Sand Barrier Research Articles

Microstructure and biodegradation of long-established Salix psammophila sand barriers on sand dunes

Salix psammophila has been extensively used as a sand barrier material for various desertification control applications over the years. Thus, elucidating the long-term degradation processes of this sand barrier in desert environments is of great importance. In this study, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and chemometric methods were used to evaluate and compare the structure and performance of the S. psammophila sand barrier during degradation. The results clearly showed that the structure and performance of the S. psammophila sand barrier varied in the different vertical sections of the barrier. With the increase in the setting period of the sand barriers, the atmospheric exposure section (AES) and stable sand buried section (SSBS) exhibited deterioration and decay, respectively. The mass loss rate was SSBS>AES>ASDI, which also exhibited different degrees of decrease in mechanical properties such as in the modulus of rupture, ultimately resulting in lodging, damage, and the loss of the function of the S. psammophila sand barrier in preventing wind–sand movement and fixing quicksand. Microstructural changes showed that after eight years of setting, the vessel and parenchyma cells were severely damaged and the corresponding chemical components, such as cellulose, hemicellulose, and lignin, were degraded to a certain extent. The decrease in the crystallinity index values based on the XRD analysis confirmed the deterioration and obvious changes in the crystallinity, which affected the strength of the S. psammophila sand barrier. The FT-IR analysis indicated that several characteristic peaks of cellulose, hemicellulose, and lignin in the AES and SSBS sections disappeared or were weakened compared with the ASDI section. Comprehensive analysis showed that the primary reason for the serious deterioration in AES was the aging caused by exposure to continuous UV radiation in the atmospheric environment, while the serious decay of SSBS was mainly caused by microbial and fungal activity in the sandy environment, ultimately leading to the degradation of the S. psammophila sand barrier. Our findings suggest that it is necessary to further strengthen the anti-aging and anti-corrosion measures in the resource utilization process of the S. psammophila sand barrier in the future. • Long-established Salix psammophila sand barriers on sand dunes, the AES and SSBS exhibited deterioration and decay phenomena, respectively. • The main explanation for the severe deterioration of the AES was the aging caused by exposure to continuous strong UV exposure in the atmospheric environment. • The serious decay of the SSBS was primarily caused by the microbial and fungal activities in the sandy environment. • It is necessary to further strengthen anti-aging and anti-corrosion measures in the resource utilization process of S. psammophila sand barriers.

Structural Design and Experimental Analysis on Key Structure of Sand Barrier Burying Machine

Structural Design and Experimental Analysis on Key Structure of Sand Barrier Burying Machine

Dissemination of Isaria fumosorosea Spores by Steinernema feltiae and Heterorhabditis bacteriophora.

Entomopathogenic nematodes and fungi are globally distributed soil organisms that are frequently used as bioagents in biological control and integrated pest management. Many studies have demonstrated that the combination of biocontrol agents can increase their efficacy against target hosts. In our study, we focused on another potential benefit of the synergy of two species of nematodes, Steinernema feltiae and Heterorhabditis bacteriophora, and the fungus Isaria fumosorosea. According to our hypothesis, these nematodes may be able to disseminate this fungus into the environment. To test this hypothesis, we studied fungal dispersal by the nematodes in different arenas, including potato dextrose agar (PDA) plates, sand heaps, sand barriers, and glass tubes filled with soil. The results of our study showed, for the first time, that the spreading of both conidia and blastospores of I. fumosorosea is significantly enhanced by the presence of entomopathogenic nematodes, but the efficacy of dissemination is negatively influenced by the heterogeneity of the testing arena. We also found that H. bacteriophora spread fungi more effectively than S. feltiae. This phenomenon could be explained by the differences in the presence and persistence of second-stage cuticles or by different foraging behavior. Finally, we observed that blastospores are disseminated more effectively than conidia, which might be due to the different adherence of these spores (conidia are hydrophobic, while blastospores are hydrophilic). The obtained results showed that entomopathogenic nematodes (EPNs) can enhance the efficiency of fungal dispersal.

Sand barrier morphological evolution based on time series remote sensing images: a case study of Anhaiao, Pingtan

The morphological evolution of the sand barrier in the Anhaiao coastal zone of Pingtan from 1996 to 2018 was studied. Tidal correction was used to refine the location of the coastline. A standard deviation ellipse method was applied to further analyze the movement of the barrier head with the axis and rotation angle. A natural neighbor interpolation (NNI) method was carried out to calculate the terrain of the intertidal area, and the erosion and deposition characteristics were illustrated based on the terrain. The results showed that the northern part of the sand barrier facing the lagoon area was deposited over the whole studied period, while erosion has always occurred in the southern part of the sand barrier facing the open sea. The erosion and deposition were slightly different on both sides of the barrier head due to hydrodynamic turbulence. The middle sand barrier moved 102.60 m away from its original location in 1996, and the end of the barrier moved 65.45 m. The head of the sand barrier continued moving 379 m to the northwest. Consequently, the preliminary morphological evolution of the sand barrier corresponding to the distance and direction of movement was detected.

Stratigraphic analysis and geomorphological reconstruction of Grumari coastal plain, Rio de Janeiro, Brazil

Between Marambaia spit and Jacarepagua barrier island system, two major coastal plains in Rio de Janeiro State, Grumari's type of evolution remains unknown, since it was anthropologically modified from the 1960s, where all superficial sedimentary deposits were devastated, intensively changing its natural landscape, and hiding how it has been formed through the Holocene. Aiming to fill these blanks in Grumari's geological history and complementing Rio de Janeiro's coastal studies, the Ground Penetrating Radar method (GPR) was applied to enable the 2D subsurface imaging. The reflection patterns recognition and their correlation with geological features allow a radarfacies interpretation, in a radar stratigraphy context. For coastal plain studies, geological interpretation takes into consideration the sedimentary processes involved in their formation, driven by the balance between sedimentary supply and sea level variations. In the adjacent areas' researches, geological and geophysical data show, from bottom to top, continental deposits formed during the last regional marine regression, in the Late Pleistocene, covered by sand deposits and marine fossils deposited during the last marine trangression, already in the Holocene, followed by sand barriers and lagoons formed and exposed during the last sea falling until the present shoreline. For Grumari coastal plain, this work presents geophysical data interpretation of five GPR sections, collected in about 15 m thick sedimentary deposit, with a sequence of three main units, separated by regional stratigraphic surfaces: a transgressive unit followed by a regressive one, being this one covered by the most recent deposits composing a third unit. The Unit 1 is related to the Holocene sea level rise, from about 7,000 yr BP, and is characterized by truncation relationships between seawards downlapping reflectors and flat-parallel ones, showing a constant change in deposition direction, as the accommodation space was still small at the beginning of this process. At the Unit 1 top, as the accommodation space rate increased, the deposition became more regular, seen by a flat-parallel reflection pattern. While mean sea level reached its maximum range, from about 5,500 yr BP, its rising rate decreased, while the sedimentary supply rate raised due to the continental shelf and the mountain system erosion. This variation in radarfacies sequence is registered by a regional surface, marking the regressive Unit 2 beginning. The change in the rates led to the continental progradation through sand ridges formation, represented by seawards sigmoidal radarfacies. The mean sea level continued to drop gradually to the current level, exposing the sand ridges to erosion, and newer aeolian, fluvial, lagoonal and storm deposits could be formed above them, composing the Unit 3, limited at the bottom by a second regional high amplitude surface. Storm deposits from 4,450 ± 180 yr BP and 3,780 ± 200 yr BP, as washover fans, have been already identified in Jacaperagua plain, therefore, there were episodical events in the region, in the last 4,450 years, seen also in Grumari's data. This primary radar stratigraphic analysis and geomorphological reconstruction of Grumari most recent deposits show that the most recent evolution occurred through the prograding sand ridges formation, mostly attached to each other, with some inter-ridge areas development, and then is likely to be considered as a strandplain.

Damage by wind-blown sand and its control measures along the Taklimakan Desert Highway in China

Desertification is one of the most serious environmental problems in the world, especially in the arid desert regions. Combating desertification, therefore, is an urgent task on a regional or even global scale. The Taklimakan Desert in China is the second largest mobile desert in the world and has been called the “Dead Sea” due to few organisms can exist in such a harsh environment. The Taklimakan Desert Highway, the longest desert highway (a total length of 446 km) across the mobile desert in the world, was built in the 1990s within the Taklimakan Desert. It has an important strategic significance regarding oil and gas resources exploration and plays a vital role in the socio-economic development of southern Xinjiang, China. However, wind-blow sand seriously damages the smoothness of the desert highway and, in this case, mechanical sand control system (including sand barrier fences and straw checkerboards) was used early in the life of the desert highway to protect the road. Unfortunately, more than 70% of the sand barrier fences and straw checkerboards have lost their functions, and the desert highway has often been buried and frequently blocked since 1999. To solve this problem, a long artificial shelterbelt with the length of 437 km was built along the desert highway since 2000. However, some potential problems still exist for the sustainable development of the desert highway, such as water shortage, strong sandstorms, extreme environmental characteristics and large maintenance costs. The study aims to provide an overview of the damages caused by wind-blown sand and the effects of sand control measures along the Taklimakan Desert Highway. Ultimately, we provide some suggestions for the biological sand control system to ensure the sustainable development of the Taklimakan Desert Highway, such as screening drought-resistant species to reduce the irrigation requirement and ensure the sound development of groundwater, screening halophytes to restore vegetation in the case of soil salinization, and planting cash crops, such as Cistanche, Wolfberry, Apocynum and other cash crops to decrease the high cost of maintenance on highways and shelterbelts.

Effect of desert photovoltaic on sand prevention and control—taking Gansu Gulang Zhenfa photovoltaic DC field as an example

In recent years, the photovoltaic industry in desert and Gobi has developed rapidly. In order to reveal the effect of photovoltaic industry on sand prevention and control, this study was performed by taking GuLang Zhenfa photovoltaic DC field on the southern edge of Tengger Desert as an example. Through continuous observation of air temperature, wind speed and air pressure inside and outside the photovoltaic field, combined with the investigation of vegetation inside and outside the photovoltaic field in desert and Gobi of the central and eastern part of Hexi Corridor, this study analyzed the ecological effect of photovoltaic industry on sand prevention and control from three aspects: the balance of surface heat by the transformation of solar radiation of desert photovoltaic, the function of wind barriers and sand barriers of the photovoltaic DC field, and the effect of the photovoltaic DC field on vegetation. The results showed that the photovoltaic DC field in desert and Gobi had very significant ecological functions for desert prevention and control, and the ecological functions were mainly as follows: 1) the photovoltaic DC field could effectively transform solar radiation, adjust the thermal balance of the desert, and weaken the power (i.e., the gale) for the occurrence and development of sandstorms and sand flow; 2) the photovoltaic panel had a strong function of wind barriers, and its function of wind-proof and sand-fixing were several times that of sand barriers; 3) the rain-collecting effect of photovoltaic panel could promote the growth of plants. The development of photovoltaic industry in desert and Gobi not only has remarkable economic benefits, but also has the ecological function of sand prevention and control. China has a vast area of desert and Gobi, and there are broad prospects for the development of desert and Gobi photovoltaic industry. The photovoltaic industry in desert and Gobi is expected to become the third new way of sand prevention and control after afforestation and desertification control and sand fixation by sand barriers.

Effect of groundwater chemistry and temperature on swelling and microstructural properties of sand–bentonite for barriers of radioactive waste repositories

Compacted bentonite–sand mixtures are commonly considered as the key materials for the construction of engineered barrier systems (EBSs) in deep geological repositories (DGRs) in Canada and other countries. These bentonite-based barriers can be simultaneously exposed to a wide range of chemical and thermal (nuclear waste heat decay) conditions of underground water. Thus, an understanding of the effects of groundwater chemistry and temperature and their interactions on the changes in the swelling properties as well as the microstructure of bentonite-based barriers is essential for assessing the durability and safety of an EBS in a DGR. This study experimentally investigates the impact of a Canadian deep underground water chemistry (C; total dissolved solids up to 300 g/L), temperature (T; 23 °C, 40 °C, and 80 °C), and the coupled effects of C and T on the swelling properties and microstructure of bentonite–sand barrier mixtures (30 to 70% by weight). The results show that the groundwater chemistry of southwestern Ontario (Canada) has a significant impact on the swelling characteristics of the examined bentonite–sand material. The swelling ability significantly decreases with respect to the groundwater chemistry. The mineralogical composition of the bentonite changes. Most of the Na-montmorillonite is mainly transformed to Ca-montmorillonite and traces of illite with a lower swelling capacity when the bentonite–sand barrier material is exposed mixed to saline water solutions. The temperature (alone) has a limited effect. However, the temperature–groundwater chemistry interactions significantly affect the swelling capacity of the studied bentonite–sand material. Future safety assessments and the final engineering design of engineered barriers for DGRs in Ontario should take into consideration the possibility of the long-term deterioration of bentonite–sand barriers from chemical attacks and/or thermochemical attacks induced by the high salinity of the groundwater and by simultaneous impact of the chemistry of the groundwater and the heat generated by the nuclear wastes, respectively.

Holocene evolution of the Ninety Mile Beach sand barrier, Victoria, Australia: The role of sea level, sediment supply and climate.

The Ninety-Mile Beach (NMB) barrier system in southeastern Australia is the largest active barrier island system in Australia. The response of a sandy barrier system to a warming climate is dependent on the boundary conditions of sediment supply and sea level. Deposition during the Holocene can therefore provide an indication of how these barriers may change in the future. In this study airborne LiDAR, ground penetrating radar and subsurface coring were combined with 46 optically-stimulated luminescence and 32 radiocarbon ages to provide a detailed understanding of sedimentation of NMB through the Holocene. The barrier complex formed in three distinct phases dating back to the earliest stabilisation of sea level after the Postglacial Marine Transgression. First, restriction of the flooded open-ocean embayment that had formed around a Last Interglacial beach-barrier sequence occurred with accretion of an island complex at around 8000 years BP, sourced from transgressive sands reworked from the shelf. In the second phase, at around 6000 years BP, a second barrier island formed seaward of the Last Interglacial barrier but disconnected from the earlier Holocene barrier islands by a large tidal inlet. Waning sediment supply from the shelf meant that aggradation of these islands slowed by 4000 years BP. The third and final phase occurred after 3000 years with the initiation of sediment supply at the southwestern end of the barrier. The island system which formed seaward of the Last Interglacial barrier then prograded by several hundred metres and elongated in a northeasterly direction by tens of kilometres infilling the tidal inlet and enclosing the earliest Holocene barrier landward of a newly created lake. Sediment supply appears to be the primary limiting factor in the development of NMB with indications of a change in wave climate and sea level have an influence on barrier evolution.

Multi-scale experiments for a coarse sand barrier against backward erosion piping

Backward erosion piping poses a severe threat for embankments founded on sandy deposits. The physical mechanism by which a pipe progresses upstream beneath the embankment is conceptually understood, and assessments indicate high failure probabilities in the Netherlands. Rising sea levels and economic growth increase the risk of flooding, and the need for remediation measures. Conventional measures have undesired side effects, in terms of costs, maintenance, space requirements and sustainability. The coarse sand barrier (CSB) is a novel nature-based solution lacking these side effects. The CSB is a trench filled with coarse sand that is placed below the downstream toe of the embankment, which prevents the pipe from progressing upstream. The effectiveness of the CSB is based on its higher resistance against erosion and its effect on groundwater flow. This paper presents experimental work that was conducted to test the feasibility of a CSB for application at a pilot site in the Netherlands. This involved experiments with seepage lengths of 0·34, 1·34 and 15 m, using different barrier materials and background sands. A conceptual model is presented for the physical mechanism of pipe formation in the presence of a barrier. As the resistance of the barrier can be characterised by a local scale-independent strength criterion, laboratory results are applicable for design practice.

A GIS-based assessment combined with local ecological knowledge to support the management of Juncus acutus L. spreading in the floodplain of a protected coastal lagoon

The floodplains of brackish coastal lagoons are subject to a highly dynamic hydrological regimen mainly due to their intermittent connection with the ocean. Coastal lagoons generally support fisheries, while livestock ranching and human settlements are found in the floodplain. Therefore, it is common practice to artificially open the sand barrier to avoid floods and manage fish stocks. Saltmarsh species are subject to grazing pressure and to changes in flooding and salinity regimens, affecting plants’ community structure. In the Laguna de Rocha Protected Landscape, a shallow brackish coastal lagoon located in Uruguay (South America), livestock ranchers complain about the spreading of the native cyperacea Juncus acutus L. The plant forms dense mats in the outermost zones of the floodplain, apparently displacing natural grasslands where the cattle graze. Also, stakeholders have encouraged the park authorities to artificially open the lagoon to obtain short-term benefits for fisheries and cattle raising. The study evaluated the increase in the surface area occupied by J. acutus and analyzed the possible causes of this increase as a basis for suggesting management actions. Historical and current aerial and satellite images, historical hydrological and climatic data and local ecological knowledge about the biology of the species and its spatial distribution over time were analyzed. The results indicate that J. acutus expanded in the floodplain of Laguna de Rocha, possibly starting ca. 2000, to cover less than 100 ha of the study area at low and high density. The results confirm most of the information obtained from the local stakeholders, whose local ecological knowledge was highly useful in understanding some local processes and providing information regarding periods for which data were not available. The expansion of J. acutus can be explained by a multiplicity of causes that acted synergistically to favor the species through a series of changes in the management of the sand barrier, livestock management and climate variability. However, a quantification of the economic effects of J. acutus on cattle feeding and fisheries is needed. Possible actions to control J. acutus expansion involve management of the grazing pressure using sheep, burning with fire, mechanical removal and avoiding artificial opening of the lagoon to allow larger and longer floods to occur and permit recovery of the previous, more natural hydrological regime. Our results suggest that it is important to be cautious before taking management actions to avoid costly solutions that are only short-term palliatives that could trigger other unforeseen environmental impacts.

Using sediment grain size characteristics to assess effectiveness of mechanical sand barriers in reducing erosion

Wind and sand control features are important tools for limiting desertification. Sand barriers are one of the oldest engineering measures used to reduce wind-sand hazards. Their efficacy and exact mechanism by which they work has remained a topic of scientific debate however. Sediment grain-size distributions can help constrain their utility and function. This research analyzed sediment grain size distributions in samples collected from areas around six different types of sand barriers installed along the southeastern margin of the Tengger Desert. Results were compared with sediment from a bare dune area (no barriers) used as a control. The barrier area samples contained high proportions of coarse sand and relatively low proportions of silty sand and very fine sand. Fine and medium sand were present but clay was not. The lower proportions of fine sand and higher proportions of coarse sand relative to bare dunes documented an effective reduction in aeolian transport by the barriers. Samples from the barrier areas also showed poorer sorting relative to bare dune areas. This appeared as lower kurtosis values and wider frequency distribution curves relative to those measured from bare dunes samples. The wider cumulative frequency curves for samples from the barrier areas likely reflects the higher proportion of coarse-grained material. The Straw/1.5 and PLA/1 barrier types hosted greater sediment accumulation than that observed for the other barrier types (Straw/1, PLA/1.5, Mixed/1 and Mixed/1.5). Sediment grain size distributions showed that the base and middle slope areas of the dune experienced deposition, while the top of the dunes experienced erosion. The Straw/1 barrier (straw installed as a 1 × 1 m grid) performed best in terms of installation costs and protective effects for the study area. This study demonstrates how sediment grain size distributions can be used as quantitative proxies for sand barrier performance in reducing desertification.

A 7300 year record of environmental changes in a coastal wetland (Moawhitu), New Zealand, and evidence for catastrophic overwash (tsunami?)

Three sedimentary sequences from a coastal wetland behind a sand barrier, on the west coast of d'Urville Island, New Zealand, were examined using a multi-proxy approach, including sedimentological, geochemical and microfossil (diatom) analyses, with the chronology established using radiocarbon and 210Pb dating. Data show that a brackish lagoon started developing 7300 year ago after formation of the sand barrier in Moawhitu. This was followed by periods of alternating wetland encroachment and open water, displaying spatial variations, until a peatland was established about 1300 cal. yr BP. The wetland was then partially drained in the early 1900s, leading to compaction of the peat near the surface. A coarse layer containing gravel, sand and shells, with a sharp lower contact, in the northern area of the wetland, is attributed to an overwash about 2500–3000 yr BP, most probably a tsunami generated by the rupture of a local or regional fault. The high-resolution continuous record obtained with XRF core scanning revealed a geochemical signature (Ca and S) for the overwash 600 m inland in the middle area of the wetland, while it was absent from the southern site 1.1 km from the shore. This suggests that, except at the northern end of Moawhitu, the sand dune acted as an effective barrier preventing any sediment from overtopping 2500–3000 yr BP, with only a geochemical evidence marking the extent of seawater inundation. No sedimentological or geochemical evidence could be found in the wetland for the 15th century tsunami that had destroyed almost an entire community in Moawhitu, as recounted in Māori oral tradition (pūrākau), although pebbles at the surface of the dune are likely to be linked to this event. Thus, the sand dune appears to have again acted as an effective barrier for the overwash in the 15th century. However, our study suggests that the area might have been impacted by more than one tsunami in the last 3000 years. It also shows that a high-resolution continuous XRF record can provide the evidence for short-term changes (catastrophic or not) that did not leave any clear sedimentological signature, thus providing a better insight of environmental changes in any depositional environment.

Analysis of development and depth of backward erosion pipes in the presence of a coarse sand barrier

Backward erosion piping (BEP) is a failure mechanism that can affect the safety of water-retaining structures. It can occur when a local anomaly on the downstream side of an embankment causes a concentration of seepage flow at that location. Shallow pipes may then form, progressing in the upstream direction and leading to a collapse of the water-retaining structure. A novel and economically appealing measure against BEP is the coarse sand barrier (CSB), which is now being developed in a multiscale experimental programme in the Netherlands. The method involves placing a trench filled with coarse sand below the blanket layer on the downstream side of the embankment. The CSB prevents the upstream progression of the pipe and significantly enhances resistance to BEP. This paper presents medium-scale laboratory tests involving a range of sands, barrier depths and relative densities. The piping process and the observations of pipe progression in the presence of a CSB are presented, followed by a conceptual model. The presence of a CSB changed the erosion pattern. It resulted in pipe formation perpendicular to the flow direction over the entire width of the barrier before the barrier was damaged. The findings also demonstrate the effect of material properties on pipe initiation, progression and pipe depth. Measurements of the pipe depth are presented and analysed, revealing the significance of pipe depth for understanding the piping process. This analysis shows considerable erosion in the downstream background sand and demonstrates that erosion profiles and measured pipe depths are significantly larger than in BEP tests without a CSB.

Alternated desorption-absorption accelerated aging of Salix psammophila sand barrier

Salix psammophila has been extensively used as a sand barrier material in many desertification control applications. Thus, understanding its degradation processes with long-term environmental moisture changes is essential. In this paper, via alternated desorption-absorption treatment of the S. psammophila sand barrier, damage of differing degrees occurred, and moisture variation was simulated. Through FTIR, X-ray diffraction, SEM, and other characterization methods, changes in macroscopic morphology and physical-mechanical properties of S. psammophila sand barrier were tracked, evaluated, and compared, and the causes were analyzed. The results showed that the alternated desorption-absorption accelerated aging treatment weakened the physical-mechanical properties of the S. psammophila sand barrier. The microscopic manifestation was the decrease in space between the tracheids, which caused the formation of cracks on the macroscopic level. Carbohydrates (cellulose, hemicellulose, and lignin) degraded, which reduced the crystallinity of cellulose, and cracks appeared on the surface of the S. psammophila sand barrier. As the aging degree increased, the number of cracks increased, and the cracks continued to extend to both ends. Therefore, the degradation of the S. psammophila sand barrier was mainly caused by shrinkage cracking in the alternated desorption-absorption aging process, which reduced the ability of the S. psammophila sand barrier to resist lodging damage.

Late Quaternary evolution model for a coastal embayment with low sediment input and bedrock control (southeast Brazil)

This study developed the first palaeoenvironmental evolutionary model for the coastal plain of the region of Vitoria (ES, Brazil). Most previous research in Brazil has focused on large estuarine and deltaic plain systems, whereas Vitoria is characterized by a narrow fluvial-marine plain within an embayed rocky coast, with limited sediment input. Fluvial, embayment, estuarine and beach palaeoenvironments have been interpreted in a previous study from 4 boreholes (each 20 m long) retrieved across the coastal plain. The chronological evolution of these palaeoenvironments is reconstructed based on taxonomic molluscan classification and dating (radiocarbon and OSL). The results show that all mollusk shells are marine, which corroborates the sedimentological interpretations. A wide estuarine bay with a free connection to the sea is inferred to have formed during the last interglacial maximum (MIS 5e). The low-energy environment inhibited formation of sandy Pleistocene barriers in the inner part of the plain. Results from this research evidence a MIS 3 transgression in the study area suggesting a sea level higher than generally shown in established sea-level curves. A shallow embayment with sub-environments is formed around 14C 50-38 ka BP. These sub-environments vary along the embayment, as shown by distinct facies and mollusk shells. The Pleistocene radiocarbon ages match with the OSL fluvial sand age (36 OSL ka) in the upper part of the plain, representing the subsequent regression, where there is no marine influence. During the Holocene transgression (8900 and 7100 cal BP) an estuarine bay connected to the sea was again formed. Around 7800 cal BP, a transgressive sandy barrier was formed at the entrance of the embayment and was subsequently drowned (7500 cal BP) due to sea-level rise. During the Holocene regression (last 5000 years), inner areas were filled and transformed into wetlands. Seaward, a regressive sand barrier developed, dated between 3200 and 3000 cal BP. The Pleistocene evolution presented for the Vitoria region partially agrees with the existing models for the Brazilian coast. The main difference is the limited contribution of quartz sands transported from nearshore under low-energy hydrodynamic conditions during the filling of the embayment.

Effects of an oasis protective system on aeolian sediment deposition: a case study from Gelintan oasis, southeastern edge of the Tengger Desert, China

Desert-oasis ecotones are boundary areas between oases and desert ecosystems. Large efforts to control sediment and stabilize these boundaries depend on understanding sedimentary processes, especially aeolian transport and deposition. Previous studies on aeolian sediment deposition have focused primarily on a single land surface type or a single engineering approach. Few studies have considered deposition in a multi-layer oasis protective system. A complete oasis protective system consists of an outer bare sand area, a sand barrier zone, a shrub and herbaceous plant zone, and a farmland shelter zone. This study used sedimentary analysis to quantify grain-size characteristics in samples from the four land surfaces under different types of weather conditions in the Gelintan oasis of the Tengger Desert, the fourth largest desert in China. The results showed that aeolian sediment deposition decreased from the outer bare sand area through the oasis protective system and into the interior. The four land surface types showed significant differences in deposition volume (P < 0.05). Deposited sediment showed gradual decrease in dominant grain-size from sand to silt, but sediment deposited during dust weather contained a larger coarse-grained fraction. From the outer desert to the inner oasis, transport mechanisms shifted from saltation (sand) to suspension (silt and smaller) in non-dust weather. During dust weather, deposition primarily occurs from near-surface aeolian sand transport with saltation. Sediment sorting decreased from exterior to interior zones of the protective system while skewness and kurtosis showed no significant change (P < 0.05). These results can help inform strategies for stabilizing and protecting desert-oasis ecotones in this region and other localities.

Monitoring of Morphological Changes in an Estuary based on Time-Series Analysis of Sediment Discharge Using a Hydrophone

Jun, K.W.; Kin, S.D.; Lee, H.J., and Choi, J.H., 2020. Monitoring of morphological changes in an estuary based on time-series analysis of sediment discharge using a hydrophone. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 516–521. Coconut Creek (Florida), ISSN 0749-0208.The purpose of this study is to predict the littoral transport rate and morphological changes of estuaries by measuring the discharge of sediments from rivers into the sea in a time series using a hydrophone. To identify the problem of longshore sediments, an understanding of waves and currents is necessary. However, the runoff characteristics of sediments in river estuary that serve as the main source of sediments should be grasped first. It is important to predict the discharge of sediments from rivers into the sea and understand the coastal processes involved in the formation of sandbars in the estuary and the transport of sediments to coastal waters. The selected study area was the Gagok River located in the East Coast of Korea, where periodic estuary occlusion occurs due to the behavior of rivers and waves. This study investigated the morphological changes in the estuary according to the changes in sediment discharge. The sediment discharge was measured using a hydrophone capable of measuring the continuous sediment transport from the acoustic information based on the movement of the sediments. Based on this method, the hydrophone was applied to the field, and measurements of major rainfall events were taken to investigate the influence of changes in sediment discharge on the morphological changes in the estuary. In addition, to verify the results, the morphological changes in the estuary were linked to the ground LiDAR data measured over several years. The results of the survey confirmed that the occlusion phenomenon of the Gagok River estuary occurred according to the seasonal changes. Except for the flood season, there was a small amount of runoff through the river. As a result, a sand barrier developed in the estuary due to the influence of the sediments transported by the waves from the open sea.

Stratigraphy, provenance and localisation of the titanomagnetite placer at Waikato North Head, South Auckland, New Zealand

The sequence of coastal and river sands of Pleistocene to Holocene age at the north head of the Waikato River is ~80-m thick; the sands are located in a fault-angle depression at the southern end of the Awhitu Peninsula, a 40-km-long coastal sand barrier. The sequence at Waikato North Head (WNH) consists of three main formations: Awhitu Sands, Hood Sands and Mitiwai Sands. The Waiuku Black Sand member of the Hood Sands and the Entrican Sand member of the Mitiwai Sands contain titanomagnetite-rich dune sands, which are currently mined by New Zealand Steel and constitute a giant placer deposit that has a total resource of ~90 Mt Fe. A tephra at the top of the Awhitu Sands is correlated with the ~1000 ka Waiuku (Potaka) tephra. The Mitiwai Sands overlie the 1.85 ka Taupo Pumice. Comparison of electron probe microanalyses (EPMA) of titanomagnetites in heavy mineral separates of surface and drill-hole samples indicated that the bulk of the titanomagnetite in the Waiuku Black sand and the Entrican Sand is derived from andesitic rocks of the Taranaki Volcanoes 220 km to the south. The Waiuku Black Sand may correlate with an influx of andesitic clasts and mafic minerals in the cover beds of the ~400 ka Ararata Terrace in south Taranaki. There is also a contribution of titanomagnetite and minor ilmenite from the ignimbrites of the Taupo Volcanic Zone (TVZ), particularly in the Lower Hood and Entrican sands. Automated mineralogy data collected on selected sand samples contain silicate and resistate minerals that indicate other potential sources in addition to the Taranaki andesites and TVZ ignimbrites. Minor olivine was likely derived from the late Pleistocene basalts of the South Auckland volcanic field, whereas almandine and epidote were likely sourced from metasedimentary rocks of the Murihiku and Waipapa terranes. The formation of the giant placer at WNH was a multistage process involving (1) a supply of titanomagnetite-bearing sand eroded from the late Pleistocene–Holocene andesites of the Taranaki volcanoes that was transported northwards along the coast by the prevailing longshore drift; (2) concentration of titanomagnetite by wave action on beach faces and collection in a coastal embayment on the northern side of a headland of basement rocks at Port Waikato; (3) further concentration by wind action into dune sands during interglacial low sea levels; and (4) preservation by coeval subsidence in a fault-angle depression on the down-thrown north side of the Waikato Fault.

Groundwater mean residence times of a subtropical barrier sand island

Abstract. Fresh groundwater on barrier islands is affected by changing sea levels and precipitation variability due to climate change and is also vulnerable to anthropogenic processes, such as contamination and groundwater over-abstraction. Constraining groundwater mean residence times (MRTs) and flow paths is essential for understanding and managing these resources. This study uses tritium (3H) and carbon-14 (14C) to determine the MRTs of groundwater along a transect across subtropical North Stradbroke Island, south-east Queensland, Australia. Hydraulic properties, major ion geochemistry and stable isotopes are used to validate residence times and to identify the processes responsible for their variability. 3H activities range from less than 0.01 to 1 TU (tritium units), which are values lower than those of local average rainfall (1.6–2.0 TU). 14C concentrations range from 62.5 to 111 pMC (percent modern carbon). Estimated MRTs determined using lumped parameter models and 3H activities range from 37 to more than 50 years. Recharge occurs over the entire island, and groundwater MRTs generally increase vertically and laterally towards the coastal discharge areas, although no systematic pattern is observed. MRTs estimated from 14C concentrations display similar spatial relationships but have a much greater range (from modern to approximately 5000 years). Water diversion and retention by lower-permeability units in the unsaturated parts of the dune systems are the most likely course for relatively long MRTs to date. The results indicate that the internal structures within the dune systems increase MRTs in the groundwater system and potentially divert flow paths. The structures produce perched aquifer systems that are wide-spread and have a significant influence on regional recharge. The geochemical composition of groundwater remains relatively consistent throughout the island, with the only irregularities attributed to old groundwater stored within coastal peat. The outcomes of this study enhance the understanding of groundwater flow, recharge diversion and inhibition for large coastal sand masses in general, especially for older sand masses that have developed structures from pedogenesis and dune movement. With respect to south-east Queensland, it allows the existing regional groundwater flow model to be refined by incorporating independent MRTs to test models' validity. The location of this large fresh groundwater reservoir, in dry and populous south-east Queensland, means that its potential to be used as a water source is always high. Background information on aquifer distribution and groundwater MRTs is crucial to better validate impact assessment for water abstraction.