4.3 Temporal variations of water discharges and sediment yields
Both water discharge and suspended sediment flux in Ming Yong catchment
are characterised byseasonal variations (Figure 6). The monthly maximum
sediment loads, all occurring in July, amounted to 12.5 kt (2014), 30.3
kt (2016), and 25.1 kt (2017). Of the total annual sediment load, the
majority (65% in 2013, 73% in 2015, and 78% in 2016) was highly
concentrated in summer from June to August. In contrast, the dry season
month of February has the lowest monthly load at around 0.25% of the
total annual load.
Concurrently, the monthly sediment load was significantly correlated
with the monthly water discharge, with the R2 value of
0.82. The high sediment load during periods of high discharge suggests
the predominance of supraglacial and subglacial sediment mobilization.
However, more studies are still needed to differentiate the transport of
sediment load by meltwater or that by precipitation.
The water discharge for hydrological years 2013, 2015, and 2016 – 0.50
km3/year, 0.46 km3/year, and 0.53
km3/year, respectively –did not vary significantly,
implying little variations in annual water discharge for the Ming Yong
catchment. However, annual sediment load variability was large, ranging
from 44 kilotons (kt) in 2013 to 91 kt in 2015, and 73 kt in 2016
(Figure 7). Together, the sediment yield for Ming Yong glacial catchment
was derived to be 1104 t/km2/year in 2013, 2281
t/km2/year in 2015, and 1833
t/km2/year in 2016.
. The high variation of annual suspended sediment yield might be induced
by what is known as threshold effect in sediment transport, with
disproportionally high sediment delivery efficacy in excess of the
critical level (Lane & Nienow, 2019). Also, the type of substrate and
subglacial deposits, rates of glacier movement, characteristics of the
glacier drainage system, and the basin topography can affect the
interannual variability of sediment yields (Herman et al., 2021). The
competing effects of these confounding factors can be further
investigated in a future study.