Main methods and means of hydrogeological exploration

There are 10 kinds of basic methods or jobs used in hydrogeological investigation, namely, hydrogeological mapping, hydrogeological drilling, hydrogeological geophysical exploration, hydrogeological field test, long-term observation of groundwater dynamics, indoor analysis experiment, application of isotope technology in hydrogeological investigation, application of global positioning system (GPS), application of remote sensing (RS) technology, application of geographic information system (GIS), etc. Any hydrogeological survey is basically organized by these methods and means, and the accuracy of these methods and means (or jobs) directly determines the quality of exploration results. In recent years, new technologies and methods, such as geological and hydrogeological interpretation of aerial photographs, GPS technology, geographic information system (GIS), groundwater isotope testing technology, nuclear magnetic resonance technology, and direct determination of hydrogeological parameters, have been applied in hydrogeological investigation, greatly improving the accuracy and efficiency of hydrogeological investigation.

1. Hydrogeological mapping

Hydrogeological mapping is to observe, measure, describe and investigate the geological and hydrogeological boundaries and phenomena in a region according to certain accuracy requirements, and draw a map to summarize the hydrogeological laws of a region. Hydrogeological mapping is the first step to understand the hydrogeological conditions in a region, and it is also the basis of all hydrogeological work. At present, remote sensing technologies such as aerial photo interpretation are widely becoming modern and effective means of hydrogeological mapping.

2. Hydrogeological drilling

Hydrogeological drilling is not only a direct means to explore groundwater, but also the main method to exploit groundwater. Because of its high efficiency and deep exploration depth, it is a major exploration work. In order to obtain better results, hydrogeological drilling must be based on hydrogeological mapping and other work. In addition, when it is only necessary to expose groundwater outcrops near the surface or some strata and structural phenomena related to groundwater, pits and grooves can be directly used.

3. Hydrogeological geophysical exploration

Geophysical exploration is one of the important means of hydrogeological exploration. It can effectively identify many geological and hydrogeological problems by combining hydrogeological mapping and drilling, thus saving the workload of other types of work. It should be emphasized that all geophysical methods have limitations and the results are multi-solution. In use, analysis, comparison and comprehensive research should be carried out according to specific geological conditions, so that the interpretation results can truly reflect the objective situation. The main geophysical methods used in hydrogeology include electrical method, magnetic method, seismic method and radioactive method. In recent years, new technologies and methods such as geological radar, geophysical tomography (CT) and nuclear magnetic resonance (NMR) have also been widely used.

4. Hydrogeological test

In the field investigation, in order to obtain various hydrogeological parameters or solve some hydrogeological problems, it is necessary to carry out related hydrogeological experiments. Hydrogeological field tests mainly include: pumping test, water injection test, permeability test, groundwater velocity and direction determination test, connectivity test, dispersion test and so on. According to the needs of investigation, these tests should be arranged reasonably.

5. Dynamic observation of groundwater

Because groundwater is changing, in order to find its changing law, it is necessary to observe the groundwater dynamics (including water level, water quantity, water quality and water temperature) of the main aquifers in the area for a long time. According to the observation results, the formation and change law of groundwater, water quality, water quantity and water level in the area are correctly evaluated and predicted.

6. Laboratory experiment, analysis and identification

Laboratory experiments, analysis, identification and other work, mainly to obtain groundwater quality, rock hydraulic properties, rock failure and dissolution mechanism, aquifer particle composition, groundwater movement and groundwater age and other information.

7. Application of Isotope Technology in Hydrogeological Survey

During the formation and migration of groundwater, the isotopic composition of various chemical components will enter the water, and these isotopic tracing can provide important information for studying groundwater and its relationship with environmental media. Environmental isotopes can mark groundwater and record time. Therefore, it is widely used in hydrogeological exploration. At present, the application of isotope technology in hydrogeological investigation mainly solves the following problems: ① determining the age of groundwater by radioactive environmental isotopes; ② Using stable environmental isotopes to study the source and formation process of groundwater; ③ Using radioactive environmental isotopes to study the movement of water in vadose zone; ④ Using environmentally stable isotopes to study the sources of chemical components in water; ⑤ Using radioisotope tracer to study groundwater movement and hydrogeological process.

8. Application of Global Positioning System technology

Global positioning system (GPS), also known as global satellite positioning system. GPS has global, all-weather, continuous three-dimensional speed measurement, navigation, positioning and timing capabilities, and has good anti-interference and confidentiality. At present, GPS has become an all-weather, high-precision continuous positioning system, which has the characteristics of high positioning accuracy, automation, high speed, simple instrument operation, high efficiency and practicality, and flexible and diverse methods. In recent ten years, GPS has been widely used in hydrogeology and engineering geology.

GPS is mainly used in the following aspects in hydrogeological work: ① Determine the positions and coordinates (or latitude and longitude) of various geological points (geological structures, landforms, Quaternary geology, lithologic points, sampling points, etc.). ), and determine its trend or inclination; ② Determine the positions and coordinates of various hydrogeological points such as wells, springs and underground rivers; ③ Determine the elevation of various geological points and hydrogeological points such as wells, caves and springs; (4) determine the distance between local particles and hydrogeological points; ⑤ Map function, navigation function, etc. ⑥ Determine the direction of exploration line or the orientation of hydrogeological section line; ⑦ Find relevant information points and interest points on the map; ⑧ Data storage and memory function, which can establish database, download and convert data, etc.

9. Application of Remote Sensing Technology in Hydrogeological Survey

Remote sensing (RS for short), that is, "remote sensing", is a comprehensive detection technology that records the electromagnetic wave characteristics of the target from a distance by using detection instruments without contacting the target, and reveals the characteristics and changes of the target through analysis. In other words, according to the electromagnetic wave theory, remote sensing technology uses special instruments installed on various aircraft such as airplanes or artificial satellites to receive various spectral information emitted or reflected by various geological bodies on the ground. Because different geological-hydrogeological bodies emit, absorb, reflect, scatter and transmit electromagnetic waves with different wavelengths and frequencies, we can interpret and judge the geomorphological, geological and hydrogeological conditions in the survey area and draw various maps. It has the characteristics of large survey area, fast cycle and wide application, and has unique advantages in improving survey quality, speeding up survey progress, reducing surveying and mapping and exploration workload, and reducing manual labor.

There are many remote sensing technologies. At present, aerial photography, infrared detection and multi-band measurement are commonly used in hydrogeological investigation. Using aerial photos, we can interpret aquifers and water-bearing structures, find out regional hydrogeological conditions, delineate water-rich areas and divide catchment areas. Infrared remote sensing technology has a good effect in finding shallow groundwater (such as finding ancient rivers, finding out the location, size and quantity of groundwater outcrops, detecting underground hot water, studying hydrogeological conditions in karst areas, etc.). ). Earth satellite images can be used to investigate the earth's resources and monitor the environment, explain the regional landform, stratigraphic lithology and geological structure, delineate alluvial aquifers, find the overflow zones of springs and groundwater and the distribution areas of shallow groundwater, and can also be used to investigate surface water resources and monitor environmental pollution.

10. Application of Geographic Information System (GIS) in Hydrogeological Survey

Geographic Information System (GIS) is a computer technology system for acquiring, processing, analyzing and applying various geographic or spatial information.

Geographic Information System (GIS) has been used in groundwater research. The application of GIS in hydrogeological investigation mainly includes the following aspects: ① Establishment of groundwater database and simulation system. (2) Identify aquifers and rationally develop and utilize groundwater resources. ③ Study on groundwater quality. ④ Management of groundwater resources. ⑤ Prepare hydrogeological map. ⑥ Groundwater simulation and visualization.

Global positioning system (GPS), remote sensing technology (RS) and geographic information system (GIS), referred to as "3S" technology. "3S" technology is a spatial information processing technology developed gradually since 1960s. Due to the maturity of "3S" technology, Australia, the United States, Canada and other countries began to use "3S" technology to carry out digital geological mapping in the 1980s, which realized the computerization and informatization of geological mapping and greatly improved the work efficiency. Digital geological mapping in China began in 1990s. At present, digital geological mapping based on "3S" technology is gradually being popularized and applied in geological and hydrogeological surveys.