characteristic patterns in the shoreline response and whether these patterns displayed forced or self-organized behavior. The investigated beach is located at Lubiatowo on the Polish Coast and is mildly sloping with multiple bars having a median grain size of 0.22 mm, being typical for the coast in the southern Baltic Sea. Data on coastal morphology have been collected at Lubiatowo including (1) bathymetric surveys since 1987 twice a year to cover changes in the seabed (along 27 lines covering a longshore×cross-shore area of 2600×1000 m), and (2) beach topography surveys since 1983 every 4 weeks on the average, extending from the shoreline to the dune foot (along the same 27 lines). Furthermore, several dedicated field campaigns have been carried out at Lubiatowo, as well as measurements of deep-water wave properties since 1998. SSA was employed to the time series of shoreline position from all 27 survey lines. The analysis method demonstrated a large potential for detecting temporal patterns from fairly short and noisy time series with irregular sampling interval. In summary, three dominant patterns emerged jointly reproducing 70–90% of the overall variation in the data for the different survey lines. These temporal patterns were demonstrated to represent forced and self-organized components describing the variation in shoreline position. The forced components could be related to the mean properties of the wave climate, whereas the self-organized components were mainly influenced by particular events or features of the beach such as storm waves, storm surges, beach type (dune, cliff), and sediment characteristics.