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.