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.