Analyzing the boundary conditions of the innovative technique of agitation dredging, the Tiamat

Abstract

Sedimentation is a common issue in navigating through channels, berths and anchorages of many ports and harbors. In order to address this issue, maintenance dredging can be done in three different ways; relocating of the sediments, keeping the sediments in place, or dredging with nature and using the natural currents to remove sediment. Trailing Suction Hopper Dredging (TSHD) is currently the preferred method for dredging and relocating sediment, however, this method is both costly and time-consuming. As a result, more nature-based solutions are becoming attractive, like the Water Injection Dredger (WID). The Underwater Plough (UWP) is another commonly used method usually for dealing with irregularities in the seabed. Harwich Haven Authority has recently developed a new dredging technique called the Tiamat, this is a new agitation dredging method and a potential environmentally friendly solution. The Tiamat employs a water injection technique to dredge sediment from the seabed. The system injects water into the seabed to fluidize the sediments and then uses a suction pump to bring the sediment plume higher in the water column, such that it can be carried away by the natural currents.

To ascertain the boundary conditions for the Tiamat, tests were conducted at three locations in the Port of Rotterdam, each with different sediment classifications (cohesive and non-cohesive), current strengths (high and low), and depths. Because the Tiamat was developed by the Harwich Haven Authority, it was expected that the Tiamat would perform optimally in areas with strong currents and cohesive sediment at moderate depths. In order to evaluate the performance of the Tiamat, two other dredging techniques - WID and UWP - were tested alongside the Tiamat in these areas.

The results of the pilots and monitoring indicated that the boundary conditions for the Tiamat are primarily influenced by the depth, currents, and sediment characteristics. The depth is limited by the length of the discharge pipe. The Tiamat has the highest production rate in cohesive sediments, as production rates tend to be lower in coarser sand sediments due to their higher tendency to settle. For non-cohesive sediments, a highly energetic river with strong currents is necessary to achieve a certain sediment transport distance.

In order to estimate the performance of the Tiamat, the dredging technique is compared with the WID and UWP. Different parameters such as turbidity, sediment transport, development of the top sediment layer, depth limitations, the production rate in different grain sizes, fuel consumption and costs are compared and discussed.