Coastal Structure Underwater Inspection Technologies By Ten-i L. Prickett PURPOSE

To introduce multibeam sonar technology for use in performing high-resolution, quantitative surveys of coastal structures. BACKGROUND Much of the damage to coastal structures, especially rubble-mound breakwaters and jetties, occurs to the underwater portion of the structure. Underwater damage such as scour, settlement, and scattering and breakage of armor units is not often exhibited on the surface, and damage can progress until a major structural collapse occurs. Detection of underwater damage and deterioration is cost-effective for coastal engineers in terms of planning for structure repairs and rehabilitation, and management of coastal structures over their lifetimes. Using divers for underwater inspection or surveys of coastal structures is often d&cult and risky because of the normal occurrence of waves and currents and limited underwater Lisibility around the structure. Information from diver surveys is subjective and spatial detail is sparse. Side-scan sonars (SSS) were investigated and proved as a viable tool for structural surveys (Kucharski and Clausner 1990). Although SSS surveys provide good spatial coverage, the results are semi-quantitative and often distorted because of energetic wave and current conditions around the structure. In response to a need for objective, detailed, and quantitative definition of the underwater shape of coastal structures, research conducted at the U.S. Army Engineer Waterway