Boston Barrier
In 2013, a major flood on the east coast of England flooded 800 Boston households. The government has set up a program to protect the coastline. One of these projects is the Boston Barrier, a £ 100 million project for Boston town and the Lincolnshire hinterland.
Following our Ipswich Tidal Barrier project, the local government, Enviroment Agency, awarded the contract for the Boston Barrier to the Joint Venture of BAM Nuttall and Mott Mac Donald with again Hollandia Infra as subcontractor, this time under BAM Nuttall. The project includes earthwork, dredging, quay work and the realization of 2 flood defences for Hollandia Infra.
Large tidal differences due to open connection with the North Sea
The city of Boston (UK) is located on the river The Haven with a direct open connection to the North Sea. This river is the entrance to Boston Harbor. The open connection ensures that the river adapts to the large tidal range, which hinders availability for shipping. Boston and the hinterland (Lincolnshire region) also suffers from flooding at extreme water levels. As was the case in 2013 when more than 800 households in Boston were flooded. The new storm surge barrier will protect Boston and the Lincolnshire hinterland from future storm surge flooding.
The Boston Barrier will consist of 2 flood defence barriers.
One barrier, the “Barrier”, a “Rising Sector Gate (RSG)” (see image above) shuts off the river at extreme water levels. This RSG, also called segment door, is part of phase 1 of the project. After completion of the RSG, the realization of the “Wet Dock Gates”, two “Vertical Sector Gates (VSG)”, will start. These VSG doors come in front of the entrance to the port to protect it during high water and to regulate the indoor water level in the port.
Two gates: Rising Sector Gate and 2 Vertical Segment Gates
A “Rising Sector Gate” will be built in the estuary, a flood defence in the form of a segment door that normally lies on the river bed and will only be turned upwards in a storm to close off the river. In addition, the entrance to Boston Harbor will also be protected against flooding by 2 “Vertical Sector Gates”. These turning devices together close off the passage, retaining water in 2 directions. This is because they also have to ensure every day that the ships in the port do not run dry at low tide.
Design
In the Ipswich project, the main design of the RSG was provided by the client. But within this project, Hollandia Infra has proven its Knowledge & Skills, which contributed to Hollandia Infra being fully responsible for the design for the Boston project. In addition, Hollandia Infra has made some noteworthy adjustments compared to the intended design. Changes that were received with skepticism, but were ultimately implemented with enthusiasm.
How does the Rising Sector Gate work?
The Rising Sector Gate, or the segment door, is a single retaining defence, a closed construction with a convex side towards the high water. The door is 29 meters wide and weighs 330 tons. By means of 2 arms the door turns up and down between 2 pivot points in the quay walls. Air chambers in the construction help the hydraulic cylinders of the door drive, by means of the upward force, to turn the door above water. The ballast chambers in the construction are filled with 400m3 mains water and help the cylinders to turn the door underwater.
The Vertical Sector Gates are two quarter-round retaining structures, open frame structures with a closed retaining wall. When closing the doors, the doors rotate horizontally around the vertical pivot points on the quay wall and the two radial shapes touch each other in the middle of the passage. When the doors open, they turn into niches in the concrete quay walls.
The fully symmetrical shape of the doors ensures that all resulting forces from the water forces pass through the pivot point and no resulting rotational force remains. These segment doors therefore do not move under the influence of water pressure.
Time-line
This construction was driven by a SPMT-wagons onto a pontoon from the Hollandia yard and sailed to England. Construction on the SPMTs will ride on a temporary platform at a height of 10 meters in the excavation pit and be mounted in the pivots after jacking. On November 1, 2019, the Rising Sector Gate was loaded onto a pontoon from the Hollandia yard and sailed directly to Boston, after which we immediately started the assembly.
The tests with this door were successfully carried out in the spring. In April the construction pits will be demolished and we can start with the fabrication of the 2 Vertical Sector Gates (the VSGs). These VSGs will be assembled in the summer of 2021 and will be lifted, in full assembly, by a hydraulic crane on the sea pontoon in the pivots.
This construction was driven by a SPMT-wagons onto a pontoon from the Hollandia yard and sailed to England. Construction on the SPMTs will ride on a temporary platform at a height of 10 meters in the excavation pit and be mounted in the pivots after jacking. On November 1, 2019, the Rising Sector Gate was loaded onto a pontoon from the Hollandia yard and sailed directly to Boston, after which we immediately started the assembly.
Links:
BAM Nuttall Case Study Boston Barrier
Lincolnshire County Council
Photo’s in slider: Danny Cornelissen, Port Pictures