Abstract: Acoustic methods of depth survey and bottom profiler array parameter measurement were used to detect underwater riprap, taking the artificial island in the Gulf of Bohai as the case history. The thickness and distribution pattern of the riprap were revealed. Data show that the calculation of the thickness of seabed riprap should take the erosion and siltation of the artificial island into account. The thickness of the riprap in the erosional seabed can be directly used to judge the change in submarine topography. In the siltation area, however, the siltated sediments should be deducted to monitor the topographic changes.