The natural environment of Tuotuo River

The Tuotuo River Basin is located deep in the hinterland of the Qinghai-Tibet Plateau. It has a high terrain, thin air, high mountains in the north and south, closed terrain, and is weakly affected by the oceanic wind system. It is an area controlled by high-altitude westerly winds. The climate is dry and cold, with more wind and less rain, changeable weather, and low temperatures all year round. There are no obvious four seasons, only the difference between dry and wet seasons. The dry season is from October to April, and the wet season is from May to September. The annual average temperature along the Tuotuo River is -4.2℃, the hottest average temperature in July is 7.5℃, the coldest average temperature in January is -24.8℃, and the extreme minimum is -33.8℃. The annual freezing period lasts for 7 months. If the vertical lapse rate of temperature increases by 100 meters and the temperature drops by 0.6°C, the source of the Tuotuo River at an altitude of 5820 meters is 1287 meters higher than the altitude of the Tuotuo River at an altitude of 4533 meters. Then the annual average temperature at the source of the Tuotuo River should be approximately is -12℃, and the average monthly temperatures are all negative.

The Tuotuo River Basin is in the westerly wind belt, and westerly winds prevail in the winter half of the year. The wind season is from November to March of the following year. The annual average wind speed along the Tuotuo River is 3.9 meters/second, and the maximum wind speed is about 40 meters/second, which is equivalent to level 12. There are an average of 74.5 days of strong winds above level 6 per year, accounting for 72% of the annual windy days. In 1972, there were 134 days of strong winds above Category 6. There are many sandstorms from January to May every year. In March 1966, a sandstorm lasted for 12 days near the Tuotuo River. Due to the high altitude and low air pressure, the oxygen content of the air is only 43% of that at sea level. People in this area are prone to altitude maladaptation, which is a reaction to high altitude hypoxia, such as dizziness, headache, weakness in limbs, rapid heartbeat, nausea and vomiting, etc.

The climate in the basin is dry and precipitation is low. According to actual measurement data, the annual average precipitation along the Tuotuo River is 283.1 mm, the maximum monthly precipitation is 174 mm (July 1972), and the maximum daily precipitation is 34.4 mm (July 17, 1963). Precipitation is concentrated in July and July. There are three months: August and September, with July being the largest. May to September account for 85% to 96.7% of the annual precipitation. Of the 98.7 average annual precipitation days, 57.9 days have snowfall. The average annual thunderstorm days are 58.2 days. The annual average number of hail days is 18.4, with a maximum of 30 days, concentrated from June to September. The annual evaporation is between 1170.8 and 1660.8 mm. The Tuotuo River has a long freezing period. In April every year, the temperature rises, the melting water from ice and snow begins to recharge, and the water level rises. With the arrival of the wet season on the plateau, precipitation increases, and the water level increases after June. The annual highest water level appears in August, and the water level gradually decreases in October, with an annual range of about 0.90 to 1.60 meters. Changes in water regimes and freezing and thawing processes are all controlled by climate conditions.

The Tuotuo River has many wide and shallow sections, so there are many scattered flows, overflow rivers, branches and ditches. The water is shallow and the flow speed is not high.

The water collection area controlled by the hydrological station along the Tuotuo River is 15,924 square kilometers, with an average annual precipitation of 283.1 mm, an average annual runoff depth of 51.9 mm, a measured maximum flow of 750 cubic meters/second, a minimum flow of 0, and a multi-year average The flow rate is 26.2 cubic meters/second, and the multi-year average annual runoff is 826 million cubic meters. The water catchment area above the mouth of the Bayongtuo River in Nangji is 17,616 square kilometers. According to the Qinghai Provincial Hydrological Station, the multi-year average flow of the Tuotuo River Estuary is 29.1 cubic meters per second, and the multi-year average annual runoff is 918 million cubic meters. The annual runoff of the Tuotuo River accounts for approximately 7.7% of the annual runoff of the Tongtian River Yushu Zhimenda Hydrological Station.

In 1978, the Yangtze River Source Investigation Team measured the water level, flow velocity and flow rate in some areas of the Tuotuo River. At 17:00 on July 10, the flow rate of the Tuotuo River estuary was measured to be 35.4 cubic meters per second, the cross-sectional area was 42.1 square meters, and the water surface was 61 meters wide. On July 23, it was measured that the average velocity of glacier water on the north side of Jianggendiru Peak was 1.14 meters/second, the average water depth was 0.4 meters, the water surface was 5 meters wide, and the flow rate was 2.28 cubic meters/second. On July 24, it was measured that the average velocity of the glacier water on the south side was 0.88 meters/second, the average water depth was 0.40 meters, the water surface was 14 meters wide, and the flow rate was 4.97 cubic meters/second. On July 18, the measured flow rate at the confluence of Naqinqu and Chesumeiqu was 12.1 cubic meters per second, with an average flow speed of 0.87 meters per second, a maximum flow speed of 1.24 meters per second, an average water depth of 0.3 meters, a maximum water depth of 0.7 meters, and a wide water surface. 46.4 meters.

From Qie Sumei Qukou to Bolong Qukou, the water source of Tuotuo River mainly relies on the melting water of mountain ice and snow. On July 19, 1978, the Jiangyuan expedition team observed the water level at the mouth of the Naqinqu Canyon. At that time, the daily temperature was -3.2°C at 8 a.m. and 25°C at 14:00, with a daily range of 28.2°C. As the daily temperature changes, the water level rises and falls regularly throughout the day. The water gauge reading was 0.12 meters at 12:00 that day and 0.44 meters at 24:00, with a variation of 32 centimeters.

The average slope drop of the Tuotuo River from Bolongqukou to Nangji Bayong is 1.29‰, and the maximum water level variation over the years is less than 2 meters.

The upper sources of the main branches and tributaries of the Tuotuo River are mostly snow-capped mountains and glaciers, which provide a large amount of melted ice and snow water. Because the ground temperature and air temperature are both low, the water temperature is also low. The average monthly water temperature along the Tuotuo River from July to September 1978 was 3.7°C to 6.9°C, with the maximum value being 9.2°C.

The sediment particle size of the Tuotuo River changes greatly along the way.

The median particle size of bed sand is 41.5 mm at the confluence of Chesumequ, 43.9 kilometers away from the river source, 16.5 mm 2 kilometers below the confluence of Larigan Muzhangba River, 61.1 kilometers away from the river source, and 16.5 mm at 285.9 kilometers away from the river source. The Tuotuo Riverside is only 3.5 mm, and the Nangji Bayong is 3.3 mm. Modern glaciers are very developed in the snow-capped mountains such as Geladandong, Gaqiadiru Gang and Gangqin at the source of the Tuotuo River. The types of glaciers include cirque glaciers, hanging glaciers, valley glaciers, flat-top glaciers and transitional cirque hanging glaciers. , cirque valley glaciers, etc.

Glacier area: There are 55 glaciers in the outflow water system of the Gradandong Snow Mountain Group, covering an area of ??394 square kilometers; there are 30 glaciers in the inland water system, covering an area of ??268 square kilometers, totaling 662 square kilometers. There are 16 glaciers in the outflow water system of Gaqiadi Rugang Snow Mountain Group, covering an area of ??94.4 square kilometers, and 10 glaciers in the inland water system, covering an area of ??111.0 square kilometers, totaling 205.4 square kilometers. There are 14 glaciers in the outflow system of Zulken Ula Mountain, covering an area of ??73.8 square kilometers, and 6 glaciers in the inflow system, covering an area of ??20.0 square kilometers, totaling 93.8 square kilometers. There are 85 glaciers in the outflow water system of the three snow-capped mountain groups of Geladandong, Gaqiadiru Gang and Zulkenwula Mountains, with a total area of ??562.2 square kilometers; there are 46 glaciers in the inland water system with a total area of ??399 square kilometers.

According to the development of fore moraine, there are also conditions such as the existence of ice core ridge and the separation of branch glaciers from the main glacier in the lower reaches of the glacier tongue. Glaciers in the Tuotuo River Basin continue to experience periodic decline after the Little Ice Age. During the inspection in 1978, it was found that the glacier had significantly melted and retreated. The ice cave during the inspection in 1976 had melted and collapsed two years later and no longer existed.

The glaciers in the Jiangyuan area have the following characteristics:

1. High snow line

Due to the dry and cold climate, the high altitude of the snow area, the development of glaciers has the characteristics of continental glaciers. The snow line on the west slope of the Gradandong Snow Mountain Group reaches an altitude of 5820-5870 meters, on the south slope it is 5760-5770 meters, on the east slope it is 5740 meters, and on the north slope the lowest is 5540 meters. It is higher than most snow-capped mountains and glaciers on the Qinghai-Tibet Plateau.

2． The snow line temperature is low

Based on the temperature along the Tuotuo River, the average annual temperature at 5540 meters above the snow line on the northern slope of the Gradandong Snow Mountain Group is -10.2°C.

3． The development of glaciers on yin and yang slopes is asymmetric

The snow line of yin slopes in the Gradandong Snow Mountain Group is lower than that on sunny slopes, and the scale of glaciers on sunny slopes is larger than that on shady slopes. Affected by the terrain, valley glaciers with large snow basins develop on a larger scale due to sufficient supply.

4. Glacier ablation is not intense

In summer, solar radiation heat is the main heat source for glacier ablation. The average temperature in July at the 5,500-meter snowline of Gradandong Snow Mountain is 0°C. The expedition team spent four days on the glacier on the north side of Jianggendiru Peak from July 22 to 26. The average temperature was 1.2°C at 8 a.m. and 5.1°C at 8 p.m. , so the glacier melt is not strong.

The glaciers in the eastern Gradand area are mostly white, with very little blue ice. The pores are small and the tubular pores are not large. The ice at the front of the glacier tongue is denser and solid. On the glacier shear surface, a considerable amount of mud and gravel are often carried, and the glacier is highly polluted. The source area of ??the Yangtze River has been strongly uplifted since the Quaternary Period and has become a high plain with an altitude of more than 4,500 meters. With the arrival of the ice age, the climate turned colder and the earth's surface gradually cooled. Permafrost forms when surface heat consumption exceeds heat flow from the Earth's interior. The northern boundary of the permafrost in the Jiangyuan area is near Banxi Beach, Qinghai-Tibet Highway No. 61 on the northern slope of Kunlun Mountain, with an altitude of 4,350 meters; the southern boundary is at Qinghai-Tibet Highway No. 116-117 on the southern slope of Tanggula Mountain, with an altitude of 4,780 meters and a width of about 600 kilometers from north to south. Extending westward to the Qiangtang area in northern Tibet, it is the only area in the world's middle and low latitudes that has a large area of ??thick permafrost. The permafrost layer in the Tuotuo River Valley in between is about 8 to 88 meters thick, and the higher parts of Tanggula Mountain and Kunlun Pass are 128 to 175 meters thick.

The frozen soil in the Tuotuo River Basin will appear frost-heaving cracks, frost-heaved soil, ice vertebrae, frost-heaved hills and other phenomena in the winter half of the year. In the summer half of the year, ice melting, melting and freezing collapse, etc. will occur. Thermal melt subsidence, thermal melt lakes and ponds, and thaw-frozen mudflow phenomena. In summer, only the surface layer 1 to 4 meters thaws. In winter, the surface layer freezes again and is connected to the permafrost below. It develops deeper and increases the thickness of the frozen soil.