In response to the land subsidence phenomenon in Yunlin and Changhua area due to groundwater overuse, since 2003, BOHSR has been supervising THSRC to conduct annual monitoring inspections on HSR piers and report results to central and local governmental authorities for record and reference. Based on the monitoring records in 2015, areas that suffered most from this issue currently are Hsichou Township District in Changhua, Huwei Township, Tuku Township, Yuanchang Township and Beigang Township in Yunlin and Hsingang Township in Chiayi. According to 2015 records, significant subsiding sections are TK216~TK234 in Huwei and Tuku Township with maximum subsidence value of 6.6 cm at TK218+465 which was a 5.1 cm increase comparing to 2014 values. In addition, the subsidence value in Chiayi Taibao section was 3 cm, a 1.1 cm increase comparing to 2014. Via assessment by THSRC, the subsiding situation will not endanger the structural and operational safety of HSR. Currently, the angle variables of piers are lower than the allowable value indicating that the HSR structure is safe for operation. The subsiding values and angle variables in recent three years of the four significant areas, Hsichou Township, Yunlin Station District and the area crossing Yunlin No.158 Country Road and Provincial Highway No. 78, have been listed out in the following table showing increase in only Yunlin Station District due to overall subsidence in the area and the angle variables of the remaining three places remained stable ensuring HSR safety.
To eradicate the land subsidence issue along HSR routes, the Executive Yuan ratified "Speciﬁc Solutions and Action Plans Confronting Land Subsidence in Yunlin and Changhua Areas (the 1st amendment)" in 2013 May. The project has successfully reduced groundwater usage which effectively slowed down the land subsidence issue in Yunlin and Changhua areas and brought positive impact toward HSR structural and operational safety in that area.
BOHSR will continue to monitor the subsiding status of HSR bridge piers and carry out specific emergency measures to ensure HSR operational safety.