Geographical environment of Caotang town

Caotang Town is located about 9 kilometers southeast of Huxian County, bordering Taiping River in the east, Dongda in Chang 'an District, Taiping Township at the northern foot of Qinling Mountain in the south, Pangguang Town in the west and Qin Dou Town in the north. The total area is 40 square kilometers. The center position is about east longitude108 43' and north latitude 34 03'.

Caotang town can be roughly divided into two parts in geological structure: the southern mountainous area is mainly a part of the North Qinling fold belt; The northern plain is an integral part of the Weihe graben. The North Qinling fold belt is a complex structural belt with long-term activities, diverse magmatic intrusion activities, strong rock metamorphism and frequent structural changes. Its stratigraphic age belongs to Archaean to Proterozoic in geological history, with Qinling Group of Pre-Sinian system and Kuanping Group of Great Wall system as the main bodies, and the rocks are medium-deep metamorphic rocks, mainly schist, gneiss, granulite, marble, amphibole and migmatite. Weihe graben is a long-term declining fault basin since Mesozoic. Quaternary sediments in the latest geological history are distributed in China graben, including Middle Pleistocene, Upper Pleistocene and Holocene. The Middle Pleistocene is mainly distributed in shallow mountainous areas and low gentle slopes in front of mountains, and consists of brown, brownish yellow loess and gravelly clayey silt, mostly aeolian deposits. The Upper Pleistocene is distributed in the piedmont area and consists of gravel, clayey silt and loam with different sizes. The main reason is proluvial, which is mixed with alluvial and aeolian deposits. Holocene is mainly distributed in the riverbed, floodplain and river terrace of Taiping River, and is composed of gravel, sand and loam of different sizes, which is formed by alluvial.

The southern part of the town is the Qinling Mountains, and the mountain ridges are all north-south. The northern part is loess plateau, alluvial fan and fan-edge depression. The terrain of the town is high in the south and low in the north, with a slight inclination from west to east. Caotang Town has a warm tropical and semi-humid continental monsoon climate, with distinct cold, warm, dry and wet seasons and abundant light, heat and water resources.

The annual total solar radiation in Caotang Town is 109.69 kcal/cm2, and the annual sunshine hours are 1983.4 hours, accounting for 44% of the available sunshine hours. The sunshine percentage of each month is the highest in June and August, and the lowest in September and June, 65,438+00 months. Autumn is rainy and rainy, with more clouds and less sunshine. The general monthly variation law of temperature: centered on July, the middle is high and the two ends are low, showing a saddle shape. The annual average temperature is 13.50℃, the hottest month is July, the average temperature is 26.80℃, the most Leng Yue is 65438+ 10, the average temperature is -0.50℃, the annual average maximum temperature is 19. 10℃, and the annual average minimum temperature is 8.

The general characteristics of natural precipitation are: large interannual variation and uneven seasonal distribution. The annual average rainfall is 627.6 mm, the maximum is 957.5 mm, and the minimum is 39 1.8 mm. The winter rainfall is the least, only 24.8 mm, accounting for 4% of the annual precipitation, which causes drought in winter and the largest in autumn, accounting for 34.6% of the annual precipitation. The annual average humidity is 0.68, and the annual evaporation is 1223mm. The annual average frost-free period is 2 16 days. The main surface water in Caotang Town is Taiping River and Gaoguan River system, which runs through the north and south of the town, forming a water network to replenish groundwater in the plain. The change of surface water is generally consistent with the distribution of atmospheric precipitation, and the runoff depth decreases from south to north.

The Taiping River originates from Jingyunao, Qinling Mountains, with a total length of 32 kilometers, a drainage area of 200.09 square kilometers, and a catchment area of 179.0438+0 square kilometers in mountainous areas, with a total drop of 380 meters. After coming out of the mountain, the flowing water from Shenshui Valley, Zigou Valley, Shifang Valley, Tudi Valley and Niuxin Valley will flow to Guo Village in Chang 'an District and throw into Fenghe River to the north.

Gaoguan River, which originated in Qinling Mountains, is the boundary river between Huxian County and Chang 'an District. Huxian county is 23 kilometers long, with catchment area of 1.58 square kilometers, annual total runoff of 63 million cubic meters, and maximum flood volume of 1.54 cubic meters per second. After the river comes out of the mountain, it is 0.68 kilometers away from Caotang Town.

Caotang Town is a water-rich area. Except for the poor water-bearing medium of igneous rocks in mountainous areas, shallow water layers are mainly distributed in plains, which can be basically divided into four rock groups according to burial conditions: Weihe second-order area, burial depth 1.6 ~ 18.2m, and unit water inflow of 0.55 ~ 7.99L/m; The buried depth of alluvial plain is 3 ~ 7 1m, and the unit water inflow is 3. 17 ~ 7.9 1l/sec. Diluvial fan group area, buried depth 15 ~ 70m, unit water inflow 0.15 ~1.63l/m; The water inflow is less than 0.0 1 l/s due to the poor water quantity in the loess hilly region.