The application of side-scan sonar system in monitoring benthic artificial reefs

The physical status of two types of cubic concrete artificial reefs was investigated by means of a side-scan sonar system on a testing site off Yung-an LNG port, south-western part of Taiwan. The ultimate goal of this investigation was intended to deduce the mechanisms which cause the excess subsidence of these reefs, and to propose pertinent procedures in preventing this excess subsidence. The heights of the reefs were fairly constant for the first 5 months. However, a sudden height decrease of about 0.3 m was detected for most of the reefs thereafter. This sudden height decrease event was closely correlated with the strong sea state caused by a storm. According to the information obtained during a period of 10 months, the major factors influence the subsidence of these artificial reefs in this test site were scouring effects. The side-scan sonar system showed its effectiveness in searching, positioning, and height measurement of benthic artificial reefs.