MA Jin-rong，GUO Ya-qiong，NAN Wei

（1.Key Sediment Research Lab. of Harbors and Waterways of the Ministry of Communications，Nanjing Hydraulic Research Institute，Nanjing 210029，China；2.College of Hydrology and Water Resources，Hohai University，Nanjing 210098，China；3.China Nuclear Power Design Company LTD.，Shenzhen 518045，China）

The wrack or the ship out of control will drift with flow.One of the most important factors that drive the ship is flow current which moves circularly in tidal area.The wrack from same place always drifts in different ways if the start time is different.So，during the ship drifting period，the drift trace is also determined by both wave and wind forces.The drift direction is limited by water depth which must be deeper than ship draft.These marine structures that can not afford the hit of wrack or will destroy the wrack must be well considered when they are placed near harbor and waterway or other water area with ship running.The risk zone should be consulted according to tide and weather conditions to protect structures and ships in necessary.A method is presented here to simulate the risk zone by 2D numerical hydraulic model with tidal current，wave，wind and water depth considered.This model can be used to built early-warning and protect system for special marine structure.

drift；trace；risk zone；simulation