圖書典藏及影音數位平台

台灣部分地區為加速產業發展,在地面水源供應量不足下,轉而長期仰賴抽取地下水,並造成地層下陷災害.為減少地層下陷災害對環境與國土之破壞,政府自民國84年至民國97年即陸續推動第一期與第二期地層下陷防治執行方案,而本計畫主要為延續第二期地層下陷防治執行方案之工作成果來實施.

This project lingers on the stage Ⅱ plan for the mitigation of land subsidence. Its objectives are to monitor the land subsidence and to explore the subsidence mechanisms in Taiwan. Consequently, these results will provide precaution for the potential areas of land subsidence and to develop the conceptual strategy for the mitigation of serious land subsidence. This project contains five tasks including: (1) leveling survey in land-subsidence area, (2) maintenance and measurement of the existed land subsidence monitoring wells and GPS continuous stations, (3) radar interferometry data analysis, (4) the integrated analysis of monitored data obtained from the land subsidence area, (5) renewal and maintenance of land subsidence database as well as a Web site inquiring system. The main results are summarized as follows. (1) The results of leveling survey The areas of leveling survey include Taipei basin (90km), Changhua (380km) and Yunlin (450km). The total length of surveyed routes is about 920 km. The surveyed routes’ closed errors are all satisfied the standard requirement of 3mm√k. The results of the leveling survey are as follows: The length of surveyed routes in Changhua, Yunlin, Chiayi and Tainan are 380, 450, 310, and 120 kilometers respectively. Meanwhile, the leveling measurement of the elevation of groundwater monitoring well are including Changhua (20km), Yunlin (30km), and Chiayi (50km). The total length of surveyed routes is about 1,360 kilometers in 2010. The surveyed routes’ closed errors are all satisfied the standard requirement of 3mm√k. The detail results of the leveling survey are as follows: (a) In Changhua County, the maximum subsidence rate is about 6.4 cm/yr and the continuously subsiding area (the area of over 3 cm/yr) is about 138.9 km2. Both of the maximum subsidence rate and the continuously subsiding area in 2010 are bigger than those surveyed in 2009 (about 5.7 cm/yr and 78.1 km2 respectively), it reveals that the subsidence has a tendency of slightly aggravating. (b) In Yunlin County, the maximum subsidence rate is about 6.4 cm/yr and the continuously subsiding area is about 267.1 km2. Both of the maximum subsidence rate and the continuously subsiding area in 2010 are less than those surveyed in 2009 (about 7.3 cm/yr and 414 km2 respectively), it reveals that the subsidence has a tendency of slightly mitigating but still serious. (c) In Chiayi County, the maximum subsidence rate is about 5.4 cm/yr and the continuously subsiding area (the area of over 3 cm/yr) is about 198 km2. The continuously subsiding area in 2010 is bigger than surveyed in 2009, it reveals that land subsidence is slightly aggravating. (d) In Tainan County, the subsidence rate in most area is smaller than 3.0 cm/yr,besides some area in Anding and Beimen Township. The continuously subsiding area in 2010 is about 29 km2. (2) Maintenance and measurement of the existed land subsidence monitoring wells and GPS continuous stations (a) Eight GPS permanent stations are located at Shinshing elementary school, Tuku junior high school, Linnei junior high school, Kecuo elementary school and Guangfu elementary school in Yunlin County, and Shigang elementary school Hunan elementary school in Changhua County, as well as Putai elementary school in Chiayi. The GPS permanent stations provide real-time and continuous monitoring data. The data quality is approved by checking the MP1 and MP2 values, both are less than 1, it reveals that the signal is stable. (3) Radar interferometry data analysis (a) From the monitoring results of CRAF area, radar interferometry is proven a powerful, effective and economy technology to observe wide surface deformation, especially in subsidence survey. Compared with leveling and GPS observing, radar interferometry illustrates not only high spectral resolution but also high measuring accuracy. Even in some small areas where no leveling points or GPS stations, it could also show the information about ground deformation. Moreover, the results from radar interferometry could be compared with other monitoring results to calibrate, as well as combined with leveling data to obtain more completely deformation map. (4) Integrated analysis of monitored data in land subsidence area (a) The main compression depth in Xihu Township is in a range of 150 to 260 meter. Its possible water pumping source are waterworks and leather factories. The suggestion for Changhua government is to keep focusing on the subsidence tendency , as well as to manage the water usage around this zone. (b) In Sijhou Township, the main subsidence area is about 1 km north of the section passed over the Zhongshan Highway and the Taiwan High Speed Rail. According to the results from subsidence monitoring wells and leveling survey the major subsidence occurs in the range of over 300 meters in depth due to deep groundwater pumping. (c) Erlin Township is currently the most serious subsidence area in Changhua County. According to the result from the subsidence monitoring well, the compression depth have exceeded the third aquifer (the major subsidence occurred in aquifer 2 or aquifer 3 in the past). It reveals that some land subsidence in Erlin Township is induced by the compression of deep strata. (d) In Changhua County, the maximum compression rate in unit thickness for long term arises in aquifer 2 or aquifer 3; however, the rate for short term arises in aquifer 3 or aquifer 4 . According to the monitoring data, the compression depth of Singhua Elementary School in Erlin Township have reached the third aquifer. We should pay special attention to this phenomenon in the future. (e) In Yunlin County, the maximum compression rate in unit thickness for long term arises in aquifer 3 or aquifer 4; however, the rate for short term arises in aquifer 4. It reveals that land subsidence in inland Yunlin is major induced by the compression of deep strata. (f) To compare with the GPS and the subsidence monitoring well data, the main subsidence areas in Yunlin are Huwei Township, Tuku Township and Yuan Chang Township. These townships occurred stratum compression below underground 300 meters, meanwhile, the stratum compression is continually. Consequently, there are many pumping wells withdraw water from below underground 300 meters reached the fourth aquifer in the inland areas in Yunlin. In order to reduce the subsidence obviously, the first thing we should do is to restrain people from withdrawing from deep aquifer. (5) Renewal/maintenance of land subsidence database and Web inquiring system A database of land subsidence and a Web site for data inquiring were set up to allow convenient inquiry in 2001. The Microsoft SQL Server has been adopted in the system. A website is set up to enable data access and offers the updated information about land subsidence and relevant symposiums for clients. The user must be authorized by Water Resources Agency to inquire the raw data. The address of the website is www.subsidence.org.tw. This inquiring system is updated monthly to renew the relevant information about land subsidence. The analysis results of leveling survey and monitoring wells have been updated to 2010.