SIDE-SCAN SONAR APPLICATIONS FOR EVALUATING COASTAL STRUCTURES 

 PART I: INTRODUCTION 



1 . Side-scan sonar is a commercially available acoustical tool for 

 remotely acquiring a qualitative image of submerged objects, including the 

 bottom. The resultant image or sonograph provides a strip map of the area on 

 either side of the towing vessel. The image characteristics, ease of 

 interpretation, and efficiency of operation result in side-scan sonar being an 

 effective tool for planning, designing, constructing, and monitoring coastal 

 works. Side-scan sonar can be used to document an extensive area of structure 

 where water turbidity, currents, or other conditions preclude the use of an 

 optical-based system or diver inspection. 



2. Most documented experience with side-scan sonar is in locating 

 debris and obstructions to navigation, finding lost objects, or for mapping 

 and interpreting geological conditions. Williams (1982) describes the use of 

 side-scan sonar for geologic mapping. Side-scan sonar has also proven to be a 

 valuable tool in coastal and nearshore exploration for mapping sources of 

 potential beach nourishment material (Prins 1980). Some monitoring of locks 

 and dams has also been conducted. 



3. This report is not a substitute for an operator's manual. A report 

 being prepared under the Repair, Evaluation, Maintenance, and Rehabilitation 

 (REMR) Program (Kurcharski and Clausner, in preparation) provides details on 

 the operation of side-scan sonar in the coastal zone. Rather, this report 

 describes the capabilities of the tool and provides examples of types of 

 coastal structures and particular features that have been imaged using side- 

 scan sonar. It also discusses the effective use of side-scan sonar in 

 documenting coastal construction practices, making qualitative structure 

 condition assessments, and documenting sediment movement patterns around 

 structures. Side-scan sonar techniques have not yet proved to be capable of 

 providing information needed to provide specific design guidance. For 

 example, a side-scan sonar image can show that armoring material has been 

 displaced from the face of a structure and is now lying on or beyond the 

 toe. However, a side-scan sonar image by itself cannot be used to determine 

 what caused the armor to move or give an accurate estimate of the percentage 

 of armor displaced but still remaining on the face. 



