YIN Ping, PHUNG Van Phach, TRAN Dinh Lan, DO Huy Cuong, BUI Van Vuong, and DUAN Xiaoyong, *

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Introduction to the China-Vietnam Cooperation Project: A Comparative Study of the Holocene Sedimentary Evolution of the Yangtze and Red River Deltas

YIN Ping1), 2), PHUNG Van Phach3), TRAN Dinh Lan4), DO Huy Cuong3), BUI Van Vuong4), and DUAN Xiaoyong1), 2), *

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Both China and Vietnam confront the challenges of natural geohazards and environmental changes in their deltas and coastal zones due to rapid urbanization, economic development, and the impacts of global climate change. China and Vietnam initiated a comparative study of the Holocene sedimentary evolution of the Yangtze River Delta (YRD) and Red River Delta (RRD) for the period 2015–2018 in order to improve the understanding of the two delta evolution histories in the Holocene. Previous investigative data of the two rivers, onshore delta plains, and offshore subaqueous deltas have been explored and reinterpreted. New data gleaned from boreholes, piston cores, shallow seismic and hydrodynamic sources have been collected from the offshore YRD and the East China Sea inner shelf, and surface sediments and short cores have been collected from the RRD near-shore areas. Six focal areas of the joint project have been defined for comparative studies of the two deltas, including morphological development, sequential stratigraphy, coastline shifting, sedimentary characteristics, sedimentary dynamics, and correlation with anthropogenic global climate change. The results of these study areas are presented herein. The joint project also includes cooperative capacity building; exchanges of young scientists have been organized during the project period, and hands-on training in laboratory geochemical analysis, numerical modeling, and seismic data processing and interpretation have been provided by China and its Vietnamese geoscientist partners. Joint field excursions were organized to the upstream of the Yangtze and Red Rivers in Yunan Province, China, all the way downstream along the Vietnamese portion of the Red River. These joint studies have, over the past three years, improved understanding of the evolutionary history of these two major rivers and their mechanisms of source to sink. Joint project results of these two major deltas are not limited to the geosciences; the cooperative mechanical and operational experiences have been helpful for future cooperation in the field of marine geoscience between China and Vietnam, as well for cooperative activities with other ASEAN member countries.

Yangtze River Delta; Red River Delta; Holocene; sedimentary environment

1 Cooperation Background

The Yangtze River is the third largest river in the world and the largest river in China with an annual average seaward discharge of 9.2×1011m3and sediment discharge of 4.8×108t (Chen., 2001). The YRD region, centered on Shanghai, is one of the most developed areas in China. The Red River is the second largest river in Vietnam with annual average discharge of 1.6×1011m3and sediment dis-charge of 1.3×108t (Dang., 2010). The RRD extends from Hanoi to Haiphong and is also the economic center of northern Vietnam. Like all deltas and coastal regions of the world, both the YRD and RRD regions confront the challenges of natural geohazards and environmental exchanges under the pressure of rapid urbanization and global climate change (Yin., 2017). These two deltas were all developed since 7000–8000yrsB.P. after a maximum sea level rise during the Holocene. The major stages and developmental characteristics of the two deltas are comparable (Satio., 2001; Tanabe., 2006). However, due to contrasting geological settings, sediment and water discharges, and offshore sedimentary basins and hydrodynamics, these two deltas feature differences in geomorphology, dominant hydrodynamics, shoreline stability,. Both the Yangtze River and Red River originate from the Tibetan Plateau and share similar upstream bedrock, making the two deltas desirable for comparative source-to-sink study. Both deltas accommodate major cities with rapid urban expansion, where groundwater extraction has caused distinct land subsidence (Wu., 2008). Shanghai, in the YRD, has experienced >2m subsidence over the past century (Chai., 2004), while Hanoi has suffered more recent and less subsidence compared to Shanghai, although its rate and areal coverage of subsidence are increasing with population growth and urbanization.

Damming on the rivers has led to a decrease in sediment supplies, which has strongly impacted the delta and coast regions (Li., 2013; Miao., 2016). The YRD shoreline has resisted a seawards progradation due to its large sediment supply, land reclamation and coastal defense, while its offshore subaqueous delta is slowly eroded after the major damming of the river catchment (Zhao, 2011). The shoreline of the RRD has displayed accretion and erosion in different sections, with the shoreline nearest the present branch estuaries prograding seawards, while the section between its branch estuaries is shifting landward due to strong erosion (Murooka., 2015). Sea level rise due to global warming has a strong potential impact on the deltas and a proper corresponding strategy for coastal defense and geohazard mitigation should be provided based on ongoing integrated research and comparative studies.

2 Project Organization

Comparative Study of Holocene Sedimentary Evolution of the Yangtze River Delta and Red River Delta (the so- called Co-Delta Project) has been funded for the years 2015–2018 by the Chinese and Vietnamese governments under the framework of Chinese-Vietnamese collaboration on the less contentious maritime issues. Based on previous investigation and research in the YRD and RRD and their adjacent offshore areas, the cooperative parties have carried out joint investigation and research in the two deltas. The goal is to recognize the similarities and differences in the development between the two deltas, and to understand the historical and future evolution of the delta and coastal zones in order to mitigate the negative impacts of global climate change and human activities, and to provide geological solutions for coastal management and sustainable development.

This project was co-organized by the Ministry of Natural Resources of China (former Ministry of Land and Resources) and the Ministry of Science and Technology of Vietnam, and was implemented by the China Geological Survey (CGS) and the Vietnam Academy of Science and Technology (VAST). The Qingdao Institute of Marine Geology of CGS, Tongji University and Ocean University of China are the major of Chinese project partners, and the Institute of Marine Geology and Geophysics of VAST and the Institute of Marine Environment and Resources of VAST are the major of Vietnamese project partners. The Shanghai Institute of Geological Survey, Zhejiang Institute of Hydrogeology and Engineering Geology, and the Yunnan University provide great assistance during the field excursions.

3 Cooperation Content

Six focal areas of collaboration were designed for the comparative study of the two deltas to investigate the similarities and differences between their evolution patterns, and to explore the distribution of coastal geohazards and their relevant controlling factors.

1) Morphological variation of the deltas and their adjacent shelf areas,., to classify the morphological pattern of deltas and determinate their morphological origins.

2)Late Pleistocene–Holocene sequence stratigraphy,., determination of the erosional surfaces (SB1) formed during the last glacial maximum (LGM), construction of late Pleistocene–Holocene stratigraphic sequences by using high-resolution seismic data and sedimentary core data, correlation of sedimentary sequences with sea level rise pulses on the shelf and incised channel infilling since the LGM, and application of stratigraphic numerical models in reconstructing the delta evolution of the late Pleistocene– Holocene.

3) The Holocene coastline shifting and its controlling factors,., Holocene coastline shifting in response to sea level changes, causes and solutions for erosion along the delta coasts, and application of remote sensing technology in investigating coastline changes during the last decades.

4)Surface sedimentary characteristics of the subaqueous delta and adjacent shelf area,., surface sediment distribution, elemental geochemistry of surface sediment, and recent sediment accumulation rates using210Pb and137Cs dating.

5) Sedimentary dynamics of the offshore estuary offshore and numerical modeling,., hydrodynamic factors such as salinity, temperature, currents, and suspended sediment concentration and their spatial-temporal variations, application of numerical modeling for hydrodynamics, and sediment transport in the estuary and offshore.

6) Delta evolution under the impacts of global climate change and human activity in the Holocene and last century,., carbon cycle and carbon storage capacities in response to Holocene delta evolution, marine pollution (heavy metals, chlorine pesticides, and some persistent organic pollutants), change in delta sediment accumulation rates after constructing hydro-electric power dams on the upper courses.

4 Project Implementation

Previous investigative data and publications about river drainage in the two deltas and adjacent offshore regions were well explored and reinterpreted for thematic comparison. Meanwhile, new data were collected based on the funding of research from China and Vietnam: In the YRD, 12 drilling cores with a total footage of 423.4m were collected from the offshore zone and East China Sea inner shelf together with 20 short piston cores and 3140km of shallow seismic track lines. Threeseabed sedimentary dynamics monitoring stations were set up, and sedimentary dynamics navigations were conducted in both the summer and winter seasons. In the RRD, due to the limitation of projected budgets, surface sediments and short cores were collected from the coast and near-shore area. This volume introduced the preliminary results of the research focal areas by partners from the two countries. A joint project report was delivered to both authorities to summarize the first stage of collaboration.

Capacity building is one of the main targets of cooperation. Exchanges of young scientists have been organized as part of the project, with hands-on training in laboratory geochemical analysis, numerical modeling, and seismic processing and interpretation having been provided by China for its young science partners in Vietnam. Seminars and workshops were organized for synchronous updating of project progress. Joint field excursions were organized to the upstream parts of the Yangtze and Red Rivers and their deltas and coastal regions. During the three years of collaboration, eighty-two people from both countries have participated in a total of fifteen exchange activities, including five joint field excursions, seven project meetings, three capacity training sessions, and five rounds of China-Vietnam negotiations on collaboration on less contentious maritime issues. In the meantime, the Chinese government has provided two master and one PhD scholarship for young Vietnamese scientists. Additionally, a good channel of communication has been developed after years of collaborative efforts, which will significantly enhance understanding and friendship between the geoscientists of China and Vietnam, as well as cooperative activities with other ASEAN member countries.

5 Introduction for the Special Issue

After three years of ongoing research, some preliminary results are presented in this special issue (SI), including 13 original research papers. This SI serves as a present-past linkage to understand YRD and RRD evolution in the Holocene. The following three sections were included:

1) Morphological variation of the deltas.

2) Records of depositional environment changes.

3) Modern sedimentary environment.

Future research is needed to quantify the influences of global climate change and anthropogenic forcing on the evolution of the deltas and their marginal sea environments.

Chai, J. C., Shen, S. L., Zhu, H. H., and Zhang, X. L., 2004. Land subsidence due to groundwater drawdown in Shanghai., 56 (2): 143-147.

Chen, Z., Li, J., Shen, H. T., and Wang, Z. H., 2001. Yangtze River of China: Historical analysis of discharge variability and sediment flux., 41 (2-3): 77-91.

Dang, T. H., Coynel, A., Orange, D., Blanc, G., Etcheber, H., and Le, L. A., 2010. Long-term monitoring (1960–2008) of the river-sediment transport in the Red River Watershed (Vietnam): Temporal variability and dam-reservoir impact., 408 (20): 4654-4664.

Li, K. F., Zhu, C., and Huang, L. Y., 2013. Problems caused by the Three Gorges Dam construction in the Yangtze River basin: A review., 21 (3): 127-135.

Murooka, M., Kuwahara, Y., and Haruyama, S., 2015. Mapping coastal erosion risk in the southern Red River Delta, Vietnam. In:. Li, J.,., eds., Springer, Netherlands, 199- 220.

Miao, A. Y., Chu, Z. X., and Li, Y. K., 2016. Three Gorges Dam controls sediment coarsening of the mud patch on the inner East China Sea Shelf., 15 (3): 414-422.

Saito, Y., Yang, Z., and Hori, K., 2001. The Huanghe (Yellow River) and Changjiang (Yangtze River) deltas: A review on their characteristics, evolution and sediment discharge during the Holocene., 41 (2): 219-231.

Tanabe, S., Saito, Y., Vu, Q. L., Hanebuth, T. J. J., Ngo, Q. L., and Kitamura, A., 2006. Holocene evolution of the Song Hong (Red River) delta system, northern Vietnam., 187(1):29-61.

Wu, J. C., Shi, X. Q., Xue, Y. Q., Zhang, Y., Wei, Z. X., and Wu, Y., 2008.The development and control of the land subsidence in the Yangtze Delta, China., 55(8):1725-1735.

Yin, P., Lin, J. L., Chen, B., Xiao, G. Q., Cao, K., Yang, J. L., Li, M. N., Duan, X. Y., Qiu, J. D., Hu, Y. Z., Wang, L., and Sun, X. M., 2017. Coastal zone geo-resources and geo-environment in China., 4 (5): 842-856 (in Chinese with English abstract).

Zhao, M. X., 2011. Evolution of network and spatial structure in Yangtze River Delta., 30 (2): 311-323 (in Chinese with English abstract).

August 24, 2018;

September 18, 2018;

October 21, 2018

? Ocean University of China, Science Press and Springer-Verlag GmbH Germany 2018

. E-mail: dxiaoyong@mail.cgs.gov.cn

(Edited by Chen Wenwen)