Water Injection Dredger UKD Seadragon
Continuous maintenance dredging
The UKD Seadragon is a Damen Shoalbuster 2711 fitted out with a customised Water Injection Dredging system. The multipurpose dredge vessel has been specifically designed for UK Dredging, ensuring the flexible use of the 27 m long workboat. Its maintenance dredging activities using the Water Injection Dredging gear are one task, the others include bed-levelling, buoy handling, pushing, supply and survey jobs. The workboat houses a crew of max 5 in its living quarters. The max speed is 10.5 kn, whereas during WID activities it moves at approx. 1.5 kn.
A practical dredger
Maintenance dredging can be optimised by adding a Water Injection Dredger [WID] to the dredge vessel fleet. Combined with a Trailing Suction Hopper Dredger [TSHD], the Water Injection Dredger can prepare critical areas along underwater port infrastructure by flushing them. Due to its high maneuverability, it can work closely along quay walls and jetties, and it can flush locks without any interruption to the port traffic. The TSHD can now make more efficient sweeps by removing sedimentation from more easily reachable areas such as the navigation channel.
Electrically driven E-DOP450L
The Shoalbuster 2711 has been fitted out with a dedicated A-frame aft, which hoists and lowers the electrically driven submersible dredge pump, type DOP450L. The wear resistant dredge pump sucks up 4000 m³/h of surrounding water, pumping is through the nozzles in the water injection beam into the sediment layer at a max pressure of 2.5 bar. This sediment is thus refloated and taken away by the local current or tide. The flexible dredge system can be used for WID dredging at depths ranging from 5 to 20 metres.
Rapid deployment
The UKD Seadragon started its duties by conducting a number of trial runs in various ports around the Bristol Channel. The highly maneuverable vessel used its Water Injection Dredging system in a variety of situations to familiarise the crew with the new dredging equipment. The dredge productions have proven to be impressive, with low fuel consumption. The excellent results of the first few dredging campaigns were repeated during maintenance dredging works at other British ports.
What is Water Injection Dredging?
Water injection Dredging [WID] is a practical way to remove fine sand and silt by making use of natural phenomena. While Cutter Suction Dredgers and Trailing Suction Hopper Dredgers actually pump up this sediment and bring it to the surface, WID operations merely move the sediment away from the inconvenient location. These ‘dredging with nature’ operations can only be successful under certain conditions.
Dredging with nature
First of all, the sediment layer to be brought into suspension should consist of silt or fine sand. Recently deposited, non-compacted bottom material can be refloated using the jet water nozzles. These fines will create a density current, forming a fluidized soil layer that moves over the bottom of non-refloated sediment.
The second vital element is the presence of natural phenomena creating this movement. When fine-grained non-cohesive sediment deposits are refloated by the WID jet beam, it needs to flow further downstream while the WID vessel slowly moves forward at 1 to 2 knots. For this sediment transport, the current of the river or the force of the outgoing tide is used. It is also possible to make use of the bottom profile, with the sediment flowing down a slope to a deeper area such as a navigation channel.
As is the case in many ports, the British harbours where the UKD Seadragon is working encounter the natural sediment transport from areas upstream. River transport this sediment, which settles in more quiet corners of ports and locks.The integration of Water Injection Dredging (WID) into the dredge vessel fleet has proven to be an efficient and environmentally friendly method for maintaining port infrastructure, ensuring smooth and uninterrupted port operations.