圖書典藏及影音數位平台

彰化及雲林地區之主要地層下陷地區早期分布於沿海區域，近年已逐漸轉變為內陸地區（例如彰化溪湖鎮、溪州鄉，以及雲林虎尾鎮、土庫鎮、元長鄉、褒忠鄉等地區），不僅容易造成該等地區逢雨成災，且有高鐵行車安全顧慮，若無及時監測其變化情勢，問題恐將更為嚴重。 為有效監測彰化及雲林地區之地層下陷行為，減緩地層下陷之發生趨勢，本計畫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）之因應策略，持續辦理彰化及雲林地區地層下陷監測工作，並整合相關監測資料進行分析探討，釐清下陷發生機制，及時研擬因應對策，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 Changhua and Yunlin, 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 3 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 monitored data obtained from the land subsidence area. The main results are summarized as follows: 1. The results of leveling survey The areas of leveling survey include Changhua and Yunlin, and the total length of surveyed routes is about 970 km (Changhua 430km, Yunlin 540km). The results of the leveling survey are as follows: (1) In Changhua County, 2018, the maximum subsidence rate is about 3.4 cm/yr and the continuously subsiding area (the area of subsidence rate over 3 cm/yr) is about 9.1 km2. Xizhou and Xihu Townships are the areas of subsidence rate over 3 cm/yr. (2) In Yunlin County, 2018, the maximum subsidence rate is about 6.6 cm/yr and the continuously subsiding area is about 296.2 km2. Huwei, Tuku, Yuanchang, Baozhong, Beigang, Shuilin, Sihhu, Kouhu, Taixi, Dongshi and Lunbei Townships are the areas of subsidence rate over 3 cm/yr. 2. Maintenance and measurement of the existed land subsidence monitoring wells, continuous GPS stations and deep benchmarks (1) The maintenance of 8 land subsidence monitoring wells in Changhua and 26 land subsidence monitoring wells in Yunlin (including 1 new stations in 2018) have been accomplished. All of the survey stations and instruments are with good status of all systems facilities. (2) The maintenance of 4 continuous GPS stations in Changhua and 16 continuous GPS stations in Yunlin (including 3 new stations in 2018) have been accomplished. All of the continuous GPS stations worked stable in project duration. Data acquisition are more than 20000 per day, with cycle slip index between 0~15 and MP1 and MP2 value between 0.1~1.0. Moreover, the GPS data from High Speed Railways Co.(HSR), National Land Surveying and Mapping Center(NLSC), Central Geological Survey(CGS), Central Weather Bureau(CWB), 7 tracking stations and 2 IGS stations also joined into the computation. (3) The maintenance of 1 deep benchmark in Changhua and 5 deep benchmarks in Yunlin have been accomplished. All of the deep benchmarks and instruments are with good status of all systems facilities. 3. Developments of continuous GPS stations and land subsidence monitoring well (1) Due to the subsidence rate over 3 cm/yr in Baozhong, Dongshi and Sihhu Townships, and the amount of subsidence are more than 3.6 cm from leveling survey in 2017, three new continuous GPS stations have been built up in Longyan Elementary School, Annan Elementary School and Nangwang Elementary School in Yunlin County on May 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 2 and 4, and MP1 and MP2 values between 0.1 and 0.3. (2) Due to the subsidence rate which was more than 5 cm/yr in Sihhu Township in 2017, the new land subsidence monitoring well has been built up in Nangwang Elementary School on June 2018. All instruments were installed completely and with good status of all systems facilities and internet. And the accuracy of the uncertainty analysis of monitoring well is approximately ±0.064 cm. 4. Analysis of the integrated monitoring data in land subsidence area (1) Changhua area In 2018, the compaction trends from the land surface to a depth of about 300 meters in inland areas were more serious than in coastal areas. And the compaction rates of land subsidence monitoring wells in Sinsheng elementary school, Zhutang Workstation and Hunan elementary school are between 2.2 and 2.5 cm/yr in recently. The main survy results are summarized as follows: A. Xihu Township (a) The results of benchmark NBI008 indicated that the subsidence tendency was gradually decreased from 2004 to 2013. And the subsidence rates in the past five years ranged from 3.0 cm/yr to 3.5 cm/yr. (b) The largest subsidence rate in Xihu area was 14.2 cm/yr previously but reduced to 3.5 cm/yr recently. According to the recent results obtained from monitoring wells, the mainly compression situation was occurred in the third aquifer. Moreover, the long-term subsidence trend was gradually mitigated but still influenced by global climate changed and groundwater pumping within a short period. B. Xizhou Township (a) The results of benchmark NB1109 indicated that the subsidence tendency was gradually mitigated from 2012 to 2014, but it was slightly increasing in 2015 which attributed to the fall of rainfall and groundwater level in the dry season. The main subsidence area in Xizhou Township was around the HSR station, and the subsidence rate was 3.4 cm/yr in 2018. (b) The maximum subsidence rate in Xizhou Township was 3.4 cm/yr in 2018. According to the results of leveling, GPS and monitoring well, the compaction in depth over 300 meters was obvious. Therefore, taking note of the water resources in this depth should be needed in the future. (c) The accumulated amount of subsidence in Xizhou area was over 80 cm from 1992 to 2018. In the future, this area should be focused on monitoring continuously for the safety issue of HSR. C. Erlin Township (a) The results of benchmark SSESWELL indicated that the subsidence tendency was gradually increased from 2013 to 2015 but slightly increased in 2017. And the subsidence rate in 2018 decreased to 2.6 cm/yr in 2018. (b) The integrated monitoring results in Sinsheng elementary school area indicated that all monitoring results were consistent with error ±1 cm. The GPS results was larger than the results of land subsidence monitoring wells illuminated the deep compaction in this area was ongoing obviously. Therefore, taking note of the water resources in this depth should be needed in the future. (2) Yunlin area In 2018, the compaction trends from the land surface to a depth of about 300 meters in inland areas were more serious than in coastal areas. And the compaction rates of land subsidence monitoring wells in Sioutan elementary school, Neiliau station, Yuanchang elementary school, Hunglun elementary school、Dongguang elementary school and Ketsuo elementary school are between 3.0 and 4.6 cm/yr in recently, and the others in Yunlin area are less than 3.0 cm/yr. The main survy results are summarized as follows: A. Huwei Township (a) The results of benchmark YLSZ110 indicated the subsidence tendency from 2011 to 2014 was gradually mitigated. The subsidence rate in 2015 reached the high point of 6.0 cm/yr. After 2015, the subsidence tendency mitigated to 4.7 and 3.8cm/yr in 2016 and 2017, respectively. However, the subsidence rate in 2018 was slightly increased to 4.0 cm/yr. (b) The results of land subsidence monitoring wells in Guangfu elementary school indicated that the main compression occurred from the land surface to a depth of about 295 meters. And the result of ground water monitoring station also showed the large groundwater level changed in the same range between 0 and 295 meters in depth. B. Tuku Township (a) The time series of land subsidence monitoring wells in Sioutan elementary school showed the increased tendency of subsidence rate after 2013. And the subsidence rate in 2015 reached high point of 7.1 cm/yr. From 2016 to 2018, the subsidence rate fluctuated between 3.6 cm/yr and 6.6 cm/yr, and the subsidence rate in 2018 was 5.6 cm/yr. (b) According to the recent results obtained from monitoring wells in Tuku junior high school, the mainly compression situation was occurred from the first aquifer to the fourth aquifer. Moreover, the comparison result between leveling, GPS and monitoring well was shown, which demonstrated that the deep compaction occurred obviously over 300 meters in depth. C. Yuanchang Township (a) The results of benchmark YLSZ72 indicated that the subsidence tendency was gradually increased from 2013 to 2015 and reached a peak of 6.5 cm/yr in 2015. The subsidence rate in 2017 reached to 6.0 cm/yr and decreased to 4.9 cm/yr slightly in 2018. (b) The integrated monitoring results in Ketsuo elementary school indicated that all monitoring results were quite consistent. The GPS results was larger than the results of land subsidence monitoring wells showed that the deep compaction occureed obviously in this area. D. Baozhong Township The results of benchmark NBI025 indicated the subsidence tendency was gradually mitigated after 2009. The dry seasons between 2014 to 2015 led the subsidence rate increased to 5.9 cm/yr. The subsidence rate in 2017 reached to 3.9 cm/yr and increased slightly to 4.0 cm/yr in 2018. E. Sihhu Township (a) The results of benchmark TGBM indicated that the subsidence tendency from 2007 to 2013 was gradually mitigated but slightly increasing in 2015 which attributed to the fall of rainfall and groundwater level in the dry season. During 2016 to 2018, the subsidence rate fluctuated between 0.9 cm/yr and 4.1 cm/yr, and the subsidence rate in 2018 was 3.8 cm/yr. (b) The results of land subsidence monitoring wells in Dongguang elementary school indicated that the main compression occurred from land surface to 300 meters in depth. And the result of groundwater monitoring station also indicated the same phenomenon. F. Kouhu Township The results of benchmark WGWS indicated that the subsidence rate reached to 4.0 cm/yr in 2014. and gradually decreased with time. The subsidence rate in 2018 was 2.6 cm/yr. F. Taixi Township The results of benchmark YLBM27 indicated the subsidence tendency was gradually mitigated after 2008. And the subsidence rate flucated between 0 cm/yr and 4.3 cm/yr, and the subsidence rate in 2018 was 2.6 cm/yr.