Datong Basin

Datong Basin is located in the northern part of Shanxi Province, including 7 counties (cities) including Datong City, Datong County, Huairen County, Shanyin County, Ying County, Hunyuan County, and Shuozhou City. The total area of ??Pingyuan District is The area is approximately 7440km2.

1. Physical geographical conditions

1. Climate

Datong Basin belongs to the continental semi-arid climate zone. The climate is dry, with less rain, more wind and sand, a large temperature difference between day and night, and sufficient sunshine. The annual average temperature is 6.5~7.5℃, the highest temperature over the years is 38.3℃, the lowest temperature is -37.3℃, the frost-free period is 120~140 days, the maximum frozen soil depth is 1.0~1.8m, the average wind speed is 3.0m/s, and the maximum wind speed can reach 14 ~16m/s.

The average annual precipitation in this area is 363~414mm, with more precipitation in the surrounding mountainous areas than in the center of the basin. Only Hunyuan County and Shuozhou City have annual average precipitation greater than 400mm, while the remaining areas are less than 400mm. Compared with the 1980s, the annual average precipitation in this area has a decreasing trend. Precipitation is unevenly distributed throughout the year. Summer (June to September) has the most precipitation, accounting for 74% to 79% of the annual precipitation; winter (December to February) has the least precipitation, accounting for only 1.5% of the annual precipitation. ~3%; spring (March to May) precipitation accounts for about 15% of the annual precipitation; autumn (October to November) precipitation accounts for 6% to 8% of the annual precipitation.

The multi-year evaporation in this area is 4.7 times that of precipitation. The average multi-year evaporation is about 1883mm. The areas with the largest evaporation are Huairen County and Shanyin County, which are greater than 2000mm. In winter and spring, evaporation is 10 to 21 times that of precipitation. Winter and spring are relatively dry, and spring drought is prominent.

2. Hydrology

The rivers in this area belong to the Haihe River system, with Sanggan River as the main river, and its tributaries include Huihe River, Huangshui River, Shili River, Yuhe River and Hunhe River. The Sangqian River originates from the Tianchi Lake in Guanlui Mountain, Ningwu. It enters the basin from Yangfangkou and flows through Shuocheng District, Shanyin, Yingxian, Huairen, and Datong to the provincial border of Yanggao, where it enters Hebei and flows into the Yongding River. The main stream is long. 221km.

Sanggan River is one of the drainage channels of groundwater in the basin. The distribution of runoff is extremely uneven throughout the year. It is a typical summer rain type feature. Floods rise and fall violently. The maximum peak flow occurs in July and August. The minimum flow is generally from May to June, and the interannual changes in runoff are very significant. According to data from the Dongyulin Hydrological Station on the Sanggan River, the maximum monthly flow rate is 62.9m3/s and the minimum is 0; the maximum monthly flow rate at the Fixed Bridge Station on the Sanggan River is 78.8m3/s and the minimum is 0.

3. Landform

Datong Basin is surrounded by mountains, with Guanchuan Mountain to the southwest, Hongtao Mountain and Qifeng Mountain to the west, and Liuling Mountain, Hengshan Mountain, and Mantou Mountain from northeast to southwest. Among the mountains, Mantou Mountain is the highest, with an altitude of 2426m. The terrain in the basin is flat and open, high in the southwest and low in the northeast, with an altitude of 950 to 1100m. Alluvial fans of different sizes are distributed in the piedmont on both sides of the basin, forming a piedmont sloping plain, and the central part of the basin is an alluvial plain. The basin generally spreads in the NE-SW direction, with a length of about 180km, a widest point of 48km, and a narrowest point of only 15km. The piedmont sloping plain has a slope of 3° to 15°, tilting toward the basin, and an elevation of 1000 to 1200m; the Sanggan River passes through the basin, and the alluvial plain area is located in the middle of the basin, with a flat terrain, a slope of 1° to 3°, and an elevation of 1000 to 1200m. The elevation is 950~1100m.

II. Stratigraphy and Structure

The Datong Basin is a Cenozoic graben-type faulted basin developed on the Mesozoic fold basement. NE, EW and SN faults constitute the basin respectively. boundary. See Figure 3-4-6.

Figure 3-4-6 Structural sketch of Datong Basin (according to Han Ying et al., 2006)

(1) Faults

1. Basin boundary faults

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(1) Kouquan Fault Zone

The Kouquan Fault is the western boundary fault of the Datong Basin, with an overall trend of NE30°, starting from Shanyin Shangshenquan in the south, passing through Dayukou and Efei in Huairen County Kouquan, Datong City, to the Zhenchuanbao area in the north, is about 100km long, has an influence bandwidth of 2 to 3km, and a fault distance of 1500 to 2000m. It is an active basement fault and has still been active since the Cenozoic. In the Mesozoic Era, this fault consisted of a series of thrust faults arranged in an echelon pattern, trending NE. After the Cenozoic, it transforms into tensile fracture.

(2) Xinguangwu Dongshan Piedmont Fault

It is the boundary fault between the Datong Basin and the southeastern mountainous area, trending NE65°.

(3) The EW-trending fault in the northern part of Datong County

It is the northern boundary fault of the Datong Basin. It runs EW, starting from Datong City in the west, passing through Gelaoshan, and heading east to the border of Hebei Province. It is 60km long, with the northern mountainous area rising and the southern mountainous area descending. There are Cenozoic basalts erupting near the fault zone.

(4) Danshuigou Fault

It starts from Baijiayao in the west and ends at Dafuzhuang in the east. It is 38km long. It is a normal fault that strikes nearly EW, tilts south, and has a dip angle of 60°. ~70°, the drop between the two plates is greater than 300m, and the drop at the east end is smaller, 100~150m. The fault planes in the Xiamoshigou and Damingyi Danshuigou areas are clear, with a fracture width of about 5m. Fault mud and fault breccia can be seen, and they have experienced multiple periods of activity.

(5) The nearly SN-trending fault in the eastern part of Yingxian County

Strikes NW350° and is 30km long. It is the boundary fault between the Hunyuan shallow sag and the Housuo sag.

(6) Mayi Fault

It runs through the north and south of Shuozhou Basin from Dafuzhuang to Shenwu, about 48km long, trending NE18°, and is a normal fault, leaning eastward with an inclination angle greater than 60° . The burial depth of the bedrock on the western side of the fault is less than 300m, and the burial depth of the bedrock on the eastern side is greater than 500m. The bedrock burial depth in the Nanyulin area of ??the southern section of the fault is greater than 1000m. It is a stepped fault group. There is a significant difference in water richness between the two fault plates, forming the eastern boundary of the Shentou Spring area.

2. Main faults within the basin

(1) Datong-Huairen fault

Trends NE30°~40°, starting from the Great Wall in the north and ending at Guojia in the south Yao, extending 120km, is a controlling fault between Huairen Depression and Huanghualiang Depression Uplift. It is a normal fault, rising in the east and falling in the west, with a fault distance of about 100-200m.

(2) Datong-Zhengzhuang-Shanyin Fault

Trends N40°~55°E, starting from Tianzhen in the north to Shanyin in the south, extending 170km, and is the Huanghualiang Depression The controlling fault between the uplift and Housuo depression is a normal fault, rising in the west and falling in the east, with a fault distance of 300-800m.

(3) Donghouzikou-Yingxian North-Zurun Fault

Trends NE40°~50°, starting from Liyu in the north, passing through Donghouzikou-Mijiayao- From Bianyao to the north of Yingxian County to the south of Shanyin Old City to Douzhuang to Zirun, it is 120km long. To the north of Bianyao is the boundary fault between the eastern mountainous area and the basin, and the Bianyao-Zunrun section is the fault within the Housuo depression.

(2) Folds

Folds are mainly distributed in the western part of the Datong Basin, mainly including: Yungang-Heiliushui syncline, trending NE45°, 30km long, and composed of Jurassic coal Basin; Suancihe-Shijiatun-Pinglu syncline, trending NE50°, 105km long, is a Carboniferous-Permian coal basin, with asymmetrical wings, with an inclination angle of 20° to 30° in the east wing and 10° in the west wing; Ma Ying anticline, trending NW320°~350°, starts from Wumaying in the north and ends at Huaqituo in the south. It is about 12km long. Its two wings are asymmetrical, with an inclination angle of 30° on the west wing and 15° on the east wing; Shuoxian syncline is hidden in Under the Cenozoic, the axial SN runs through the Shuozhou Basin in the west, showing an S-shaped distribution, starting from Xiatuanbao in the north and ending at Yangfangkou in the south. It is about 28km long, and the southern end of the syncline is intercepted by the Wangwanzhuang fault.

(3) Stratigraphy

The mountainous areas around the basin mainly expose the Archaean Yusanggan Group and Wutai Group metamorphic rock series, Meso-Neoproterozoic Changcheng System and Jixian System gray-white The chert strips are associated with gray-white to light gray-red thick layered dolomite, Lower Paleozoic Cambrian-Ordovician thick-bedded limestone, and Carboniferous-Jurassic marine-continental alternating phases and continental coal-measure strata.

The Cenozoic strata are described as follows:

1. Neogene system

(1) Baode Formation (N2b)

Based on volcanic It is characterized by eruptive basalt deposits, mainly developed in the Datong Basin, with sporadic exposures at the edges of the basin and hilly areas. It is mainly gray, gray-purple and gray-black olivine basalt, in the form of dense blocks and pores, with a few breccias and almond structure. The exposed thickness of basalt is generally 40-120m, and can reach about 150m in the Xisierliang area of ??Zhenchuanbao Village. At the edge of the basin, "Baode red soil" is sporadically exposed, mostly brown-purple, brown-yellow, and brown-red gravelly clay and silty clay, interspersed with sporadic or layered calcareous nodules, sandy gravel layers, and gravel layers. Thickness 5~10m.

The basin is dominated by lacustrine sediments, and its lithology is gray-green sand and mudstone interbedded with silt layers and marl. Basalt interlayers are common near Yingxian, Shanyin and Zhenchuanbao. The thickness of lacustrine strata varies greatly, ranging from 5 to 100m, and can reach more than 370m in the center of the depression.

(2) Jingle Formation (N2j)

Distributed in the basin, with sporadic distribution and exposure in the hilly areas on the edge of the basin, the lithology is mainly purple-red, dark red or dark brown Red clay, interlayered calcareous nodules, with a gravel layer or gravel layer lens at the bottom, 5 to 20 meters thick.

The lithology of the uplifted zone in the basin is mostly brown, reddish brown and brown clay, silty clay, silt and sand, gravel and gravel layers with varying numbers and thicknesses. . The burial depth is 100~200m and the thickness is 10~40m.

2. Quaternary System

(1) Lower Pleistocene

Nihewan Formation (Q1n): widely developed in the basin, mainly rivers and lakes phase deposition. The lithology is grey-green, variegated clay, silty clay, silt and sand, gravel or gravel layers, often intercalated with calcium-rich clay, marl, silt or peat layers. The thickness of the basin center is 200-400m, and the thickness of the basin edge is 30-100m.

(2) Middle Pleistocene

Lishi Formation (Q2l): widely exposed in the hilly areas on the edge of the basin, mainly Lishi loess, including gray-yellow, brown-yellow silt, Silty clay, sandwiched between 2 to 5 layers of brown-red ancient soil and calcareous concretion layers, with unstable distribution of gravel layers at the bottom or lower part. The thickness is generally 5 to 20m, and can reach 30 to 40m in individual sections. In the basin, there are fluvial and lacustrine facies deposits, and the lithology is brown sand layer, sandy gravel and gravel layer, often intercalated with gray-green sand and mudstone. Thickness is 10~50m.

(3) Upper Pleistocene

Xujiayao Formation (Q3x): widely distributed in the Datong Basin and on the edge of the basin.

The edge of the basin is the alluvial deposits of the Sanggan River, the Nanyang River and their main tributaries, forming the river's III-level terraces and the bottom of the II-level terraces. The lithology is gray-yellow, brown-yellow and gray-brown silt, silty clay, clay and sand. Sand and gravel layer or gravel layer; in the basin, there are several layers of gray-green sand, mud layers, and thin layers of calcium-rich and carbon-rich silty clay. In the Datong volcanic group distribution area, the middle and upper part of the lacustrine sedimentary layer is sandwiched with Datong basalt of the same period. At the edge of the basin, the thickness seen is 5 to 30 m, and within the basin it is 10 to 50 m. From the edge of the basin to the inside of the basin, the gray-green sand and mud layers increase, and the thickness of the single layer increases.

Malan Formation (Q3m): Malan loess is mainly distributed on the edge of the basin. It is gray-yellow or light yellow silt, homogeneous and loose, with developed vertical joints and large pores. In some areas, there is a layer of brown-yellow to light brown-red ancient soil in the lower part. Thickness 2~20m.

Zhiyu Formation (Q3s): widely distributed, composed of alluvial deposits of Sangqian River and Nanyang River, forming a second-level terrace. It has a binary structure. The upper lithology is mainly silt and silty clay in gray-yellow, light brown, brown and light brown tones, and the lower part is sand and gravel layer. The plain area is composed of fluvial and lacustrine facies deposits, and the lithology is gray-green sand and mud layers interspersed with gray-white thin-layered marl or black peat layers. The horizontal bedding is clear and 5-30m thick.

(4) Holocene

It is a modern alluvial sedimentation, and its lithology is mainly sand layer, gravel layer and gravel layer. Level I terraces are formed along the Sanggan River, Nanyang River and other larger tributaries.

3. Basin Development History

The Datong Fault Basin is part of the Fenwei Graben, located at the northern end of the basin. It is a Cenozoic basin developed on the Mesozoic NE-trending fold structure base. . See Figure 3-4-7.

Figure 3-4-7 Geological structure section of the new rift in the Sanggan River (according to data from the Shanxi Provincial Geological and Petroleum Survey Team, 1980)

In the Paleogene, in the NW-SE direction Under the action of regional tensile stress, three groups of NE, NNE and NEE faults were stretched. Some faults reached as deep as the upper mantle, triggering basalt eruptions and forming a large amount of Fanzhi basalt. Fault block collapse occurred along these faults, and the basin began. form.

In the Neogene, the basin entered the rifting stage. The basin continued to rupture and subside, forming a lake basin, where hundreds of meters of fluvial and lacustrine strata of the Baode Formation and Jingle Formation were deposited. In the early stage, basalt erupted violently, forming a large amount of Huanghualing period basalt, which was distributed in the lacustrine strata of the Baode Formation; in the later stage, the volcanic activity weakened, and the paleoclimate became cool and humid, forming the Jingle Formation with brown-yellow and brown-red colors. and fluvial and lacustrine strata characterized by brown clay, silty clay, and silt.

In the Early Pleistocene, the basin entered a depression period, the climate was warm and humid, the lake basin area expanded, most areas were covered by water bodies, and lakes developed at their peak, forming the Nihewan Formation fluvial-lacustrine sediments. From the end of the Early Pleistocene to the Middle Pleistocene, the basin stopped subsidence and turned to uplift. The lake entered a contraction period, the climate became dry and cold, the scope of the water body gradually shrank, and the water body became salty. From the end of the Middle Pleistocene to the Late Pleistocene, the climate changed from warm and cool to dry and cold, evaporation was intense, and the lakes shrank. The unified large lake decomposed into several small lakes, and the lake water gradually became salty and finally died. From the late Pleistocene to the Holocene, the climate was relatively mild. The Sanggan River cut through the lake basin. The basin was dominated by alluvial deposits. There were also volcanic eruptions in some areas, forming the Datong Volcanic Group.

During the formation and development of the basin, sediments from different periods formed the Baode Formation, the Jingle Formation deep confined water-bearing rock formation, the Nihewan Formation confined water-bearing rock formation, and the Xujiayao Formation. The Hezhiyu Formation phreatic-slightly confined water-bearing rock formation.

IV. Groundwater system

1. Karst water-bearing system

The Cambrian-Ordovician system is exposed on a large scale in Hongtao Mountain in Shuozhou and Lu County in the region Limestone, karst development, constitutes a karst water-bearing system, and its bottom boundary is the shale of the Lower Cambrian System. The Shentou Spring Group in Shuozhou is a natural concentrated discharge zone of karst water.

Shentou Spring is one of the famous karst springs in Shanxi. It is located on the northern edge of Shuozhou Basin in the southwest of Datong Basin and on the southern slope of Hongtao Mountain. The total area of ??the spring area is 4950km2. It is a huge spring mainly composed of Pinglu syncline. As a karst water storage structure, the NE-SW-trending Hongtaoshan Piedmont fault intersects with the NWW-trending Danshuigou fault's secondary fault, forming a water-blocking structure that rises to form a spring. The large spring discharge points are distributed within 5km2 in the middle and upper part of the Yuanzi River alluvial fan. There are more than 100 large and small spring points, with a multi-year average total flow of 8690L/s. Hidden karst develops in the area west of Xiaomingyi to Xiayaogou and Maguan River, and karst groundwater is abundant. The water output of a single well is 8000-27000m3/d.

In the Shuozhou Basin, nearly SN-trending and NE-trending faults are relatively developed, which are the channels through which the Ordovician karst water from Shenchi and Ningwu in the southern part of the spring basin drains to Shentou Spring. The karst water pressure head in this area is relatively high. The 700-900m deep borehole in Fushanzhuang, Shuimoutou on the east side revealed that the karst water head of the Middle Cambrian and Lower Ordovician is about 2m above the ground, and the free flow can reach 60m3/ h.

2. Basalt fissure-pore aquifer system

Cenozoic basalt erupted in multiple stages. Among them, the olivine basalt of the same period developed joint fissures and many pores, forming a basalt fissure-pore aquifer. It is mainly distributed in the volcanic group east of Datong, along the Sanggan River, Huanghualiang and other places in Shanyin, as well as on the north bank of the Sanggan River in Datong County and around the Datong volcanic group. The Quaternary basalt forms a large area of ??gentle slope and low platform. There are springs exposed in some shallow ditches and on the banks of the Sanggan River. The flow rate is generally about 1L/s, and the water inflow in a single well can reach 500-1000m3/d.

In the area around Huanghualiang in the middle of the basin, the groundwater is shallowly buried, and the water output from a single well is 500m3/d. The water quality of basalt fissures and pores is good, it is HCO3-Ca·Mg type water, and the salinity is less than 0.5g/L.

3. Bedrock fissure water-bearing system

The bedrock fissure water-bearing system in the area is mainly composed of structural cracks and weathered crack networks. Due to scarce precipitation and insufficient recharge, the water richness is weak. For example, in the Efeokou section of the Quangou Fault, both sides of the fault zone are mainly clastic rocks. Pumping tests at different layers of an exploration hole at a depth of 420.63m at 3km in the Efeokou trench showed that the Permian depth dropped by more than 120 meters, and the water inflow was only 1.2 m3/d; the Carboniferous system pumped water to a depth of more than 150 meters, and the water inflow was 5.4m3/d; the Ordovician system pumped water to a depth of 25m, and the water inflow was only 16m3/d.

4. Quaternary pore water-bearing system

The Cenozoic loose sediments in the Datong Basin are hundreds of meters thick, reaching 1000-1500m in depressions. The piedmont zone at the edge of the basin is mainly composed of alluvial facies sand, pebbles, and gravel layers, forming a phreatic water-bearing system; toward the center of the basin, it gradually changes to fluvial and lacustrine interlayers of sand and mud, becoming the main distribution area of ??the confined water-bearing system. The middle and upper Pleistocene alluvial and alluvial sand and gravel layers in the area are the main aquifers, with a thickness of 50 to 100m.

(1) Phreatic aquifer system

Mainly distributed in piedmont sloping plains on the edge of basins. Sloping plains formed by larger rivers are composed of coarse pebbles and gravels, with large thickness and high permeability. It has a large water storage space and is directly supplied by river seepage. It has abundant water, especially the alluvial fan axis. The water output of a single well can reach 10,000m3/d. It is one of the most water-rich areas in the region and has become an urban area. Important water supply source. It can be divided into the following subsystems:

Hengshan piedmont phreatic water-bearing subsystem: distributed in the Hengshan piedmont sloping plain, controlled by the large piedmont faults to form more than 30 large and small connected alluvial fans, aquifers The lithology is pebble and sand layer, 30-80m thick, and highly water-rich. The water output of a single well is more than 1500-2000m3/d, and in some sections it reaches 3000-8000m3/d. The water richness of the edges of alluvial fans and the inter-fan depressions is poor, and the water output of a single well is generally less than 1000m3/d. The water level in the upstream axes of New and Old Guangwu, Malanyu, Ruyue, Xiaoshiyu and Beiloukou alluvial fans is 10-60m deep, and the water output of a single well is about 3000m3/d. The water output of a single well in Wangqianzhuang, Tangyuhe and Lingyungou alluvial fans can reach 3000-8000m3/d.

The Leigongshan-Qifengshan piedmont phreatic water subsystem: consists of five alluvial fans: Shili River, Kouquan River, Efeokou River and Xiaoyukou. Among them, the Shili River alluvial fan is the largest, with the largest area. 40km2, the lower reaches intersect and overlap with the Yuhe alluvial layer. The area of ??Kouquan, Efeokou and Dayukou alluvial fans is about 20-30km2. Medium and coarse sand and gravel layers are developed in the alluvial fan axis, and groundwater is relatively abundant. There are tens to dozens of aquifer layers within 100 to 150 meters, with a thickness of 15 to 60 meters. The water output of a single well is about 1000m3/d, and the water output in richer areas can reach 1500 ~2000m3/d.

Shuozhou Yuanzi River phreatic aquifer subsystem: distributed in the alluvial fan of Yuanzi River in Shuozhou City. The aquifer lithology is a sandy gravel layer, 30 to 70m thick, and the water level is 20 to 38m deep. , supported by hidden karst water, the groundwater is rich, and the water output of a single well is 1500-3000m3/d.

(2) The phreatic-confined aquifer system

is distributed in the middle of the Datong Basin, along the Sanggan River and Huangshui River. The upper part is diving and the lower part is pressurized water.

Upper diving: It is alluvial and siltated sub-sand soil and sub-clay. Below 10-30m, it is mainly composed of lacustrine variegated clay soil, intercalated with fine sand or silt layer, with a thickness of 5 ~10m, and the thickness can reach 15~20m in the transition zone between the alluvial sloping plain and the alluvial lake plain or in the ancient river channel. The depth of the water table is very shallow, mostly 2 to 3 meters, and the evaporation and concentration effect is strong, forming a large area of ??salinization, which accounts for 25% to 30% of the plain area.

Lower pressurized water: The water below 30 to 50m in plain areas is pressurized water and is partially self-flowing. The aquifer is mainly composed of the Nihewan Formation and the middle and late Pleistocene lacustrine sand and silty sand layers. The aquifer is 50 to 100 meters thick. The water inflow in a single well is 500 to 1500m3/d, and the salinity is 1 to 3g. /L, in places such as Shanyin Heshengbao and Dachongbao, the fluoride ion content is relatively high.

5. Groundwater circulation

The groundwater recharge, runoff and discharge in the Datong Basin are mainly affected by hydrogeology, geomorphological conditions, meteorology, hydrology and other factors.

1. Groundwater recharge

The main sources of groundwater recharge in the basin include atmospheric precipitation infiltration, river leakage recharge, and lateral recharge from bedrock in mountainous areas.

The phreatic aquifer system of the piedmont slope plain is the most important water supply source in the region. Its supply mainly comes from river seepage supply, atmospheric precipitation infiltration and lateral supply from mountainous bedrock. The groundwater recharge conditions are good, the water level is shallow, the hydraulic gradient is moderate, the water alternates actively, the water richness is strong, the water quality is good, and the underground runoff converges towards the center of the basin.

In the alluvial lake plain in the center of the basin, groundwater recharge mainly comes from infiltration of atmospheric precipitation, lateral runoff recharge and irrigation backseepage, while underground runoff is stagnant.

2. Groundwater runoff

The Sanggan River and its tributaries traverse the entire region and are the erosion base of the basin, and the groundwater movement is basically controlled by it. Groundwater moves from the alluvial sloping plain to the center of the basin. At the center of the basin, the particles of the water-bearing medium become finer, the hydraulic slope becomes gentle, and the groundwater flow becomes stagnant and slowly discharges to the Sanggan River.

3. Groundwater discharge

Groundwater discharge is mainly artificial mining, evaporation and underground runoff discharge. The groundwater supply conditions in the alluvial sloping plain are good, the water level is shallow, the water inflow from a single well is large, the water quality is good, and it is easy to mine. Artificial water extraction has become an important way to discharge groundwater. In some areas, long-term over-exploitation has caused water levels to drop in large areas, forming a falling funnel. For example, Datong City exploits a large amount of groundwater in the alluvial sloping plains of the Western Mountain Piedmont and the floodplain terraces along the Yuhe River (the water extraction volume reaches 31×104m3/d), which causes the groundwater level to generally drop and becomes a regional downward funnel. In Datong City alone, there are areas in the west and south of the city. , Chengbei Gudian-Baima City and Yuhe Railway Bridge 4 groundwater landing funnels.

Evaporation mainly occurs in the alluvial lake plain in the middle of the basin. The terrain in this area is flat, the water flow is sluggish, and the groundwater level is mostly 2 to 3 meters deep. Phreatic evaporation has become the main discharge method.

Part of the groundwater in the alluvial lake plain is discharged into the artificial drainage canal system and the Sanggan River system.

6. Groundwater Chemical Characteristics

1. Shallow Groundwater

The hydrochemical types of shallow pore groundwater in the Datong Basin are distributed in a ring shape, from the edge of the basin to In the center, the water chemical type evolves from HCO3 type → HCO3·SO4 type → HCO3·SO4·Cl type and ·SO4·Cl type. The water chemistry functions are dissolved filtration type, runoff type and evaporation type.

The piedmont sloping plain mainly receives infiltration of atmospheric precipitation, river seepage and lateral recharge from bedrock mountainous areas. The water alternates actively and is dominated by solution and filtration. From the top to the edge of the alluvial fan, most of the water is HCO3-Ca·Mg type water with a salinity of 0.2-0.5g/L.

The alluvial lacustrine plain in the central part of the basin has a gentle terrain, and the groundwater burial depth is small. It is mainly discharged by evaporation. The chemical type of groundwater changes from HCO3·SO4 type → HCO3·Cl type → Cl·HCO3 type → Cl·SO4 type. , is brackish water with a salinity greater than 1.0g/L, and some areas are salt water with a salinity greater than 5g/L.

2. Mid-deep groundwater

From the upper part of the piedmont slope plain to the edge, the water chemical types change in order: HCO3-Ca type, HCO3-Ca·Mg type and HCO3-Ca· Mg·Na type, salinity is 0.23~0.71g/L. The Shentou area of ??Shuozhou is supported by the karst water of the underlying Shentou Spring. The water quality is good and is HCO3-Ca·Mg type water with a salinity of 0.35g/L. In some areas, affected by coal-bearing strata, HCO3·SO4 type water appears, and the degree of salinity is also high.

In the alluvial lake plain, the water chemistry types are mainly HCO3·SO4 type, HCO3·SO4·Cl type, HCO3·Cl type and SO4·Cl type, with Cl·SO4 type and Cl·HCO3 type appearing locally. . Brackish water with a salinity of 1 to 3 g/L.

7. Groundwater Resources

According to the "Survey and Evaluation of Groundwater Resources and Environmental Issues in Six Major Basins in Shanxi" report (2006) completed by the Shanxi Provincial Geological Survey Institute, the Quaternary System of the Datong Basin The annual average recharge of pore water is 7.17×108m3/a. Among them, the infiltration recharge amount of atmospheric precipitation is 2.53×108m3/a, the lateral recharge amount is 3.13×108m3/a, the river leakage recharge amount is 0.596×108m3/a, and the canal leakage recharge amount is 0.363×108m3/a. , the infiltration recharge amount for surface water irrigation is 0.12×108m3/a, and the infiltration recharge amount for groundwater irrigation is 0.432×108m3/a.