Repair work underway on De Blauwe Dromer

The repair work is being carried out for the provincial authority of Flevoland by contractor Van den Herik. Deltares, a research institute for water, subsurface and infrastructure, is the technical consultant for the project.

The provincial authority of Flevoland closed De Blauwe Dromer in October 2012 because of the risk of the lock subsiding. The problem is groundwater seeping upwards under the lock. This phenomenon can happen anywhere but it can be a threat in the vicinity of a lock because the water can wash away sand, making the lock unstable. The situation near the lock is highly complex and so the provincial authority called in Deltares last year to provide specialist advice.

Deltares recommended three measures. The first includes using a technique known as ‘biosealing’ to stop the flow of deep groundwater upwards through the clay layer. Biosealing is an advanced technique developed by Deltares involving the injection of special bacteria that seal off the hole in the clay layer. Second, Deltares recommended the injection of grout below the concrete bottom to repair the foundations that have been undermined. It also recommended ballasting the ground in the polder by positioning extremely heavy concrete blocks on permeable sheeting, in order to prevent sand being washed away. To ensure that the work can be done safely, a temporary dam is being installed in the Hoge Dwarsvaart canal. The work will be completed later this year.