Sediment load in the Lower Mekong River
Based on an analysis of long-term sediment data, we estimated the sediment load in the mainstem Mekong River averaged 72± 38 Mt at Kratie (1993-2017), and averaged 78±22 Mt at Chroy Changvar (1995-2018). Estimation of the total flux of Mekong to the Delta is complicated by interactions with the Tonle Sap system (Kummu & Varis, 2007) since large volumes of flood water enter the floodplain of Tonle Sap, where a part of the sediment can be deposited. Our estimated loads at Kratie and Chroy Chanva are similar to those proposed by prior authors, such as Manh, Dung, Hung, Merz, and Apel (2014) estimate of 106 Mt/yr at Kratie (2010-2011). Dang, Cochrane, Arias, Van, and de Vries (2016) reported suspended sediment load of 87.4±28.7 Mt/yr (1981–2005). XiXi Lu, Kummu, Oeurng, and Landforms (2014) calculated a suspended sediment load of 50-91 Mt/yr from 2008 to 2010 measurements. However, these recent estimates are lower than long-term rates reflecting pre-dam conditions in the upper Mekong mainstem. The depositional record in the Mekong Delta indicates a long-term average sediment flux (over the past 3 ka) of 144±34 Mt/yr (Ta et al., 2002), which is in accord with Cheng Liu et al. (2013) value of 145 Mt/yr based on gauge data prior estimates of the pre-dam sediment flux of the Mekong River into the South China Sea. A. Gupta and Liew (2007) stated that most of the sediment in the Mekong upstream of Cambodia appears to be stored inside the channel, either on the bed or as insets against rock-cut banks. Unlike some other large alluvial rivers such as the Amazon, little sediment exchange occurs between channel and floodplain in the Mekong, except in downstream alluvial reaches below Kratie, in the Cambodian lowlands and the Mekong Delta in Vietnam, where the river overtops its banks during the rainy season and also has a laterally-shifting channel (A. Gupta, Hock, Xiaojing, & Ping, 2002; A. Gupta & Liew, 2007). The annual sediment load of the Mekong is comparable with loads reported for other major rivers in Asia and elsewhere (Table 7).
Table 7: The annual mean of sediment is comparable with other major rivers in Asia and continents.