Sand Barrier Research Articles

Prevention and management of wind-blown sand damage along Qinghai-Tibet Railway in Cuonahu Lake area

This paper analyzes the characteristics of climate, geology and geomorphology, vegetation, and sand dune distribution in the Cuonahu Lake area beside the Qinghai-Tibet Railway. The types and causes of railway blown-sand hazards are discussed, and the effectiveness of various sand-controlling measures is assessed. From the perspective of integrated management, a sand-controlling system that combines several engineering measures, including nylon net sand barriers, concrete sand barriers, movable-board sand barriers, sand interception ditches, gravel/rock cover, film sandbags, and permanent vegetation is most beneficial.

Using MOSAND to mitigate the desertification of Minqin Oasis, Gansu Province, China

In semi-arid and arid regions, civil engineers may be required to plan measures, such as sand fences, to control sand movement affecting developed areas or transportation corridors. In this paper, considering the desertification process for the Minqin Oasis in Gansu Province, China, the design of sand fences and overall sand control strategies to lessen the rate of desertification are discussed. A sand transport model called MOSAND was developed to predict the sand transport rate for the Minqin Oasis. The model was based on a bed load transport (creep and saltation) equation and a logarithmic velocity profile for the wind. Using the measured wind data for the Minqin area, a monthly average sand transport rate was calculated that was used to determine an effective life span of a 3 m high sand fence. Sand fences in conjunction with straw checkerboard sand barriers are recommended to control sand drifts into the Minqin Oasis.

Study on Lowcost Revegetation Technical Measures on Ferrum Tailings Bank in Huludao, Northeast China

This study focused on the technical measures of revegetation on ferrum tailings bank in Huludao, China. Adopting field test method, a revegetation trial was conducted on the Yangjiazhangzi waste ferrum tailings bank. By composting the urban sludge + river mud + straw inside planting pit to ameliorate tailings matrix, planting perennial herb to establish closed type sand barrier to shelter bush-herbage growth, transplanting nutrition cup bush seedlings and sowing herbage seed on the composting pit to establish bush-herbage clump, these technical measures can solve the major constraints to plant growth and establish survival bush-herbage vegetation at lowcost. The results show that Pit layered composting is the cost-effective measure to improve ferrum tailings planting matrix; Planting perennial herb sand barrier t is a good measure to improve microhabitat; Planting bush-herbage clump is a good pattern to resist the extreme ferrum tailing environment; Hippophae rhamnoides Linn., Caragana Korshinskii Kom., Medicago sativa Linn.and Astragalus adsurgens Pall are good pioneer species for revegetation on the ferrum tailings bank. Experiment proved that the combination of these technical measures can reconstruct vegetation, this revegetation pattern is worthy of reference for similar mine ecological restoration.

Influence of Dry Soil on the Ability of Formosan Subterranean Termites,Coptotermes formosanus, to Locate Food Sources

The effect of barriers of dry soil on the ability of Formosan subterranean termites, Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae), to construct tunnels and find food was evaluated. Termite movement and wood consumption in a three—chambered apparatus were compared between treatments with dry soil in the center container and treatments where the soil in the center container was moist. When a wood block was located in the release container, termites fed significantly more on that block, regardless of treatment or soil type. In the treatment with dry clay, none of the termites tunneled through the dry clay barrier to reach the distal container. When termites had to tunnel through a barrier of dry sand, topsoil, or clay to reach the sole wood block, there was no effect on wood consumption for the sand treatment, but there was significantly less feeding on wood in the treatments with dry topsoil or clay. When foraging arenas had a section of dry sand in the center, the dry sand significantly reduced tunneling in the distal section after 3 days, but not after 10 days. There was a highly significant effect on the ability of termites to colonize food located in dry sand. Only one feeding station located in dry sand was colonized by termites, compared with 11 feeding stations located in moist sand.

EFFECT OF SANDY SEDIMENTS PRODUCED BY THE MECHANICAL CONTROL OF SAND DEPOSITION ON THE THERMAL REGIME OF UNDERLYING PERMAFROST ALONG THE QINGHAI‐TIBET RAILWAY

ABSTRACTTo date, the mechanical control of drifting sand is the main method used for the protection of the Qinghai‐Tibet Railway from damage. The thermal effect of sandy sediments which are held in place on the underlying permafrost is a key area of interest and the focus of this paper. A ground temperature investigation of the permafrost along the railway route was undertaken and results were related to the different mechanical control measures used to control moving sand which had resulted in varying sandy sediment thicknesses. The studies were conducted in the Hongliang River area of the Qinghai‐Tibet Plateau from June 2010 to September 2010 using thermistor sensors. The results showed that the permafrost ground temperature and its daily variation, as well as the thawing depth of the active layer, decreased after the setting‐up of sand movement controls which had resulted in the accumulation of thick sandy sediments within the outside fringe of sand‐control engineering, or a covering of thin sandy sediments within the inside trackside (fringe) of sand‐control engineering. Below the thick sandy sediment cover accumulated by sand‐blocking fences, the average maximum temperature decreased. Average temperature decreased and the average depth of seasonal thawing (average thinning) were 3·38°C, 0·54°C and 0·48 m, respectively. Below the thin sand sediment cover accumulated by the checkerboard sand barriers, the values for the same parameters were 1·02°C, 0·21°C and 0·5 m, respectively. This study found that the mechanical control of sand does not only protect the railway from obstruction, but also facilitates permafrost stability, which in turn can help promote safety in railway operations. Copyright © 2011 John Wiley & Sons, Ltd.

Artificial modifications of the coast in response to the Deepwater Horizon oil spill: quick solutions or long‐term liabilities?

The Deepwater Horizon oil spill threatened many coastal ecosystems in the Gulf of Mexico during the spring and summer of 2010. Mitigation strategies included the construction of barrier sand berms, the restriction or blocking of inlets, and the diversion of freshwater from rivers to the coastal marshes and into the ocean, in order to flush away the oil, on the premise that these measures could reduce the quantity of oil reaching sensitive coastal environments such as wetlands or estuaries. These projects result in changes to the ecosystems that they were intended to protect. Long‐term effects include alterations of the hydrological and ecological characteristics of estuaries, changes in sediment transport along the coastal barrier islands, the loss of sand resources, and adverse impacts to benthic and pelagic organisms. Although there are no easy solutions for minimizing the impacts of the Deepwater Horizon disaster on coastal ecosystems, we recommend that federal, state, and local agencies return to the strategic use of long‐term restoration plans for this region.

Ostracod evidence for the Neolithic environment of Rio Sizandro, Portugal

Boreholes made to investigate the Neolithic occupation of the Rio Sizandro, western Portugal, were analysed for ostracods and associated micro-biota. Two boreholes in the middle reaches of the valley, near the village of Benfica, provide evidence of brackish estuarine conditions during the interval 6,500–6,200 cal BP of the late Neolithic followed by a decline in palaeosalinity towards freshwater conditions. Following the high-stand of eustatic sea level at about 6,500 cal BP, and possible formation of a coastal sand barrier, the influence of the rivers in the hinterland became predominant with dramatically increased erosion and sediment supply to the river valley, with consequent westward movement of marine conditions to the modern coastline.

Heavy Mineral Sands in the Eucla Basin, Southern Australia: Deposition and Province-Scale Prospectivity

The marine Eucla basin in southern Australia is emerging as a major new heavy minerals province in Australia. Beach placers are associated with a series of partially buried Cenozoic coastal barrier sands formed along an arcuate 2,000-km-long basin margin, the trace of which is up to 320 km inland of the present coastline. The presence of high-grade deposits with dominant zircon over ilmenite and lesser amounts of rutile and leucoxene was established with the discovery of the Jacinth and Ambrosia heavy mineral deposits in late 2004. An additional 10 heavy mineral prospects were subsequently identified and are at various stages of evaluation. The Eucla basin and its adjacent paleovalley system have a large areal extent that contains a complicated succession of marine and nonmarine strata spanning a wide range of depositional environments. Four distinct constructional phases for the development of shorelines can be recognized and correlated with major third-order sea-level events, established by others from the marine depositional record as occurring during the middle Eocene (~42.5 Ma), late middle Eocene (39–36 Ma), late Eocene (36–34 Ma), and Miocene-Pliocene (15–2.6 Ma). Prevailing westerly winds built extensive dune systems by longshore drift. Sediment movement was from west to east. Detrital zircon rocks from the Ooldea and Barton barriers show a distribution of zircon age that is consistent with the Proterozoic Musgrave province to the north of the basin as the dominant primary source area of the heavy minerals, with a contribution from the Albany Fraser orogen to the west. The likelihood is that these heavy minerals have been recycled via sedimentary basins that flank the Musgrave province and include the Neoproterozoic to Cambrian Officer basin and Permian to Mesozoic deposits of the Bight basin. Our current depositional model is summarized as follows: (1) initial rapid transgression and deposition of a shallow marine sand sheet subsequently overlain by shallow marine limestone during middle Eocene; (2) a major Eocene transgression and deposition of a shelf, barrier, and lagoonal shoreface marine complex during the late middle Eocene; ( 3) further transgression and highstand deposition during the late Eocene; (4) renewed transgression of barrier, lagoonal, and possibly flooding deltaic sand blanket in the southeastern coastal plain with neotectonic uplift tilting in the western Eucla margin during Mio-Pliocene time. Each stage of reworking increased the potential for heavy mineral concentration in placer deposits.

Model for the genesis of coastal dune fields with vegetation

Vegetation greatly affects the formation and dynamics of dune fields in coastal areas. In the present work, we use dune modeling in order to investigate the genesis and early development stages of coastal dune fields in the presence of vegetation. The model, which consists of a set of coupled equations for the turbulent wind field over the landscape, the saltation flux and the growth of vegetation cover on the surface, is applied to calculate the evolution of a sand patch placed upwind of a vegetated terrain and submitted to unidirectional wind and constant sand influx. Different dune morphologies are obtained, depending on the characteristic rate of vegetation growth relative to wind strength: barchans, transverse dunes with trailing ridges, parabolic dunes and vegetated, alongshore sand barriers or foredunes. The existence of a vegetation-free backshore is found to be important for the nucleation timescale of coastal dune generations. The role of the sand influx and of the maximum vegetation cover density for the dune shape is also discussed.

Dynamic morphology of small south-eastern Mediterranean river mouths: a conceptual model

River mouths along the Israeli Mediterranean coast are characterized by a dynamic morphology as their channels migrate hundreds of meters along the coast. This study examines the dynamic morphology of seven such river mouths. It offers a conceptual model aimed at generalizing and describing their spatial and temporal morphological patterns, and the environmental factors influencing them. The study methodology comprised a detailed monitoring and mapping by GIS techniques, with quantitative data derived from historic aerial photographs, river discharge records, wave measurements, and a digital elevation model. These data were incorporated into a homogenous database and subsequently applied in the investigation of the morphological patterns of these mouths, and the analysis of their influencing factors. River mouths in this study occur in two distinctive topographic settings. In one setting (here termed barrier topography) the river mouth is deflected alongshore by a sandy barrier. In the second setting (termed funnel topography) the river mouth is confined to a funnel-shaped topographic depression perpendicular to the coast. The behavior of river mouths in these two settings is quite distinctive. Barrier mouths usually migrate over larger distances, as they tend to deflect along a sand barrier and establish semi-permanent channels along the dune toe. This enables the wide range migration of semi-permanent channels over decades. Funnel topography mouths deflect over shorter distances and they rapidly migrate within the funnel boundaries. This study concludes that the topographic setting of the beach, a constant element in the temporal scale of this study, is the primary influencing factor on the morphology of the mouths studied. The influence of other factors on the morphology of these mouths differs in space and time and depends on the topographic settings.

Impact of rubble mound groyne structural interventions in restoration of Koggala lagoon, Sri Lanka; numerical modelling approach

Physical processes of the lagoon are influenced by structural interventions. Understanding the complex reality of physical processes sometimes difficult with field observations thus a model provides a simplified abstract view. Two dimensional hydrodynamic model is used to describe, restoration efforts to Koggala lagoon, a combined freshwater and estuarine complex of rich ecosystem on the southern coast of Sri Lanka. The lagoon mouth was naturally closed by a sand bar which controlled the seawater intrusion. Due to large-scale sand removal at lagoon mouth, formation of the sandbar shifted towards the lagoon. After the removal of natural sand barrier, rubble mound groyne structures were built to avoid sand deposition in the lagoon and to protect the highway bridge from the sea wave attack. Construction of the groyne resulted in the lagoon mouth being permanently open which in turn led to many environmental problems with saline intrusion. The aim of this study is to evaluate the current situation of the lagoon and propose alternative structural interventions for minimization of seawater intrusion and subsequently improve lagoon ecosystem. Hydrological parameters were investigated and mathematical models for hydrodynamic behavior of the lagoon were applied in order to describe the lagoon physical processes and flow characteristics. Existing rubble mound structures were redesigned in order to minimize the seawater intrusion. Numerical simulations were carried out for two different mouth widths (40 m and 20 m) with appropriate structural interventions. Existing salting factor for the lagoon is 0.68 and numerical simulation results showed salting factor for 40 m and 20 m openings are 0.61 and 0.54 respectively. This shows the mouth width can be reduced up to 20 m in order to obtain a slating factor close to 0.5, which indicates the predominant influence of fresh water which in turn leads lagoon to a fresh water ecosystem.

Thickness and grain-size distribution of the 2004 Indian Ocean tsunami deposits in Periya Kalapuwa Lagoon, eastern Sri Lanka

In this paper we describe the sedimentary characteristics of the 2004 Indian Ocean tsunami deposits in and around Periya Kalapuwa Lagoon, Sri Lanka. Periya Kalapuwa is a coastal lagoon of about 13 km 2 area and has an average depth of about 1 m. It is separated from the Indian Ocean by coastal barrier sand dunes of up to 9-m elevation through which two inlet channels open the lagoon to the ocean. This region was hit by three waves during the 2004 Indian Ocean tsunami. The second wave was largest (4–6 m) and entered the lagoon not only via the two inlet channels, but also by flowing over the sand dunes. Erosive scars were found on the sand dunes adjacent to the two inlets. Twenty-seven core samples, along with trenching and hand-auger data, show that the tsunami deposits are 9 cm thick on average (up to 35 cm in the lagoon and up to 66 cm on the shore) and are composed mainly of medium sand (mean grain size 1.06 φ) with low mud content (0.61 wt.%), which is similar to the composition of sand from near the erosive scars in the sand dunes (mean grain size 0.94 φ), but different from the lagoon deposits (mean grain size 1.68 φ; mud content 4.7 wt.%). The distribution of the tsunami deposits was limited to within about 1 km from each inlet. The tsunami deposits become thinner and finer grained with increasing distance from the inlets. Most of the tsunami deposits are massive, but some show sedimentary structures: single or multiple-graded bedding structures, parallel laminations defined by layers of heavy minerals, and muddy laminations. Our observations and analyses suggest that the tsunami deposits were formed mainly from sand eroded from sand dunes near the two inlets. We estimated the total volume of tsunami sediments to be 83 000 m 3. By assuming that the sediments of the tsunami deposits were supplied only by erosion of sand dunes from near the two inlets, this is equivalent to erosion of 83 m 3 of sand per meter of sand dune traversed by the tsunami wave.

Influence of Horqin Sandy Land Plant Sand Barrier on Soil Moisture

In this paper, the shrub windbreak and sand-fixing sand barrier of Bairin Youqi in Chifeng in the east of Horqin Sandy Land is the research object, three different types of plant barriers including hedysarum laeve grid sand barrier, Salix gordejevii and hedysarum laeve grid sand barrier and caragana and hedysarum laeve patch sand barrier are respectively selected, and the shifting sandy land is selected as a contrast at the same time to study its influence on the soil moisture of sandy land in the method of field locating observation method from early May to late September of 2005. Except for the contrasted sandy land, the monthly average soil moisture in each layer of plant sand barrier presents a fluctuation trend. The monthly change trend of soil moisture in the 10~20cm soil layer of hedysarum laeve grid sand barrier is the same as that of caragana and hedysarum laeve patch sand barrier. The soil moisture in 20~40cm soil layer of the three plant barriers in every month shows a big change, with the fluctuation range larger than the contrasted sandy land. The 20~60 cm soil layer is the area where the roots of sand barrier plant are centralized, therefore, the soil moisture in the root intensive area is reduced. The monthly change trend of soil moisture in 60~80cm soil layer of hedysarum laeve grid sand barrier, caragana and hedysarum laeve patch sand barrier is the same as that of the contrasted sandy land. The monthly change trend of soil moisture in the 80~100 soil layers is basically same. The minimum value of monthly average soil moisture of all kinds of plant sand barriers appears when the contrasted sandy land is 1.40%, and the maximum value appears when caragana and hedysarum laeve patch sand barrier is 4.79%, 3.4 times higher than the contrasted sandy land. The annual dynamic condition of soil moisture can be divided into: consumption period from April to June, supply period from July to August, stable period in September, which shows that the plant sand barrier is favorable for increasing the soil moisture.

Late Holocene morphodynamics in the littoral zone of the Iwik Peninsula area (Banc d'Arguin — Mauritania)

In the littoral zone of the Banc d'Arguin both littoral sedimentary units and man-made deposits (shell-middens) abound. They were formed during the Late Holocene after the final onset of the post-glacial transgression. Here, a geo-archaeological approach is used to study them. The geomorphological and sedimentological characteristics of the coastal features define two distinct coastal sedimentary units in the Iwik–Aouatil zone between an ancient shoreline which formed on the Tafaritian substratum ca 6.7–5.7 cal. ka BP and the present one: (i) very extensive sand flats and (ii) linear relief features, both covered by a thin veneer of anthropogenic Anadara senilis shell-middens. They developed under a stable sea-level regime. The sand flats expanded at variable rates throughout the period. The linear relief features represent beach barriers and coastal dunes which can be dated archaeologically thanks to the superimposed shell-middens, supplemented by 14C dating. Two series of linear sedimentary units are identified. First, a complex north–south system of dunes and hook-ended sand barriers developed from 4.8 to 4.1 cal. ka BP and, secondly, two regular and linear beach barriers developed between 3.7 and 3.3 cal. ka BP. Their morphological characteristics suggest that they were generated through littoral drift processes. Directional changes observed between the first and the second groups demonstrate that the wave refraction pattern was dramatically modified after the closure of the strait between the former Iwik Island and the land. A comparison with the nearby Jerf el Oustani coastal area in the Late Holocene shows that both sites shared similarities in depositional patterns but also differences in the chronology of the sedimentary units. Processes involved in the development of the linear units are indicative of the enhancement of both sand influx and longshore drift due to climatic change.

Simulative research on the mechanism of rocky checkerboard sand barriers along Qinghai-Tibet Railway in wind tunnel

Based on the simulative research on the characteristics of wind speed,sand-fixed rate of rocky checkerboard sand barriers along Qinghai-Tibet Railway in wind tunnel,several conclusions were drawn as follows.Horizontal wind speed rapidly decreases when it flows to the fringe of rocky checkerboard sand barriers.Weaken efficiency of rocky checkerboard sand barrier on airflow is distinct,with about 50%.Wind speed changes little over rocky checkerboard sand barrier.In contrast,although the wind speed decreases from rocky checkerboard sand barrier to its lower reach,its magnitude is very small.Wind speed varies logarithmically with height.Variation of wind speed is similar among rocky checkerboard sand barriers as height increases.Roughness is about 5.2 cm and drag velocity is 2.4 cm/s for rocky checkerboard sand barrier.Sand-fixing mass increased with inlet wind speed.For a given wind speed,sand-fixing mass increased exponentially with distance to sand sources.

Significance of shallow seismic reflection (SSR) and ground penetrating radar (GPR) profiling on the Modern Coast line History of the Bedre area, Eğirdir Lake, Isparta, Turkey

Lake level changes and settlement places constitute the main problems in controlling the coastal environment along the Eğirdir Lake, SW Turkey. The Quaternary geology in the Bedre Coast was studied based on shallow seismic reflection (SSR) survey, ground penetrating radar (GPR) profiles, and the data derived from boreholes and investigations in the field. Thus, six seismic and five radar facies were determined respectively. The geological units from the basement rock to the Holocene deposits were imaged by the SSR technique. GPR technique is used for the shallower part, ranging from the ancient to the Modern lacustrin sediments. The Quaternary lake level changes, borehole, seismic and radar data indicate that a pond with a connected to the Lake around the Bedre area existed in the last century. Sand barriers, climate, topographical elevation and erosions of the basement rocks control the sedimentation of the back barrier of the coastal line. Marsh muddies and ancient beach sands are the main sediments of the pond area. From the profiles, ancient buried sand barriers were also seen in the lake side. In our view, as the previous lake level dropped from the highstand, the ancient sand barrier was formed which divided the lake and the pond and isolated a small inland lake which lies 4 m below the level of the coastal barrier. For agricultural purposes, artificial man-made constructions were done on the barrier and channels. Thus, dry agricultural land appeared in the last 50 years on the pond side.

Estuarine infill and formation of Deltaic Plains, Shoalhaven River.

The Shoalhaven River is an example of a mature, infilled estuary on a wave-dominated coast. The river presently flows between prominent levees towards the coast, periodically exiting at Shoalhaven Heads, but having much of its flow artificially diverted to exit at Crookhaven Heads. The alluvial plains east of Nowra are the result of estuarine infilling behind a sand barrier, represented by Comerong Island, a southern continuation of the Seven Mile Beach beach-ridge plain. Drilli has revealed marine sands adjacent to this eastern sand barrier, and extensive muds deposited in a barrier estuary beneath most of the plains. The molluscan composition of these sediments indicates deposition in brackish water conditions, with Notospisula trigonella especially widespread. Estuarine infill occurred progressively around deltaic channels, isolating smaller basins which accreted subsequently. Most of the estuarine sedimentation occurred 5500 – 3500 radiocarbon years BP. Brackish-water muds grade upwards into fresh-water alluvial muds deposited from fluvial overbank flows, and the transition is indicated from analysis of the diatoms within sediments in an augerhole near Jaspers Brush. Levees overlie these estuarine sediments in places and indicate natural changes in river channel location. There is an extensive potential acid sulphate soil hazard throughout the plains as a result of the occurrence of pyrite-rich estuarine muds up to an elevation close to mean sea level beneath most of the plains.

Coastal lagoons in New South Wales

With the exception of Tasmania, Australia as a whole is deficient in surface waters. There are only a few sizable inland lakes in New South Wales and most of these, certainly the ones around the major population centres along the coast, are water supply reservoirs which are protected and not accessible to the public. There are however, numerous brackish “lakes” along the New South Wales coast many of which are important holiday centres for the population of Sydney, Newcastle and Wollongong. These so called “lakes” are in fact coas tal lagoons. A coastal lagoon is defined by Barnes (1980) as a body of brackish or salt water separated from the adjacent sea by a low lying sand or shingle barrier and these coastal “lakes” certainly fit well into this definition. The literature on the Australian coastal lagoons is sparse and partly inaccessible. The Lake Macquarie study by the CSIRO was by far the most comprehensive and resulted in the publication in 1959 of a series of 12 papers on various aspects of the lagoon’s ecology (Baas Becking, Thomson and Wood, 1959; Spencer, 1959; Baas Becking, 1959; Wood, 1959a, b; Davies, 1959; MacIntyre, 1959; Thomson, 1959a,b,c,d,e). Typically lagoons are shallow with sandy bottoms and are usually fed by one or more short streams. Although the normal freshwater input is not great, floods do occur at irregular intervals due to the relatively large catchment areas surrounding the lagoons. The greatly increased hydraulic gradient generated by the extra quantity of water during floods frequently is sufficient to sweep away the sand barriers, allowing free interchange with the sea. Otherwise the sand barriers, which are constantly being reformed, are quite effective barriers and a lagoon may be isolated from the sea for many years at a time. Under normal conditions, there is very little exchange between the sea and the lagoon so that salinity and water level of the lagoon are functions of rainfall and evaporative loss of water. The extent of salinity fluctuation can be very large. In Tuggerah lakes, during the period 1979-1980 the measured salinity ranged from 20ppt to 42ppt (hypersaline). But salinity as low as 5ppt had been recorded at the end of previous floods (Higginson, 1865). The effect of rainfall on salinity changes can be more dramatic in a smaller lagoon. In Narrabeen Lagoon for example, each major fall of rain can cause steep vertical and longitudinal salinity gradients to be developed due to the rapid input of freshwater from the feeder creeks.

Timing of Holocene sand accumulation along the coast of central and SE Vietnam

In Vietnam, the coastal sand barriers and dunes located in front of the steep slopes of the high rising Truong Son Mountains are sensitive to climate and environment change and give evidence for Holocene sea-level rise. The outer barrier sands were deposited shortly before or contemporaneous with the local sea-level high stand along the Van Phong Bay postdating the last glacial maximum (LGM). Optically stimulated luminescence (OSL) dating yielded deposition ages ranging from 8.3 ± 0.6 to 6.2 ± 0.3 ka for the stratigraphically oldest exposed barrier sands. Further periods of sand accumulation took place between 2.7 and 2.5 ka and between 0.7 and 0.5 ka. The youngest period of sand mobilisation was dated to 0.2 ± 0.01 ka and is most likely related to reworked sand from mining activities. At the Suoi Tien section in southern central Vietnam, the deposition of the inner barrier sands very likely correlate with an earlier sea-level high stand prior to the last glaciation. OSL age estimates range from 276 ± 17 to 139 ± 15 ka. OSL dating significantly improves our knowledge about the sedimentary dynamics along the coast of Vietnam during the Holocene.

Geographical Influences on Settlement‐Location Choices by Initial Colonizers: a Case Study of the Fiji Islands

AbstractFrom 3200 to 2850 cal BP (1250–900 BCE), the Lapita people of the Bismarck Archipelago (Papua New Guinea) undertook voyages eastward that led to their colonization of the eastern outer Solomon Islands, Vanuatu, New Caledonia, Fiji, Tonga and Samoa. The earliest (Lapita) settlements in Fiji were along the Rove Peninsula in southwest Viti Levu Island. At the time of colonization, sea level was 1.5 m higher than today. The Rove Peninsula was then a smaller island off the coast of larger Viti Levu, with a broad, fringing reef along its windward coasts, which was probably the main attraction for Lapita colonizers. As elsewhere during Lapita times in the western tropical Pacific Islands, settlement choice for the initial colonizers of the Fiji Islands was at one level driven by site access, at another by the presence of broad, fringing coral reefs suitable for marine foraging.The earliest settlement along the Rove Peninsula was at Bourewa, occupied first in 3050 cal BP (1100 BCE), where people lived in houses on stilt platforms built along the axis of a subtidal sand barrier; on one side was a broad coral reef, on the other a partly‐enclosed tidal inlet. There is no evidence that the Bourewa settlers practised horticulture or agriculture at this time, their subsistence being predominantly marine foraging. After some 300 years of following this subsistence strategy, the inhabitants of Bourewa responded to sea‐level fall and the arrival of cultivars (of taro and yam) by including horticulture. As sea level fell further, a total of 550 mm during the Lapita era, the tidal inlet dried up and marine‐food resources diminished to a point where the natural environment of the Rove Peninsula could no longer sustain its Lapita inhabitants. All Lapita sites in the area were abandoned about 2500 cal BP (550 BCE), at the same time as the Lapita culture, marked by the end of dentate‐pottery manufacture, came to an end in Fiji.