Land Subsidence in Chiayi, Taiwan, from Compaction Well, Leveling and ALOS/PALSAR: Aquaculture-Induced Relative Sea Level Rise

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.

Sinking Tide Gauge Revealed by Space-borne InSAR: Implications for Sea Level Acceleration at Pohang, South Korea

“…As tide gauges measure relative SLR with reference to a tidal benchmark grounded on the adjacent coast, even minor ground motions will significantly affect sea level height measurements. Previous studies have reported on vulnerable sites for coastal subsidence and short-term sea level rise, including Hampton Roads, Virginia [14], New York City [15], Taiwan [16], and North Carolina [17]. Hence, the estimation and correction of the local ground motion at and around the tide gauges is important to minimize uncertainties in the local and global sea level changes observed [18][19][20][21][22][23].…”

Land Subsidence Monitoring in Jagadhri City Using Sentinel 1 Data and DInSAR Processing

“…For the feasibility of this study, Sentinel-1A Interferometric SAR data has been collected from Alaska Satellite Facility website (https://vertex.daac.asf.alaska.edu) and the DORIS data of Verified Orbit has collected from the European Space Agency website (https://qc.sentinel1.eo.esa.int/aux_poeorb/) which is available 20 days after the actual satellite acquisition. Generally, the perpendicular baseline and time difference between the images are important in such land subsidence-related studies because several attempts have been done in different areas with different spatial baselines to find an identical rate of subsidence [19,21]. The distance between the two SAR image acquisitions represents a baseline, hence, there are three spatial baselines 110, 136, and 121 m and three temporal baselines of 108, 102 and 120 days for the years 2017, 2018, and 2019 respectively.…”

“…Nevertheless, this technique indeed provides a scope of rapid assessment of land subsidence over a large region. The occurrence of land subsidence has been studied in many places around the world, including Tokyo in Japan [13], Mexico city in Mexico [14], western Saudi Arabia [15], Jakarta in Indonesia [16], Ravenna in Italy [17], Bangkok in Thailand [18], Pingtung plain in Taiwan [19], Beijing in China [20] etc. In the Indian context few cities such as Delhi [21], Kolkata [11,22], etc.…”

A procedure to use GNSS data to calibrate satellite PSI data for the study of subsidence:an example from the north-western Adriatic coast (Italy)

“…The Persistent Scatterers Interferometry (PSI) techniques (e.g. Ferretti, Prati, & Rocca, 2001;Berardino et al, 2002;Hooper et al, 2004;Ferretti et al, 2011) have been successfully adopted for a wide range of applications in disaster management, and it has extensively proven to be a valuable tool to detect ground deformations due to landslides (Solari et al, 2018;Del Soldato, Riquelme, et al, 2018a;Ciampalini et al, 2016) or subsidence (Bonì et al, 2017;Da Lio & Teatini, 2018;Gao et al, 2018;Hung et al, 2017;Minh, Van Trung, & Toan, 2015;Aslan, Cakır, Ergintav, Lasserre, & Renard, 2018;Sun et al, 2017) or infrastructures stability (Di Pasquale et al, 2018).…”