This contract took us to the heart of Suffolk, to aid with the construction of a new Tidal Barrier Gate for the River Orwell, to reduce the risk and impact of flooding to the coastal town of Ipswich.
Ipswich, located at the mouth of the River Orwell, has long been affected by flooding from both high river flows and tidal surges. The Environment Agency determined that the best way to prevent these surges and control the flow of the river, and to minimise the impact of any flooding was the construction of a new 20m wide tidal barrier gate across the mouth of the river.
In order to facilitate this it was necessary to undertake to install 12 deepwells to a depth of 20m around the perimeter of the cofferdam, installed inside the pans of the sheet piles. The deepwell system was complemented with monitoring wells installed to 20m depth within the cofferdam, and monitoring wells to 14m depth external to the cofferdam, allowing us to accurately monitor the groundwater levels both within and external to the cofferdam. All wells were installed in river sand and gravel deposits. The installation process was particularly challenging due to access constraints, and therefore it was necessary to undertake a trial well installation using an innovative ‘Lost Bit’ technique which prevented the well from filling up with material, prior to the main installation works.
The deepwell system was pumped successfully over a period of approximately 10 months, inline with the client’s programme. Discharge flow rates between 65 l/s and 90 l/s were recorded, with discharge going straight back in to the River Orwell. Once the works had progressed and the discharge flow rates had reduced it became necessary to down-grade the pumps on site. This posed a logistical challenge as the excavation had already progressed significantly below the installation level of the wells, and they had to be accessed from the handrail level of the cofferdam. Working with Volker, our skilled and experienced operatives and using our unique pump riser system, we were able to minimise the amount of time the crane was utilised for the pump exchange.
Upon completion of the excavation work, pumping was no longer required, and it was necessary for the wells to be decommissioned. This again posed a logistical challenge, as the pumps again had to be removed from the existing cofferdam handrail level, additionally, it was necessary for a phased removal of the pumps and pumping equipment over the space of approximately 1 month, in order to minimise disruption to the construction works – WJ’s famous flexibility and ability to respond at short notice ensured that other work was not affected.
- LOCATION: Ipswich
- CLIENT: Environment Agency
- MAIN CONTRACTOR: VBA (VolkerStevin, Boskalis Westminster & Atkins).
Read more about the project here