Yifan Xie, Hohai University, State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Nanjing, China, Jichun Wu, Nanjing University, School of Earth Sciences and Engineering, Nanjing, China, Chunhui Lu, Hohai University, Nanjing, China and Chunhong Xie, Nanjing University, Department of Mathematics, Nanjing, China