The construction method chosen by Tarmac was to divert the River Tees around the barrage site to allow the barrage to be built "in the dry" and avoid the need for providing time consuming and expensive cofferdams and jetties in the existing river. To prevent uplift of the dry river bed, deep pressure relief wells were required which needed to be fully functional until the barrage was built and the site flooded. The wells were installed and maintained by WJ Groundwater Limited under a subcontract with Tarmac.