Environmentally-friendly dredging in the Bisan-Seto Shipping Route

摘要

Japan's Bisan-Seto Shipping Route serves as both a key a route for domestic shipping between Osaka and Kyushu and as an international sea trade route. Between fiscal year 1963 and 1972, the Ministry of Land, Infrastructure and Transport implemented a government-controlled program to improve this sea route. Approximately 38.4 million cubic meters of solids, including bedrock, were dredged to increase the depth of the northern shipping route to -19 m, the southern and connecting shipping route to -13 m, and the Mizushima Shipping Route to -17 m.The Ministry of Land, Infrastructure and Transtport performed every few years this dredging in response to the complex surrounding geography and tidal characteristics of the shipping route, which cause sediment build-up and reduce the functionality of the shipping route. The dredging involves barge-loading pump dredgers, with the dredged material loaded onto barges for transportation to disposal areas. This work lead to the overflow of turbid water from hopper of barges into surrounding sea areas, causing marine turbidity.The most recent Bisan-Seto Shipping Route dredging program was carried out over a five-year period, from fiscal year 2001 through 2005. The program incorporated studies on environmentally-friendly dredging methods that do not generate turbidity, leading to the selection of a method that recirculates overflow water from the barge to the dredger suction inlet, and realized an approach to prevent the generation of turbidity without reducing dredging efficiency. The pump dredger was equipped with an operational control system, GPS, and a Christmas tree to handle sandbanks and wakes from passing ships, which tend to complicate loading operations.This report describes the barge-loading pump dredger equipment used in the Bisan-Seto Shipping Route dredging program, along with the nature and conditions of the dredging work performed in fiscal year 2001.