Supplementary adjustment of groundwater dynamic observation network in reservoir area and its function

The construction and operation of the long-term observation network of groundwater dynamics in the reservoir area is the infrastructure for studying geological disasters in the reservoir area and an indispensable means for monitoring the changes of groundwater level around the reservoir area.

During the period of 1956 ~ 1959, the long-term observation network of groundwater dynamics in the reservoir area, which was explored and set up by the geological corps, was laid out according to the surrounding areas of the reservoir area that may be affected when the water level of the reservoir is 350m, and its distribution range extended from the dam site to the upstream, reaching Jiamakou of the Yellow River in the north, and reaching Gengzhen of Weihe River and Shecun of Luohe River in the west, with a control area of 7000km2.

The observation well was built and put into use, so the observation work began at 1956, which was the responsibility of the observation group (station) of the geological corps, and was merged into the hydrological experimental station of Sanmenxia reservoir area of the Yellow River Committee at 1958. In September, 1960, the reservoir began to store water. Due to the serious sediment deposition under the high water level operation mode, it was forced to use the low water level on March 1962, and then most observation wells were closed. By June 1975, all observation work stopped.

However, the sediment deposition in the Weihe section of the reservoir area is still developing from the source, that is, the so-called "tail-up" deposition, which causes the water level of the same flow to rise, and the groundwater level along the coast to rise. The threat of immersion to the eastern Guanzhong Basin and the granaries in Xi City is still very prominent. In view of this, the Fifth Brigade of the former Ministry of Geology and the Second Hydrogeological Team of Shaanxi Province supplemented and adjusted the observation profile and observation well four times from 1966 to 1976. The low terrace of Lintong-Tongguan section on the south bank of Weihe River, that is, the submerged area when the original high water level was used, was studied emphatically. There were 9 observation profiles 70 ~ 78 and 62 observation wells. At the same time, some observation wells originally managed by hydrological stations were received and maintained. Up to 1986, there are 13 sections still under observation and 8 1 observation wells. These include the Weihe River North Bank 10 section (4 holes) and the Henan Lingbao 57 section (5 holes) (see Figure 12).

The groundwater dynamic observation data of Sanmenxia Reservoir in the past 25 years have been compiled and published by the Second Hydrogeological Team of Shaanxi Province. The full name is the Yearbook of Groundwater Level in Sanmenxia Reservoir Area of Yellow River (1960 ~ 1985), which is divided into two volumes, * * *13/page. The yearbook editing work was undertaken by the Power Group of the Second Hydrogeological Team of Shaanxi Province, with Bai Enhui as the technical director and comrades Yu, Sun Chuanyao, Jiang,, and Wu Xian as participants.

The immersion saline-alkali group established after the establishment of the fifth brigade of the Ministry of Geology is responsible for the long-term observation of groundwater dynamics in the reservoir area, and later renamed as the dynamic group. The team leaders are Ma Hongyun, Li Zhicun, Mao, Bai Enhui, Yu, Li Zhongxue, Wang and Qiu Yulong, and three on-the-job personnel are responsible for observation management and maintenance. The symposium of farmers' observers will be held from time to time, and the Weinan Municipal Government and the Second Hydrogeology Team of the Provincial Geological Bureau will be invited to issue an announcement on the protection of observation wells. The observation project is simplified, and there is only one groundwater level, which is summarized and analyzed month by month. Collect water level, discharge and local meteorological data of hydrological stations every year, as well as investigation data of interference factors such as irrigation areas and water sources. Prepare the groundwater dynamic analysis chart year by year and prepare the annual report.

Before and after the operation of the reservoir, the dynamic observation results of groundwater in the reservoir area play an important role, which is briefly described as follows:

1. Before the reservoir was put into operation, only the observation data of 1 ~ 3 years were used to further study and master the hydrogeological conditions of Sanmenxia dam site and reservoir area, and to predict geological disasters such as reservoir immersion and bank collapse. This purpose and function have been achieved.

2. During the impoundment period, study and master the dynamic characteristics of groundwater under different hydrogeological conditions around the reservoir, divide the types of dynamic causes of groundwater, delineate the range of phreatic surge, study the occurrence and development of reservoir geological disasters and their prevention measures, explore the phreatic surge of reservoirs in sediment-laden rivers under the action of backwater, and study the method of immersion prediction, so as to provide geological basis for rational utilization of reservoirs and accumulate practical experience for selecting reservoirs and dam sites and preventing reservoir geological disasters in the future. In the past 20 years, the Fifth Brigade and the Second Hydrogeology Team have sorted out 28 thematic, comprehensive, phased and summative geological research achievements (see the catalogue of geological achievements) according to the dynamic data of groundwater in the reservoir area, and most of them have been provided to relevant departments and localities for use, which reflects the role of long-term observation of groundwater and achieves or even exceeds the expected purpose.

3. Since Sanmenxia Reservoir changed to control the low water level all the year round, the long-term observation of groundwater in the lower reaches of Weihe River and the published yearbook of groundwater level in the reservoir area (1960 ~ 1985) have played a positive role in the development of groundwater and water resources in industry and agriculture and the rational use of water in canal irrigation areas. For example, Detailed Hydrogeological Investigation Report of Huayin and Huaxian Plain in Shaanxi Province submitted by 1993 (edited by Jiang and Zhang Mao), and Groundwater Dynamic Research Report of Weinan City submitted by 1985 ~ 1997 (edited by Qiu Yulong, Wu Jiaying and Zhao).

It is worth mentioning here that the increase of underground water sources and the continuous expansion of its scope have promoted the desalination process of saline-alkali land, making it a fertile field with high yield. Thus, the desalination principle of soil salt accumulation expounded in the report of "Well Irrigation in Saline-alkali Land" submitted by 1972 is verified, and the prevention and control ways of reservoir flooding disaster are revealed.

4. It must also be mentioned that the second hydrogeological team asked whether to stop long-term observation of groundwater. 1In August, 1983, the Department of Hydrogeology and Engineering Geology of the Ministry of Geology and Mineral Resources pointed out in a reply to the Shaanxi Provincial Bureau of Geology and Mineral Resources: "Although the research report on engineering geological problems in the operation stage of Sanmenxia Reservoir of the Yellow River has been submitted, the hydrogeological engineering geological problems in Sanmenxia reservoir area still exist. The accumulation of long-term dynamic observation data of groundwater is a very important work, but short-term exploration cannot be collected. In April 2000, according to the regulations of the provincial geological environment monitoring station, the long-term observation of groundwater in the reservoir area was handed over to the geological environment monitoring station of Weinan Mining Administration. In 2002, it was changed to Weinan Municipal Bureau of Land and Resources.