Geographical environment of Chengxiang District

Chengxiang District is located at the intersection of Changle-Nan 'ao fault zone and Zhangping-Xianyou east-west structural zone, and the geotectonics belongs to the eastern subsidence zone of the second uplift zone of New Cathaysia in East Asia. The northwest of the structural unit is Fuding-Xiao Yun fault depression zone in Yanshan fault depression zone in eastern Fujian; The southeast is the metamorphic belt along the southeast coast of Fujian. This area is dominated by east-west fault structures. Zhangping-Xianyou east-west fault zone formed in the early stage runs through the main stream of Mulan River. The structure consists of a series of east-west compound folds and thrust faults, mainly including: Yongchun Chengguan-Xianyou Gaiwei, Suburb-Putian Huangshi, Hushi fault, etc. Its eastern end passes through Xinghua Plain and reaches Xinghua Bay. Generally, the fault length is about 5km, and the longest is12km. The width of extrusion crushing is generally 3 ~ 5 meters, and the widest point is 50 ~ 70 meters. There are many hot springs exposed along the fault, which are distributed in the east-west direction. Mulan Village in Chengnan Township has Huangtou, Shanghang Bridge, Goutou Village and Guanghua Temple.

The differential fluctuation of neotectonic movement in China is characterized by gradual transition. Northwest China rises more along fault blocks, forming hills and mountains, generally between 300-500 meters above sea level; The middle part is a low hill platform, which is located in the piedmont zone where the crust rises and falls alternately; The lower reaches of Mulan River in the southeast are fault blocks cut by multiple sets of faults, which are relatively gentle and open areas, forming the Beiyang Plain (a part of Xinghua Plain) with mixed accumulation of rivers and seas, which is composed of fine sand, silt, silt and marine materials. The landform of Chengxiang District is generally high in the northwest, hilly and mountainous, low in the southeast, open and flat, and it is Beiyang Plain. Geomorphological combinations in China can be divided into three different types.

Erosion and denudation-low mountains with structural landforms, distributed in the western and northwestern border areas, mainly including Jijiaoji and Shiguan Mountain, with an altitude of 500-600 meters. Due to long-term erosion and river cutting, the mountain fluctuates greatly, and the slope is generally above 30 degrees. Area13300mu, accounting for 1 1.22% of the total area of the whole region. Mountain valleys, distributed in the western and northwestern mountainous areas, are 200 ~ 300 meters above sea level. Valley basins are small in scale and different in shape, and their extension direction belongs to structural valley basins, mainly including Baiyanggu Basin and Zhukenggu Basin. The area is 0.65438 0.8 million mu, accounting for 65438 0.52% of the total area of the whole region. The erosion and denudation landform is hilly, distributed on both sides of mountains and valleys, with an altitude of 50-500m and a slope of 10-25 degrees. The area is 19600 mu, accounting for 16.54% of the total area of the whole region. Terraces, distributed around the plain and in the piedmont area at the edge of the valley, are below 50 meters above sea level and the slope is below 10 degrees. The area is 20 10000 mu, accounting for 16.96% of the total area of the whole region. The accumulation landform plain is distributed in the coastal areas downstream of Mulan River and Yanshou River. The landform is characterized by low altitude (2-6 meters) and flat terrain, forming a new era. In the process of landform development, it is not only influenced by flowing water erosion and river accumulation, but also influenced by ocean dynamics, forming the Beiyang Plain with mixed accumulation of rivers and seas. It covers an area of 63,700 mu, accounting for 53.76% of the total area of the region. Cheng Xiang belongs to the south subtropical maritime monsoon climate, with evergreen seasons. The monsoon is obvious, and the main wind directions are northeast wind and southwest wind. The wind direction of winter and summer monsoon changes obviously with the seasons. The northerly winds prevail in winter, southerly winds prevail in summer, and spring and autumn are the seasons when the wind direction changes. The wind power is generally 4 ~ 5, and the maximum is above 7. There are more windy days, about 20 days per month, short time 1 day, and old people1day. At the turn of summer and autumn, there are 1 1 typhoons in the maximum year and 2 typhoons in the minimum year. It is warm in winter and hot in summer, and the annual average temperature is 19.0 ~ 20.2℃. The southeast plain area is influenced by the maritime climate, and the annual average temperature is >: 20℃; The northwest is located in the piedmont zone, with a slightly lower temperature, and the annual average temperature is ≥ 19℃. Summer is long and winter is short, with 165 days in summer, accounting for 45% of the total days in the whole year. Winter is the shortest, only 28 days, accounting for 8% of the total days of the year. The spring and autumn confrontation accounts for 47% of the total number of days in the whole year. The annual average temperature is 20℃, the annual average sunshine 1947 hours, the annual average water volume 1300mm, and the frost-free period is 320-350 days.

There are many kinds of disastrous weather, such as rainstorm, flood, drought and typhoon. Rivers in this area belong to mountainous rivers, which are characterized by abundant water, large seasonal changes and short flow. The main rivers are Mulan River, Yanshou River and Xiamoxi River. The river flows from northwest to southeast and flows into the open sea from west to east. Mulan River is the largest river in China, which originates from the bridge head of Huangkeng in Xianxi Village, Xiyuan Township, Xianyou County, passes through Xianyou to Laixi in Huating Town, Putian County, crosses Beiyang Plain from west to east, and winds in Mulan, Xiaocuo, Huang Xia, Xinxi, Kuankou, Gushan, Dai Li, Lipu, Doumen, Jang Jin, Zhu Xi, Dongyang and other villages. Total length 105km, with a domestic length of 20.4km. The total drainage area is 1732 km2, and the domestic drainage area is 48. 1 km2. Runoff: 65.438+56.4 million cubic meters in wet year, 979 million cubic meters in normal year and 559 million cubic meters in dry year (Mulan Control Station). Yanshou River is the largest tributary of Mulan River in China. Originated in Linquan Temple, Xinlian Village, Zhongshan Town, Xianyou County, it flows through Jiuli Lake and enters Juxi and Dongzhen Reservoir in Changtai Town, Putian County. It flows through Huasi, Yanshou, Changlin, Nanjiao, Xinjiao Village and Doumen Village in suburban township, and flows into the main stream of Mulan River. The total length is 5 1 km, and the domestic total length is 13.5 km. The total basin area is 386 square kilometers, and the domestic basin area is 24.2 square kilometers. The average slope decreased to 9.4‰. Runoff: 572 million cubic meters in wet year, 356 million cubic meters in normal year and 200 million cubic meters in dry year (Caozhu Control Station). Xiamoxi, also known as Beimoxi, originates from Qiao Lin Village in Chengnan Township, flows through the urban area and the south gate, and joins the mainstream of Mulan River at Doumen in suburban township. The total length is 4. 1km, and the drainage area is 6.7km2 ... This stream is the largest flood discharge channel crossing the urban area in China, with the flood discharge of 18 ~ 24 cubic meters per second.