Groundwater geological environment problems

I. Development and utilization of groundwater

Before the founding of New China, the development and utilization of groundwater in China was only carried out in local areas, mostly in rural areas, and shallow wells were used to solve the problem of water use for people and livestock. After the founding of New China, the country has carried out a national hydrogeological survey and urban water supply exploration, and groundwater has been widely developed throughout the country, becoming an important source of industrial and agricultural water and urban domestic water, especially in the northern region.

In the second half of the 20th century, with the development of economic construction, the development and utilization of groundwater in China can be roughly divided into two stages. The first stage was 1950 ~ 1980, and the groundwater exploitation increased sharply from a small amount to 70 billion m3/a, accounting for about 18% of the national water consumption at that time. The second stage is 1980 ~ 2000. During this period, China's national economy has entered a period of steady and rapid development, and the demand for water resources is increasing day by day. Groundwater exploitation has exceeded1000 billion m3/a, accounting for about 20% of the national water consumption.

From 1950 to 1960, the focus of groundwater development in China is to solve urban water supply. In the 1960s, due to the severe drought in North China, the geological and mineral departments launched the drought-resistant well drilling campaign, focusing on the establishment of a large-scale well irrigation system in North China, and gradually extended it to Northeast and Northwest China.

According to the statistics of national groundwater exploitation in 1980, the total exploitation amount is 75.9 billion m3/a, accounting for about 12% of natural resources. Among them, the plain area accounts for 75% and the mountainous area accounts for 25%. Geographically, the north accounts for 84% and the south accounts for 16%. The northern plain area accounts for 7 1% of the national exploitation, while the southern area only accounts for 3.5%. It can be seen that the northern plain area occupies a major position in groundwater exploitation in China.

According to statistics of relevant departments, the total water supply in China was1556.045 billion m3 in 1997, of which 17.4% came from groundwater. The groundwater supply accounts for more than 50% of the total water supply in four provinces (cities), Hebei (75%), Beijing (66.6%), Shanxi and Henan. Followed by Shandong, Liaoning, Shaanxi, Inner Mongolia, Heilongjiang, Tianjin, Jilin and other provinces (cities, autonomous regions), the groundwater supply accounts for about 30% ~ 40% of the total water supply. 1997 In the actual groundwater exploitation in China, agricultural water accounts for 54.3%, industrial water accounts for 17.5%, urban and rural domestic water accounts for 20.2%, and others account for 8%.

According to incomplete statistics, there are 792 large, medium and small groundwater sources in China. Among them, there are 240 water sources with an exploitation amount exceeding 50,000 m3/d, and most of these large or extra-large water sources are located in North China, such as Beijing, Tianjin, Hebei, Shandong, Shanxi, Henan and other provinces and cities, with * *115, accounting for 47.9% of the total number of large or extra-large water sources in China. There are 30 northeastern provinces, accounting for 12.5% of the total. There are 48 provinces and autonomous regions in northwest China, accounting for 20% of the total. The above-mentioned 15 provinces, municipalities and autonomous regions have 193 large or extra-large water sources, accounting for 80.4% of the national total, and the exploitation amount accounts for 82.2% of the actual exploitation amount of large or extra-large water sources in China.

According to the statistical results of 1980, 1993 and 2000, the proportion of surface water in the water source composition of China's actual water supply has been declining, while the proportion of groundwater has increased. Irrigation agricultural water accounts for the highest proportion in the total water consumption, but the water consumption is decreasing, while the industrial and urban domestic water consumption is rising rapidly.

Second, the main environmental geological problems caused by groundwater development

With the growth of population, the promotion of urbanization and the development of industry and agriculture, the demand for water supply in China has greatly increased. Groundwater is one of the urban water supply sources in China, especially in the northern region, and most cities use groundwater as the main water supply source. There are two kinds of impacts of large-scale exploitation of groundwater, namely, positive impact and negative impact. Judging from the positive effects of groundwater exploitation, it has largely met the needs of industrial and agricultural production and people's life, promoted the development of national economy and improved people's living standards. Rational exploitation of groundwater can also maintain the stability of water quality and quantity, which is beneficial to the healthy development of urban ecosystem. The negative effects of groundwater exploitation are mainly the adverse effects of over-exploitation of groundwater on cities or the environment, which are mainly manifested in water resource depletion, land subsidence, seawater intrusion, karst collapse, and deterioration of ecological environment. Due to the increasingly acute contradiction between supply and demand, it often forms a vicious circle, which constitutes a geological disaster and causes great losses or serious threats to the urban environment and people's lives and property.

(A) the depletion of groundwater resources

The water resources in any area are always limited to a certain range, and no matter how abundant the water resources are, it is impossible to expand the exploitation indefinitely. Water resources science puts forward the concept of recoverable resources, which refers to the amount of groundwater exploitation that ensures the stability of water quality and quantity and does not have any adverse impact on the social environment.

However, most cities in China are dominated by industry, and most industrial enterprises are concentrated in urban areas or suburbs, so the demand and consumption of water are great, so the water sources are mainly distributed around the urban areas. With the growth of urban population and the expansion of urban scale, due to the surge of water demand, the amount of groundwater exploitation has risen sharply, and the original water source has not been adjusted in time, so the situation of groundwater overexploitation is very serious.

According to the statistics of China Geological Environment Monitoring Institute (2006) on 125 cities in China, there are 2 16 underground drip funnels in China, including 120 shallow underground drip funnels, 9/kloc-0 deep underground drip funnels and 5 karst underground drip funnels. Shallow groundwater drop funnels are mainly distributed in North China and East China, and the funnel area ranges from tens of square kilometers to thousands of square kilometers. Deep groundwater drop funnels are widely distributed in North China, Northeast China and East China, and the funnel area is mostly 100km2, even thousands of square kilometers.

Since 1980s, urban groundwater overexploitation has become a common phenomenon in China. In some northern cities, such as Taiyuan, Xi, Shijiazhuang, Baoding and Cangzhou, the groundwater level has dropped by more than 10m annually. In the northern region, due to the continuous decline of groundwater level and the continuous expansion of funnel scope, the water output of production wells is seriously exhausted, a large number of well pumps are scrapped, and even some water sources are forced to stop production. In the southern region, the groundwater level is basically stable or slowly decreasing.

(2) Land subsidence

One of the consequences of over-exploitation of groundwater, especially in basins filled with loose alluvial deposits, lakes or shallow sea sediments, is ground subsidence or subsidence.

Most of the land subsidence occurs in coastal industrial cities and agricultural production areas where a large amount of groundwater is exploited. Urban land subsidence often brings harm to industrial production, municipal facilities and people's lives. Such as Tokyo, Niigata and Osaka, Houston-Galveston coastal area in Texas, Santa Clara Valley in California, Venice in Italy, North China Plain, Yangtze River Delta and Wei Fen Basin in China. Land subsidence has become one of the most important public hazards in the world today. Taking Shanghai as an example, groundwater has been the main source of industrial water supply for a long time. Land subsidence in Shanghai was first discovered in 192 1 year. By 2004, the average land subsidence was 1947.6 mm, and the maximum subsidence was about 2998.5 mm (Gong Shiliang et al., 2005). Land subsidence is a kind of gradual geological disaster that people are not easy to perceive, and its loss is a continuous and cumulative incremental change process. When people realize this kind of damage, the loss it has brought has been very huge, and its influence has been very extensive and lasting. In cities or regions where land subsidence has occurred or is occurring all over the world, the losses caused by land subsidence include drainage system failure, urban flood discharge capacity reduction, underground pipe network damage, serious damage to houses, traffic facilities damage, and more frequent and serious storm surges.

According to the statistical analysis of a large number of data, land subsidence increases with the increase of groundwater exploitation. Moreover, the range of land subsidence area and groundwater falling funnel is basically the same. The main reason of land subsidence is that a large amount of groundwater is exploited, which leads to dehydration and compression of soft soil layer in funnel area where groundwater level drops.

Land subsidence in China first occurred in Shanghai and Tianjin in the 1920s. Since then, land subsidence has also occurred in major cities in the Yangtze River Delta, such as Suzhou, Wuxi, Changzhou, Tianjin Plain and Jidong Plain. By 2002, there were 96 cities and regions in China with different degrees of land subsidence, mainly distributed in the Yangtze River Delta, North China Plain, Wei Fen Basin, Songnen Plain, Pearl River Delta, Jianghan Plain and other places, among which the first three areas were the three major areas where land subsidence disasters occurred in China. North China Plain is the area with the largest land subsidence in China. Due to the long-term over-exploitation of groundwater, a deep drop funnel of groundwater level has been formed in all parts of Beijing, Tianjin and Hebei. The range of deep underground water level below sea level in the whole region has reached 76732km2, accounting for 55% of the total area of the whole North China Plain. At present, the land subsidence area of North China Plain has exceeded 1/3 of the total plain area.

(3) seawater intrusion

In the natural state, underground aquifers in coastal areas generally extend from land to sea. Because the fresh groundwater in the terrestrial aquifer keeps a high head, which can prevent the invasion of high-density seawater to the land, they are in a dynamic balance. When a large amount of groundwater is exploited in coastal areas, the groundwater level drops, the original balance relationship between salt and fresh water is broken, and seawater begins to invade the land, resulting in seawater intrusion.

Seawater intrusion is a common environmental deterioration phenomenon mainly caused by improper exploitation of groundwater resources in coastal areas, and it is also a unique resource and environmental problem in modern society. Seawater intrusion often leads to the destruction of the ecological environment in coastal areas, the reduction of fresh water resources, and the scrapping of a large number of motor wells, which has a serious impact on local industrial and agricultural production and residents' lives and caused huge economic losses, especially in economically developed coastal areas. At present, seawater intrusion has been found in hundreds of areas in more than 50 countries and regions around the world, mainly distributed in coastal plains, estuary deltas and island areas with high socio-economic development, such as Long Island in the United States, Hermes City in Mexico, and coastal areas of Japan, Israel, the Netherlands and Australia.

China's coastline is as long as 1800 kilometers, and coastal areas have become the strategic focus of economic development because of their superior marine geographical location. However, since 1980s, seawater intrusion in many coastal areas has intensified due to over-exploitation of groundwater. Liaoning, Hebei, Shandong, Jiangsu, Tianjin, Shanghai, Guangxi and other provinces, cities and autonomous regions have all occurred, causing huge economic losses and seriously affecting the development of the national economy. In Laizhou Bay, Shandong Province, by the end of 1995, the seawater intrusion area had grown to more than 970 square kilometers, which caused more than 400,000 people to have difficulty drinking water, more than 8,000 agricultural wells were scrapped due to salinization of water quality, and more than 40,000 hectares of cultivated land lost irrigation capacity, resulting in an annual grain yield reduction of 300 million Jin.

(d) karst collapse

In areas where carbonate rocks are widely distributed, underground caves are developed and karst collapse is very common. These karst collapses are mostly caused by human activities except a few natural actions, such as the massive drainage of karst deposits in mining areas and the massive exploitation of karst groundwater. Among them, in cities and industrial areas, the collapse caused by massive exploitation of karst water has caused serious harm and economic losses. This kind of collapse mainly occurs in shallow karst area of plain. Quaternary porous aquifer with different overlying thickness and underlying karst aquifer form a double-layer structure, and they are often closely related hydraulically. Most underground caves are filled with sediments, which keeps the ground stable. However, in the case of strong pumping, the sediment filled in the cave is washed away by the undercurrent, which is the main reason for the ground collapse.

According to the investigation, karst collapse is not only very common in South China and Southwest China, but also very serious in North China. At present, karst collapse has been found in 23 provinces and regions in China, with more than 800 places and nearly 30 thousand collapse pits, most of which are caused by the exploitation of karst water. The cities with serious karst collapse in China are Wuhan, Huangshi and Xianning in Hubei, Zhuzhou, Huaihua and Xiangtan in Hunan, Nanjing and Xuzhou in Jiangsu, Hangzhou in Zhejiang, Jiujiang and Chongqing in Jiangxi, Kunming in Yunnan, Guiyang, Shuicheng, Anshun and Zunyi in Guizhou, Guilin, Liuzhou and Yulin in Guangxi, and Guangzhou and Zhaoqing in Guangdong. In the north, there are Dalian and Anshan in Liaoning, Qinhuangdao and Tangshan in Hebei, Jinan, Tai 'an, Zibo and Zaozhuang in Shandong.

Karst collapse will cause serious damage to urban buildings, railways, highways, mining facilities, bridges, farmland and people's lives and property, and destroy water sources and ecological environment. There are more than 50 major landslides in domestic railway lines and stations alone, and the cumulative traffic interruption exceeds 1.700 hours, causing many traffic subversion accidents, and the treatment cost alone exceeds 1 100 million yuan. Capital cities such as Guiyang, Kunming, Wuhan, Hangzhou, Nanjing, Guangzhou and more than 20 small and medium-sized cities such as Guilin have all caused different degrees of damage to urban buildings due to karst collapse.

(v) Desertification

Desertification mainly refers to the process that non-desert areas, such as oases or grasslands, are destroyed by natural or human activities, so that the original cultivated land or grassland gradually evolves into desert. The main feature of desert is that there is basically no surface water, vegetation is scarce, and it is difficult for ordinary animals to survive, forming a barren land. The concept of desertification clearly put forward by the United Nations Environment Programme is "land degradation in arid areas caused by unreasonable human activities". Desertification formed by natural processes generally evolves very slowly, such as climate drought, which often takes hundreds or thousands of years; Desertification caused by human activities can have serious consequences in just a few decades.

There are many reasons for desertification caused by human activities, such as man-made destruction of forests and vegetation, blind large-scale reclamation, reclamation and overgrazing of grasslands. However, land desertification in many areas is mainly caused by unreasonable development of water resources, especially Shiyang River Basin in Hexi Corridor.

According to the results of the national survey of desertification land, the area of desertification land in China has increased faster and faster in recent decades. From 1950s to 1970s, the average annual growth of desertified land was 65,438+560 km2. In 1980s, it increased by 2400km2 every year. The annual economic loss caused by desertification is as high as 54 billion yuan.

Desertification has brought about the deterioration of regional climate, especially the sharp increase of sandstorm and sand blowing weather. The arid area in western China is an important part of the sandstorm area in Central Asia. From 1950 to 1993, there were 76 strong sandstorms in this area, with an average of 1.76 per year; Since 1990, the annual average occurrence rate of extremely strong sandstorms has more than doubled. The direct economic loss caused by extremely strong sandstorm has exceeded 1 100 million yuan. For example, on May 5, 1993, particularly strong sandstorms occurred in Xinjiang, Gansu, Ningxia and parts of Inner Mongolia, causing direct economic losses of 540 million yuan; The direct economic loss caused by the sandstorm that hit northwest China 12 county in April reached 800 million yuan. 1April, 998 18, the direct economic losses caused by the extremely serious sandstorms in Junggar basin and Turpan basin in Xinjiang exceeded 65,438 billion yuan.