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Title: Land subsidence in Chiayi, Taiwan, from compaction well, leveling and ALOS/PALSAR : aquaculture-induced relative sea level rise
Authors: Hung, WC
Hwang, C
Chen, YA
Zhang, L 
Chen, KH
Wei, SH
Huang, DR
Lin, SH
Issue Date: 2018
Source: Remote sensing, Jan. 2018, v. 10, no. 1, 40, p. 1-22
Abstract: Chiayi County is located in the largest alluvial plain of Taiwan with extensive aquaculture and rice farming sustained by water extracted from groundwater wells. Chiayi is a typical aquaculture area affected by land subsidence, yet such lands worldwide combine to provide nearly 90% of global aquaculture products, greatly reducing oceanic overfishing problems. This study uses precision leveling, multi-layer compaction monitoring well (MLCW) and spaceborne SAR interferometry (InSAR) to examine the cause and effect of land subsidence in Chiayi associated with groundwater extractions and changes. Heights at benchmarks in a leveling network are measured annually and soil compactions at 24-26 layers up to 300-m depths at 7 MLCWs are collected at one-month intervals. Over 2007-2011, 15 ALOS/PALSAR images are processed by the method of TCPInSAR to produce subsidence rates. All sensors show that land subsidence occur in most parts of Chiayi, with rates reaching 4.5 cm/year around its coast, a result of groundwater pumping from shallow to deep aquifers. MLCWs detect mm-accuracy seasonal soil compactions coinciding with groundwater level fluctuations and causing dynamic compactions. Compactions near Taiwan High Speed Rail may reduce the strength of the rail's supporting columns to degrade its safety. The SAR images yield subsidence rates consistent with those from leveling and compaction wells after corrections for systematic errors by the leveling result. Subsidence in Chiayi's coastal area leads to relative sea level rises at rates up to 15 times larger than the global eustatic sea level rising rate, a risk typical for world's aquaculture-rich regions. At the fish pond-covered Budai Township, InSAR identifies subsidence spots not detected by leveling, providing crucial geo-information for a sustainable land management for aquaculture industry.
Compaction well
Land subsidence
Precision leveling
Relative sea level rise
Publisher: Molecular Diversity Preservation International (MDPI)
Journal: Remote sensing 
EISSN: 2072-4292
DOI: 10.3390/rs10010040
Rights: © 2017 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (
The following publication Hung, W. C., Hwang, C., Chen, Y. A., Zhang, L., Chen, K. H., Wei, S. H., … Lin, S. H. (2018). Land subsidence in Chiayi, Taiwan, from compaction well, leveling and ALOS/PALSAR : aquaculture-induced relative sea level rise. Remote Sensing, 10(1), (Suppl. ), 40, - is available at
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