[H-DS07] Landslides and related phenomena

[HDS07-10] Development of the Pop-up type Ocean Bottom Turbidity Current Detector (Ver. 3)

*Hisatoshi Baba¹, Izumi Sakamoto¹, Yuka Yokoyama¹, Taichi Kawakami³, Asahiko Taira² (1.Department of Marine and Ocean Engineering, Tokai University, 2.Institute of Oceanic Research and Development, Tokai University, 3.Kaiyo Denshi Co., Ltd.)

Keywords:Turbulent current, Suruga Bay, Instrument Development, Natural disaster, Estuary of Mt Fuji

In order to clarify the existence (Baba et al., 2021) and behavior of turbidity currents originating from typhoons off the Fuji River in Suruga Bay, Institute of Oceanic Research and Development,Tokai University has developed the Pop-up type Ocean Bottom Turbidity Current Detector (TCD: Turbidity Current Detector) and has continued turbidity current observations in the fan-shaped ocean basin off the Fuji River in Suruga Bay. The initial TCD (Ver. 1) developed in 2021 was not hit by a typhoon during the observation period (July to October 2021) and therefore did not generate turbidity currents, but we found some problems with the recording device and camera built into the TCD. We developed an advanced TCD (Ver. 2) that corrected these problems, and installed it in the fan-shaped basin off the Fuji River in August 2022. During the observation period, Typhoon No. 15 caused intense rainfall and flooding in Shizuoka, and the acoustic equipment confirmed that the TCD (Ver. 2) moved 2,722 m to the south on the seafloor (washed away in the direction of deeper water). However, the TCD (Ver. 2) suffered from a problem in that it did not surface even though a detachment and surfacing command was sent to the TCD from the research vessel, so the TCD (Ver. 2) was recovered by ROV in December 2022. The recovered TCD was severely damaged due to being swept away by the turbulent current, and data could not be obtained due to damage to the internal equipment.
Based on this experience, we have developed an improved TCD (Ver. 3) in cooperation with Kaiyo Denshi Co. Ltd. The improved TCD (Ver. 3) differs significantly from conventional TCDs in that it uses a galvanic releaser as the detachment device to raise the TCD, it is smaller and has fewer protrusions to facilitate its escape from various plant fragments, artificial objects, and surface sand and gravel when caught in a turbulent current, and its internal equipment is designed to withstand impacts. The internal components were designed to withstand impacts. The improved TCD (Ver. 3) is almost complete at this point, and will undergo various tests (confirmation of surfacing in the sea area, confirmation of surfacing in various positions (upright, sideways, and inverted), confirmation of buoyancy after surfacing and communication using the internal antenna, and confirmation of the durability of the internal devices), and in FY2025, it will be used to obtain dynamic data on turbulent flows. In 2025, we plan to conduct observations in the actual sea area (for 100 days from July 2025) in order to obtain dynamic data on turbulent flows.