The United States is an early country to study the sustainable utilization of groundwater. As early as 1883, American scholars' room? Lin published the article "artesian well", which first discussed the well-forming conditions and development theory of artesian well. 1897 Norton of Iowa Geological Survey first used the concept of "aquifer" in the report of artesian well in Iowa. Todd proposed in 1900 that too many artesian wells will lead to the attenuation of confined water. 1923, Mainzer published the Formation and Theory of Groundwater in the United States and the Literature Review of Groundwater, which systematically summarized the research work and theoretical progress of hydrogeology, and at the same time made a qualitative assessment of groundwater resources in China for the first time, expounding the occurrence, recharge, discharge, runoff, quantity, quality, development and utilization of groundwater in the United States (Chen Meizhen, 2006; Chen Rensheng et al., 2003). The author put forward the unsteady flow theory in 1935, which solved many practical problems well.
In the development of groundwater, people began to realize that groundwater resources are limited. In 1930s, tolman and his colleagues discovered seawater intrusion and land subsidence caused by groundwater exploitation. In the mid-1960s, the investigation of groundwater resources in various states and the evaluation of groundwater resources by balance method were successively carried out. 1963 McGuinness summarized the research results of groundwater resources evaluation in various states and regions.
1977, a serious drought occurred in the United States. 1978, the United States Geological Survey (USGS) started the Regional Water System Analysis Project (RASA), which lasted for nearly 20 years. It investigated and studied 28 water systems in China, and simulated the dynamic changes of groundwater before and after groundwater development by using a three-dimensional finite difference groundwater flow numerical model. 1990 ~ 2000, the groundwater atlas of various water systems was compiled and published (scale:1:250,000 ~ 1: 1 000,000).
At present, the amount of groundwater exploitation in the United States accounts for 20.7% of the total water consumption. Among them, 98.3% of domestic water, 57.4% of livestock water and 4 1.5% of irrigation water all depend on groundwater recharge, and the awareness of improving and protecting the ecological environment is getting stronger and stronger. To this end, the United States is implementing a new round of Groundwater Resources Plan (GWRP). The research focus has shifted from the previous state to the whole water system, hydrological system and ecological environment system, from the previous emphasis on the supply function of groundwater resources to the comprehensive investigation and evaluation of groundwater resources, ecological functions and geological environment functions, and emphasized the research on sustainable utilization of groundwater.
The history of groundwater development and utilization in the United States in the past hundred years shows that economic and social development has played an important role in promoting the concept of groundwater development and utilization and the study of its ecological-geological environment function. /kloc-before the 0/9th century, groundwater was only a supplementary resource in economic and social development, and the development and utilization of surface water was the main water resource. Since the 1960s, groundwater has increasingly become the basic resource on which economic and social development depends. Especially in the years of continuous drought, the development and utilization of groundwater has received unprecedented attention. At the same time, environmental problems such as aquifer dehydration, rapid degradation of ecosystems dependent on groundwater, land subsidence and seawater intrusion have become more and more obvious. According to USGS statistics, the proportion of groundwater in public water supply in the United States increased from 26% in 1950 to 37% in 2000. In 1980s, more attention was paid to groundwater protection. The federal government of the United States has formulated many protection laws and regulations to improve sewage discharge standards and water utilization efficiency. By 2000, the average irrigation amount per mu was reduced by 30% compared with 1950. In USGS 2000-20 10's Scientific Strategy of the Ministry of Geology and 1998-2008's Development Strategy of the Ministry of Water Resources, the research on the availability and sustainability of groundwater is highlighted, including the investigation on the influence of urbanization and suburbanization on groundwater, the investigation on the influence of coastal land use and population growth on groundwater and the study on the interaction between groundwater and surface water.
(B) Domestic groundwater evaluation research trends
Since 1950s, the Ministry of Geology and Mineral Resources and relevant departments have conducted a large number of investigations and evaluations on groundwater and its environmental geological problems nationwide, including regional hydrogeology, water supply hydrogeology, environmental hydrogeology, groundwater resources evaluation and the application of new technologies and methods. After more than 50 years of hydrogeological work, the regional distribution law of groundwater resources in China has been basically found out, and a lot of work has been done to investigate and study groundwater in northwest and north China as the main strategic task, realizing the collection, processing, storage, transmission and exchange of all kinds of information. Groundwater has been regarded as an integral part of hydrosphere and lithosphere and an important environmental factor, and the relationship between the four major circles on the earth's surface and the continental water cycle and global change has been studied. Thinking about groundwater under the global integration environment and studying groundwater circulation mode by using large profile and isotope have greatly changed the traditional thinking and mode of groundwater evaluation, especially the development of information technology in recent years, which has accelerated the speed of groundwater evaluation.
Groundwater evaluation for more than 50 years has the following characteristics: ① The purpose of groundwater evaluation is to reflect the national will and obey the national goals; (2) Give full play to the advantages of hydrogeological work, reflect the regional and basic evaluation of groundwater, and serve the national construction; (3) Abundant data and experience have laid a foundation for the study of groundwater evaluation methods. Since 1970s, due to the mutual penetration of applied mathematics and groundwater dynamics, and the popularization and application of computer technology, the content of traditional hydrogeology has been enriched and broken through, and groundwater evaluation has developed from qualitative research to quantitative research. The basic theory of groundwater resources evaluation has experienced the development from stable flow to unsteady flow, from two-dimensional flow to three-dimensional flow, from general equilibrium method and analogy method to analytical method and finite element or finite difference numerical method and correlation analysis method. Groundwater quality evaluation has developed from single evaluation to comprehensive evaluation, from general mathematical statistics method to clustering, neural network and grey system evaluation method.
In the late 1980s, the evaluation of groundwater resources began to shift its main objective to the study of management mode, involving natural environment, social environment, technical and economic environment and other issues related to groundwater development activities.
However, facing the requirement of sustainable development in 2 1 century, new problems have appeared in groundwater evaluation to varying degrees. The first round of national groundwater resources evaluation, which began in 1980s, was based on the development process of consuming resources and sacrificing the environment. There are historical limitations in the guiding ideology, concept and method of evaluation, which urgently need to be improved and developed according to the new requirements. For example, due to the limitation of cognitive ability and technical level at that time, the basic understanding and evaluation methods of resources, environment, ecological attributes and functions of groundwater system were insufficient in the reflection of sustainable development thought and water cycle thought, and static thinking was more prominent.
1. Classification and concept evolution of groundwater resources
In 1950s and 1960s, the concept of "four reserves" of the former Soviet Union was generally adopted in the evaluation of groundwater resources in China, namely, dynamic reserves, static reserves, regulated reserves and mining reserves. These concepts are also used in some countries in Europe and America (Qu et al., 199 1). After years of practice, hydrogeologists generally feel that there are many defects in applying the concept of "four major reserves" to evaluate groundwater resources (Chen,1982; Liu Guangya,1982; Wang et al., 1982), has basically stopped using now.
In 1970s, the concepts of "three kinds of water quantity" were put forward, namely, recharge quantity, reservoir capacity and allowable exploitation quantity, and were incorporated into the national standard (GBJ27-88) in 1989. But with the development of practice and theory, its limitations and theoretical defects are gradually exposed (Xu Hengli et al., 200 1). The scheme follows the thinking mode of taking aquifer (or water source) as the evaluation unit, and does not reflect the integrity and systematicness of groundwater resources; The concept of recharge time and space is vague, which easily leads to repeated calculation of water quantity; The allowable exploitation amount is only a general formulation, which is difficult to operate in practice.
In 1980s, the concept of "resources" was gradually accepted by people, and countries and regions such as Europe, America and Japan successively adopted the concept of groundwater resources. Potential renewable resources, actual renewable resources, renewable resources and safe production have appeared one after another. "Sustainable output" and "actual sustainable output", etc.
Chinese scholar Professor Wang (1995) and others divide groundwater resources into "recharge resources" and "storage resources" based on their natural attributes. "Recharge resources" is defined as "the amount of water that can be regenerated by aquifer system". Take the average recharge of aquifer system for many years as the recharge resource, with the unit of m3/a. "Storage resource" is defined as "the water quantity accumulated and preserved by aquifer system in geological history". The gravity water volume below the multi-year average low water level of the water-bearing system is used as the storage resource, and the unit is m3.
The classification of groundwater resources proposed by Academician Chen Mengxiong in 1983 has been continuously adjusted and supplemented (in 2002), and it is also widely representative. In this classification, groundwater resources are divided into "natural resources" and "recoverable resources". "Natural resources" is defined as "in a complete hydrogeological unit (groundwater system), groundwater is directly or indirectly replenished by atmospheric precipitation or surface water infiltration under natural conditions, which has certain hydrochemical characteristics, can be utilized and changes according to the hydrological cycle law", and can generally be expressed by the sum of various recharge or discharge in the region. "Recoverable resources" is defined as "groundwater resources that can be exploited under reasonable economic and technical conditions without deterioration of water quality or other adverse geological phenomena (such as ground subsidence and ground collapse). During the mining period, it did not adversely affect the ecological balance. "
2. Research status of groundwater resources evaluation methods.
Darcy's law and water balance are the theoretical basis of quantitative evaluation of groundwater resources, which leads to two evaluation methods, namely "water balance method of groundwater system" and "hydrodynamic method of groundwater system"
"Water balance method of groundwater system" is to determine the quantity of groundwater resources directly by establishing the water quantity relationship between recharge, discharge and storage variables of groundwater system and using the principle of mass balance. The "groundwater system water balance method" can be used to calculate the water quantity of regional and local groundwater resources. It can not only estimate the total recharge and discharge of groundwater system, but also calculate the single quantity of groundwater system. It is the most commonly used basic method in groundwater resources evaluation, and it is also a relatively reliable method.
According to Darcy's law and the principle of water balance, the "hydrodynamic method of groundwater system" establishes a differential equation describing the law of groundwater movement, and evaluates the water state of groundwater system by solving the differential equation.
According to the differential equation, the analytical method is divided into "analytical method" and "numerical method". The analytical method is based on the groundwater flow theory to evaluate the groundwater quantity, which is mainly suitable for homogeneous water-bearing systems with small equilibrium area and simple hydrogeological conditions. Before 1950s, analytical method played an important role in groundwater resources evaluation, and it is still the main method to determine hydrogeological parameters in groundwater resources evaluation. However, when the analytical method is applied to large-scale water systems, its limitations are exposed because the actual hydrogeological conditions are much more complicated than those assumed by the analytical method (Xue Yuqun et al., 1986).
In order to solve the problems caused by the further expansion of groundwater exploitation scale, physical simulation (electric simulation and sand tank simulation, etc. ) technology rose in 1950s and 1960s, but it still failed to solve the problems faced by regional groundwater resources evaluation under complex hydrogeological conditions. The application and popularization of computer technology and numerical calculation in groundwater resources evaluation makes it possible to simulate some complex groundwater flows, and begins to consider the heterogeneity and anisotropy of water-bearing media. The complex overflow system and various irregular boundary conditions, as well as multiphase flow and dual media, are also deeply studied, and the natural characteristics of solid systems are more preserved in the conceptual model. Because the numerical method can be used not only for the evaluation of large-scale groundwater resources, but also for the evaluation of local water sources; It can not only deal with complex hydrogeological problems, but also have high calculation accuracy. Therefore, it has gradually become an important method of groundwater resources evaluation, and is widely used in groundwater resources evaluation and management because it is easier to achieve the purpose of systematic analysis.
In the evaluation of groundwater resources, the commonly used methods are hydrological analysis, correlation analysis and hydrogeological analogy. "Hydrological analysis method" is a method to calculate groundwater recharge by imitating the flow measurement and analysis of land water literature. It is mainly used in areas where groundwater recharge is completely converted into groundwater discharge, such as karst pipeline flow area, karst water system with total discharge of karst springs or fissure water system in bedrock mountain areas. Other methods are difficult to apply, mainly including underground runoff modulus method and base flow division method. "Hydrogeological analogy method" is often used in areas lacking actual data, mainly based on the similarity of hydrogeological conditions, comparing the actual data of local areas or other areas with similar conditions with the whole area or research area to evaluate groundwater resources, and is mostly used to estimate the recoverable resources. This method is a last resort when there is a lack of information in the research area, and its evaluation results are not accurate enough. "Correlation analysis method" is a statistical method, which is mainly used in areas with insufficient regional hydrogeological exploration test data but more groundwater dynamic data. When extrapolated by this method, its reliability is difficult to guarantee. "Mining test method", in the non-recharge period of groundwater (dry season), according to the mining conditions close to the design of water intake project, carries out long-term pumping test, and then calculates the recharge amount of water source in dry season according to the pumping amount, water level decline dynamics or water balance equation under mining conditions, and takes it as the allowable exploitation amount of water source. This method is mainly used to evaluate the allowable exploitation of water resources and to obtain parameters in the evaluation of regional groundwater resources.
Looking at the achievements of groundwater evaluation at home and abroad, the most commonly used methods are "groundwater system water balance method" and "numerical method". The "Regional Water System Analysis Plan" (RASAP, 1978 ~ 1995) carried out in the United States used numerical method and balance method to evaluate the water resources of 25 major groundwater systems in China (USGS,/kloc-0). In the new round of groundwater resources evaluation (groundwater resources planning) since 2000, numerical method is still the main method (USGS, 200 1). In the evaluation of regional groundwater resources jointly carried out by EU countries, water balance method is the main method (Fried,1982; Reese and Cole, 1997). In addition, some countries in Asia and Africa mostly use water balance method and numerical method to evaluate regional groundwater resources (Leslie B.Smith and Kadri Külm, 2002; Shaheen,1989; Lloyd,1990; Ulf Thorweihe and Manfred Heinl, 2002). Balance method and numerical method were also the main evaluation methods of the first round of national groundwater resources evaluation in China in 1980s.
With the development of mathematical geology, some new theoretical methods have appeared in groundwater evaluation at home and abroad in recent years, such as stochastic theory and neural network (Kitanidis,1985; Bates,1992; Gaerhar,1993; Brannan,1993; Yang Jinzhong et al., 2000), but these methods are still in the stage of theoretical exploration, and it is difficult to be widely used in practice.
3. Research status of groundwater quality evaluation
In the early evaluation of groundwater quality, China generally draws lessons from the evaluation models designed by foreign scholars, such as Nemerow N.L index method. However, in the process of application, these evaluation models gradually found their shortcomings in theory and practice, so Chinese groundwater quality evaluation workers put forward many water quality evaluation methods suitable for different purposes according to their own practical experience and actual situation. For example, in the 1960s, people used the "comprehensive index of environmental quality" to express the environmental quality quantitatively. So far, many mathematical models for calculating the comprehensive index have been put forward, which have played a positive role in the division of environmental quality.
There was no "National Groundwater Quality Standard" in the early national groundwater quality evaluation, which was mainly based on the Hygienic Standard for Drinking Water (TJ20-76) approved by the State Construction Committee and the Ministry of Health, and with reference to the Quality Standard for Drinking Water published by the World Health Organization (WHO) 1958, the local Quality Standard for Drinking Water was considered for individual evaluation parameters. The evaluation methods mainly include exponential method, multi-parameter method and fuzzy mathematics method. In today's national groundwater quality evaluation, although some changes have taken place in the selection, classification and pollution grade division of evaluation items, its ideas and technical methods have followed this model.
Since 1980s, with the rapid development and wide application of computer technology, fuzzy mathematics, grey clustering and neural network have been widely used in groundwater quality evaluation, and with the improvement of methods, people pay more and more attention to the rationality of evaluation results. However, due to many factors affecting groundwater quality, each evaluation method has certain limitations. For example, in the "hard classification" of comprehensive pollution index method, grey and fuzzy systems need to design several different utility functions (whitening function of grey system, membership function of fuzzy mathematics, etc.). ), and artificially give the weight (or weight function) of each evaluation index. These utility functions and index weights are inevitably subjective, which makes the evaluation method difficult to be universal, increases the difficulty of application and the influence of artificial assumptions on the conclusion. In groundwater quality evaluation methods, there is a common problem of "parameter weight", such as the index method equating all water quality parameters, and the model method is subjective in parameter selection and parameter weight setting. At present, the rapid development of artificial neural network evaluation method broadens the field of vision of groundwater quality evaluation method.
4. Research status of groundwater vulnerability assessment
After Margat first put forward the term "groundwater vulnerability" in 1968, despite decades of development, there is still no unified definition of "groundwater vulnerability" at home and abroad, and many scholars have given different definitions of "groundwater vulnerability" from different angles according to their own factors.
With the issue of 1987 as the boundary, the development process of the concept of "groundwater vulnerability" can be divided into two stages. Before 1987, the concept of groundwater vulnerability was mostly defined from the perspective of the inherent factors of hydrogeology itself. The vulnerability of groundwater proposed by Margat and Albiet in 1970 refers to the possibility of pollution sources infiltrating and diffusing from the surface to the surface of groundwater under natural conditions. Olmer and Rezac believe that groundwater vulnerability is the degree to which groundwater may be harmed, which is determined by natural conditions and has nothing to do with existing pollution sources. Flana pointed out that groundwater vulnerability is the complexity of surface and underground conditions that affect pollutants entering aquifers. Villumsen et al. in 1983 defined groundwater vulnerability as the hazard of chemicals used or abandoned on the surface to groundwater. 1987 "International Conference on Soil and Groundwater Vulnerability" opened a new stage of groundwater vulnerability research. Most scholars argue that when defining groundwater vulnerability, the vulnerability of aquifer itself and the influence of human activities and pollution sources should be considered. Some scholars put forward that groundwater vulnerability refers to the sensitivity of groundwater quality to its present or future use value.
The vulnerability of groundwater system has been widely regarded as the ability of the system to cope with external (natural and human activities) that affect its state and nature in time and space. In 199 1, the US Audit Office uses "hydrogeological vulnerability" to represent the vulnerability of aquifers under natural conditions and "total vulnerability" to represent the vulnerability of aquifers under the influence of human activities. In 1993, the National Scientific Research Council of the United States put forward that groundwater vulnerability is the trend and possibility of pollutants reaching a specific position above the top aquifer, and divided groundwater vulnerability into two categories: one is essential vulnerability, that is, only the vulnerability of hydrogeological internal factors is considered, and human activities and pollution sources are not considered; The other is special vulnerability, that is, the vulnerability of groundwater to specific pollution sources or groups or human activities. In Europe, North America, Australia and other regions, the focus of groundwater pollution prevention has shifted from pollution control to pollution prevention, groundwater environmental vulnerability assessment has been carried out, and an assessment atlas has been compiled.
So far, there is no clear definition of "groundwater vulnerability" in China, and most of the definitions refer to foreign data. Most of them study the essential vulnerability of groundwater from the perspective of hydrogeological internal factors, including the work of "groundwater development model and series mapping in environmentally and ecologically fragile areas". The term "groundwater vulnerability" is often replaced by "groundwater pollution potential" and "pollution prevention performance".
5. There is a problem
Since the founding of New China, groundwater evaluation has provided an important support for ensuring the needs of national economic and social development. However, from the perspective of sustainable utilization of groundwater, there are still the following problems in groundwater evaluation:
1) the previous work focused on the study of groundwater occurrence conditions, and the research degree of groundwater aquifer structure, groundwater recharge, diameter and discharge conditions needs to be deepened. Groundwater system structure and groundwater dynamics, as the occurrence space of groundwater, are the basis of groundwater resources evaluation.
2) Groundwater is closely related to environmental protection and is an important restrictive factor. In the past, insufficient attention was paid to the evaluation of groundwater quality, environment and ecological attributes.
3) The research on the sustainable utilization degree and trend prediction of groundwater resources lacks depth and cannot meet the forward-looking requirements of the national economy for groundwater.
4) Due to the construction of a large number of water conservancy projects, the circulation conditions of surface water and groundwater have changed, and many new water environment problems have emerged, especially the change of groundwater recharge conditions, which has reduced groundwater recharge in some areas and worsened the ecological environment. Therefore, it is urgent to consider the influence of these changes in the new groundwater evaluation.
(III) Present situation of groundwater function evaluation and zoning research
1998, Xu Zhirong published the Preliminary Study on the Division of Groundwater Functional Zones in Hydrogeology Engineering Geology (No.5), and put forward the necessity of developing groundwater functional zoning. 1999, Shi Ruiqing and others introduced the technology of "application of grey clustering analysis in groundwater zoning" in the first issue of Engineering Investigation. 200 1 published "Application of Fast Grey System Clustering Method in Groundwater Function Zoning" in Groundwater (Phase IV), and proposed that the grey system clustering method is a concise groundwater function zoning method. The study of groundwater function in this period is based on the rational utilization of groundwater resources and the traditional concept of groundwater resources evaluation.
In 2002, the Water Environment Department of China Geological Survey put forward "Special Study on Groundwater Function Evaluation" as a constraint condition from the perspective of ecological and geological environment protection. Researcher Zhang Guanghui from Institute of Hydrogeology and Environmental Geology, Chinese Academy of Geological Sciences made an exploratory study on the concept, evaluation theory and method of groundwater function, and put forward the basic framework and evaluation index system of groundwater function evaluation in 2003. In June, 2004, the project team completed the construction and demonstration of "the scientific evaluation system of groundwater resources function, ecological function and geological environment function", including basic concepts, evaluation theory, evaluation index system and evaluation key technologies. , and compiled the groundwater function evaluation and zoning technology, which was compiled by China Geological Survey into the series of technical requirements for investigation and evaluation of groundwater resources and its environmental problems in China (II and III). And has held technical backbone training courses in Lanzhou, Wuhan, Shijiazhuang, Beijing, Shenyang, Hohhot and other places, which have been fully promoted and applied in northwest, north and northeast China. In 2004, Tang Kewang and others published "On the Division of Groundwater Function Zones" in the fifth issue of Water Resources Protection, and introduced the basic idea of groundwater function zoning in water conservancy departments. In 2005, the Ministry of Water Resources issued the Notice on Delineating the National Groundwater Functional Zones. In 2006, Zhang Guanghui and others published the article "Theory and Method of Evaluation of Regional Groundwater Function and Sustainable Utilization" in the fourth issue of Hydrogeology Engineering Geology, which comprehensively expounded the theory and method of groundwater function evaluation. Huang Pengfei and others published the Application of Analytic Hierarchy Process in Groundwater Function Evaluation in Minqin Oasis in China Environmental Management (the second issue in 2006), and introduced the resource function, ecological function and geological environment function of groundwater. In 2007, Luo Yuchi and others published "Evaluation and Zoning of Shallow Groundwater Based on MapGIS" in china rural water and hydropower (No.9). Hong Lv and others published the Preliminary Study on Groundwater Function Zoning in Shandong Province in Hydrology (No.3, 2007), pointing out that groundwater function zoning is an important basis for the government to exercise its management functions; Yan Chengyun and others published "Groundwater Function Evaluation and Zoning in the Middle and Lower Reaches of Shule River Basin" in Hydrogeology Engineering Geology (No.3 and No.4, 2007), and cited a large number of examples to illustrate the practical effectiveness of groundwater function evaluation and zoning. In 2007, Fan Wei completed the master's degree thesis of "Evaluation of Groundwater Function in Plain Area of Jilin Province". Zhang Guanghui and others demonstrated the relationship between groundwater function evaluation and sustainable exploitation in Geological Bulletin (No.6, 2008).
(d) Research status and trend of groundwater development and utilization
The general trend of groundwater development and utilization research is the continuous expansion of subject connotation, giving priority to ecological geological environment protection, focusing on safety and security capacity building, and taking harmonious and sustainable development with economy and society as the foundation.
1) Paying equal attention to resources, environment and ecology has become the theme of groundwater development and utilization research. The sustainable utilization of groundwater should not only ensure the stable water supply of society, but also not sacrifice the ecological-geological environmental benefits, and at the same time, it can not affect the long-term utilization of water resources in the future. At present, it is an important research topic to restore the function of groundwater degraded by human influence, quantitatively track and control the discharge area of groundwater, strengthen the ways and mechanisms of groundwater aquifer recharge, and jointly regulate and coordinate the development of surface water and groundwater, the socio-economic laws and management models of groundwater utilization and distribution.
2) The research on the hydrogeologic process of the earth's surface system has become an important topic in the evolution of modern groundwater science. Soil, vadose zone, shallow groundwater, wetlands and lakes, oases, rivers and agricultural land are closely related to the study of sustainable utilization of groundwater. The vadose zone is a porous medium between the groundwater level and the surface. Chemical weathering, organic matter decomposition, nitrogen fixation and other chemical cycling processes all occur in the vadose zone, which is also the only way for groundwater recharge and pollutant migration to groundwater. The physical, chemical and biological processes of vadose zone are more and more closely related to hydrogeology, pedology, ecology and environmentology (Gansu Geological Survey, 2007).
3) It is more and more urgent to establish an efficient groundwater monitoring, situation investigation and emergency response mechanism. 1996 the working group of international hydrological plan defines "sustainable utilization of water resources" as "the management and use of water to support society and its welfare needs from now on to the future without destroying the hydrological cycle and ecosystem integrity on which society depends". It is required to seek the best connection and coordination among economic development, environmental protection and human social welfare in the planning, development and management of water resources, emphasize the integrity of future changes, social welfare, hydrological cycle and ecosystem protection, and minimize the possibility of future regret. At the Symposium on Integrated Water Resources Management held in the United States in 2000, it was concluded that unified river basin management is an inevitable choice to prevent land degradation, protect freshwater resources and biodiversity, and realize the sustainable utilization of water resources.
4) Sustainability is the most concerned core in the development and utilization of groundwater. It means that groundwater can continue in time and space. Serageldin and Steer summarized sustainability as weak sustainability, medium sustainability, strong sustainability and excessive sustainability. "Weak sustainability" does not care about parts, but only the whole; "Moderate sustainability" mainly aims at maintaining the integrity of the system, but it also takes care of its components properly; "Strong sustainability" requires keeping the components of the system in good condition and taking care of the whole system. Each component can't replace each other, and according to some understandings, even within the component, the substitutability is limited; "Excessive sustainability" means keeping all elements of the system intact without any loss.