A, karst groundwater recharge
1. Precipitation infiltration recharge
The exposed area of carbonate rocks in the working area is 77,800 km2, covering an area of 87,400 km2. The precipitation in the exposed area of carbonate rock and the area covered by unstable water-resisting layer will permeate along various fracture channels and become an important recharge source of karst groundwater. The distribution of carbonate rocks in 13 karst water system is shown in Table 4- 1.
Table 4- 1 Statistical Table of Carbonate Area and Precipitation of Karst Water System
In the whole area 1 19 system, the total exposed area of carbonate rocks is 533 16.42km2, accounting for 69% of the total exposed area of carbonate rocks in the whole area. The precipitation calculated by the subsystem ranges from 152.66mm in the karst water system at the northern end of Liqian Mountain in Inner Mongolia in the northwest to 945.08mm in the karst water system in Sesame Pearl Spring Area in Huainan, Anhui Province in the southeast, with an order of magnitude change of 6.2 times, and the average precipitation of each system is 604.05438+0 mm According to previous calculations, The precipitation infiltration coefficient in the exposed area of carbonate rocks ranges from 0.093 in Cambrian in Zhuozishan area of Inner Mongolia (0. 13 in Ordovician) to 0.34 in western Henan and Shandong areas, and the variation range is more than 3.5 times, which reflects the control of climate on karst development intensity. In Shanxi-Shaanxi Plateau, where carbonate rocks are most exposed, the precipitation infiltration coefficient of each system is mostly between 0.2 and 0.25. The infiltration coefficient of carbonate exposed area in the whole region is 0.20, and the calculated precipitation infiltration recharge in carbonate exposed area of 1 19 system reaches 64,465,438+1100 million m3/a, which is absolutely dominant in the recharge composition of karst groundwater in the north.
The research results of groundwater in loose layer of North China Plain and karst water in Yangzhuang Basin of Shandong Province show that the precipitation infiltration coefficient in the same area is a variable value. According to the study of Niangziguan spring area in Shanxi and Jiuli spring area in Henan, the difference between annual infiltration coefficient and precipitation is more than double. However, after years of balanced monitoring in a complete and closed spring area in the northern karst area, the research on obtaining an accurate relationship curve between precipitation and infiltration coefficient has not been established, which needs further research. The karst water system in Qianligou spring area of Inner Mongolia has a complete boundary with the karst water system in Paoma Shenquan-Xiakou spring area of Shanxi, and the spring water system is a completely drained spring, which has natural good conditions for carrying out balanced experimental research.
In the demarcated 1 19 system, the coverage area of carbonate rocks is 33473.42km2, and the infiltration recharge of karst water by precipitation in these areas depends on the lithology, thickness and other conditions of the coverage. Neogene, this area is generally distributed under Quaternary, mostly red clay layer. The water resistance is strong, and the vertical infiltration of karst water is basically mismatched. The thickness of loose layer also has some influence on infiltration recharge. In the past, it was considered that it was difficult to recharge when the thickness of overburden was more than 50m in the loess area of northwest China. However, according to our field investigation, when there is no stable water-resisting layer in the overburden, there is intermittent infiltration regardless of the thickness of the overburden. The most typical example is the Baimiao Loess Plateau in the north of Pingliang, Gansu. The elevation of Baimiao Plateau is nearly 200 meters higher than that of Jinghe River Valley and Daluhe River Valley on both sides. The Quaternary bottom conglomerate and Neogene red clay layer are cut on the valley shoulder, and the thickness of the overburden on the bottom conglomerate is about1.80m. Under the barrier of the Paleogene and Neogene aquicludes, a large amount of spring water flows out along the bottom conglomerate and does not dry up all the year round. According to the analysis of hydrogeological conditions, the infiltration recharge of plateau surface precipitation is the only recharge source of these springs, and the discharge of a large number of springs shows the fact that rainwater can completely cross the thick overburden to reach the lower aquifer. The precipitation infiltration coefficient calculated by predecessors in carbonate rock coverage area also changes greatly. For example, the data we used in Weibei area of Shaanxi Province is 0.05, and the result calculated by researcher Zhang Zhigan in Niangziguan spring area of Shanxi Province is 0. 10, and the data we got through balance calculation in Sangu spring area of Jincheng City of Shanxi Province is 0. 13. In Tianqiaoquan District, we swam across the Lanyi River of Dongchuan River. At present, the exact area of the infiltration recharge area in the whole area cannot be fully grasped, so it is impossible to estimate this composition.
2. Surface water leakage recharge
There are two main situations in which surface water supplies karst groundwater. One is that when the river passes through the carbonate area and the groundwater level is lower than the river, the karst groundwater will be replenished. The other is that reservoirs built in carbonate areas for many years will replenish karst water through leakage.
(1) River leakage recharge
River leakage also plays an important role in the resource composition of karst groundwater recharge in northern China. Take some big rivers in this area as an example.
The Yellow River enters the karst groundwater system in Tianqiao Spring Area through Lamawan, Inner Mongolia, with a flow length of 190km, in which the karst leakage section from Lamawan to Hequ Road, Shanxi Province is 75km, and the previous calculation shows that the total leakage is 6.92m3/s (including the leakage recharge of Wanjiazhai Reservoir). The leakage section of the Red River in Tianqiao Spring Area is 8km long, and the total leakage reaches1.36 m3/s/s.
Jinghe River has a 2.63km long leakage section in the Sanguankou area of Pengyang-Pingliang karst water system, and the measured average leakage for many years is 0.575m3/s ... Jinghe River enters the karst water system in Sizhudong spring area after crossing the Laolongshan fault in Shaanxi. When it reaches the leakage section of Dashapo fault, the river water level is 20 ~ 30m higher than the karst groundwater level. After calculation, the average leakage for many years is1.516m3/s. ..
Luohe River originates from Luochuan Platform, and Sanyanqiao to Shanghe Village is a carbonate rock section with a length of 9.2km. The karst groundwater level in this section is 65 ~ 75m, which constitutes a river leakage section, and the measured leakage is 2.741m3/s. ..
There are 6 seepage sections in Sanchuan River in the karst water system in Liulin Spring Area, with a total leakage of 0.666 m3/s. ..
The total leakage of the 80.8 1km section of Fenhe River from Luojiaqu to Shanglan Village is 3.06m3/s, which flows through the karst water systems of Jinci Spring and Lancun Spring. After entering the karst water system of Guo Zhuang spring area in the middle reaches, the flow loss from Tangyi to Shilin karst seepage section is1.438+0.03m3/s. ..
The Wenhe River, Taohe River, Nanchuan River, Songxi River and Qingzhang River in the karst water system in Niangziguan spring area, starting from the Carboniferous-Permian coal measures in the west and reaching the carbonate exposed area in the east, have an average leakage of 2. 17m3/s for many years, accounting for 19% of the total natural recharge resources of karst groundwater in the whole system.
According to relevant data, the annual leakage of Yongding River, a karst water system in Yuquan mountain spring area of Beijing, can reach 1.73 m3/s in Qingshuijian-Junzhuang leakage section.
The Dan River flows through two karst water systems, Sanguquan in Shanxi Province and Jiuliquan in Henan Province, to recharge the karst groundwater in Sanguquan in the upper reaches of Jincheng City, to receive the discharge and recharge of the karst water in Sanguquan in the lower reaches, and then to enter Jiuliquan in Henan Province downstream, and then to recharge the karst groundwater.
According to the stable isotope data of hydrogen and oxygen, the tracer test and the measured results of the cross-section flow of Xiaotanghe River, the recharge of Shuidong underground river in Liaoning Province mainly comes from the leakage recharge of Xiaotanghe River (Shen,1998; Wu Fawei, 2007).
Zhuzhuang Reservoir in the karst water system in Baiquan area of Xingtai collects the surface runoff from Archean metamorphic rock area in the upper reaches of 1220km2. According to the data analysis after the completion of the reservoir, it is measured that the leakage recharge coefficient of abandoned water from Zhuzhuang Reservoir to the downstream karst leakage section is 0.437 ~ 0.543 (Qiao Guangjian, 2006). According to the measured data of Mianchi karst water system by Henan Provincial Department of Geology and Mineral Resources, the leakage of the Shihe River is 1.75 m3/s in high water period and 0.78m3/s in normal water period.
According to the measured data of Qingyang River 18km long leakage of karst water system in Mingshui spring area of Zhangqiu from July to September, 2003, the leakage reached 2.48 m3/s ... At the same time, the leakage of 9km long reach from Dongguolou to Hanjiazhuang of Dongbalou River (downstream called Luohe River) was1.175m3/s.
Zhuangyan River in the karst water system of Guoniang Spring Area is located in the karst leakage section where Yuezhuang Village in the southeast of Li Xinzhuang meets Zhengwangzhuang River. Eight times of leakage measured by Shandong 80 1 hydrological team in different periods are 0.047 ~ 0.792m3/s.
The Zi River in the karst water system of Zibo Fengshui Spring Area is known as the "Eighteen Leaks of Zi River". Before the completion of Taihe Reservoir, the leakage under the reservoir reached 3.026 m3/s..
In addition, there are a large number of secondary river leakage sections that replenish karst water. According to our incomplete statistics, only in leakage section ***49, a secondary tributary of carbonate rocks around Ordos Basin, the total leakage length is about 245km. See Figure 4- 1 for the distribution map of river leakage section in the whole region.
Figure 4- 1 Distribution Map of Karst Seepage Sections and Karst Seepage Reservoirs of Major Rivers in Northern China
The leakage capacity of a river can be expressed by the leakage coefficient per unit length, which is closely related to the geological structure of the river (the lithologic structure of the loose layer of the river, the intensity of karst development, etc.). ), inflow, river leakage state (vertical free leakage, jacking leakage, lateral leakage, etc. ) and the hydrodynamic relationship between rivers and karst groundwater. Its value can be calculated by measuring the flow of the upper and lower sections, and the specific equation is as follows:
Environmental problems and protection of karst groundwater in northern China
If there is no spacer water, the equation can be simplified as follows
Environmental problems and protection of karst groundwater in northern China
Where: q is the upper flow; Q is the lower flow; Q area is interval inflow; β is the leakage coefficient per unit length of the river; L 1 is the leakage length of the river in the carbonate area (km); L2 is the leakage length (km) from the inlet of the well interval to the lower well interval.
Table 4-2 is a numerical summary of the leakage coefficient per kilometer in some karst leakage reaches, which is obtained by measuring and collecting previous leakage flow data and calculating in some projects in the north.
Table 4-2 Summary Table of Leakage Coefficient per kilometer in the north part of China.
sequential
sequential
As can be seen from the table, the leakage coefficient per unit kilometer of different river sections is quite different, with a difference of more than 1,000 times. The results of the same leakage reach affected by inflow are not consistent, which will be discussed in the following chapters.
(2) Reservoir leakage recharge
There are dozens of large and small reservoirs in carbonate rock areas in the region, many of which have leakage recharge to karst groundwater, and some reservoirs have considerable leakage. For example, Taoqupo Reservoir on Qishui River in Yuanjiapoquan-Wentangquan-Lingquan karst water system in Shaanxi Province has a maximum leakage of 27.8m3/s at the initial stage of water storage. Wanjiazhai Reservoir is located in Tianqiao Spring Karst Water System on the Yellow River, and the calculated leakage is 5.5m3/s. The dam site of Maomaowan Reservoir in longyan temple Karst Spring Water Resources System is located on the limestone at the bottom of Sandaogou Formation (Majiagou Formation). There are 46 karst caves in the area of 0.6km2 at the dam site, and the annual leakage in the initial stage of reservoir construction is more than 20 million m3. See Table 4-3 and Figure 4-2 for the main seepage reservoirs.
Table 4-3 Summary Table of Main Karst Seepage in Karst Areas in Northern China
sequential
Figure 4-2 Schematic diagram of karst groundwater system mode of overpass
3. Other supplies
In addition to the above three main recharge sources, karst groundwater in northern China has the following recharge sources:
(1) Overflow recharge of Carboniferous and Permian coal-bearing strata to the underlying Middle Ordovician.
Macroscopically speaking, there are water-resisting layers such as aluminum mudstone and shale between sandstone, interlayer limestone groundwater aquifer and Ordovician karst aquifer in coal measures strata, but the existence of water-conducting channels such as faults, fault structures and collapse columns does not mean that there is no water exchange. Considering the small proportion of recharge water, in most cases, the over-flow recharge water of overlying coal-bearing stratum aquifer is no longer considered, but in the northwest region with small precipitation (such as Zhuozishan area in Inner Mongolia), its proportion can not be ignored.
(2) groundwater recharge in loose layer
In the southeast of Luzhong, Yuxi and Xuhuai, there will be lateral undercurrent and vertical overflow recharge between karst groundwater and overlying loose layer groundwater. The karst water system in Pingyin, Shandong Province, the karst water system in Jiuxian County and the karst water system in Guoliji, the karst water overflows downward from the pore water in the loose layer and is replenished. In Tangshan karst water system, under natural conditions, karst groundwater flows upward to replenish pore groundwater in shallow loose layer. Due to the exploitation of karst groundwater and the drainage of coal mine, the relationship between the two types of groundwater is reversed, and porous groundwater flows downward to supplement karst groundwater.
(3) Supply of condensed water
Isotope study in Zhuozishan area of Inner Mongolia shows that there is condensate supply in this area.
Two. Runoff, Enrichment and Discharge of Karst Groundwater
The circulation conditions of karst water are strictly controlled by lithology, regional structure, topography and spatial factors of groundwater occurrence. After being replenished by local atmospheric precipitation, surface water and groundwater in overlying aquifer, karst groundwater in recharge area moves to its respective discharge direction through various runoff paths such as fault zone, karst gap, interlayer crack and solution gap. However, due to the internal structural characteristics of the system, groundwater runoff is by no means single. Topographic and geomorphological factors, large recharge water bodies on the surface, distribution of aquifuge in internal aquifers, stratigraphic tendency and structural water control factors will all affect the groundwater flow field, and the conditions for cyclic transformation are extremely complicated, with various control factors and different runoff modes. To sum up, the karst water system model restricted by geological structure and other factors has strong regularity in regional distribution. In order to avoid lengthy description and listing, we will discuss the typical representatives of the first four karst water system models, each with its own characteristics.
1. "In-situ monocline" karst water system model
Tianqiaoquan karst water system in the west of Luliang Mountain is the largest karst water system in the north, and it is also a typical representative of the "monoclinic-dominated" karst water system model (Figure 4-2). Controlled by Lvliang anticlinorium Uplift and the Yellow River-karst groundwater discharge standard on the west side, the karst groundwater in the system is recharged by precipitation infiltration in the exposed area on the east side, and then converges to the west along the inclined direction of the aquifer. When the waterproof roof is blocked, the discharge outlet is found, forming three discharge areas along the Yellow River, namely Laoniuwan, Longkou and Tianqiao. At present, the total flow is1.7m3/s. The carbonate rocks in Tianqiao area, where the axis of Tianqiao anticline is cut by the Yellow River, are in the lowest exposed position in the spring area and become the final concentrated drainage area of karst groundwater.
In the process of runoff, the hydraulic gradient of groundwater also changes from recharge area to discharge area. The hydraulic gradient in the recharge area is much larger than that in the discharge area, for example, the hydraulic gradient from the easternmost warm cliff to Hongyazi is reduced to 8.7 ‰; Hongyazi to Lougou central area is12.2 ‰; However, the hydraulic ratio from the old county to Tianqiao in the basin is only 0.64‰, and the hydraulic ratio from Yaowa to the blacksmith shop on the north side of Baode County is reduced to 0.5‰. This change of hydraulic gradient reflects the resistance of aquifer medium to groundwater to some extent. Karst in recharge area is relatively undeveloped with large hydraulic gradient, while karst in discharge area is relatively developed with small hydraulic gradient. The groundwater flow field is fan-shaped and convergent (Figure 4-3).
Karst groundwater generally flows from east to west along the stratum, and flows along the contact surface between Ordovician and coal measures after encountering the water-resisting roof in the Carboniferous-Permian region in the west, forming a strong runoff zone (Figure 4-4), and finally the carbonate aquifer in the system is discharged in the form of a big spring in Tianqiao area cut by the Yellow River.
Figure 4-3 Isobar Diagram of Karst Water in Tianqiao Spring Area
2. The model of "monoclinic inversion" karst water system
The general flow direction of karst groundwater in "monoclinic inversion" system is opposite to the dip angle of strata, but many of these systems are controlled by the dip angle of aquifer in recharge area. The flow direction of groundwater is consistent with the dip angle of strata at first, and changes after the water-resisting roof is blocked, and gradually converges to form a strong runoff zone under certain conditions. For example, the karst water in the south wing of Niangziguan karst water system, the eastern part of Pingding, the Gaoping karst water system in Sanguquan area and the carbonate outcropping area in the eastern part of Bagong Basin first flows along the bedding, and then flows north (Niangziguan system) and south (Sanguquan system) along the contact surface in the west, forming Xiyang-Pingding-Yangquan and Gaoping-Bagong-Jincheng karst groundwater strong runoff zones respectively.
The geotectonic structure of karst water system in Yanhe spring area is located at the southern end of Qinshui syncline, which is controlled by Qinshui syncline and the western half of southeast gable structure. The strata strike east-west, and the southwest strata turn to northwest and tend to northeast, forming a dustpan-shaped catchment structure with an opening to the north. The northern part of the system is Carboniferous-Permian coal measures strata, and the southern part is Cambrian-Ordovician carbonate rocks. The Qinhe River flows through the system from north to south, cutting off the karst water level, and along the Qinhe River, under the barrier of the Cambrian-Ordovician relative water-resisting layer, a drainage zone composed of multiple springs is formed (Figure 4-5).
Figure 4-4 Distribution Map of Strong Runoff Zone of Karst Groundwater in Northern China
Figure 4-5 Hydrogeological Profile of Karst Water System in Yanhe Spring Area
With the reduction of the discharge standard of Qinhe River, karst groundwater flows from north to south, forming a "monoclinic inversion" karst water system model (Figure 4-6). The plane hydrodynamic field of karst water in the system shows that the natural flow field converges, and the groundwater collects from all sides to the middle (between Yangcheng, Runcheng and Yanhe Springs), leaving only a gap in the Qinhe River Valley. The hydraulic gradient of catchment area is only 1‰, while the marginal recharge area is 5‰, which shows the characteristics of catchment basin, and the regional water-resisting floor controls the outflow of karst springs. Karst groundwater flows to the long river in the northeast of the system.
Figure 4-6 Isogram of Karst Water System in Yanhe Spring Area
The southeast side of runoff zone is obviously controlled by aquifer tendency.
Most "monocline inversion" model systems in the north (such as Niangziguan spring karst water system, Xin 'an village spring karst water system, Yuanjiapo spring-Wentangquan-Lingquan karst water system, etc.). ), the surface water from the upstream coal measures strata (or the Pleistocene strata) often leaks a lot after entering the exposed area of carbonate rocks downstream, forming a recharge to karst groundwater.
3. Runoff flow of karst water in the "trend" system model
The biggest feature of the "strike-type" system model is that the strike of the system karst aquifer is consistent with the main runoff direction of karst groundwater. Due to the steep dip angle of carbonate aquifer in this model, it is massive, and there are few large and small rivers in the system. Atmospheric precipitation is the main recharge source of karst groundwater in the system. Karst water seeps into the drainage area along the direction of the aquifer, and is discharged in the form of spring water at the inclined end of the fault block aquifer (a few systems, such as Shangqingquan area in Beijing, are cut by rivers and discharged from both sides to the drainage point), and the groundwater flow field is mostly rectangular (Figure 4-7). Due to the small exposed area and system development scale of carbonate aquifer, the enrichment degree of groundwater is relatively low. Generally speaking, the strong runoff zone of groundwater is rare in this kind of system, and its rich parts are mainly distributed in the basin.
Figure 4-7 Flow Field Diagram of Karst Water System in Taiyangquan Area
4. Groundwater runoff and discharge of karst water system in syncline basin.
The "syncline-basin type" karst water system is mainly supplied by precipitation infiltration in carbonate outcropping areas around the basin (or on the two wings of syncline), and generally converges to the middle of the basin (syncline axis) in a ring shape. In the river cutting section of the basin or the appropriate part of the carbonate skylight, it is discharged in the form of spring water, and the nature of spring water is mostly erosion overflow spring. Such as Qilihe Spring in Yuxian County, Hebei Province, Shuishentang Spring in Guangling County, Shanxi Province, Shangquan Spring in Wutai County, Laiyuan Spring in Laiyuan Basin, Shuimo Grass Spring in Lingshan Syncline, etc. The karst water system in Shili Spring Area formed in Zaozhuang Basin of Shandong Province is a typical representative of "syncline-basin type" karst water system, and the runoff discharge characteristics of karst water shown in Figures 4-8 and 4-9 are outstanding examples. At the same time, the karst water system in Yangzhuang spring area in the northwest and Yicheng karst water system in the south of the system are composed of Yangzhuang basin and Yicheng basin respectively.
Figure 4-8 Hydrogeological Schematic Diagram of Karst Water System in Shili Spring Area of Zaozhuang
Figure 4-9 Hydrogeological Profile of Karst Water System in Shili Spring Area in Dingzhuang-Dongwangzhuang Area