The maximum annual subsidence rate in 2020 is 3.3 cm/year. It is located in Jiadong Township with a significant subsidence area of 0.9 square kilometers. The leveling test results show that the significant subsidence area in Pingtung area in the past five years is within 5 square kilometers, and the maximum annual subsidence rate is Within 4 cm/year, 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 mouth of Linbian River. The main sag detection points in Pingtung area in 2020 are shown in Table 4; the average sag rate from 2019 to 2020 is shown in Fig. 4.

The main subsidence areas in Pingtung are Linbian Township, Jiadong Township and Fangliao Township. The following is a breakdown of the relevant analysis of each subsidence area

1.Linbian Township

(1)The internal G127 and water conservancy screen 60 calendar diagrams of the main subsidence points in the analysis area show that the subsidence rate has an upward trend from 2007 to 2011. The subsidence rate in 2011 was more than 5 cm/year and ranked first in the past, after 2015 The sinking is gradually slowing down. From 2016 to 2019, it will be between 2.0 and 2.9 cm/year, and the sinking rate in 2020 will be 2.1 and 2.0 cm/year respectively.

(2)Analyzing the data from the monitoring wells of the Linbian Guozhong depression in Linbian Township shows that the stratum from the surface to the depth of 270 meters has been compressed, but the main compression range is concentrated in the stratum between the depth of 58 and 267 meters, which belongs to the aquifer.

2.Jiadong Township

(1)According to the main subsidence points in the area, the water conservancy screen 71-1 and the Yanfeng water level station calendar chart, the subsidence rate of the water conservancy screen 71-1 has stabilized at about 3 cm/year after 2017, and the subsidence rate will be 3.2 cm in 2020 /Year; the Shifeng water level station is stable at about 2.5 cm/year, and the subsidence rate in 2020 is 2.6 cm/year.

(2)The data of the small sag monitoring well in Jiadong Country in the inland area of ​​Jiadong Township shows that the main compression range covers the stratum from the surface to the depth of 104 meters. This phenomenon is mainly because the inland areas are mainly agricultural areas and the pumping depth is about Within 100 meters. According to data from the Dingliao Security Check Station in the coastal area and the monitoring wells in the Dazhuang Subsidence, the coastal area mainly occurs between 56 and 184 meters. Of particular note is the groundwater level at Dazhuang Water Level Station. Since 2012, the groundwater level of aquifer 3 has been increasing year by year, and has shown a long-term downward trend. It broke through the historical low water level in 2018, so special attention should be paid in the future. The use of groundwater in this area, while continuing to track the cause of the large volatility of the groundwater level and possible subsequent impacts.

3.Fangliao Township

(1)The main subsidence point T018 in the analysis area and the calendar chart of the Dazhuang water level station show that the leveling subsidence rate has gradually increased after 2016, and the rate is between 1.7 and 2.8 cm. The subsidence rate of T018 in 2020 is 2.7 Cm/year, the Dazhuang water level station will be 2.5 cm/year in 2020.

(2)Analyzing the monitoring well data of the Fangliao national depression in Fangliao Township shows that the stratum from the surface to the depth of 200 meters is compressed, but the main compression range is between the depth of 0-27 and 83-167 meters. According to data from the neighboring Dexing Water Level Station, since 2016, the groundwater level has been increasing year by year, and has shown a long-term downward trend. It broke through the lowest water level in history in 2018, and achieved both leveling and radar interference results in 2020. It shows that the Fangliao area has an increasing trend of subsidence. Therefore, in the future, special attention should be paid to the use of groundwater in this area, and at the same time, continue to track the cause of the large fluctuation of the groundwater level and possible subsequent effects.

1.Analysis of subsidence in Pingtung area from August 2019 to August 2020

Analysis of the average subsidence rate of the Pingtung area from 2019 to 109 is shown in Figure 3-66. The significant subsidence area of the Pingtung area in this period is 0.9 square kilometers, and the maximum annual average subsidence rate is about 3.3 cm/year. It is located in Jiadong Township.

The average subsidence rate from 2018 to 2019 and 2019 to 2020 is shown in Figure 3-67. The main subsidence areas in the last two years have been concentrated near the mouth of the Linbian River (including Linbian Township and Jiadong Township). In 2019, The significant subsidence area is 0.9 square kilometers, and the maximum annual subsidence rate is 3.1 cm/year; the significant subsidence area in 2020 is 0.9 square kilometers, and the maximum annual subsidence rate is 3.3 cm/year. The significant subsidence area and maximum subsidence rate this year are the same as 2019 The annual schedule is slightly the same.

The main inspection points this year are shown in Table 3-39. The following is for the main subsidence areas (Linbian Township, Jiadong Township and Fangliao Township) to further analyze the subsidence situation in this area.

2.Analysis of cumulative subsidence in Pingtung area from 1991 to 2000, 2001 to 2010 and 2019 to 2020

Applying the leveling results of Pingtung area from 1991 to 2020 to analyze the changes in subsidence every 10 years, the explanation is as follows:

（1）Cumulative change in Pingtung area from 1991 to 2000

Cumulative change in Pingtung area from 1991 to 2000 Analyze the cumulative changes in Pingtung from 1991 to 2000 as shown in Figure 3-74. During the above period, Pingtung's main subsidence centers were Linbian Township, Jiadong Township and Fangliao Town. From 1981 to 1991, the Pingtung area was the most severely subsided area in Taiwan. The average subsidence rate in the past year was higher than 15 cm/year. Before 1997, the area of ​​significant subsidence in Pingtung remained above 100 square kilometers. Afterwards, the area of ​​significant subsidence gradually decreased. In total, between 1991 and 2000, the maximum cumulative subsidence reached 76.4 cm, which mainly occurred in Jiadong Township. The total cumulative subsidence was more than 20 cm. The subsidence area was distributed from Xinyuan and Nanzhou along Pingnan. From the Taiyixian highway in the industrial zone to Fangliao and other coastal areas.

（2）Cumulative changes in Pingtung area from 2001 to 2010

Analyze the cumulative changes in Pingtung from 2001 to 2010 as shown in Figure 3-75. During the above period, the Pingtung area was mainly centered on the subsidence of Linbian Township and Jiadong Township. During this period, it can be seen that the prevention and control of stratum subsidence has produced results. Most of the time, the area of ​​significant subsidence remained within 10 square kilometers. In 2010, the area of ​​significant subsidence increased significantly to 47.5 square kilometers due to the obvious drought that year. During this period, the maximum accumulated subsidence reached 32.2 cm, which mainly occurred in Linbian Township and Jiadong Township.

（3）Cumulative changes in Pingtung area from 2011 to 2020

Analyze the cumulative change of Pingtung area from 2011 to 2020 as shown in Figure 3-76. During the above period, Pingtung area mainly had Linbian Township and Jiadong Township as the main subsidence centers. During this period, the prevention of stratum subsidence has been under stable control. Most of the time, the area of ​​significant subsidence has been reduced to less than 5 square kilometers, only in 2011, 2014 and 2015. Because of the poor water conditions in that year, the area of ​​significant subsidence was different. Increase to 48.9, 17.6 and 44.5 square kilometers. During this period, the maximum cumulative sag amount reached 29.0 cm, which mainly occurred in Jiadong Township

3.Analysis of subsidence in Pingtung area from 1994 to 2020

The cumulative subsidence results from 1994 to 2020 are shown in Figure 3-77. Over the past 20 years, the cumulative total subsidence is more than 20 cm. The subsidence areas are distributed from Xinyuan and Nanzhou along the Pingnan Industrial Zone along the Taiyi Road to Fangliao. The main subsidence center occurred in Fangliao Township in the early stage. After 1998, it moved to the towns (Linbian Township and Jiadong Township) on both sides of the Linbian River estuary, and the cumulative maximum subsidence exceeded 100 cm.

Analyze the changes in the area of significant subsidence in Pingtung from 1994 to 2020, as shown in Table 3-43. The subsidence trend of the display east area in the table has been reduced year by year. After 1998, the area of significant subsidence was within 10 square kilometers and increased to 47.5 square kilometers in 2010. In 2011, it increased to 48.9 square kilometers. Because the increase in the rate of subsidence in 2010 and 2011 was related to the Morakot rehabilitation project, most of the above projects were completed in 2011. In recent years, it was only in 2014 and 2015 due to poor water conditions. Good, in addition to a significant increase in subsidence, the area of significant subsidence in other years is controlled within 5 square kilometers.