UNDERWATER INSPECTION OF COASTAL STRUCTURES 

 USING COMMERCIALLY AVAILABLE SONARS 



PART I: INTRODUCTION 



1. The purpose of this report is to give a general Introduction to the 

 side scan sonar (SSS) and its uses in coastal engineering studies, including 

 some operating rules -of -thumb and suggestions based on the authors' experi- 

 ence. Several systems currently on the market are evaluated in paragraphs 35 

 through 44 as an aid to further research before purchasing equipment. 



Current Coastal Engineering Applications 



2. Perhaps the most important use of SSS for coastal engineering in 

 terms of potential cost savings is early detection of damage and deterioration 

 of underwater portions of coastal structures, thus permitting the responsible 

 engineer to take action to minimize further degradation and to plan for 

 repairs and rehabilitation with greater lead time. The ability of sonar to 

 penetrate through waters too turbid or too dangerous for visual or optical 

 inspection makes it the only effective means of surveying many coastal 

 structures. 



3. SSS has already proven useful in surveys of breakwaters, jetties, 

 groins, port structures (bulkheads, pilings), and inland waterway facilities 

 such as locks, dams, and hydroelectric works. It has proven especially effec- 

 tive in examining the toe portion of rubble structures for scour and displace- 

 ment or armor units. Thus inspection, to qualitatively assess damage or 

 simply to periodically check the condition of structures (including as-built 

 surveys), is a proven and important application of SSS. Real-time display 

 capability permits onsite decisions based on knowledge rather than guesses, 

 and allows onsite improvements to the data collection plan in view of the 

 results. Historically, SSS has been used primarily in reconnaissance and 

 search applications such as pipeline and cable tracking, exploration, 

 wreckage/debris location, navigational hazard mapping, and identification of 

 bottom material (sand, rock, mud, etc.). Other current coastal engineering 

 applications of the technology are found in dredging work (identification of 



