Stratigraphy and optically stimulated luminescence (OSL) dating of a Quaternary sequence along the Dong Nai River, southern Vietnam   总被引：1，自引：0，他引：1  

Toshiyuki Kitazawa  Takahiro Nakagawa  Tetsuo Hashimoto  Masaaki Tateishi 《Journal of Asian Earth Sciences》2006,27(6):788-804

The pre-Holocene Cenozoic sequence outcrops in the terrestrial part of the eastern margin of the Mekong Basin. However, the stratigraphy of the sequence is still unclear. Its detailed stratigraphy and chronology were therefore studied along the Dong Nai River, southern Vietnam, and the lithofacies and the relations among the formations were investigated from the outcrops. The ages of the deposits were determined by using optically stimulated luminescence (OSL) dating.The Ba Mieu Formation was deposited about 176±52 ka during marine isotope stage (MIS) 7–6. The Thu Duc Formation was deposited about 97±27 ka during MIS 5. Both the Ba Mieu and Thu Duc formations are composed of fluvial and tidally influenced coastal deposits. The newly proposed Nhon Trach Formation was originally an eolian (blanket) deposit, but it has been partly reworked by fluvial processes. The Nhon Trach Formation was deposited about 10.9±4.7 ka, in the last part of the Pleistocene to the beginning of the Holocene. The OSL ages for the Ba Mieu, Thu Duc, and Nhon Trach formations are younger than the ages previously assigned to these formations.  相似文献   

The data‐driven approach as an operational real‐time flood forecasting model     

Phuoc Khac‐Tien Nguyen  Lloyd Hock‐Chye Chua 《水文研究》2012,26(19):2878-2893

Accurate water level forecasts are essential for flood warning. This study adopts a data‐driven approach based on the adaptive network–based fuzzy inference system (ANFIS) to forecast the daily water levels of the Lower Mekong River at Pakse, Lao People's Democratic Republic. ANFIS is a hybrid system combining fuzzy inference system and artificial neural networks. Five ANFIS models were developed to provide water level forecasts from 1 to 5 days ahead, respectively. The results show that although ANFIS forecasts of water levels up to three lead days satisfied the benchmark, four‐ and five‐lead‐day forecasts were only slightly better in performance compared with the currently adopted operational model. This limitation is imposed by the auto‐ and cross‐correlations of the water level time series. Output updating procedures based on the autoregressive (AR) and recursive AR (RAR) models were used to enhance ANFIS model outputs. The RAR model performed better than the AR model. In addition, a partial recursive procedure that reduced the number of recursive steps when applying the AR or the RAR model for multi‐step‐ahead error prediction was superior to the fully recursive procedure. The RAR‐based partial recursive updating procedure significantly improved three‐, four‐ and five‐lead‐day forecasts. Our study further shows that for long lead times, ANFIS model errors are dominated by lag time errors. Although the ANFIS model with the RAR‐based partial recursive updating procedure provided the best results, this method was able to reduce the lag time errors significantly for the falling limbs only. Improvements for the rising limbs were modest. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Integrating farmers’ adaptive knowledge into flood management and adaptation policies in the Vietnamese Mekong Delta: A social learning perspective     

《Global Environmental Change》2019

Flood management and adaptation are important elements in sustaining farming production in the Vietnamese Mekong Delta (VMD). While over the past decades hydraulic development introduced by the central government has substantially benefited the rural economy, it has simultaneously caused multiple barriers to rural adaptation. We investigate the relational practices (i.e., learning interactions) taking place within and across the flood management and adaptation boundaries from the perspective of social learning. We explore whether and how adaptive knowledge (i.e., experimental and experiential knowledge) derived from farmers’ everyday adaptation practices contributes to local flood management and adaptation policies in the selected areas. We collected data through nine focus groups with farmers and thirty-three interviews with government officials, environmental scientists, and farmers. Qualitative analysis suggests that such processes are largely shaped by the institutional context where the boundary is embedded. This study found that while the highly bureaucratic operation of flood management creates constraints for feedback, the more informal arrangements set in place at the local level provide flexible platforms conducive to open communication, collaborative learning, and exchange of knowledge among the different actors. This study highlights the pivotal role of shadow systems that provide space for establishing and maintaining informal interactions and relationships between social actors (e.g., interactions between farmers and extension officials) in stimulating and influencing, from the bottom-up, the emergence of adaptive knowledge about flood management and adaptation in a local context.  相似文献   

Globalisation, Regionalisation and Local Voices: The Asian Development Bank and Rescaled Politics of Environment in the Mekong Region   总被引：1，自引：0，他引：1  

Philip Hirsch 《Singapore journal of tropical geography》2001,22(3):237-251

Globalisation is manifested in the Mekong Region both through processes and discourses that reflect the ideology of a borderless world allowing easy passage of capital and commodities, and through resistance to such processes in an increasingly transnationalised civil society movement. However, more immediately significant supranational integrative agendas take the form of regionalisation, a process that has received less attention but which raises analogous concerns of re-scaled governance. The Asian Development Bank (ADB) has been a catalysing force for regionalisation amidst a host of regional processes and initiatives; as such it has found itself the object of critique as an institution and through the specific projects it has supported that have impacted on local communities and ecosystems. Meanwhile, local and NGO voices associated with the emergence of a vibrant civil society in Thailand and nascent civil society responses in neighbouring countries have challenged claims on resources made in the name of national development and regional integration.
This paper considers some key issues of re-scaling resource and environmental politics in the Mekong Region, and the extent to which challenges have been recast from national to regional development agendas. Politics of environment are shown to exist as a general rather than exceptional response to the region's development direction, and it is suggested that equitable and sustainable development increasingly needs to address simultaneously the re-scaling and reconfigurations of power in both environmental politics and the "infrapolitics" of environment. The paper is illustrated with case studies of dams in Laos and Thailand.  相似文献   

Glacial paleoceanography off the mouth of the Mekong River, southern South China Sea, during the last 500 ka     

Qianyu Li  Fan Zheng  Muhong Chen  Rong Xiang  Peijun Qiao  Lei Shao  Xinrong Cheng 《Quaternary Research》2010,73(3):563-572

We have analyzed core MD01-2392, ∼ 360 km east of the Mekong River mouth in the South China Sea (SCS). Over the past 500 ka, planktonic foraminiferal oxygen-isotopic values are consistently lighter than northern SCS and open-ocean records by up to 0.5‰, indicating the influence of run-off from the Mekong River during both glacial and interglacial periods. Carbonate content is higher during interglacials; sedimentation rates were higher during glacials. Increased sedimentation rates since 30 ka imply increased run-off during the last glacial maximum and Holocene Period. Contrary to general experience, in which it is classed as a warm species for temperature estimates, the thermocline-dwelling species Pulleniatina obliquiloculata increased its numbers during glacial periods. This implies an estuarine circulation and even brackish-water caps during glacial periods, reinforcing the sense of strong run-off. In an overall decline of warm water, the thermocline shoaled stepwise, with rapid rises across the glacial terminations. We infer that the southern SCS was opened to an influx of Indian Ocean waters through southern passages at those times of rising sea levels.  相似文献   

基于多源卫星数据的南海油气井平台遥感提取方法研究——以湄公盆地周边海域为例          下载免费PDF全文

王明珠  陈颖民  韩飞  陈婕  许国强  李柏权  江佳琳 《海洋开发与管理》2022,39(3):72-78

文章以湄公盆地周边海域为研究区,利用遥感技术手段,综合多时相、多源卫星数据,探讨不同数据源海上油气井平台提取方法。本次研究,首先基于1992—2018年27景多时相夜间灯光数据和2019年两期SAR数据,分别采用高斯滤波法和双参数CFAR法,实现了全区域油气井平台的自动化提取;然后,针对有确定性资料辅助判定的区域,采用人工目视解译的方法,对长时间序列Landsat-8 OLI及YG24号光学卫星影像进行提取,并将解译结果作为标准数据,用于验证前两种自动提取方法的精度。结果表明：夜间灯光影像数据易获取、成本低,提取方法简单,而SAR影像提取结果的精度高、流程烦琐,建议根据多源卫星数据的特点相互结合,实现快速、高效、精确的信息提取,应用于海上油气井平台监测。  相似文献   

Floodplain hydrology of the Mekong Delta,Vietnam     

Nguyen Nghia Hung  José Miguel Delgado  Vo Khac Tri  Le Manh Hung  Bruno Merz  András Bárdossy  Heiko Apel 《水文研究》2012,26(5):674-686

The Mekong Delta is one of the largest and most intensively used estuaries in the world. Each year it witnesses widespread flooding which is both the basis of the livelihood for more than 17 million people but also the major hazard. Therefore, a thorough understanding of the hydrologic and hydraulic features is urgently required for various planning purposes. While the general causes and characteristics of the annual floods are understood, the inundation dynamics in the floodplains in Vietnam which are highly controlled by dikes and other control structures have not been investigated in depth. Especially, quantitative analyses are lacking, mainly due to scarce data about the inundation processes in the floodplains. Therefore, a comprehensive monitoring scheme for channel and floodplain inundation was established in a study area in the Plain of Reeds in the northeastern part of the Vietnamese Delta. This in situ data collection was complemented by a series of high‐resolution inundation maps derived from the TerraSAR‐X satellite for the flood seasons 2008 and 2009. Hence, the inundation dynamics in the channels and floodplains, and the interaction between channels and floodplains, could be quantified for the first time. The study identifies the strong human interference which is governed by flood protection levels, cropping patterns and communal water management. In addition, we examine the tidal influence on the inundation in various parts of the Delta, since it is expected that climate change‐induced sea level rise will increase the tidal contribution to floodplain inundation. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Clay mineral records of East Asian monsoon evolution during late Quaternary in the southern South China Sea   总被引：3，自引：2，他引：1  

C.Colin  A.Trentesaux  D.Blamart 《中国科学D辑(英文版)》2005,48(1):84-92

High-resolution clay mineral records combined with oxygen isotopic stratigraphy over the past 190 ka during late Quaternary from core MD01-2393 off the Mekong River in the southern South China Sea are reported to reconstruct a history of East Asian monsoon evolution. The dominating clay mineral components indicate a strong glacial-interglacial cyclicity, with high glacial illite, chlorite, and kaolinite contents and high interglacial smectites content. The provenance analysis indicates the direct input of clay minerals via the Mekong River drainage basin. Illite and chlorite derived mainly from the upper reach of the Mekong River, where physical erosion of meta-sedimentary rocks is dominant. Kaolinite derived mainly from active erosion of inhered clays from reworked sediments in the middle reaches. Smectites originated mainly through bisiallitic soils in the middle to lower reaches of the Mekong River. The smectites/(illite+chlorite) and smectites/kaolinite ratios are determined as mineralogical indicato  相似文献   

Effects of riverbed incision on the hydrology of the Vietnamese Mekong Delta     

Doan Van Binh  Sameh A. Kantoush  Tetsuya Sumi  Nguyen Phuong Mai  Trieu Anh Ngoc  La Vinh Trung  Tran Dang An 《水文研究》2021,35(2):e14030

The hydrogeomorphology of the Vietnamese Mekong Delta (VMD) has been significantly altered by natural and anthropogenic drivers. In this study, the spatiotemporal changes of the flow regime were examined by analysing the long-term daily, monthly, annual and extreme discharges and water levels from 1980 to 2018, supported by further investigation of the long-term annual sediment load (from the 1960s to 2015), river bathymetric data (in 1998, 2014 and 2017) and daily salinity concentration (from the 1990s to 2015) using various statistical methods and a coupled numerical model. Then, the effects of riverbed incision on the hydrology were investigated. The results show that the dry season discharge (i.e., in March–June) of the Tien River increased by up to 23% from the predam period (1980–1992) to the postdam period (1993–2018) but that the dry season water level at My Thuan decreased by up to −46%. The annual mean and monthly water levels in June at Tan Chau and in January and June–October at My Thuan in the Tien River decreased statistically, even though the respective discharges increased significantly. These decreased water levels instead of the increased discharges were attributed to the accelerated riverbed incision upstream from My Thuan, which increased by more than three times, from a mean rate of −0.16 m/year (−16.7 Mm³/year) in 1998–2014 to −0.5 m/year (−52.5 Mm³/year) in 2014–2017. This accelerated riverbed incision was likely caused by the reduction in the sediment load of the VMD (from 166.7 Mt/year in the predam period to 57.6 Mt/year in the postdam period) and increase in sand mining (from 3.9 Mm³ in 2012 to 13.43 Mm³ in 2018). Collectively, the decreased dry season water level in the Tien River is likely one of the main causes of the enhanced salinity intrusion.  相似文献   

Identification of groundwater mean transit times of precipitation and riverbank infiltration by two‐component lumped parameter models     

Nguyen Le Duy  Nguyen Viet Dung  Ingo Heidbüchel  Hanno Meyer  Markus Weiler  Bruno Merz  Heiko Apel 《水文研究》2019,33(24):3098-3118

Groundwater transit time is an essential hydrologic metric for groundwater resources management. However, especially in tropical environments, studies on the transit time distribution (TTD) of groundwater infiltration and its corresponding mean transit time (mTT) have been extremely limited due to data sparsity. In this study, we primarily use stable isotopes to examine the TTDs and their mTTs of both vertical and horizontal infiltration at a riverbank infiltration area in the Vietnamese Mekong Delta (VMD), representative of the tropical climate in Asian monsoon regions. Precipitation, river water, groundwater, and local ponding surface water were sampled for 3 to 9 years and analysed for stable isotopes (δ¹⁸O and δ²H), providing a unique data set of stable isotope records for a tropical region. We quantified the contribution that the two sources contributed to the local shallow groundwater by a novel concept of two‐component lumped parameter models (LPMs) that are solved using δ¹⁸O records. The study illustrates that two‐component LPMs, in conjunction with hydrological and isotopic measurements, are able to identify subsurface flow conditions and water mixing at riverbank infiltration systems. However, the predictive skill and the reliability of the models decrease for locations farther from the river, where recharge by precipitation dominates, and a low‐permeable aquitard layer above the highly permeable aquifer is present. This specific setting impairs the identifiability of model parameters. For river infiltration, short mTTs (<40 weeks) were determined for sites closer to the river (<200 m), whereas for the precipitation infiltration, the mTTs were longer (>80 weeks) and independent of the distance to the river. The results not only enhance the understanding of the groundwater recharge dynamics in the VMD but also suggest that the highly complex mechanisms of surface–groundwater interaction can be conceptualized by exploiting two‐component LPMs in general. The model concept could thus be a powerful tool for better understanding both the hydrological functioning of mixing processes and the movement of different water components in riverbank infiltration systems.  相似文献