American Journal of Water Resources, 2020, Vol. 8, No. 2, 92-107 Available online at http://pubs.sciepub.com/ajwr/8/2/5 Published by Science and Education Publishing DOI:10.12691/ajwr-8-2-5 Estimating of Sediment Mass on the Floodplain of Long Xuyen Quadrangle - An Giang, Vietnam Tran Thi Hong Ngoc 1,* , Baranya Sandor 2 , Mark Honti 3 , Vo Khac Tri 4 1 Faculty of Engineering-Technology-Environment, An Giang University – Vietnam National University, Ho Chi Minh City, Vietnam. No 18 Ung Van Khiem Street, Dong Xuyen Ward, Long Xuyen City, An Giang Province, Vietnam 2 Department of Hydraulic and Water Resources Engineering, Budapest University of Technology and Economics, Megyetem rkp. 3, H-1111 Budapest, Hungary 3 MTA-BME Water Research Group, Hungarian Academy of Sciences, Megyetem rkp. 3, H-1111 Budapest, Hungary 4 The Southern Institute of Water Resources Research, 658 Vo Van Kiet Street, Ward 1, District 5, Ho Chi Minh City, Vietnam *Corresponding author: tthngocagu@gmail.com Received March 10, 2020; Revised April 11, 2020; Accepted April 22, 2020 Abstract This paper presents the result of suspended and deposited sediment measurements on the floodplain of Long Xuyen Quadrangle-An Giang (LXQ-AG) along the Cambodia - Vietnam border during a flood event in 2018. GIS and Remote sensing techniques were used to build maps for the flooded areas. Water level and discharge were also measured on main channels and on the floodplain. The two correlation equations between deposition sediment, SSC and discharge were build. The results of Landsat interpretting showed that inundation area of the floodplain was 35,765 ha. SSC and deposited sediment decreased with distance from the main channels. The results showed thattotal deposited sediment mass brought to the floodplain during a single flood event in 2018 was 5.023 million tons (14.04 kg/m 2 ). Keywords: GIS, remote sensing, floodplain, deposited sediment, suspended sediment, Long Xuyen Quadrangle Cite This Article: Tran Thi Hong Ngoc, Baranya Sandor, Mark Honti, and Vo Khac Tri, “Estimating of Sediment Mass on the Floodplain of Long Xuyen Quadrangle - An Giang, Vietnam.” American Journal of Water Resources, vol. 8, no. 2 (2020): 92-107. doi: 10.12691/ajwr-8-2-5. 1. Introduction In Long Xuyen Quadrangle-AnGiang (LXQ-AG) an area of 353,666.85 hectares, in which there are not only two major rivers, the Mekong River (Tien River), the Bassac River (Hau River) but also many small rivers, canals, lakes and streams; they form a vast river network with a total length of 7,351 km covering most of the province. River density of the whole province reaches 1.6 km/km 2 , at the highest level in the Mekong Delta. The hydrological regime depends predominantly on the Mekong River water regime. In rainy seasons, the flow velocity increases significantly, and the river water carries huge amount sediments [1]. In the flood seasons, at the estuary, SSC ranges from 500 to 1.000 mg/l of river water, while in the floodplain away from the estuary it ranges from 40 to 80 mg/l. In the riparian zone of the Tien and Hau Rivers, annual silt deposits on the soil surface layer around 5-7cm thick, and in the floodplain are 6-7.5cm [2]. Lu et al. (2014) estimated 67 million tons sediment by the floods in 2000 for Hau River [3]. Flooding also improves soil quality by flushing out fields, which reduces acidity and agrochemical residues, while contributing to wetland protection and biodiversity conservation [4,5]. After decades of exploitation, LXQ-AG became rich agricultural fields with flood mitigation projects such as building 5,393,468m dykes to protect crops [6]. This transformation as achieved remarkable results and changed the face of rural areas today. Although, these embankments have achieved considerable economic benefits, it also has drawbacks. There are many suggestions that the flood prevention dykes system has been causing unforeseen consequences such as soil degradation, increased activity by pests, decreased crop yields due to blocking of annual silt deposits on the floodplains [7], water quality problems [8,9], riverbank erosion [10], and salt water intrusion [11,12]. The quality, quantity and timing of flooding overflows from rivers and waterways into the LXQ has led to a lot hydrological changes. The water level and its oscillations are no longer seasonal anymore as they are now dependent on the operation of a system of culverts [13]. This decreased sediment, and loss of its associated nutrients, will have a largely negatively impact on agricultural production in the floodplain, which will lead to a major impact on the ecological environment, and economic development of the region [14]. Reduced sediment will increase sharply the cost of agricultural production. Agricultural development can provide additional and alternative sources of nutrition for humans, but the exact impact of these activities on the delta are still developing and not yet well understood. Another problem is that sediment is a major concern across borders in neighbouring countries. The Mekong basin plan is for the construction of 88 hydropower dams