Development of a Fiber-Optic Cable Monitoring System for Storm-Generated Bathymetric Change in the Surf Zone

Abstract

A monitoring system, called the optic sediment sensor (OSS), for study of the detailed processes of bathymetric changes in the surf zone has been developed. The OSS system consists of an array of fiber gap sensors (FGSs), a support structure (steel pipes), an electronics unit that transmits and receives light through fiber-optic cables, and a data acquisition system. The FGSs are mounted in a 2-m long vertical steel pipe; the sensor spacing is 10 cm. Steel pipes containing FGSs were embedded in the seafloor at two plaices at water depths of 4–5 m beneath a pier at the Hazaki Oceanographical Research Station (HORS) (Port and Airport Research Institute) on the Sudahama Coast, facing the Pacific Ocean, Japan. The electronics unit and the data acquisition system were installed in an observation room on the pier. The OSS systems successfully recorded well-defined and consecutive bathymetric changes caused by storm waves (maximum significant wave-height = 3 m); e.g. reversal of seabed erosion and deposition within a day could be recognized. If the OSS system could be installed in many more locations along the pier, the consecutive process of the formation, migration, and deformation of the whole of the longshore bar may be clarified.

Keywords:

• Optic sediment sensor
• bathymetric change
• monitoring
• high-energy surf zone