The investigation of the overall subsidence of the Taoyuan area began in 1998. In 1998, the Ministry of Economic Affairs and Water Resources set up a total of 100 detection points in the Taoyuan area, and 9 major-level surveying networks. In 2001, the business was transferred to the Water Resources Agency (former Water Resources Bureau) belong to the Ministry of Economic Affairs. At that time, it only monitored some areas in Taoyuan County. In 2002, the subterranean subsidence monitoring was conducted again in the entire Taoyuan area, and the monitoring was carried out according to the leveling network deployed in 1998. In 2006, Water Resources Agency not only covered the leveling network in 2002 but added the new survey line to Xinfeng and Hukou in Hsinchu County. In 2010, another survey line was added to Luzhu Township in Taoyuan County. In 2017, the measurement will be carried out according to the 2010 level grid in the following year. The monitoring results for this year will be described below. In 2018, the monitoring results will be explained based on the monitoring results of Multilevel layer compression-monitoring wells.

(1) Analysis of subsidence of Taoyuan in 2018

According to the data from the monitoring wells of Shulin Country Subsidence in Guanyin District, the long-term stratigraphic changes in the Taoyuan area present a rebound state. The rebound amount from the 1993 to 2018 was 0.5 cm, and the average long-term and short-term compression deformation rates are both Less than 1 cm/year, showing that the current stratum compression behavior in this area is not obvious.

(2)Analysis of subsidence in Taoyuan area in 2017

The maps of the average subsidence rates for the 2006-2010 and 2010-2017 (Figure 4.3-5) show that there has been no significant subsidence (most of them are uplifted) in the Taoyuan area in the past 10 years, and the rate of surface change is mostly within ±1 cm With reference to the changes in the groundwater level in the Taoyuan area (refer to Section 5.2.2 4-52), the groundwater level in the Taoyuan area has rebounded significantly in the past 10 years, so there is no significant risk of subsidence in the Taoyuan area at this stage.

The amount of subsidence of the main subsidence survey points in Taoyuan area is shown in Table 4.3-3, which shows that the amount of subsidence is within ±1 cm.

(3) Analysis of the subsidence of Taoyuan area from September 1991 to May 2017

Based on the analysis of the elevation data of Taoyuan leveling points from 2002 to 2017, the cumulative subsidence map is shown in Figure 4.3-6. As the figure displays, Taoyuan area only has a slight subsidence, and the maximum cumulative subsidence was only about 2.7 cm. In recent years, the main subsidence area is distributed in the Xinwu area, and the remaining subsidence was within ± 1 cm (within the measurement error range). According to the data, the subsidence in Taoyuan area has stabilized without significant subsidence.