Hiroshima Bay (Cont.)

surrounding water did not occur. The success of the sand-spreading dem-

onstration was above expectations, but it was concluded that a new type of

sand spreader would be needed for larger scale operations.

A conveyor barge (Figure 11) with 18 hopper bins was used in Hi-

roshima Bay for another sand-spreading test (Togashi 1983). The barge

could discharge 2,000 m3 in 1 hr. A telescopic tremie tube was installed,

and the length of the tube was adjusted so that the sand discharged would

not disturb the spread of the sludge as it contacted the seafloor. The sea

sand had a average specific gravity of 2.62 and silt content of 0.6 to

1.5 percent. The design thickness was 0.5 m. Results of the field tests

showed the average 0.5-m thickness was obtained using a volume equiva-

lent of 0.25 m of overlay placed twice from a height of 10 to 12 m above

the bottom. The sand thickness was stable; the impact on the bottom sedi-

ment was diminished at this height, and turbidity and resettling were mini-

mized. This conveyor barge method was considered to be an efficient and

mobile technique for sand overlaying and is applicable in a wide range of

areas.

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Chapter 10 Case Studies