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How does overflowing in trailing suction hopper dredger affect the water regime?

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Trailing suction hopper dredger contains a large hopper for storage and transport of dredged materials. The dredging operation is implemented by a hydraulic dredging system including draghead, suction pip, pumps for taking up the material from seabed and putting them into the hopper.

When dredging materials, overflowing may occur to increase the solid loads in the hopper and improve the efficiency of dredging operation. The removal of excess water and soil/water mixture with low density enhances the storage of soils mixture with higher density. Hence, this lowers the cost of dredging by increasing the rate of production. If no overflow is allowed during the dredging operation, trailing suction hopper dredger can normally carry about 10% of normal load and this essentially increases the cost of dredging operation.

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If overflowing is allowed in the dredging operation, it shall work on unrestricted basis as the rate of overflow is nearly constant over the entire overflowing process. For dredging with overflowing, the particle size distribution of sand may differ from the in-situ grading because overflowing tends to remove the fine content of sand.

The loss of sediment associated with overflowing poses environmental problems to the nearby water zone in the following ways:

(i) increased sedimentation
(ii) decrease in dissolved oxygen
(iii) increased turbidity
(iv) increased amount of nutrients

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This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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