Combining the gray system model and nonlinear poroelastic model to evaluate the subsidence in Tainan area

The topography is very low in Tainan area which is located at a high risk area of flood due the climate change. If a subsidence problem takes place in Tainan area, it will cause the saltwater intrusion and a large area flooded and induce a disaster. Therefore, it is important to investigate the subsidence mechanism and evaluate the settlement under the climate change situation in the future. Knowing the subsidence behavior and the possible settlement can help retard the problem. This study combines two different theories of a black box model, gray system model, and a physical model, nonlinear poroelastic model, to simulate the subsidence behavior and evaluate the settlement under the climate change situation. From the poroelastic model, the maximum additional pumping quantity around the subsidence wells is 0~52.5 ton/day. The most serious subsidence area in 2039 is around the Xiaying well and the quantity is 0.34 ± 0.07 m based on 2002. From the gray system model, the most serious subsidence areas are around the Annan, Xuejia, and Beimen Dist and the quantity is 0.89 m based on 2003. Considering the climate change effect of 30% additional usage of groundwater, the most serious subsidence areas in 2039 are also around the Annan, Xuejia, and Beimen Dist. The quantity of settlement reaches 1.16 m and the areas with settlement larger than 0.36 m are about 120 km ². From the results of this study, subsidence in Tainan areas will be a problem in the future if the situation is maintained. The manager should pay attention to the situation in Tainan areas to avoid the future subsidence problem.