5.3 Implications for the Lower Mekong River
Our quantification of sediment fluxes from Ming Yong glacial catchment
provides baseline measurements to better understand changes in erosion
rates within the context of wider climatic alterations (Li et al.,
2021). As the Ming Yong glacial region is part of the upper reach of the
Mekong River and Salween River, our study also provides insights into
the contribution of sediment to the upper reaches of these transboundary
rivers under the fast pace of temperature increase (Figure 2c). For the
Mekong Basin, better understanding of sediment supply and delivery in
its entire reach is needed for better management of its sediment fluxes.
One major issue is the potential impacts of Chinese dams in the Mekong
River. Before Manwan Dam was constructed in 1992, the upper Mekong reach
in China provided around 80 million tons of sediment to the lower reach
(Lu and Siew, 2006; Wang et al., 2011; Lu et al., 2015). However, the
high sediment supply from the proglacial catchments in the headwater
region cannot be transported downstream because of the series of cascade
dams constructed in the Upper Mekong River. According to Sun et al.
(2022), the sediment load below these cascade dams in Yunnan has dropped
to around 10% of the pre-dam level. Subsequently, the problem of
sediment starvation due to the reservoirs trapping will get worse in
future with more dams being planned or built. Further down the Mekong
Basin, this declining sediment flux, in combination with regional
sand-mining and water withdrawal for irrigations, has contributed to
drastic water level reductions in the Cambodian floodplains and
Vietnamese delta (Lu and Chua, 2021; Chua et al., 2022).