IADC: Facts about Water Injection Dredging
Water Injection Dredging is a hydrodynamic dredging technique that should be taken into consideration as a cost-effective, environmentally sound solution to some specific dredging operations.
Dredging works can be complex and costly, accounting for a substantial proportion of the budget of a maritime project. To effectively plan and execute a dredging operation, to be able to select the most appropriate dredging plant, requires extensive knowledge of the material to be dredged as well as the environmental circumstances of the site to be dredged.
Since the mobilisation and capital costs of dredging plant are quite significant, choosing the wrong vessels and methods can have severe economic consequences.
Appropriate ground and environmental surveys are fundamental to the success of dredging operations, from both a technical and an economic perspective. Water Injection Dredging has very specific limitations but in the appropriate situation it also has very specific benefits.
WHAT IS WATER INJECTION DREDGING?
Water Injection Dredging is a relatively new hydrodynamic dredging technique, developed by engineer R.N. Van Weezenbeek a little more than 25 years ago, which has been gradually gaining popularity for maintenance dredging. Since port authorities are continually confronted with the siltation of the harbours and access channels, regular maintenance dredging is a necessity to ensure safe navigation depths in these waterways. However, especially for smaller ports, the financial demands of dredging can become burdensome.
Generally speaking the larger the port project, the more cost-efficient dredging becomes using traditional dredging techniques – trailing suction hopper dredgers and cutters for instance. But for the regular maintenance of smaller harbours, the technology of Water Injection Dredging can be an effective, economical and environmentally sound solution.
WHAT IS THE THEORY BEHIND WATER INJECTION DREDGING?
Other types of hydrodynamic dredging techniques do exist, such as agitation dredging, during which sediment is dispersed vertically over the whole water column, and ploughing. In contrast, Engineer Van Weezenbeek introduced the idea of allowing sediments to flow horizontally out of a port taking advantage of natural processes and forces, while the fluidised sediment layer remains close to the water bed.
Based on his knowledge of the behaviour of sand-silt water mixtures, he proposed to use the principle of gravity-driven density currents. By fluidising the solid sediment layer into a density current, the material, under certain circumstances, will flow out of the port basin. A density current is the fluidised soil layer “on the move”. The main characteristic of Water Injection Dredging is that the horizontal transport takes place in the water column, by the combined forces of a pressure difference in the water and gravitational forces.
This method eliminates the need for the traditional dredging methods of excavating and then transporting dredged material by hoppers or barges. Dredging becomes then a matter of initiating a density current.
After trials in the Netherlands confirmed that Van Weezenbeek’s theory worked, and indeed that the production levels were similar to those of a small trailing suction hopper dredger, construction was begun on a prototype Water Injection Dredger (WID) and by 1987 the first WID vessel Jetsed was operational.
Press Release, March 5, 2013