There are two kinds of meanders: free meander and deep meander. Free meanders are developed in alluvial plains, with gentle terrain and relatively free river swings, such as Jingjiang meander, Weihe meander and Mississippi meander. Deep meanders develop in hills or mountains, and rivers are restricted by valley topography and cannot flow freely. Compared with the free meander in the flooded plain, the deep meander is even rarer. Another big difference is that the free meander swings freely on the plane, and it is difficult to climb to the top of the mountain except for its winding shape. But the deep meander is different, because the concave bank of the river is eroded by the current and retreats, forming a cut wall; The slope of the convex bank valley is gentle, gravel piles up, and the coastline extends to the river, forming terraces. Lateral erosion and accumulation are carried out at the same time, so we can find a commanding height to explore its corner or even the whole picture.
When the meander is extremely developed, it cuts into the neck of the meander and straightens, leaving the core of the meander, forming isolated hills called Lidui Mountain, whose name is quoted from the title of Yan Zhenqing, a great calligrapher in the Tang Dynasty. When Yan Zhenqing was relegated to Pengzhou (now Yinda Town, Yilong County), he passed Cangxi and saw that the Baihe Mountain in the north of the city was not connected with the surrounding mountains, so he called it "Lidui Mountain". Later, I traveled to the New Deal (now the resident of Xinxian Town, Yilong County) and found that Potou Mountain behind the town was not connected with other mountains, so I carved a stone to record the story of Xianyu leaving the pile. According to research, there are 28 Lidui Mountains on Jialing River from ningqiang county, Shaanxi to Nanchong, Sichuan, and Yanshan Mountain, which is about 100 meters behind the neck of Qingju meander, is one of them. Yanshan used to be a fortress of Shuiguan, which gathered many historical sites such as Chunyou Ancient Town, Wang Ping Tomb and Hongqi Farm. On the Yanshan Mountain, the perfect posture of the green house is in sight.
Because of its complex shape, meanders are abstracted into V-type, U-type and ω-type in geomorphology, of which V-type is the most common, followed by U-type, and ω-type is relatively rare, which is another manifestation of Qingju meander as a spectacle.
After calculation in Ainan Mountain, the closure rate of Qingju meander is 0.98, which is the same as that of Petropolis meander of Lua River in Bassirou, one of the largest meanders in the world at present. The bending coefficient of Qingju bend is 42.75, but it is less than the latter's 47.67. But the latter is a free meander, while the Qingju meander is a rare deep meander.
Jialing River has created one winding beauty after another, forming a winding belt.
Take a boat ride from Nanchong to see the meandering green house, follow the winding river, still in the right front of Yanshan Mountain, and enter the field of vision from the left front without much effort. Walking slowly around Yanshan Mountain, you can feel the winding and smooth radian of Qingju from a distance, but it is difficult to understand it when you are in it. You can only see some small continents scattered on the calm water, boats and boats, waterfowl flying, and beautiful wild flowers blooming all over the mountains along the coast.
Qingju Hequ is so peculiar because it is closely connected with Jialing River. "What color is Jialing River? Shi Dai and Jasper live together. Breaking the waves every day, spring comes and sand returns, and I pity. " Just as Du Fu, a great poet in the Tang Dynasty, said, it is the ingenuity of nature that created the wonders of the winding Jialing River, and also created one winding beauty after another, forming a winding belt. Judging from the bending coefficient, the meandering belt of Jialing River is one of the most curved sections in the world. Among them, the bending coefficient of Vu Thang meandering belt is close to 3.0, which is second only to Shenandoah River in the United States (bending coefficient 3.25) and Baibangdama River in C? te d 'Ivoire (bending coefficient 3.05). This meandering belt runs from Qingju Town in Wusheng County to Longnv Township.
In fact, when 1940 China Institute of Geography was newly established in Chongqing, an investigation team of Jialing River Basin was established, with members including Li Chengsan, Zhou Tingru, Guo Lingzhi and Gao Yongyuan. The expedition lasted more than 8 months and traveled more than 4,000 kilometers. Basically, I observed on foot and did a lot of research on the distribution, causes and evolution of meandering river, terrace and Lidui Mountain in Jialing River.
According to the research of the investigation team, the smaller the slope of the river, the easier it is to form a meander. However, the development of meandering makes the riverbed smaller, which is mutually causal. The bed gradient of Jialing River gradually decreased from 0.7 meters per kilometer to 0.26 meters per kilometer from below Zhao Huahu Tiaoyi to Li Du in Peng 'an. The meander developed and the river width widened. The downstream slope increases slightly, and the meander also decreases. Rock properties have great influence on lateral erosion of rivers. The red shale area between Peng 'an and Nanchong is extremely vulnerable to erosion, in which meanders are the most abundant.
Zhang Bin, an associate professor at the School of Land and Resources of West China Normal University, told reporters that Jialing River runs from its source to the upper reaches of Guangyuan Zhao Hua. The geological structure of this section is complex, controlled by tectonic movement and lithology, and meandering distribution is sporadic. For example, there is an obvious meandering belt around Jiheyuan Village and Wangjiazhuang Village in Fengzhou Town, Fengxian County, Shaanxi Province, a large W-shaped meandering at the junction of Huixian County and liangdang county in Gansu Province, and four large U-shaped meandering from Lueyang County in Shaanxi Province to Luojiaping in Guangyuan. From Hechuan, Chongqing to Chaotianmen, it is the lower reaches of Jialing River, and the valley is deep, forming a large U-shaped meander only in Beibei.
However, from Zhao Hua to the middle reaches of Jialing River in Hechuan, the structure is gentle, the lithology is soft, and most of the rivers along the structure are oblique basins with perfect meandering. In particular, the section from Jinxi to Hechuan is a typical deep deformation meander, known as the "nine-bend ileum", where Qingju meander is located.