圖書典藏及影音數位平台

為有效監測地層下陷行為，及時掌握地層下陷之發生趨勢，依據地下水保育管理暨地層下陷防治第2期計畫（104～109年度）持續辦理臺北、苗栗、臺中、嘉義、屏東及宜蘭地區地層下陷監測，並維護相關監測設備（包含4站GPS固定式監測站、20口地層下陷監測井及1支深層水準樁），同時蒐集相關監測資料進行分析探討，釐清下陷發生機制，據以研擬因應對策，有效達成地層下陷之防治目標。

The objectives of project are to monitor the land subsidence and to explore the subsidence mechanisms in Taipei, Miaoli, Taichung, Chiayi, Pingtung and Ilan, Taiwan. Consequently, these results will provide precaution for the potential areas of land subsidence and develop the conceptual strategy for the mitigation of serious land subsidence. This project contains four tasks including: leveling survey in subsidence area, constructed 1 continuous GPS stations and 1 land subsidence monitoring well, and maintained the existed GPS stations, monitoring wells and deep benchmarks in the area, and integrated analysis of monitoring data obtained from the land subsidence areas. The main results are summarized as follows: 1. The results of leveling survey The areas of leveling survey include Taipei(260 km), Miaoli(185 km), Taichung(160 km), Chiayi(360 km), Pingtung(290 km) and Ilan(175 km), total length of surveyed routes is about 1430 km. The results of the leveling survey are as follows: (1) In Taipei City, 2018, the maximum subsidence rate is about 1.6 cm/yr and the obviously subsiding area is about 0.0 km2. (2) From 2012 to 2018, the maximum subsidence rate in Miaoli County is below 1.0 cm/yr and the obviously subsiding area is about 0.0 km2. (3) From 2012 to 2018, the maximum subsidence rate in Taichung County is also below 1.0 cm/yr and the obviously subsiding area is about 0.0 km2. (4) In Chiayi County, 2018, the maximum subsidence rate is about 3.1 cm/yr and the obviously subsiding area is about 114.2 km2. The subsidence rate and area increased noticeably from 2017 to 2018. (5) In 2018, the maximum subsidence rate in Pingtung County is about 3.1 cm/yr and the obviously subsiding area is about 0.1 km2. The subsidence rate and area decreased noticeably from 2017 to 2018. (6) In Ilan County, the maximum subsidence rate in 2018 is about 2.0 cm/yr and the obviously subsiding area is about 0.0 km2. There are no obvious land subsidence in most Ilan area but slightly subsided in Ilan City, Suao Township and Wujie Township. 2. Maintenance and measurement of the existed land subsidence monitoring wells, continuous GPS stations and deep benchmarks (1) The land subsidence monitoring wells The maintenance of land subsidence monitoring wells in Ilan(1), Taoyuan(1), Chiayi(7), Tainan(5), Kaohsiung(1) and Pingtung(6). A total of 21 land subsidence monitoring wells are in the areas. All of the monitoring wells and instruments are with good status of all systems facilities. (2) The continuous GPS stations (a) The maintenance of 1 continuous GPS stations in Budai elementary school in Chiayi and 2 continuous GPS stations in Linbian junior high school and Dingliao station in Pingtung have been accomplished. All of the continuous GPS stations worked stable in project duration. Data acquisition are more than 25000 per day, with cycle slip index between 0~3 and MP1 and MP2 value between 0.1~0.6. (b) Moreover, the GPS data from total 195 stations from Water Resources Agency (WRA), National Land Surveying and Mapping Center (NLSC), Department of Land Administration, Central Weather Bureau (CWB), Academia Sinica, International GNSS Service (IGS), Central Geological Survey (CGS) and Industrial Technology Research Institute (ITRI) also joined into the computation. ? (3) The deep benchmarks The maintenance of 1 deep benchmark in Wannei elementary school in Chiayi has been accomplished. All of the deep benchmark and instruments are with good status of all systems facilities. 3. Construction a new continuous GPS station and a 300 meters land subsidence monitoring well (1) Due to the land subsidence was obvious in Xingang Township, one new continuous GPS stations have been built up in Sinbi Elementary School in Chiayi County on June 2018. All instruments were installed completely and with good status of all systems facilities and internet. Data acquisition are more than 40000 per day, with cycle slip index between 4 and 5, and MP1 and MP2 values between 0.2 and 0.5. (2) Due to the amount of subsidence reached to 20 cm in Tainan from 2000 to 2017, and the sensitivity degradation of the original monitoring well in Tainan Hydraulics Laboratory, the new land subsidence monitoring well has been built up in Tainan Hydraulics Laboratory on July 2018. All instruments were installed completely and with good status of all systems facilities. And the accuracy of the uncertainty analysis of monitoring well is approximately ±0.080 cm. 4. Analysis of the integrated monitoring data in land subsidence area (1) Ilan area The accumulated amount of subsidence is only 4.5 cm from 2009 to 2018, and the subsidence rates no matter in short-term and long-term periods are less than 1.0 cm/yr. Therefore, there are no obvious land subsidence in Ilan area recently. ? (2) Taipei area The results of leveling survey in 2018 indicated that the maximum of subsidence rate in Taipei was nearly 1.6 cm/yr, and subsidence rates of most leveling benchmarks were around ±1 cm/yr . Moreover the ground water level data also indicated that the tendency of groundwater level was gradually increasing with time. (3) Taoyuan area The results of land subsidence monitoring well in Shulin elementary school indicated that the amount of subsidence was -0.5 cm from 2004 to 2018, and there was no obvious relationship both in groundwater and compaction domain. (4) Miaoli area The results of leveling survey from 2012 to 2018, the maximum subsidence rate in Miaoli County was less than 1.0 cm/yr and there were no obviously subsiding area present. (5) Taichung area The results of leveling survey from 2012 to 2018, the maximum subsidence rate in Taichung County was also less than 1.0 cm/yr and there were no obviously subsiding area present. (6) Chiayi area In 2018, the compaction trends from the land surface to a depth of about 300 meters in coastal areas were more serious than in inland areas. And the compaction rates of land subsidence monitoring wells between 1.0 and 2.0 cm/yr in recently. The main survy results are summarized as follows: A. Dongshih Township The results of benchmark NBG056 indicated that the maximum of subsidence rate was 9.0 cm/yr in 2004. The subsidence rates fluctuated between 0.9 cm/yr and 4.0 cm/yr in the past five years. In 2018, the subsidence rate was 3.5 cm/yr. B. Budai Township The results of benchmark CY45 indicated that the maximum of subsidence rate was 6.6 cm/yr in 2004, and the subsidence tendency was gradually mitigated from 2010 to 2014. The subsidence rates fluctuated between 0.9 cm/yr and 4.4 cm/yr in the past four years. In 2018, the subsidence rate was 3.5 cm/yr. C. Yijhu Township The results of benchmark CYSZ09 indicated that the maximum of subsidence rate was 5.5 cm/yr in 2004, and the subsidence tendency was gradually mitigated from 2010 to 2014. The subsidence rates fluctuated between 1.1 cm/yr and 3.5 cm/yr in the past four years. In 2018, the subsidence rate was obviously increased to 3.5 cm/yr. D. Puzih City The results of benchmark NBI042 indicated that the subsidence tendency was gradually mitigated from 2010 to 2014. The subsidence rates fluctuated between 1.2 cm/yr and 3.7 cm/yr in the past four years. In 2018, the subsidence rate was 2.4 cm/yr. E. Singang and Lioujiao Townships (a) The results of benchmark CYBM28 indicated that the maximum of subsidence rate was 4.3 cm/yr in 2004, and the subsidence tendency was gradually mitigated from 2010 to 2013. The subsidence rates fluctuated between 0.4 cm/yr and 3.8 cm/yr in the past five years. In 2018, the subsidence rate was 2.6 cm/yr. (b) According to the recent results obtained from monitoring wells in Anhe elementary school, the mainly compression occurred from land surface to 126 meters in depth. Moreover, the groundwater data also showed the obvious fluctuations in 96 meters and 164 meters in depth. Therefore, taking note of the water resources in this depth should be needed in the future. (7) Tainan area Due to the fall of rainfall and groundwater level in the dry season in 2018, the compaction situation in Tainan area was more serious than in 2017. The results of monitoring wells in Xiaying elementary school and Syuejia junior high school indicated that no matter the subsidence rates in long-term and short-term periods were larger than 1.0 cm/yr. (8) Kaohsiung area According to the results obtained from monitoring wells in Yantian branch school, the amount of subsidence was 4.7 cm from 2003 to 2018, and there was no obvious land subsidence. (9) Pingtung area In 2018, the maximum of subsidence rate was 3.1 cm/yr, and the obviously subsiding area near by Linbian and Jiadong Townships is about 0.1 km2. The main survy results are summarized as follows: A. Linbian Township The results of benchmark NBG127 indicated that the maximum of subsidence rate was 5.3 cm/yr in 2011, and the subsidence tendency was gradually increased from 2012 to 2015. The subsidence rates fluctuated between 2.1 cm/yr and 2.7 cm/yr recently. In 2018, the subsidence rate was 2.1 cm/yr. B. Jiadong Township The results of benchmark NBG129 indicated that the maximum of subsidence rate was 4.6 cm/yr in 2011, and the subsidence tendency was gradually increased from 2012 to 2015. The subsidence rates fluctuated between 1.4 cm/yr and 2.6 cm/yr recently. In 2018, the subsidence rate was 1.4 cm/yr.