(The First Hydrogeological Engineering Geological Team of Henan Bureau of Geology and Mineral Exploration and Development, Xinxiang, 453002)
Through the comprehensive investigation of groundwater in North Henan Plain, it is found that the main environmental geological problem is the decline of regional groundwater level, which leads to the occurrence of secondary environmental geological problems such as the disappearance of springs, the decrease of wetlands, land subsidence and groundwater pollution. Based on the comprehensive analysis of the background and conditions of environmental geological problems, it is considered that the fundamental reason is human activities, especially unreasonable exploitation of groundwater, which destroys the natural balance of groundwater circulation system, and its evolution model is two-way. Finally, the specific measures to alleviate and prevent the environmental geological problems in the northern Henan plain are put forward.
Keywords: formation conditions and evolution model countermeasures of environmental geological problems in northern Henan plain
Environmental geological problems refer to the geological phenomenon that the changes of natural hydrodynamic field and chemical field in groundwater system lead to environmental deterioration. The North Henan Plain refers to the Henan part of the North China Plain north of the Yellow River, with a total area of about 2.0× 104km2, belonging to Jiaozuo City, Xinxiang City, Hebi City, Anyang City and Puyang City. In 2000, the total population was 15084800, the total industrial output value was 42.285 billion yuan, and the economic growth rate in recent 10 years was above 8%. It is an important industrial base of energy, petrochemical, metallurgy, electronics, electric power, textile and other industries in Henan Province, and also the main producing area of grain, cotton and oil crops. Therefore, the emergence and development of environmental geological problems in the northern Henan plain have attracted more and more attention from local governments and society. Through the comprehensive analysis of a large number of measured data, the author intends to analyze the emergence, evolution and countermeasures of environmental geological problems in the northern Henan plain.
1 environmental geological problems
The environmental geological problems in the northern plain of Henan Province are mainly caused by the decline of regional groundwater level, which also leads to a series of secondary environmental geological problems such as the disappearance of springs, the decrease of wetlands, land subsidence and groundwater pollution.
1. 1 regional groundwater level drops.
199 1 ~ during 2000, six large shallow groundwater level drop funnels were formed in the northern Henan plain, and the annual cumulative drop value of the water level in the center of each funnel was: Wuzhi Funnel 5.08m, Anyang Funnel1/kloc-0.25m and Xinxiang Funnel 4.3m/kloc. The cumulative decrease of 10 in this area is about10.3m, and the formation and expansion of groundwater drop funnel have caused great losses to industry and agriculture in the northern Henan plain. 1.2 The spring water disappears and the wetland decreases.
Many famous springs in the northern Henan plain have dried up. For example, Baiquan in Huixian County, before 1978, the monthly average flow reached 3.3m3/s, and now it has dried up. In recent years, artificial water diversion to restore Baiquan scenic spot in huixian city has directly cost tens of millions of yuan. The Queen Mother Spring and Jiuli Spring in Jiaozuo have also disappeared. At the same time, the wetland area is gradually decreasing, such as the wetland reserve along the Yellow River.
Figure 1 Isogram of Shallow Groundwater Level Change in Northern Henan Plain (199 1 ~ 2000)
1.3 land subsidence
It has been found that the area where land subsidence occurred is mainly in Puyang City. If the ground elevation 1997 is taken as the initial value, the settlement and unevenness will gradually increase with the passage of time, and the cumulative settlement from 1997 to 200 1 will reach 4 1 mm ~ 57 mm respectively, with a difference of16 mm. ..
Xinxiang, Wuzhibei, Anyang and hua county are potential land subsidence areas.
1.4 groundwater pollution The groundwater content in some areas of Xinxiang County and Xunxian County exceeds 50mg/l, and it can reach 100mg/l in Xiuwu County and the suburbs of Xinxiang City. In some places, the groundwater has increased, exceeding the drinking water standard (250mg/ 1). When it is more than 450mg/l (calculated by CaCO3), the hardness reaches 450-550 mg/L, and the phenol is more than 0.001mg/L. ..
Ⅳ (poor) water is distributed in most areas, and iron, manganese and fluorine in most areas exceed the standard. Ⅴ class (extremely poor) water is distributed in the depression area where the piedmont meets the Yellow River Plain, the yellow area in the old Yellow River sand area, the northern part of Yanjin, the southeastern part of Puyang and the southern part of Fanxian. The over-standard ions are salinity and hardness, and As and Pb in the southeast of Puyang. The distribution area of Ⅳ (poor) water and Ⅴ (extremely poor) water accounts for more than 75% of the total area of North Henan Plain, and there is an expanding trend.
2 the formation background of environmental geological problems
2. 1 terrain
Taihang Mountain is adjacent to the western part of North Henan Plain, with an altitude of 203~40m. The overall terrain is high in the west and low in the east, slightly inclined to the northeast. The slope is 1 ∶ 500 ~ 1 ∶ 2000, and the terrain is relatively flat.
The northern Henan plain is dominated by accumulation landforms, that is, the western piedmont alluvial plain and the southern and eastern alluvial plain.
2.2 Formation lithology
The characteristics of Quaternary in the northern Henan plain from old to new are as follows: Lower Pleistocene (): widely distributed, generally buried below 30 ~ 180m, with a thickness of 20 ~ 200m, mainly composed of glacial mud gravel, clay, silty clay and sand.
The Middle Pleistocene Series () is distributed in Tangyin and Qixian, and other areas are buried underground about 10~80m ~ 80m, with a thickness of 20 ~ 80m. The western piedmont lithology is mainly silty clay mixed with thin sand and gravel layer. The eastern part is mainly loess silt and silty clay mixed with sand.
Upper Pleistocene series () is distributed in a belt along the western margin, buried in the east, and the depth to the east can reach 30m. The thickness is about 10~60m ~ 60m. The western piedmont lithology is mainly silty soil and silty clay. The eastern part is mainly composed of silt, silty clay and sand interbedded cyclic deposition, which has obvious "dual structure"
Holocene (Qh): The western part is distributed in alluvial fans and modern riverbeds such as Anyang River, Shimen River and Yu He River in front of the mountain, and its thickness is generally several meters. The lithology is silty clay, silt and gravel layer. The eastern region is all Holocene strata with a thickness of 10~30m ~ 30m.
2.3 Climate characteristics
The northern Henan plain has a warm temperate semi-humid and semi-arid monsoon climate. According to the meteorological data of 1990 ~ 2000, the annual average temperature is 14.2℃, and the average precipitation is 598.74 mm. From the time point of view, the annual precipitation is mostly concentrated in May to August, accounting for 7 1.2% of the annual precipitation, and the precipitation in winter and spring is relatively small. Geographically, the precipitation along the Yellow River, in front of Taihang Mountain and in Qixian-Changyuan County is relatively large. There is less precipitation in the east of Anyang and Puyang. The evaporation of water surface in the area is generally 900 ~ 1400 mm, which gradually increases from west to east.
2.4 Hydrological characteristics
The surface rivers in the northern Henan plain mainly develop the Weihe River in Haihe River system and the Yellow River in Yellow River system.
The Yellow River is located in the southern border of this area, with a length of about 3 17.5km, which is the watershed between surface water and groundwater in the Huang-Huai-Hai Plain. The average discharge for many years 1447m3/s, starting from 1970, the lower Yellow River was cut off for 20 years.
Weihe River is distributed in the middle of the area, with a total length of about 252 kilometers. At present, there is no clear water at the source, most of which are industrial wastewater, urban domestic sewage and a small amount of Yellow River irrigation water. The average annual runoff is 4m3/s.
2.5 background analysis
The topography and lithology of the northern Henan plain determine that groundwater is loose rock pore water, which provides a place for its occurrence and activity. Quaternary groundwater system is mainly shallow aquifer system, which refers to aquifer medium with buried depth of 40 ~ 160 m and its phreatic water and semi-confined water system. The water-bearing medium is mainly loose medium-fine sand, and the bottom boundary is relatively stable regional clay and silty clay.
Over the years, meteorological and hydrological characteristics have shown periodic fluctuations to a certain extent. Under their influence, the groundwater circulation system presents a corresponding change law, that is, the recharge increases in wet years, the discharge decreases, the groundwater level increases → the recharge decreases in dry years, the discharge increases, and the groundwater level decreases, which has been relatively stable for many years. Their isomorphism becomes a natural factor to maintain the natural balance of groundwater circulation system in the northern Henan plain.
3 causes of environmental geological problems
3. 1 Impact of human activities on groundwater circulation system
3. Impact of1.1on groundwater recharge
Since 1960s, more than 0/0 large and medium-sized reservoirs, such as Ma 'anshi Reservoir, Baoquan Reservoir, Zhangwu Reservoir, Xiaonanhaiquan Reservoir and Yuecheng Reservoir, have been built in Taihang Mountain area in the west of northern Henan Plain. Strengthen manual control and change the surface runoff mode in mountainous areas; With the decrease of mountain pass runoff, the amount of groundwater replenished by floods in the northern plain of Henan Province has dropped sharply, and its recharge has decreased to about 10% of the total recharge.
At present, water diversion projects such as People's Shengli Canal, Wujia Irrigation Canal, Fengshou Canal, Changhong Canal and Qunku Main Canal have been built in the northern plain of Henan Province, which will bring water from the Yellow River and mountain reservoirs to this area for irrigation or urban water supply. The infiltration of canal water or irrigated farmland increases the recharge of groundwater. Its replenishment accounts for about 29% of the total.
3. Influence of1.2 on groundwater runoff
The overall runoff direction of groundwater in the northern Henan plain is basically consistent with the topographic change, from southwest to northeast, from the western piedmont recharge source area to the east, and from the southern Yellow River recharge source area to the northeast. However, artificial mining has changed the direction of runoff and formed a local groundwater confluence mode centered on each funnel.
3. Influence of1.3 on groundwater discharge
Since 1970s, the amount of groundwater exploitation in Daxing well irrigation agriculture and double protection farmland area has been increasing. With the expansion of city scale, the growth of population and the rapid development of industry, the quantity and scale of underground water source construction are also increasing, and the exploitation amount is increasing sharply. Since 1990, the average annual groundwater exploitation in various industries is as follows: the total shallow groundwater exploitation is 2.538 billion m3, of which the industrial water consumption is 244 million m3, accounting for 9.6%; The domestic water consumption is 295 million m3, accounting for11.6%; Agricultural water consumption is 2.836 billion m3, accounting for 78.8%. Mining accounts for more than 68% of the total discharge of groundwater system, and gradually becomes the most important way of groundwater discharge.
Moreover, the distribution of groundwater resources in the northern Henan plain is uneven, and the layout of groundwater development and utilization is inconsistent with the distribution of groundwater resources. On the one hand, the piedmont alluvial fan area and the area near the Yellow River are rich in groundwater resources, but the intensity of development and utilization is low, the exploitation potential index is greater than 1.4, and a large number of groundwater resources are idle or evaporated; On the other hand, the urban (town) and agricultural areas in north-central China are not rich in groundwater resources, but the exploitation is too concentrated and the exploitation intensity is high, and the exploitation potential index is less than 0.6. This layout highlights the irrationality of groundwater exploitation.
The above-mentioned human activities, especially unreasonable groundwater exploitation, constantly change the conditions and ways of groundwater recharge and discharge, and the natural balance of groundwater circulation system is increasingly destroyed.
3.2 Impact of human activities on surface water quality
In recent years, due to the massive discharge of industrial wastewater, the extensive use of pesticides and fertilizers, the discharge of urban domestic sewage and sewage irrigation, a large number of point pollution sources have emerged. For example, in North Station District of Xinxiang City 1999, the wastewater discharge reached 20,362,300 t/a, and only a small amount of wastewater was discharged up to the standard, which made the water quality of Weihe River flowing through this area PH 7.9, turbidity 1220, total hardness 546.84mg/l, zinc 257μg/l and phenol 80 μ g/L, according to 2000. These pollution sources provide the necessary conditions for groundwater pollution.
3.3 Cause analysis
According to the balance calculation of 199 1 to the year 2000, the annual balance difference of groundwater circulation system in northern Henan plain is-154 million m3. Due to human activities, the sum of groundwater discharge, which is mainly irrational exploitation, is longer than the total recharge, and the destruction of natural balance is becoming more and more serious. With the development of this negative balance groundwater circulation system, six groundwater level drop funnels with a total area of 7748.75km2 have been gradually formed, resulting in the continuous fluctuation and decline of regional groundwater level, and the occurrence of new water alum force and hydrochemical action has directly led to the formation of a series of secondary environmental geological problems:
(1) disappearance of spring water and decrease of wetland: due to the change of runoff field, the spring water and wetland originally in the discharge area (point) gradually become the recharge area (point), and the recharge of groundwater to the funnel area is increasing, resulting in the disappearance of spring water and the decrease of wetland area.
(2) Groundwater pollution: a runoff field with the descending center as the discharge point is formed in the funnel area. Under the action of hydrodynamics and hydrochemistry, natural pollution sources such as salt water in the surrounding and upper layers and pollution sources formed by human activities such as industrial wastewater, domestic sewage, agricultural fertilizers and pesticides migrate to the mining layer, making groundwater worse.
(3) Land subsidence: Overexploitation of groundwater in the funnel area greatly reduces the groundwater head, resulting in a sharp drop in uplift pressure of overlying strata, a decrease in pore water pressure in saturated clay layer, an increase in effective stress, and land subsidence caused by drainage and consolidation of soil layer.
To sum up, the fundamental cause of hydrogeological problems in the North Henan Plain is human activities, especially the unreasonable exploitation of groundwater.
4 Evolution model of environmental geological problems
In 1950s and 1960s, human activities in the northern plain of Henan Province were relatively weak, groundwater basically followed the law of natural circulation, and the regional water level was relatively high. Since then, with the increasing intensity of human activities, especially the unreasonable exploitation of groundwater, the natural balance of groundwater circulation system has been destroyed, and it has been in a negative balance for a long time, resulting in a series of environmental geological problems. With the increase of water demand in North Henan Plain, the unreasonable exploitation of groundwater continues. Under the current conditions, environmental geological problems will become increasingly prominent, which will eventually lead to a series of geological disasters.
However, if the groundwater level continues to rise due to human activities, it will develop in another direction, causing a series of environmental geological problems, such as soil salinization in Yuanyang, Yanjin, Fengqiu and other places in the 1950s and 1960s, which will eventually lead to geological disasters. It shows that environmental geological problems have the characteristics of two-way evolution.
To sum up, the evolution model of environmental geological problems in northern Henan plain is shown in Figure 2.
Fig. 2 Evolution Model of Environmental Hydrogeological Problems in Northern Henan Plain
5 Countermeasures and suggestions
5. 1 Adjust the layout of groundwater exploitation and make scientific use of groundwater.
Due to the uneven distribution of groundwater resources in the North Henan Plain, it is of great significance to adjust the layout of groundwater exploitation, make scientific use of groundwater, and reduce and avoid the formation and evolution of environmental geological problems aggravated by unreasonable exploitation of groundwater.
5. 1. 1 Zhangweihe alluvial fan area
The floor depth of shallow water-bearing formation in Zhangwei River alluvial fan area is 40 ~ 80m, and it can reach 100m locally. Shallow water is mainly used for farmland irrigation in this area.
(1) According to the fact that the groundwater level should be less than 1/2 of the entire aquifer thickness, and the thickness of the remaining aquifer should not be less than 20m, the groundwater restricted exploitation protection zone and its restricted water level are determined. Therefore, the general groundwater level should be kept at 20 ~ 30m.
(2) There is brackish water in some areas where the front edge of alluvial-diluvial fan meets the depression. Therefore, mining should be properly strengthened to reduce the large hydraulic gradient formed by evaporation, speed up recharge, promote circulation and gradually improve groundwater quality. According to the analysis of mining for many years, the groundwater level in these areas should be controlled at 7m.
(3) In areas rich in groundwater resources, such as Anyang River in Anyang City, Yu He River in huixian city, alluvial fans in Huang Shuihe, etc., centralized water exploitation can be established, the exploitation amount can be moderately increased, and the groundwater level can be lowered, so as to seize the lateral runoff of precipitation infiltration, increase the storage capacity of air conditioners, and implement rich storage and dry use. The flood limit water level in Anyang is 28.9 meters, and the alluvial fans in Yu He and Huangshui River are 35 meters deep. ..
5. 1.2 Yellow River alluvial fan area
(1) Water sources along the Yellow River can be established in areas near the Yellow River, such as Zhandian-Wuyuan Town in Wuzhi County, Langgong Temple-Funingji Township in Xinxiang County and Zi 'an Township in Puyang City. And centralized water exploitation can be established to increase the potential of groundwater resources.
(2) In order to prevent the expansion of salt water area, corresponding measures should be taken for the main distribution areas of bitter salt water, namely, the funnel area of groundwater exploitation and the depression along the Yellow River. In the funnel area, the exploitation amount should be controlled so that the water level will not fall first and then rise; Increase the exploitation amount along the Huangwa area, appropriately reduce the groundwater level, and maximize the amount of precipitation infiltration and lateral infiltration, so as to strengthen circulation and gradually desalinate brackish water. Accordingly, the water level in the funnel area should be higher than the low water level in 2000; Along the Yellow River depression, the water level should be controlled below 8m. At the same time, increase the utilization of brackish water, but ensure the safety of wetlands in wetland reserves.
5.2 Save water resources
About 78.8% of the water supply in the northern Henan Plain is used for agricultural irrigation, and agricultural water saving, especially in the central and northern regions, is very important to reduce and avoid environmental geological problems. Canal lining can save water by 20%, plastic pipe irrigation can save water by 25%, sprinkler irrigation can save water by 30%, and drip irrigation can save water by up to 50%. At present, the irrigation area of high water-saving irrigation methods (pipe irrigation, sprinkler irrigation and drip irrigation) in this area only accounts for less than 25%, which should be popularized and applied vigorously.
At present, the reuse rate of industrial water in big cities is 70% ~ 80%, while that in small and medium-sized cities is only 20% ~ 50%. Due to backward technology, the water consumption of steel, chemical industry and paper industry is 6 ~ 8 times that of developed countries. Adjust enterprises with large water consumption, speed up the research and development of new industrial water-saving technologies and processes, and encourage the development of enterprises with good benefits, less water consumption and less pollution. Promote production with water and development with water.
The situation of water shortage in northern Henan plain will exist for a long time, so we must take water saving as a long-term fundamental measure, focus on developing agricultural water-saving irrigation and industrial water-saving, and adopt different water-saving measures according to the characteristics of different industries to fully implement water saving.
5.3 Purify waste and sewage to realize wastewater recycling.
The sewage discharge of five cities in the northern plain of Henan Province is relatively large. At present, five prefecture-level cities have built modern sewage treatment plants one after another, which not only avoids the direct discharge of sewage to form groundwater pollution sources, but also improves the reuse rate of water resources. However, the treatment capacity is still relatively small, and the reuse rate of water resources is only 30%. We should speed up the sewage treatment process and improve the sewage treatment capacity.
Thank you, Senior Engineer Ma of the First Hydrogeological Engineering Geological Team of Henan Bureau of Geology and Mineral Exploration and Development, for your valuable comments on this paper, and thank you here.
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