In order to effectively curb stratum subsidence and the resulting disasters caused by excessive pumping of groundwater due to the unbalanced consideration of industrial development, land use and water supply in some areas for a long time, the Water Resources Department has been working with relevant units to actively promote the "stratigraphic" over the years. Various prevention and control measures such as the Implementation Plan for Subsidence Prevention, the "Groundwater Conservation Management and Stratigraphic Subsidence Prevention Plan", and the "Specific Solution and Action Plan for Stratigraphic Subsidence in Yunzhang Area". A comprehensive review of the time course and area of stratum subsidence inspection over the past years (from 80 to 109 years) is shown in Figure 1-3, Figure 1-4 and Table 1-1.
(Figure 1-3) Overview of the detection of stratum subsidence in Taiwan during the Republic of China 109 year
(Figure 1-4) Map of the maximum subsidence rate and location over the years and the area of significant subsidence
The Water Resources Department completes multi-zone level elevation detection every year, and searches multiple magnetic induction loop layered stratum subsidence monitoring wells and GPS satellite tracking stations every month to grasp the annual subsidence rate and continuous subsidence area changes in various regions. The general situation of each region is as follows:
(1) Taipei area: In 2020, the maximum annual subsidence rate measured in Taipei area is 1.5 cm/year. It is located in Wugu District with a significant subsidence area of 0.0 square kilometers. The subsidence rate of most detection points is about ±1 cm/year. Significant surface changes; leveling results show that there has been no significant subsidence in the Taipei area for nearly 8 years..
(2) In 2020, the maximum annual subsidence rate in Changhua area occurred in the inspection point 1109 and Shuilizhang 59 in Xizhou Township and C078 in Xihu Town. The subsidence rate is 3.2 cm/year, and the significant subsidence area is 0.9 square kilometers. ; Townships with a subsidence rate of more than 3 cm/year include Xizhou Township and Xihu Township.
(3) In 2020, the maximum annual subsidence rate in Yunlin area occurred at Shuiliyun 78-1, a detection point in Yuanchang Township, with a subsidence rate of 5.5 cm/year and a significant subsidence area of 103.8 square kilometers; the subsidence rate exceeded 3 cm/year The main townships mentioned above include: Huwei Town, Tuku Town, Yuanchang Township, Baozhong Township, Lunbei Township and Dayi Township.
(4) In 2020, the maximum annual subsidence rate in Chiayi area is 2.9 cm/year (located in Xikou Township), and the significant subsidence area is 0.0 square kilometers. According to the results of the 2020 level inspection, the maximum annual subsidence rate in Chiayi area is lower than that in 2019.
(5) Tainan area: From 2017 to 2019, the maximum annual subsidence rate in Tainan area was 3.3 cm/year (located in Beimen District), and the area of significant subsidence was 0.9 square kilometers. According to the leveling inspection results from 2017 to 2019, there is no significant subsidence in most areas of Tainan, and the surface change rate is mostly within ±1 cm. However, subsidences continue to occur in Beimen District and Xuejia District. Therefore, the main subsidence areas in Tainan are in Beimen District and Xuejia District, and the main water industry is aquaculture fishery. In 2020, the subsidence of CYWRA28 and Youduan 07-1 in Beimen area will reach 2.9 and 2.1 cm. The subsidence rate in other areas will be less than 2 cm/year has been lowered. Analyzing the data from the monitoring wells of the Kumho Elementary School in the Beimen District showed that the formations from the surface to the depth of 300 meters all have compression behavior, but the main compression range is concentrated in the shallow layer 14 to 54 meters, which belongs to the formation of aquifer 1. The data from the monitoring wells of the Central Subsidence in the School of Analysis, District A, and Country A show that the main compression range is concentrated from the surface to a depth of 297 meters, and the amount of compression between the depth of 243 and 292 meters is relatively obvious. It belongs to the 4th aquifer. Aquifer 1 and aquifer 4 still have plastic deformation under the current water level change, indicating that the soil is still being compacted; the compression of aquifer 3 is small, showing an approximate elastic deformation behavior.
(6) Pingtung area: The maximum annual subsidence rate in 2020 is 3.3 cm/year, and it is located in Jiadong Township, with a significant subsidence area of 0.9 square kilometers; leveling inspection results show that the Pingtung area has a significant subsidence area of 5 square kilometers in the past five years Within kilometers, the maximum annual subsidence rate is within 4 cm/year, and the stratum subsidence in the east area of the display screen has gradually slowed down. The main subsidence areas are concentrated in Linbian Township, Jiadong Township and Fangliao Township on both sides of the Linbian River estuary.
(7) Kaohsiung area: From 2016 to 2020, there was no significant subsidence in Kaohsiung area. The area of significant subsidence is 0.0 square kilometers, and the maximum annual subsidence rate is 1.4 cm/year. It is located in Qifeng District, followed by 1.3 cm/year in Miduo District. The remaining subsidence rates are mostly within ±1 cm/year, and there is no significant surface change.
(8) Yilan area: The formation compression behavior in the Yilan Zhuang Encircled area continues to occur, but the cumulative compression from 2009 to 2010 is only 4.6 cm, and the long-term and short-term average compression rates are less than 1 cm/year, indicating that this is the current stage. The compression rate of the formation in this area is relatively slow.
(9) Taoyuan area: According to the data from the sag monitoring well of Shulin Elementary School in Guanyin District, the strata in the Taoyuan area have shown a slow expansion state for a long time. The accumulated expansion amount from 2004 to the present is 1.0 cm. The groundwater level of the first layer (the well depth is 66 meters) and the deep groundwater level (the well depth is 125 meters), both of which have risen by more than 30 meters.
Thanks to the efforts of relevant units, the area with significant stratum subsidence has decreased significantly in recent years compared with the 1990s. This shows that the groundwater level has been reduced due to poor water conditions and the significant stratum subsidence has been improved this year. In the future, we need to pay close attention to the changes in stratum compression in this area.