During the flood season in 2016,the Yangtze River had caused floods in the whole basin,and the 12.5 m deepwater channel regulation project phase II downstream of Nanjing had been suspended as required for environmental protection purposes,during which abnormal scouring occurred in the submerged dike area at the head of Shuangjiansha in the Yangtze River.Using flow mathematical model and theoretically analytical methods,we simulate the flow field and regime of the construction area on various water conditions during different execution stages of the project,and find the reasons for the abnormal scouring arising within and out of the limits of the bottom protection,which will give new insights into the design of mattress for bottom protection.We further discuss new jobs that designers,owners,contractors,and all the other parties concerned may encounter owning to the ecological requirement for construction suspension,which can be used as a reference for similar large-scaled inland channel regulation projects.