Yiyang weather forecast

The Yellow River, the second longest river in China, originated in Bayan Kara, Qinghai. Its main stream runs through nine provinces and regions, and flows through Qinghai, Sichuan, Gansu, Ningxia, Inner Mongolia, Shaanxi, Shanxi, Henan and Shandong, with a total length of 5,464 kilometers, a drainage area of 750,000 square kilometers, an annual runoff of 57.4 billion cubic meters and an average runoff depth of 79. But the amount of water is not as big as that of the Pearl River. There are 35 main tributaries along the way, with Huangshui River and Taohe River in the upper reaches, Qingshui River, Fenhe River, Weihe River and Qinhe River in the middle reaches, and Yihe River and Luohe River in the lower reaches. There are no lakes on both sides of the river, and the lower reaches of the Yellow River are very small, and few rivers flow into the Yellow River. The estuary of the Yellow River is1500m wide, generally 500m, the narrower part is only 300m, and the water depth is generally 2.5m.. In some places, the depth is only 1.2 ~ 1.3 meters. Geographical environment: From Heyuan to Guide, it is a mountainous and grassland plateau, belonging to the Qinghai-Tibet Plateau. The peaks are all above 3000 meters above sea level; The upper valley is over 4200 meters above sea level. The terrain on both sides of the upper valley is gentle and the drainage is not smooth; Causing large areas of swamps and many lakes. Guide's reach from Jinmeng River is the Loess Plateau, with Xibe and Weihe valleys in Lvliang in the south, Ordos Plateau in the north and Lanzhou Valley in the west. The elevation of the Loess Plateau is generally 1, 000- 1, 300m, with uneven landform and steep slope. The gully ground slope is 1.5-20 degrees, the gully area accounts for 40-50%, the gully density is 3-5km/km2, and the cutting depth exceeds/kloc-0. Below Jin Meng, it enters the low-lying North China Plain, with an altitude of no more than 50 meters. After entering the downstream, the river channel is flat, and the average gradient is only 0. 12%. The water flow slows down and a lot of sediment is deposited, which is 4-5 meters above the ground. Due to the repeated diversion of the Yellow River, the fan-shaped ancient riverbed and ancient natural dike have become inclined plains with alternating gentle hills and depressions, and the depressions are relatively open and flat. Ecological characteristics There are 98 species of pure freshwater fish 12 1 species (subspecies) in the mainstream of the Yellow River, accounting for 78.4% of the total. The main economic fish are naked spotted carp, flat-edged swallowtail, thick-lipped naked heavy-lipped fish, yellow river naked-lipped fish, yarrow, northern Tongyu, carp, crucian carp and so on. There are only 16 species of fish in the upper reaches of the Yellow River, and the composition is relatively simple. Cyprinidae and Misgurnus only have Schizothorax, Cynanchum auriculatum, yarrow, Misgurnus anguillicaudatus and so on. Fish in the middle and lower reaches are generally similar, mainly CYPRINIDAE. There are 7/kloc-0 species of fish in the middle reaches, but there are no typical plain fish such as silver carp, bighead carp, bighead carp and bream. There are Schizothorax and Misgurnus anguillicaudatus in the upper reaches of the middle reaches, and 78 species of fish in the lower reaches, including a variety of fish crossing estuaries and brackish water. According to the survey data of tributaries of the Yellow River, according to the fish statistics of Taohe River in Gansu, Weihe River in Shaanxi and Jinghe River, there are 30 species in Weihe River, followed by Taohe River 1 1 species, and only 4 species in Jinghe River. Most of the tributaries in the middle and upper reaches are small fishes of CYPRINIDAE and Misgurnus, a few are Tasmanian fishes and catfish, and the economic fishes are carp, crucian carp, yarrow fish and catfish. Fishery production: The main catch species of the Yellow River have also changed. The fish in the main stream has the highest yield ever, and the "Yellow River Carp" is famous all over the country. Now the yield has dropped significantly. Before the 1960s, carp in the middle reaches of Shanxi and Shaanxi accounted for 60-70% of the catch, ranking first in the catch composition. According to the change of catch in Shaanxi port section of the Yellow River in the last ten years, carp only accounts for 2 1% of the catch, catfish replaced the main position in 4 1. 1%, followed by Astragalus. 1983, the fishing situation of the Yellow River in Pinglu County, Shanxi Province was investigated. Among them, only 20% of carp and 60% of catfish are the main catches. In the early 1950s, carp accounted for 50-70% of the total output in the lower reaches of Shandong Province, but it dropped to 15% in the 1960s and only 7. 1% in 1982. The situation of fishery labor force in eight provinces along the main stream of the Yellow River is as follows: Except Qinghai Province, the fishery labor force in Gansu, Ningxia, Inner Mongolia, Shanxi, Shaanxi, Henan, Shandong and other seven provinces was 26,964 in 1980, and it decreased to 1 1320 in 1983, accounting for 3.0% and 2.65438+ of the total similar labor force in China respectively. Part-time fishing labor force was 24,843 in 1980, and increased to 25,873 in 1983, accounting for 8.9% and 5.7% of the total similar labor force in China respectively. In recent 30 years, the resources of carp, the main economic fish in the Yellow River, have been greatly reduced, and the composition of its catch groups has also changed accordingly. In the early 1980s, most of the carp caught in the Tongguan section of the Yellow River were 3 years old, with an average weight of 0.7 kg per tail accounting for 44.7%, followed by 28.4%, and the average weight in the fourth year was 1.5 kg. Fishing method: fishing method, the fishing gear used in fishery production in the main stream of the Yellow River, the gill net is the main fishing gear in the middle and upper reaches, and there are also beach seines. The gill net is divided into single layer and three layers, and the three layers gill net is more efficient. In addition, there are many kinds of roll fishing, including hooks and clips, only four or five in the middle reaches. Characteristics of fishing area: The upper reaches are Schizothorax subfamily, Schizothorax subfamily, Schizothorax subfamily and Schizothorax subfamily. ? ? ? There are 8 species in the family, with carp, crucian carp and catfish in the middle reaches and Coilia ectenes, grass carp and catfish in the lower reaches. Upstream: From Heyuan to Guide, there are mountainous and grassland plateaus on both sides, with an altitude of over 3,000m and a peak of over 4,000m m.. The river course is S-shaped, and the river course twists and turns within 400 kilometers of the headwaters. There are many lakes, grasslands and swamps on both sides of the strait, with clear and stable water flow, less water consumption and large water production. There are many lakes, the largest of which are Xingsuhai and Eling Lake, with cold plateaus and fish systems. Fish resources have not been exploited for a long time. Middle reaches: Jin Meng tour guide, multi-path alpine canyon, with fast current and steep slope. The Liujiaxia Valley is extremely deep, with a river width of 50-70 meters, a narrowest point of less than 15 meters, a valley depth of 100-500 meters, and water flow.