Geographical environment of Du 'an Yao Autonomous County

The geological structural unit where Du 'an is located is Duyangshan Uplift on the east side of Youjiang Regenerated Geosyncline, adjacent to Laibin Fault Fold Belt in Gui Zhong Depression in the east, Damingshan Uplift Belt in the west, Jingxi-Tiandong Uplift Belt in the south and Xilin-Baise Fault Fold Belt in Guixi Depression in the west.

The geological structure system is the middle section of the west wing of Guangxi gable front arc. Folds and faults are distributed in the northwest direction and spread all over the country. The principal compressive stress is northeast-southwest and the compressive structure is northwest. Secondly, there are northeast and north-south tectonic systems in Long Fu and Zhongjiu-Yongshun areas, and the compressive structural planes are northeast and north-south respectively. Jiangnan and Jingshan also have east-west structural systems, and the compressive structural planes are nearly east-west.

China stratum, from Middle Devonian in Upper Paleozoic to Quaternary in Cenozoic, is exposed except Jurassic stratum in the middle. Carboniferous and Permian are the most widely distributed. The total sedimentary thickness of strata in the county is 75 10/0m. Among them, the Middle Devonian to Upper Permian is a continuous shallow-sea carbonate rock with a thickness of 5300 meters, accounting for 70% of the total thickness of sedimentary rocks; Triassic marine clastic rocks and Cretaceous lacustrine clastic rocks, with a total thickness of 22 10/0m. Du 'an is located at the foot of the slope from Yunnan-Guizhou Plateau to Guangxi Basin. The terrain is high in the northwest and low in the southeast, with the highest in Long Fu, Xiaao, Baoan and Sanzhiyang areas. The elevation of mountain peaks is mostly 800 ~ 1000 meters, and that of depressions and valleys is 600 ~ 800 meters. Sudi, Chengjiang, Baiwang and other areas are low-lying, with the peak elevation of 400 ~ 600 meters and the valley elevation of 145 ~ 200 meters, of which the lowest Baiwang is only 80 meters above sea level.

Du 'an County is one of the most typical karst landform areas in China. The area is densely covered with depressions and continuous rocky mountains. Underground river skylights, peak clusters, peak forests and other geomorphic units are beautiful and spectacular, and most of the rocks on the mountain are limestone, which is known as the "kingdom of rocky mountains". Du 'an County has a subtropical monsoon climate, with continuous rainy days and few sunshine hours in spring. Summer is hot and humid, and heavy rain is concentrated; Autumn is crisp, and autumn drought often occurs; Winter is cold and rainfall is scarce. The average annual rainfall in Du 'an County is 1726 mm. ..

The temperature in Du 'an County is slightly higher in the valley and lower in the mountainous area, which is 2 ~ 3℃ lower than that in the valley. The annual average temperature is 19.6℃ ~ 2 1.6℃, of which 1 month is the lowest, and the average temperature is 12.2℃, and it is the hottest in July with an average temperature of 28.6℃. The measured extreme maximum temperature is 39.6℃ (measured by1990) and the extreme minimum temperature is-1.2℃ (measured by1977). Rivers: The surface rivers in Du 'an belong to the Xijiang River system in the Pearl River Basin. There are *** 10 rivers with a rainfall collection area of more than 20 square kilometers, among which there are three rivers with a normal flow of more than 25 cubic meters per second: Hongshui River, Diaojiang River and Chengjiang River.

Hongshui River: Originated in Maxiong Mountain, Zhanyi County, Yunnan Province, it flows into Du 'an and then into Xincheng County.

Hongshui River has a domestic flow of 95 kilometers and a rainwater collection area of 3,500 square kilometers. Annual average water level112.47m; Annual maximum flow 18700 m3/s, annual minimum flow 203 m3/s and annual average flow 2032 m3/s: average runoff depth is 538.2 mm, and runoff is 64.2 billion m3. According to the field investigation, the flood discharge force of 1926 is 2 1800 m3/s, and the water level is 150.29 m, which is the highest in the past years.

Diaojianghe: Originated in the great western slope of Chehe Town, Nandan County, it flows into the county seat from Guti Village, Baoping Township, Hechi City, and joins Hongshui River in Nahaotun, Fu Ba Village, Baiwang Township.

Living flow 124 km, rainwater collection area 1985 km2, riverbed width 50- 100 m, undercut depth 15- 18 m, and gradient1./kloc-0. Annual maximum flow 1770 m3/s (1984), annual minimum flow 3.24 m3/s (1975) and annual average flow 3.4m3/s. The average runoff depth for many years is 69.4 1 mm, and the runoff is 2.304 billion. 1945 The flood flow is 3380m3/s, and the water level is 128.88m, which is the highest over the years.

Chengjiang: It originates from the lower rock beach of Guanyin Mountain in Jiudun Village, Daxing Township and the east beach of Baiyangtun Village in Taiyang Village, the county town. It flows through Daxing, Gaoling, Anyang, Chengjiang and other towns from north to south, and finally joins the Hongshui River in Longjing Village, Chengjiang Township.

The whole distance of Chengjiang River is 4 1km, and the accumulated rainfall is 1 170 km2. The riverbed is 50-80m wide, the undercut depth is 5 5- 10/0m, the gradient is 1.55‰, and the annual maximum water level at the Yellow Sea base level is1.51.69m.. The annual maximum flow rate is 520 m3/s, the annual minimum flow rate is1m3/s (19801.2), and the annual average flow rate is 25.3m3/s. The annual average runoff depth is 84.5 1 mm, and the runoff is 892 million cubic meters.

The maximum flood flow in the last century is 790 cubic meters per second, corresponding to the water level 153.07 meters (1945). Since the founding of the People's Republic of China, the highest flood level in Chengjiang River has been151.99m (1968). Groundwater: According to the hydrogeological investigation and statistics, there are 25 underground river systems and 80 main tributaries (including 55 tributaries) in Du 'an County, with the total length of the main stream of 445.2km, the catchment area of 388 1 km2, the maximum total flow over 92 1.9m 3/s and the minimum total flow14.273. Underground rivers with a flow of1100,000 m3 and a flow exceeding 10 km include Sudi, Bangzu, Daxing, Laleng, Zhongxiu, Li Xia, Daihe, Bama and Yongren.

The largest underground river system in the county is Sudi underground river system, whose upstream originates from the mountainous area of Dahua Yao Autonomous County for more than 700 miles and flows through Baoan, Dongsi, Sudi and other places. From the underground, from northwest to south, it flows into the Hongshui River in Sudi Qingshui Village. The total length of the main stream is 57.2km, with tributaries 12, and the rainwater collection area1054km2. The maximum flow is 4 14 m3/s, the flow in flood period is over 500 m3/s, the minimum flow is 3.584 m3/s, and the annual runoff is165438+59 million m3. It is one of the largest underground river systems in Guangxi.