Establishing a Stone-Dumping Process for Constructing Man-Made Undersea Ridges
Type:
Presented during:
WODCON XIX: "Dredging makes the World a better place" - 2010, Beijing, China
Authors:
Yoshiyuki Haseyama
Abstract: It is known that a sea area with an upwelling provides an advantageous environment for the development of a highly productive food chain and hence a rich fishery. Accordingly, there are projects underway in Japan to construct man-made undersea ridges for artificial upwelling generation in order to boost the productivity of national coastal fisheries and, consequently, secure sustainable fisheries resources.
An example of such a project is provided by a group of approximately 15-meter high man-made undersea ridges constructed using ashcrete blocks or natural rocks on a 70- to 80-meter deep seabed, with the neighboring ridges spaced about 60 to 80 meters apart. When seabed current flows interact with the man-made undersea ridges, upwelling will occur and bring nutrient-rich deep water up to the surface to help the enrichment of the local food chain consisting of phytoplankton, zooplankton, and fish, with the largest species of the last being the top predator.
Successful generation of artificial upwelling depends critically on the location, design, and configuration of the man-made undersea ridges. This means that a very high level of construction accuracy is required. In order to accurately build underwater structures by dumping rocks from split hopper barges down to a deep underwater site, it is necessary to optimize the stone-dumping process that takes into consideration not only accurate determination of ship position but the natural conditions, such as tides, in the area.
This report provides introductory descriptions of the various efforts incorporated into the man-made undersea ridges constructed by Tomac Corporation, on a 76-meter deep seabed offshore west of Nagasaki City, Nagasaki Prefecture, Japan, during the period from 2008 to 2009.
Keywords: Upwelling, manmade undersea ridges, stone-dumping process, Distinct element method, post-dumping mound geometry prediction system