The groundwater observation well was established to monitor and collect the long-term, overall hydrogeological, groundwater level, and groundwater quality of Taiwan’s groundwater. After the establishment of a complete database, the spatial distribution and temporal changes of groundwater volume and water quality can be grasped to provide reliable information for decision makers to formulate countermeasures and understand the implementation and effectiveness of countermeasures. Before 1958, the Water Resources Unified Planning Committee of the Ministry of Economic Affairs commissioned the former Taiwan Provincial Water Resources Bureau to request the local farmland water conservancy associations to conduct water well registration surveys and water level observations, and selected 1,211 of the 55,996 water wells in Taiwan as observation wells, which are for Taiwan's comprehensive observation The beginning of the groundwater level.

Since 1958, with subsidies from the former Agricultural Rehabilitation Association, 20 water level observation wells have been established in the Yunlin area, laying the foundation for the groundwater level observation well pattern in Taiwan.

As of 1966, when the Engineering Office was changed to the Groundwater Engineering Department of the former Water Resources Bureau, there were 146 observation wells (including 18 self-recording and 128 ordinary) in Taiwan, and the site was abolished in June 1976. When the observation station took over, there were 300 groundwater level observation wells (including 12 self-recording type and 288 ordinary type). This well built before 1976 is called the old groundwater observation well pattern. In recent years, the groundwater level in parts of Taiwan has been decreasing year by year, which has led to increasingly serious site subsidence in southwestern Taiwan and the coastal areas of Yilan.

Since 1992, the Ministry of Economic Affairs has coordinated funds to start the "Taiwan Regional Groundwater Observation Network" project, and the Central Geological Survey and the former Water Resources Bureau are responsible for "Hydrogeological Survey" and "Groundwater Observation Station Network Establishment and Operation Management" ". In 1995, the former Ministry of Economic Affairs Department of Water Resources expanded the plan into the "Taiwan Regional Groundwater Observation Network Overall Plan" to fully grasp the hydrogeological conditions of Taiwan and obtain accurate and reliable groundwater information.訊。

Since 1988, the groundwater observation station wells considered for layered observation are collectively referred to as the new groundwater observation well pattern. The main goal of the groundwater observation station network is to understand the groundwater environment, including hydrogeology, water level, water quality, etc., to establish a complete database, to grasp the spatial distribution and temporal changes of groundwater volume and water quality, so as to provide reliable information for decision-makers to formulate countermeasures And understand the implementation and effectiveness of countermeasures.。

In order to achieve this goal, it is necessary to establish an ideal observation station network to make reliable judgments on the hydrogeology, groundwater level and water quality of the entire region with data obtained from limited locations. Only by properly planning and determining the number, location and frequency of observation wells in advance, can the network of observation stations be used to its fullest function. The establishment of the groundwater observation station network relies on the understanding of the existing data and the site, and under the constraints of budget and other objective factors, the number of observation wells, well positions, observation items and frequency are determined in conjunction with policy guidance and subjective judgment.

Generally speaking, the planning of a regional observation station network must first have an overall understanding of the groundwater dynamic behavior in the planned area. Therefore, the collection and evaluation of the existing observation station network data is the first task. After that, the observation station network was planned based on the existing data, and then some station wells were set up. With the gradual establishment of the observation station network, the survey of hydrogeology, groundwater hydrology, and groundwater quality was gradually completed, and then a complete groundwater aquifer system was established. The conceptual model of groundwater flow system is also a work to understand the dynamic behavior of groundwater. The parameters required to establish a conceptual model are very numerous and complex, covering areas including geological conditions, stratum distribution, hydrogeological characteristics, groundwater infiltration and replenishment areas, water level distribution and flow direction, water quality distribution, etc., all of which need to be investigated and clarified, especially regional Due to the vast area of ​​the planning plan, the work is more difficult. Therefore, after the observation station network is completed and more detailed information is obtained, it still needs to be reviewed, and added and modified to establish a complete groundwater observation. Site network and obtain complete and correct information required for planning.

The groundwater level analysis includes the following three items:

(1) Analysis of groundwater level during high and low seasons The natural groundwater level system changes with the seasons of high or low water. If man-made pumping occurs, the frequency of changes will increase. At this time, the stress pattern caused by the change of groundwater level is also The relative change caused a change in the behavior of stratum subsidence. Therefore, the change of groundwater level during high and low seasons is also the focus of the analysis of stratum subsidence mechanism. In the early days, the Water Resources Department has successively established a network of groundwater observation stations throughout Taiwan to observe groundwater levels. Through groundwater level observation data, the trend of groundwater level changes can be quickly understood and the relationship of stratum subsidence can be analyzed.

(2) The water level analysis of different aquifers is based on the hydrogeological data of the Central Geological Survey. Different regions can be distinguished between different aquifers and water blocking layers according to geological age and stratum water storage characteristics, and the rise and fall of the groundwater level of each aquifer will also be targeted Stratums in different depth ranges produce stress effects. Therefore, when analyzing the behavior of stratum subsidence, it is necessary to distinguish the relationship between the groundwater level changes of different aquifers, and conform to the actual mechanism of stratum subsidence.

(3) Long-term water level change trend analysis Although the groundwater level changes differently with the seasons of high and low seasons, if the overall trend is downward or upward, it will have different effects on formation compression. In addition, different soil layers have different responses to the short-term and long-term trends of the groundwater level. Therefore, we will analyze the long-term and short-term water level change trends in a specific area through the groundwater level data over the years to assist in the interpretation of the mechanism of stratum subsidence.