Longshore Sand Transport Research Articles

Disasters at Shimoniikawa Coast caused by high waves on February 24, 2008

Historically, many disasters at Shimoniikawa Coast has occurred by high waves called Yorimawarinami from east. The direction of longshore sand transport of the Shimoniikawa Coast is eastward. In Nyuuzen-machi and Asahi-machi located in the east from the Kurobe River mouth which becomes the source of supply of the sand, many houses moved because of beach erosion. In such circumstances, intense high waves by the low pressure hit these areas on February 24, 2008, so that coastal protection facilities in Kurobe-shi, Nyuuzen-machi and Asahi-cho got damaged and, furthermore houses were flooded and destroyed by overtopping waves.In this paper, various observation data in Shimoniikawa Coast of Yorimawarinami was analyzed by and the cause of the disaster was considered.

Mechanism of Development of Large-scale Circulation of Littoral Drift under Seasonally Changing Wave Direction

In the long-term basis, the direction of longshore sand transport in the shoreward zone often reverses to that in the offshore zone. This phenomenon has been observed at many coasts. The analysis using the contour-line-change model proposed by Serizawa et al.(2002) has been carried out to investigate this phenomenon, taking the Kashinmanada coast as an example. The mechanism is explained by the development of a large-scale circulation of littoral drift due to the action of waves with different energy levels under the conditions of seasonally-changing wave directions.

南九十九里浜の侵食と堆積の実態

Beach erosion and accretion of the south Kujukuri coast was investigated based on the aerial photographs and field observation. The sand supply by northward longshore sand transport has been decreasing on this coast, causing erosion of the south part of the coast close to the sand source (sea cliff). In contrast, on the north end of the coastline, a long breakwater of the Katakai fishing port was extended and a large amount of sand has been deposited in the wave shelter zone. Furthermore, the ground subsidence up to 60cm occurred along the coastline due to the pumping-up of the ground water to obtain the water-soluble gas. The coastal situation of the south Kujukuri coast has devastated year by year due to all these impacts. To save the coast, full scale sand nourishment is required.

Storm-generated morphological change and longshore sand transport in the intertidal zone of a multi-barred macrotidal beach

The morphology, hydrodynamics and sediment transport processes of a multi-barred macrotidal beach were surveyed over 21 semi-diurnal tides, the first eight of which were dominated by storm conditions with offshore wave heights ranging from 1.2 to nearly 3.5 m. The hydrodynamic conditions prevailing over the intertidal beach showed a rapid response to these storm conditions, notably through strong longshore currents that attained peak velocities of 1.6 m s − 1 , i.e. over three times the peak spring tide velocities of tide-generated longshore currents during calm conditions. The bars showed no cross-shore migration during the storm events. Morphological mapping of the beach, tracer dispersal patterns, and calculations of potential sand transport rates using the energetics-based model of Bailard [Bailard, J.A., 1981. An energetics total load sediment transport model for a plane sloping beach. J. Geophys. Res., 86, 10938–10954.] showed significant longshore sand transport, as well as longshore migration of an intertidal drainage channel. These longshore movements were bi-directional, responded to changes in incident wind and wave directions, and involved wave stirring, coupled with longshore advection of sand along the bar crests in particular. Strong trough and cross-shore channel flows also led to the longshore migration of crescentic dunes. The longshore sediment movements were embedded in a cross-shore gradient associated with increasing overall profile mobility from the lower to the upper beach in response to wave shoaling and post-breaking processes, assessed through examination of the relative wave height Hs h − 1 , based on the relationship between significant wave height (Hs) and water depth ( h). Longshore sediment transport is a characteristic feature of the long-term evolution of Wissant Bay, which is dominated by a net northeastward residual sand transport within a bay sediment cell characterised by significant updrift erosion and downdrift accumulation. Longshore transport should be considered as an essential element of the morphodynamics of bar-trough beaches subject to large tidal ranges and significant wind stress, but there is a need for a better understanding of the role of wind stress on longshore currents in the shallow intertidal zone of these beaches.

Beach impacts of shore-parallel breakwaters backing offshore submerged ridges, Western Mediterranean Coast of Egypt

Seven breakwaters were constructed behind offshore submerged ridges to create a safe area for swimming and recreational activities west of Alexandria on the Mediterranean coast of Egypt. Morphodynamic evaluation was based on the modified Perlin and Dean numerical model (ImSedTran-2D) combined with successive shoreline and beach profile surveys conducted periodically between April 2001 and May 2005. Results reveal insignificant morphologic changes behind the detached breakwaters with slight coastline changes at the down and up-drift beaches of the examined breakwaters (±10 m). These changes are associated with salient accretion (20–70 m) in the low-energy leeside of such structures. Concurrent with this sand accretion is the accumulation of a large amount of benthic algae (Sargassum) in the coastal water of the shadow area of these structures, which in turn have adverse effects on swimmers. Practical measures proposed in this study have successfully helped in mitigating such accumulation of algae in the recreation leeside of the breakwaters. The accumulation of Sargassum, together with the virtual insignificant changes in the up-drift and down-drifts of these structures, is a direct response to both coastal processes and the submerged carbonate ridges. Coastal processes encompass reversal of the directions of long-shore sand transport versus shoreline orientation, the small littoral drift rate and sand deficiency of the littoral zone. The beach response to the breakwaters together with the submerged ridges has also been confirmed by applying the ImSedTran-2D model. Results indicate that submerged ridges play a principal role in the evolution of beach morphology along the west coast of Alexandria. Although the study area is exposed to more than 70% wave exposures, the morphodynamic behavior of the beaches indicates that the submerged ridges act in a similar way as an additional natural barrier together with the artificial detached structures.

Longshore sand transport estimates along the Mediterranean coast of Israel in the Holocene

The Nile littoral cell, one of the world's longest, runs 650 km along the southeastern Mediterranean, from Abu Quir Bay near Alexandria, Egypt, to Haifa Bay on the northern Israeli coast. Haifa Bay constitutes the northernmost final depositional sink of Nile-derived quartz sand, transported from the Nile delta by longshore currents generated by approaching breaking waves. The northward net sand transport along the Mediterranean coast of Israel results from larger waves approaching from west–south–west and south–west compared to their counterparts from west–north–west and north–west. This study utilizes an extensive new database gathered from sediment drill cores, marine geophysical maps and field observations to measure the volume of sand deposited in Haifa Bay and the adjacent Zevulun Plain during the Holocene. It then compares this volume to recent data, including measurements of sand accumulation along Haifa Port's main breakwater (constructed in the southern entrance of the bay) as well as longshore sand transport estimates along the northern Carmel coast. Research findings estimate the annual average quantity of sand transported to Haifa Bay throughout the period at 80,000–90,000 m 3. The findings further conclude that this amount has not changed appreciably over the past 75 years. Evaluating calculated values over the long term, it is suggested that the characteristics of longshore sand transport along the coast of Israel have not changed significantly during the past 7900–8500 years. It is obvious that this conjecture should be treated with reservations.

神奈川県茅ケ崎中海岸の事例にみる養浜の考え方

Field experiment of beach nourishment using coarse sand and gravel was carried out on the Chigasaki-naka coast. Color sand with median diameters of 0.2, 2 and 10mm was placed on the shoreline and at a depth of 4m to investigate movement of sand due to waves. It was found that fine sand with the grain size of 0.2mm was extensively diffused in a wide area shallower than the depth of the closure hc=9 m. In contrast, coarse material deposited on the shore face was slowly transported by the longshore sand transport. Coarse material is effective for maintaining the shoreline, but it is inappropriate to maintain offshore gentle slope. To keep a sound environment of a coast, the selection of fine and medium sand as a nourishment material is also important.

等深線変化モデルによる海食崖〜海浜系の地形変化予測

A model for predicting the topographic changes of both cliffy coast and sandy beach is developed using the contour-line-change model. In this model, recession of the cliff due to waves is modeled, and sediment supplied from the cliff is transported downcoast by longshore sand transport, resulting in the formation of a sandy beach. Predicted results were compared with a movable bed experiment.

Mechanism of Deformation of Sand Bar Formed in Sanbyakken Region in Nakatsu Tidal Flat

Long-term changes in sand bar in Sanbyakken region in Nakatsu tidal flat were investigated through the comparison of the aerial photographs. Great changes have occurred in this sand bar in recent years, as aresult of increase in eastward longshore sand transport since 1998. The reason was studied in terms of change in wave field. Waves with the direction of N70deg E, which was determined from the shape of the sand bars on the tidal flat, were significantly sheltered due to the offshore breakwater of Nakatsu Port. Takingthe refraction effect of these diffracted waves into account, the tip of the sand bar was also sheltered by the waves. It was found that this caused increase in longshore sand transport.

Cause of Periodic Variation in Lakeshore Elevation at Ohyama Region in Lake Kasumigaura

Kasuga (2006) has been measuring the lakeshore elevation at a point in front of the seawall at Ohyama region in Lake Kasumigaura once a day since 1993. Due to this observation, the elevation at the point showed a strong periodicity of a year. To investigate the cause of the changes, original data taken by Kasuga was analyzed as well as seabed sounding and sampling test of seabed materials. Wave forecasting and numerical simulation using the contour-line-change model was carried out. It was found that this periodic variation of the elevation was induced by the seasonal changes in direction of longshore sand transport on a pocket beach between a drainage gate and lakeshore plants.

Beach Changes of Akiya Coast in Kanagawa Prefecture and Prediction of Effect of Beach Nourishment

Shoreline changes of the Akiya coast located in Sagami Bay were investigated on the basis of the comparison of aerial photographs. A breakwater of Kuruwa fishing port was extended forming a wave shelter zone. This induced longshore sand transport from outside to inside the wave shelter zone. Sand accumulated inside the wave shelter zone, whereas beach erosion occurred on the nearby coast. Tracer test using sand with various grain sizes was carried out. The contour-line-change model considering change in grain size given by Kumada et al.(2005) was applied to the coast to investigate the effect of beach nourishment using materials with different grain sizes. It is concluded that beach nourishment using sand composed of coarse materials is effective to recover the stable beach without damages to offshore sea grass field.

O Controle da Deriva Litorânea no Desenvolvimento do Campo de Dunas e da Antepraia no Litoral Médio do Rio Grande do Sul

Zones of erosion and accretion were delimited by comparing a DGPS shoreline mapping in 1997 and the beach line reproduced from the army chart collection of 1975. The results show extensive shore retreat along of Rio Grande do Sul central coast, while accretion was observed in Mostardas and Dunas Altas beach. Mathematical estimative of the regional longshore transport potential along the Rio Grande do Sul coast, a 630-km long holocenic fine sand barrier, resulted in a large net northward annual sand volume. Additionally, the estimated potential of sediment transport based on the CERC formula predicts a substantial variation of the energy flux into the surf zone, due to little changes in shoreline alignments and in the potential alongshore sediment transport. The reduction in the sediment flux due to changes in the shoreline alignment produce a jam in the longshore transport, meaning that part of the sediment arriving from the upstream stretch may be deposited or diverted offshore by coastal jet. Based on that, it is possible that changes in the net longshore sand transport are responsible for the increase in the shoreface width from less than 1 km to more than 3 km in Mostardas beach and Dunas Altas beach. Interesting to note that wider dune fields are associated to those beaches where shoreface is also wider. In this way, the volume of longshore sand transport and the sediment jam provide by changes on shoreline alignment in Mostardas and Dunas Altas beaches are important for both coastal dune fields and shoreface width.

Intertidal subsidence and collapse features on wave‐exposed, drift‐aligned sandy beaches subject to Amazon mud: Cayenne, French Guiana

AbstractShort‐lived collapse features affecting the intertidal sandy profile were observed on mud‐rich beaches in Cayenne. They were formed in packets of beach sand accumulating over thick (several metres) fluid to under‐consolidated foreshore mud, which adjusts to this sand loading by seaward and longshore migration of fluid mud and subsequent in situ mud dewatering, thus generating subsidence and deformation of the overlying sand sheet. These sandy collapse features required active longshore sand transport and were washed out by wave processes at each rising tide. They finally disappeared permanently as adjustment of the underlying mud enabled stabilization of the beach profile. Copyright © 2006 John Wiley & Sons, Ltd.

三重県吉崎海岸の長期的海岸線変化

Long-term shoreline changes of the Yoshizaki coast located around a mouth of a tributary of the Suzuka River flowing into Ise Bay were investigated on the basis of the comparison of past geographical maps and aerial photographs. The characteristic height of beach changes was evaluated to be 4m from the bathymetric survey data. Longshore sand transport rate of 2×104m3/yr was obtained from the shoreline changes multiplied by this characteristic height of beach changes in the natural condition. In recent years, this longshore sand transport of the coast was totally exhausted and a long shoreline was separated into several pocket beaches.

An aggregate model for the adaptation of the morphology and sand bypassing after basin reduction of the Frisian Inlet

To study the adaptation of the morphology of the Frisian Inlet after basin reduction an aggregate model is developed. In the model, especial attention is given to the sand transport to the down-drift coast. In developing the model the inlet system is divided into three elements, the ebb tidal delta, the Zoutkamperlaag and the tidal flats. Based on observations during the first 18 years after basin reduction the adaptation time scale of the tidal flats is expected to be much larger than that of the ebb tidal delta and the Zoutkamperlaag, essentially reducing the inlet schematization to a two-element system. The dependent variables in the model are the sand volume of the ebb tidal delta and the water volume of the channel. The governing equations are non-linear and for quantitative accurate results are solved numerically. To demonstrate the nature of the solution the equations are linearized assuming the morphological state is close to equilibrium. The linearized equations are solved analytically and the solution is applied to a hypothetical case where the tidal prism of the Frisian Inlet is reduced by 10%. From the analytical solution it follows that the adaptation of the volumes of the two elements, delta and channel, is governed by two system time scales. These system time scales are functions of two local time scales. The local time scales pertain to the adaptation of one element assuming the other element has reached equilibrium. Because there are two system scales the adaptation of the volumes of the delta and channel is not exponential and is not necessarily monotonic. For example, initially the transport of sand to the down-drift coast is larger than the long-shore sand transport entering the inlet system from the up-drift coast, then becomes smaller and after some time increases again to reach the value of the up-drift long-shore sand transport. Comparison of the numerical solution for the actual reduction in tidal prism of 30% with the analytical solution for the 10% reduction in tidal prism shows qualitatively the same results.

Late Quaternary stratigraphy and morphogenesis in the Danish eastern North Sea and its relation to onshore geology

AbstractGeological structures and Late Quaternary stratigraphy of the shallow subsurface along the southernmost Danish North Sea coast have been investigated using seismic data and shallow boreholes. A large-scale glaciotectonic thrust complex has been mapped in an area of 15 km by 40 km in the Fanø Bugt area. The affected succession consists of Neogene and Quaternary sediments deformed down to a depth of 200 – 360 m. A kineto-stratigraphic correlation to onshore glaciotectonic deformation suggests that the deformation took place during a westward advance stage of the Late Saalian (Warthe) glaciation. The western limit of the glaciotectonic structures constitutes an N-S striking deformation front situated 35 km off the west coast. Based on the glacial stratigraphy outside the deformation front, it is suggested that the same ice advance that caused the glaciotectonic deformation, eroded the top of the thrust sheets, and subsequently deposited a lower unit of meltwater sediments and an upper heterogenous glacigenic unit. The upper glacigenic unit forms a bank about 30 km offshore. Between the bank and the shore, the surface of the Saalian glacial landscape forms a wide depression ca. 50 m below sea level. This basin has controlled deposition in the area since the late Saalian and is filled with sediments of late Saalian, Eemian, Weichselian and Holocene age. The base of the Holocene marine deposits is thus a flat erosional surface extending eastward several kilometres below the onshore coastal areas and the northern Wadden Sea. This surface was transgressed 8800 years ago. An inverted, in plan view T-shaped, Holocene sand accumulation approximately 25 km long, 30 km wide and 15 – 25 m thick is situated on top of this surface at Blåvands Huk. According to recent estimates by the Danish Coastal Protection Board some 2.5 million m3sediments are supplied annually to the system from the north. In the last 3000 years, 25 km of the west coast and the associated shoreface slope have prograded ca. 3 km towards the west forming a barrier spit complex. Large aeolian dunes and cover sands now conceal the spit complex. Extending twenty km west of Blåvands Huk is a highly dynamic bank, the Inner Horns Rev, with active sand-accumulation on the slopes. The Inner Horns Rev bank has grown ca. 3.5 km westward during the last 800 years. The deposits seem to be sourced by the coastal longshore sand transport from the north. The Outer Horns Rev was previously assumed to be a Saalian terminal moraine. However, this investigation reveals that it is also mainly a Holocene marine accumulation landform, but sourced from the west. Other sand accumulations, which are situated 20 – 30 km west of the coast, are probably sourced from both the south and the west.

Beach-line changes at the mouth of Punta Banda Estuary, Baja California, during 1972–2003

The spatial and temporal variability of the beach-line position at the tidal inlet of Punta Banda coastal lagoon in Baja California, Mexico, is described from the analysis of ten aerial photographs and two satellite images spanning from 1972 to 2003. The results showed that the maximum tidal inlet width (995 m) occurred in 1980. Changes observed from 1980 to 1985 suggest that the extraordinary sediment fluxes that occurred during the winter storms of 1977/78, 1980/81 and 1982/83 were the main source of sediment inducing the growth of the sediment structures that delimit the tidal inlet. By the end of 1985 a new sand bar appeared on the northern side of the tidal inlet and its formation is attributed to a reduction in the ebb and flood tidal intensity as a consequence of the combined effect of the increase in width of the tidal inlet in 1980, of the extraordinary supply of sediments and of the dominant northeast to southwest longshore sand transport. The net growth of the sand bar that shapes the southern side of the tidal inlet was 53 ha from 1978 to 2003, of which 26 ha are located in the inner part of the tidal inlet. This growth and consequent reduction of the tidal inlet could be the result of a reduction in the tidal prism produced by the great amount of sediments supplied to the coastal lagoon by storms and also by the reduction of the lagoon´s flushing capacity.

卓越沿岸漂砂の阻止に起因した海岸侵食‐紋別港〜サロマ湖口の例‐

The shoreline changes along the 64-km-long coast facing Ohotsuku Sea were investigated through the comparison of aerial photographs taken in 1947 and 2001. In this area, predominant direction of longshore sand transport is east. Port breakwaters and jetties were constructed, resulting in the disruption of continuous longshore sand transport. Severe downcoast erosion was triggered by the construction of these structures. Seawalls and concrete armor units had been installed to prevent erosion locally, but it failed to accelerate further downcoast erosion. Comprehensive measures are required to change this situation.

相模川河口砂州と河口テラスの変形機構

Topographic changes of the river mouth bar and terrace of the Sagami River were investigated through field observations and numerical analysis of waves and nearshore currents. The river mouth bar of the Sagami River has retreated and deformed largely, resulting in the sand deposition to the navigation channel of Hiratsuka fishing port. In order to improve this condition, fundamental mechanism of sand movement around the terrace off the mouth was investigated. Sand deposition into the navigation channel was accelerated by the longshore sand transport along the marginal line of the terrace.

Process Based Modeling of Total Longshore Sediment Transport

Waves, currents, and longshore sand transport are calculated locally as a function of position in the nearshore region using process based numerical models. The resultant longshore sand transport is then integrated across the nearshore to provide predictions of the total longshore transport of sand due to waves and longshore currents. Model results are in close agreement with the Il–Pl correlation described by Komar and Inman (1970) and the CERC (1984) formula. Model results also indicate that the proportionality constant in the Il–Pl formula depends weakly upon the sediment size, the shape of the beach profile, and the particular local sediment flux formula that is employed. Model results indicate that the various effects and influences of sediment size tend to cancel out, resulting in little overall dependence on sediment size.