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... study area is the subaqueous Mekong River delta, extending down to ~20-25 m of water depth (Figure 1). The hydrodynamics of the study area is driven by tide, river flow and monsoon conditions. ...
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... the present study, 238 surface sediment samples were collected in coastal waters from Co Chien River mouth to the Ca Mau Penin- sula ( Figure 1). Surface sediment samples (0-5 cm) were taken using the grab samplers dur- ing three field trips in April of 2007, 2008 and 2014. ...
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... sed- iments on the adjacent shelf was poorly sorted with major mode coarser than 400 m and another fine mode of fine silt (5-8 m) that are observed in the grain size distribution curves. The coarser mode was suggested to be resulted from carbonate materials or relict ma- terials while the finer mode was likely gener- ated by the Mekong River source (Figure 10). ...
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... 08 was located westward of the Ca Mau Peninsular. The sediments on this transect were the finest in comparison to all other transects (Figure 11). The sediments on the foreset were uniform, commonly contain- ing fine silt, indicating low hydrodynamic en- ergy and steady conditions for sedimentation and a further distance of over 300 km from the sediment sources of the Mekong River mouths. ...
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... mean sediment grain size was generally <60 m in the areas from Bo De to Ca Mau Peninsula. The tendency of mean sediment grain sizes showed that fine sediments were dominant in southwestward and western part of Ca Mau Peninsula (Figure 12). The median sediment grain sizes were ap- plied widely in calculations of sediment transport. ...
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... the map of median sedi- ment grain size distribution could use to inter- pret hydrodynamics for the study area. The median sediment grain size >90 m distribut- ed in front of the Hau River mouths and was finer toward the Ganh Hao River mouth (Fig- ure 13). Around the Ganh Hao River mouth, the median grain size varied between 30-90 m and tended to be finer in the southwest- ward and western part of Ca Mau Peninsula. ...
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... sediments were characterized by two or three distribution modes in the transi- tional zone from foreset to the adjacent inner shelf or sometimes from topset to foreset re- gions ( Figure 14). Based on the distribution map, we selected the mode 1 for interpolation, because the mode 1 was dominant over mode 2 and mode 3 and half of sediment samples had only one mode (mode 1). ...
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... on the distribution map, we selected the mode 1 for interpolation, because the mode 1 was dominant over mode 2 and mode 3 and half of sediment samples had only one mode (mode 1). Mode 1 of sed- iment grain sizes >45 m mainly distributed in front of Hau River mouths and from Ganh Hao toward the Hon Khoai Island, while mode 1 of sediment grain sizes >25 m was dominant in the western part of the Ca Mau Peninsula and southeastern part of Bac Lieu Province ( Figure 15). The sand fraction was dominant, being greater than 40-60% in the front of the Hau River mouths (Figure 16). ...
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... 1 of sed- iment grain sizes >45 m mainly distributed in front of Hau River mouths and from Ganh Hao toward the Hon Khoai Island, while mode 1 of sediment grain sizes >25 m was dominant in the western part of the Ca Mau Peninsula and southeastern part of Bac Lieu Province ( Figure 15). The sand fraction was dominant, being greater than 40-60% in the front of the Hau River mouths (Figure 16). The sand fraction >30% scatted in several places from Ganh Hao River Mouth to the Hon Khoai Island. ...
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Reprint of Die Küste, 81 (2014), 409-426
Every year, in the Vietnam Mekong Delta Coastal Zone (VMDCZ), erosions cause approximately 300 ha of agricultural land loss. Therefore, measures for shoreline protection are urgently needed. This paper discusses the impacts of protection measures in the Go-Cong Coastal Zone to prevent erosion/accretion processes, predicted by two numerical models,...
Citations
... The coastal sedimentation patterns encompassing alluvial, aeolian, and lacustrine processes, depending on hydraulic conditions, typically lead to the accumulation of sedimentary sequences characterized by a broad range of grain sizes (Krumbein, 1934;Krumbein and Sloss, 1963). The succession of numerous regression-transgression cycles is the main cause for the formation of complex depositional sequences, resulting in the strong heterogeneity of many coastal aquifers (Miall, 2000;Ta et al., 2001;Nguyen et al., 2017) and a considerable impact on SI existence and characteristics. ...
The lithological and stratigraphical heterogeneity of coastal aquifers has a great influence on saltwater intrusion (SI). This makes it difficult to predict SI pathways and their persistence in time. In this context, electrical resistivity tomography (ERT) and induced polarization (IP) methods are receiving increasing attention regarding the discrimination between saltwater-bearing and clayey sediments. To simplify the interpretation of ERT data, it
is commonly assumed that the bulk conductivity mostly depends on the conductivity of pore-filling fluids, while surface conductivity is generally disregarded in the spatial and temporal variability of the aquifers, particularly, once the aquifer is affected by the presence of saltwater. Quantifying salinities based on a simplified petrophysical relationship can lead to misinterpretation in aquifers constituted by clay-rich sediments. In this study,
we rely on co-located data from drilled boreholes to formulate petrophysical relationships between bulk and fluid conductivity for clay-bearing and clay-free sediments. First, the sedimentary samples from the drilled wells were classified according to their particle size distribution and analyzed in the lab using spectral IP in controlled salinity conditions to derive their formation factors, surface conductivity, and normalized chargeability. Second,
the deduced thresholds are applied on the field to distinguish clay-bearing sediments from brackish sandy sediments. The results are validated with logging data and direct salinity measurements on water samples. We applied the approach along the Luy River catchment and found that the formation factors and surface conductivity of the different unconsolidated sedimentary classifications vary from 4.0 to 8.9 for coarse-grained sand and
clay-bearing mixtures, while normalized chargeability above 1.0 mS.m− 1 indicates the presence of clay. The clay bearing sediments are mostly distributed in discontinuous small lenses. The assumption of homogenous geological media is therefore leading to overestimating SI in the heterogeneous clay-bearing aquifers.
... The δ 13 C composition was reported as per mil (‰) deviation of the 13 C/ 12 C ratio of the sample from the Vienna Pee Dee Belemnite (VPDB) standard. Radiocarbon activity was reported as fraction modern (Szczuciński et al., 2013;Xue et al., 2014;Thanh et al., 2017;Wang et al., 2020;Narman, 2020;Bai et al., 2021). The arrows indicate prevailing current system during northeast (winter) and southwest (summer) monsoons (Section 2.1). ...
... Our TOC content, δ 13 C, F m , and SA data of a suite of 44 shelf sediment samples are combined with previously published data to yield a detailed picture of the spatial distribution in sedimentary OC characteristics in the GOT and Mekong shelf (Figs. 1 and 3; Supplementary Table D2; Szczuciński et al., 2013;Xue et al., 2014;Thanh et al., 2017;Wang et al., 2020;Narman, 2020;Bai et al., 2021). Data available in most of these earlier studies are the TOC content and δ 13 C, with a few studies reporting F m and SA data for sediments in the Mekong shelf and adjacent southeastern corner of the GOT (Xue et al., 2014;Narman, 2020). ...
... There are different opinions about the origin of the sediment, which builds up CG region. While Szczucinski et al. (2013) [30] and Xue et al. (2014) [31] assumed that sediment is transported as suspension loads during the SW monsoon from the Mekong River mouth towards CG region, Collins et al. took some sediment inputs from the Saigon-Dong Nai River system into account. However, no evidence is shown for this assumption. ...
Can Gio (CG), a mangrove forest with a dense network of tidal creeks, gradually grew
and spread seaward on a coastal platform, which was built since about 8 ka before present (BP).
Along with this development, a sand ridge began to form and moved back with the shoreline
withdrawal landward in the Late Holocene. This mangrove environment is likely abandoned from
the mainland but was, however, the place for settlement of ancient Vietnamese a few centuries BC.
The CG mangrove forest was severely destroyed during the American War and was restored since
1980. However, the historical change of the landscape along the Saigon-Dong Nai River (SG-DNR) since the Late Holocene is not completely unraveled. By analyzing sediment cores with a multiproxy approach, we investigated the recent geological development with regard to the variation of the intensity of the East Asian palaeomonsoon and regarding the accommodation space, as both regulate the development of this coastal environment. A recently significant shift in the coastline, mainly due to a change of hydroclimatic factors, was observed. A continuous coastline retreat occurred over the last millennium, changing the depositional environment and reshaping the CG mangrove landscape. Along the present coast and tidal channels, partially strong erosion and bank failures occur,
alternating with accretion at other coastal sections. This development tends to increase progressively.
... Bùn cát bồi lắng và dòng vận chuyển dưới tác động của gió mùa Đông Bắc[13]. ...
... Mức độ suy giảm bùn cát lơ lửng theo mức độ phát triển đập thượng lưu[13]. ...
... where D 50 (mean sediment diameter) = 0.0000300 m (retrieved from the previous study result in the Vietnamese Mekong Delta [31]. ...
Offshore breakwaters can be effective in reducing the energy of incident waves through dissipation, refraction or reflection. Breakwaters are increasingly constructed to stabilize eroded muddy coasts, particularly in developing countries. Accumulation of fine-grained sediment and wave attenuation are two attributes of a stable muddy coast. Effective interventions in stabilizing eroded muddy coasts include two important elements: accumulation of fine-grained sediment and wave reduction. The efficacy of offshore breakwaters in stabilizing eroded muddy coasts is, however, not yet adequately understood. A crucial question needing attention is whether accumulation of fine-grained sediment and wave attenuation should be used in evaluating the efficacy of these offshore breakwaters in stabilizing eroded muddy coasts. To address this issue, a pile-rock offshore breakwater in Huong Mai, Tieu Dua of Ca Mau, Vietnam was selected as an appropriate example in this regard. Accumulation of fine-grained sediment and wave attenuation were tested as means to investigate the efficacy of the Huong Mai structure in stabilizing the eroded muddy coast. The study was undertaken using field-based measurements and semi-structured interviews in three stages between October 2016 and December 2020. We found that this structure has had limited efficacy in stabilizing the eroded muddy coast. The structure was effective in dissipating the energy of incident waves, but we found no evidence of fine-grained sediment accumulation due to an inappropriate structural design. There was also no monitoring system in place, leading to difficulties in evaluating its efficacy in terms of wave attenuation and accumulation of fine-grained sediment. The gaps between the shoreline and the structure have not been adequately explained, resulting in substantial challenges in replicating the structure elsewhere. The Huong Mai structure should be strengthened using supplementary measures and granulometric tests in order to improve the efficacy in stabilizing eroded muddy coasts. The methods in this study provide new insights in this regard.
... The fate of terrestrial sediments discharged by the Mekong River has been a subject of numerous studies, especially intensified during the last decade (e.g., Anikiev et al., 2004;DeMaster et al., 2017;Eidam et al., 2017;Gugliotta et al., 2019;Le et al., 2018;Liu et al., 2016Liu et al., , 2017aNittrouer et al., 2017;Nowacki et al., 2015;Schimanski and Stattegger, 2005;Szczuciński et al., 2013;Thanh et al., 2017;Unverricht et al., 2013Unverricht et al., , 2014Wang et al., 2011;Xue et al., 2011Xue et al., , 2012Xue et al., , 2014. Both observational and modelling-based research indicates that the overwhelming fraction of the discharged sediments is transported and deposited within the subaqueous part of the Mekong River Delta (e.g., DeMaster et al., 2017;Eidam et al., 2017;Liu et al., 2017a;Marchesiello et al., 2019;Szczuciński et al., 2013;Unverricht et al., 2013). ...
... In the SW part, finer muddy sands and sandy muds prevail (Mien and Lam, 1996;Szczuciński et al., 2013). A south-westward fining gradient can be observed (Emery and Niinio, 1963;Unverricht et al., 2013;Thanh et al., 2017), with more sandy sediments found off the river mouths and silt dominating around the Ca Mau Peninsula (Mien and Lam, 1996;Unverricht et al., 2013;Thanh et al., 2017). The sediments of the distributary channels in the Mekong River Delta are mostly composed of sand and mud. ...
... In the SW part, finer muddy sands and sandy muds prevail (Mien and Lam, 1996;Szczuciński et al., 2013). A south-westward fining gradient can be observed (Emery and Niinio, 1963;Unverricht et al., 2013;Thanh et al., 2017), with more sandy sediments found off the river mouths and silt dominating around the Ca Mau Peninsula (Mien and Lam, 1996;Unverricht et al., 2013;Thanh et al., 2017). The sediments of the distributary channels in the Mekong River Delta are mostly composed of sand and mud. ...
The continental shelf off southern Vietnam is relatively well studied regarding the dominant transport paths of bulk and fine-grained sediments discharged by the Mekong River. Thus, this region is particularly suitable for testing the applicability of heavy mineral analysis in determining the extent and origin of the sandy fraction of continental shelf deposits supplied mainly by a large river and their distribution over the adjacent extensive shelf. The fine sand fraction of 105 sediment samples from the Mekong River Delta and neighbouring continental shelf is investigated, applying two approaches: i) considering only the transparent non-micaceous mineral assemblage and ii) considering all the identified heavy minerals. The geological complexity of the source areas and local dominance of micaceous and non-transparent heavy minerals require the inclusion of all heavy mineral components when interpreting sediment provenance and dominant transport paths. The most diagnostic heavy minerals, amphibole, chlorite, epidote, limonite, opaques, tourmaline and zircon, are used for this purpose. The investigated continental shelf can be divided into two main regions characterised by various heavy mineral assemblages, namely, SW and NE off the Mekong River Delta. The south-western region is dominated by chlorite and limonite, indicating prevailing southward sediment transport from the Mekong River, whereas the north-eastern region is characterised by amphibole, epidote, opaques, tourmaline and zircon, indicating various sources from SE Vietnam and relict sediments partly covering the continental shelf. Between the two main regions, a large mixing zone is found where sediments from all sources are present, including Mekong River sediments transported eastward.
... Offshore Quaternary and Pliocene sediments have recently attracted interest among many researchers ( Thanh et al., 2017Thanh et al., , 2018). According to the JAPC (2013), the acoustic stratigraphic classification of the Fig. 11. ...
We studied recent tectonics and present-day geodynamics in the Ninh Thuan nuclear power plants and surrounding regions to reveal seismogenic faults, deformation and evaluation of seismotectonics using various methods such as remote sensing, GPS, seismic interpretation, and stress and strain analysis. We based our study on geomorphological investigation, satellite images, fault gouge, drilling core, fault scarps and analysis of offshore seismic profiles to determine the capable faults in the studied region. Using international reference frame ITRF08, we determined the absolute velocities of the GPS stations with a slip rate to the east of 22.5 to 25.3 mm/year and to the south of 4.4 to 8.4 mm/year. The present strain rate was determined from present tectonic velocities that were consistent with the recent strain rates determined from topographic profiles, the slip rate of capable faults, and the thickness of Pleistocene sediments. The present strain rate variation from 10 to 30 nano per year demonstrated that the studied region has been weakly deformed under a stable tectonic regime. The state of stress determined from the fault population, focal mechanism, borehole breakouts and drilling-induced tensile fracture methods indicated that the area was deformed primarily under a strike-slip regime with a small extensive component. The maximum credible earthquake was determined from the dimensions of the capable fault and state of stress using various methods. From these capable faults, we suggest monitoring the faults, which could produce a Maximum Credible Earthquake (MCE) over a range of 5.9–6.5.
... Based on detailed mapping and exploration drilling of some Late Cretaceous heavy mineral deposits in San Juan Basin, New Mexico, USA, McLemore fully evaluated resource and economic potential for these deposits in current changing economic market [12]. Recent years, many studies related to marine environmental geochemistry, marine sedimentary as well as heavy mineral placer deposits in Vietnam have been interested by scientist and investing companies [9][10][11][13][14][15]. Existing survey reports indicate that there is great potential for total heavy mineral deposits along the coast of the country with high potential of titanium -zirconium heavy minerals. ...
Quang An, Thua Thien Hue province, Vietnam, is one of the areas with great heavy-mineral potential. The heavy-mineral ore body distributes along the beach with the width of 300–800 m and the length of about 6,100 m. A total of 4,398 samples were collected vertically in a grid pattern from 585 bore holes covering an area of 2.882 km². The results indicate that the ore body is in marine-eolian sediments at Late Holocene (\( {\text{mvQ}}_{ 2}^{ 2- 3} \)). Useful heavy minerals were ilmenite, rutile, leucoxene, anatase, zircon and monazite which could be found in the intrusive and other rocks in the region. The total heavy minerals (THM) content in the bulk samples is not so high with average of 1.172%. The heavy mineral grains are small with the size of 0.05–0.25 mm and they are well liberated, rounded to sub-rounded. The average thickness of ore body is about 8.3 m, however, its variation is relatively stable with the coefficient of 39.28%. The average content of TiO2 in ilmenites of 58.02% and ZiO2 in zircons of 60.89% indicate that titanium-zirconium heavy minerals in Quang An area have relatively good quality. The proven reserves of total heavy minerals in study area were determined reliably with about 406.595 thousand tons, of which the measured mineral reserve is 68.177 thousand tons and the indicated mineral reserve is 338.418 thousand tons. This paper deals with the distribution and potential of heavy minerals in the study area in order to promote efficient mineral exploitation and mineral processing.
Against the background of the rising sea level and land subsidence, protecting the progressively eroding coast along the Vietnam Mekong Delta becomes of tremendous importance. Within the presented work, design conditions for breakwaters were derived from offshore climate reanalysis data (ERA5), which were transferred to the nearshore by two numerical approaches, i.e. SwanOne and Delft3D, for different average and extreme wave 16 and weather conditions. Within this process, design wave heights and periods at the nearshore could be determined for 10-to 100-year recurrence intervals. Both models thereby showed sufficient accuracy according to measurements in the field. Limitations must be made regarding the available spatio-temporal resolution, where reanalysis data showed a lack of short but high peak values compared to the observed measurements. Both numerical approaches showed their capabilities, where SwanOne offers a simple and fast calculation method, while it lacks of continuous effects like wind-generated swell or bottom friction. The Delft3D software on the other hand provides a more complete representation, not only of wave but also current dynamics, while it requires a much broader amount of input parameters and more complex boundary conditions. Within this study, the advantages and disadvantages of both models could be demonstrated, whereas for the final calculation of nearshore wave characteristics, only SwanOne was applicable based on the input parameters extracted from statistical analysis of long term ERA5 data.
Extreme coastline erosion has become a major issue in Vietnam's Mekong Delta. Many coastal protection measures have been assessed based on their ability to dissipate incoming waves rather than their ability to facilitate environmental exchange and sedimentation processes. The goal of this study is to evaluate the ability of hollow and porous types of breakwaters to exchange suspended sediment on the deltaic coast. The experiments are set considering the hydrodynamic conditions of the Mekong Delta. We thought of four different types of breakwaters, including pile-rock porous breakwaters (CMD), two-sided perforated hollow breakwaters (TC1 & DRT/VTC), and curtain breakwaters (CWB45). Physical modeling in a wave flume was engaged to investigate the relationship between breakwater shape and sediment-capturing ability. All different breakwaters were placed on the wave flume with identical boundary conditions. Besides the physical modeling in the laboratory, Computational Fluid Dynamics (CFD) techniques using the FLOW3D model were applied. This provided an opportunity to understand the current distribution and the interactions between the fluid and the breakwater, as well as the ability to extract the vertical velocity profile and further additional insights from the interactions of waves and currents with the breakwaters. The wave parameters collected in the lab were further used to evaluate the numerical simulations in FLOW3D, and model validation demonstrated a good agreement with R² = 0.74–0.98 and NSE = 0.74–0.96 for FLOW3D calibration and validation. It was found that fine sand and mud silt deposition on the shoreline of the breakwater alignment were significantly reduced in the case of the perforated hollow breakwaters. Therefore, using these hollow breakwaters for wave energy dissipation and sediment trapping presents a dual purpose in creating an environmentally friendly solution to recover mudflats. Hollow breakwaters also provide numerous advantages for supporting the creation of favorable conditions for the revival of mangrove forests, development of regional biodiversity, and overall improvement of coastal ecosystems on the deltaic coast.
