| With ever increasing global warming, large quantity of meltwater is produced from glaciers and snow in the Tibetan Plateau, frequently in summer results in serious meltwater floods. The active and widely distributed frozen soil and moraine provide sufficient material sources for meltwater erosion. Therefore, it is of very important significance to study the mechanism and process of meltwater erosion in the high altitude/elevation and cold regions with special climate, topography and natural environments. The Nam Co Basin, located on the shade slopes of Nyainqentanglha Mountains on the Tibetan Plateau, was selected for this study. The main research contents and results are as follows:The annual variation curves of glacier and snow coverage were analyzed on the basis of the MODIS data and "the First and Second Glacier Inventory of China". The temporal variation of glacier and snow coverage in Nam Co basin was "double-peak mode", and it had significant differences in spatial distribution, as the southeast basin with a altitude, and steep slope, and large proportion of shades. Using empirical formula of glacier volume and SRM model, the annual glacier and snow meltwater runoff is estimated to be 2.99×108 m3/a and 8.10×106 m3/a respectively. Compared with the changes in air temperature, lake area increase in the Nam Co basin is mainly induced from the increase in glacier melting water from the shade slope of Nyainqentanglha Mountains. Based on the China’s first water conservation census data and the meltwater in the Nam Co Basin, the meltwater erosion intensity evaluation index was established. The mild, moderate and strong erosion account for 50.46%,31.78% and 12.36% of the total basin area, respectively.A typical watershed in the glacierized area, the Qugaqie catchment, was selected for the strong meltwater erosion region in the Nam Co Basin. Suspended sediment samples and the potential sediment sources were collected in the glacierized area (5400 m a.s.l.) in August,2013. Statistically verified composite fingerprints and a multivariate mixing model were used to identify the sediment sources of glacierized area in the Qugaqie catchment. Moraine particles were identified as the primary source of suspended sediment in the glacierized area of the catchment, contributing 57.43% to the suspended sediment. This occurred because large amounts of fine moraine particles were generated by glacial erosion at high elevations. The channel bank material provided 26.25% of suspended sediments, mainly because of the relatively weak fluvial erosion in glacierized area. The contribution ratio of alpine meadow soil was only 16.32%, due to the weak development of soil and the wide distribution of alpine meadow in this alpine environment. To make frequent and long period records of meltwater runoff and sediment processes in the very high elevation and isolated regions, an automatic system was installed near the glacier snout to measure the transient discharge and sediment processes at 5 min interval. Diurnal fluctuations of discharge, and suspended sediment concentration (SSC) were recorded at high frequency for the Zhadang glacier, before suspended sediment load (SSL) was computed. Hourly SSC varied from the range of 0.2 kg/m3 to 0.5 kg/m3 (at 8:00～9:00) to the range of 2.0 kg/m3 to 4.0 kg/m3 (at 17:00～18:00). Hourly SSC was linearly correlated with discharge (R2>0.8). Air Temperature fluctuations influence discharge, and then result in the sediment variations. The results of this study provide insight into the responses of suspended sediment delivery processes to solar irradiations.In order to further discuss the process of meltwater erosion "temperature-Discharge-Sediment", the empirical model of the meltwater erosion was established based on the data in the Qugaqie catchment. There is a good index series relationship between the temperature and meltwater runoff (R2=0.7105), and a god linear relationship between discharge and sediment. The digit-eight hysteresis loop was observed for the sediment transport in the glacier area. The meltwater erosion empirical model would be used to simulate the daily sediment yield with the temperaturein the cold regions, and the relative error is only 7.41%. Under the background of global warming, there is important realistic guiding significance for understanding the meltwater erosion mechanism and the meltwater erosion sediment yield simulation. |
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