Planning
The plans called for closing the Waal River near Nijmegen (Ooypolder) and the Neder Rhine (Lower Rhine) near Arnhem (Meinerswijk) using floating dams (caissons) placed across a river and then sunk in the riverbed on previously constructed sills. When the dams were in place and the gates closed, water would be forced into the IJssel River. A similar dam was later added at Olst, as well, to ensure sufficient water was available to inundate the land behind the dikes during dry periods. At various locations, including Olst, on the Haere Estate, water intake works were built into the dikes. In time of war, the gates could be opened to let water flow in more quickly over the land and settlements inside the dikes, resulting in a wide swath of water extending from Nijmegen to Kampen. The plans for Olst were completed during the first half of 1953, assigned top secret security, and were identified as “Emergency Pontoon Bridge Plan Deventer,” to conceal the true purpose of construction activity. To defend the installations at Olst, more than 60 bunkers and gun emplacements (pillboxes) were built in the IJssel dikes and elsewhere at elevated locations. Also, Sherman tanks left over from World War II were encased in concrete underground, with only the turret above ground, as additional defensive elements.
The plans called for closing the Waal River near Nijmegen (Ooypolder) and the Neder Rhine (Lower Rhine) near Arnhem (Meinerswijk) using floating dams (caissons) placed across a river and then sunk in the riverbed on previously constructed sills. When the dams were in place and the gates closed, water would be forced into the IJssel River. A similar dam was later added at Olst, as well, to ensure sufficient water was available to inundate the land behind the dikes during dry periods. At various locations, including Olst, on the Haere Estate, water intake works were built into the dikes. In time of war, the gates could be opened to let water flow in more quickly over the land and settlements inside the dikes, resulting in a wide swath of water extending from Nijmegen to Kampen. The plans for Olst were completed during the first half of 1953, assigned top secret security, and were identified as “Emergency Pontoon Bridge Plan Deventer,” to conceal the true purpose of construction activity. To defend the installations at Olst, more than 60 bunkers and gun emplacements (pillboxes) were built in the IJssel dikes and elsewhere at elevated locations. Also, Sherman tanks left over from World War II were encased in concrete underground, with only the turret above ground, as additional defensive elements.
Implementation
Once
the floating dams were completed, regular training
was conducted using winches and cables to move the
floating dams from storage in their harbor inlets.
The bunkers were manned only during times of crisis
and training. The inlet harbors were continuously
manned. The complete implementation of the IJssel
Line inundation would have taken about two weeks.