Abstract
Numerical simulations of coral gravel transportation were conducted to estimate the accumulation possibility in the gap which is formed by the open-cutting of the causeway in Fongafale Islet of Funafuti Atoll. In the numerical simulation of wave field, the high wave conditions were considered in the boundary condition. Calculated morphological change in the gap showed that the extremely large accumulation of coral gravels was not estimated. However the southern edge of the gap had large accumulation locally. In the middle and northern part of the gap accumulated gravel formed thin layer. Because the calculated morphological change of lower wave condition showed large accumulation as well as the results of higher wave condition, it is estimated that the direction of incident wave is important factor of the accumulation. The simulated result indicated that the rapid blockade of the gap would not be caused by accumulation of coral gravels. However, the periodic maintenance of the gap is required for keeping the function of the gap continuously.
Highlights
Funafuti Atoll, Tuvalu has the low-lying islands constructed by foraminifers, coral sands and gravels (Yamano et al, 2005: Yokoki et al, 2005)
The large accretion was detected in only a part of the gap. These results revealed the rapid blockade of the open-cut causeway would not be caused even in the high wave condition
Numerical simulations of the coral gravels movement on the excavated causeway were conducted to discussing the possibility of blockade of excavated causeway
Summary
Funafuti Atoll, Tuvalu has the low-lying islands constructed by foraminifers, coral sands and gravels (Yamano et al, 2005: Yokoki et al, 2005). The islands form on the ring-shaped shallow reef. Atoll islands have a calm lagoon that is enclosed by a circular shallow reef. Fongafale Islet on the eastern side of the atoll has a problem of coastal erosion on the lagoonal sandy beach, which is caused by poor sediment supplies from ocean-side reef-flat. The natural island maintenance system that is consisted by sediment production by reef-living organisms, sediment transportation and sediment accumulation would be collapsed by constructions. Understanding of natural processes of the sediment transport is the fundamental information for controlling the coastal erosion. The interaction between morphological changes of the islands and the driving forces such as waves is not considered enough (Yokoki et al, 2005; Kench and Brander, 2006)
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