(1)Analysis of the subsidence of the results of the monitoring wells in the Tainan area in 2020

The main subsidence areas in Tainan are in Beimen District and Xuejia District. The main water industry is aquaculture and fishery. In 2020, the subsidence rate of CYWRA28 and Youduan 07-1 in Beimen area will reach 2.9 and 2.1 cm. The subsidence rate in other areas is 2 cm /Year is down. 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 14-54 meters, which belongs to the 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.

 

(2)Analysis of subsidence in Tainan from August, 2017 to June, 2018

The average subsidence rate in Tainan from 2017 to 2019 is shown in Figure 3-51, indicating that the average annual subsidence rate in most parts of Tainan is less than 1 cm/year. However, in Beimen District and Xuejia District, there are some location where the rate of subsidence was more than 3 cm/year, and the significant subsidence area was 0.9 square kilometers. The average subsidence rate of the past two stages in Tainan area (Figure 3-52) shows that the main subsidence areas in Tainan are Beimen District and Xuejia District in the last 5 years. The maximum subsidence rate was about 2 to 3 cm/year which showed that no significant subsidence happened in Tainan at this stage. Analysis of the subsidence rate analysis table (Table 3-28) of the main subsidence detection points in Tainan in 2017-2019. Most of the average annual subsidence rate in this area has been lower than 1 cm/year.

 

(3) Analysis of cumulative subsidence in Tainan area during 2001-2019 years

Figure 3-58 is a plot of cumulative subsidence from 90 to 108 years. The figure shows that in the past 18 years in Tainan, the main subsidence areas occurred in Beimen, Xuejia, and Annan Districts. Table 3-32.