Sunday, December 20, 2009

Locking through from the North Sea

When David Kokernot's ancestors on his mother's side arrived in Amsterdam from Hamburg in 1710 they probably entered the city through this lock. Passage from Hamburg via the North Sea could be accomplished in a small vessel because the route was protected by barrier islands. From the North Sea they entered and crossed the Zuiderzee, then the Oudezijds Voorburgwal canal by way of this lock. The lock chamber is about 150 yards long and about fifteen feet wide. The Amsterdam side is shown here. The other end of the chamber connects, ultimately, to the North Sea. I had to ponder the operation of those gates before I understood their operation, for they never opened or closed during the week I was there.

The unique feature of this lock, or any in Amsterdam, is it can lift or lower a vessel, coming or going. Most locks only operate with one side higher than the other. Take the Ballard Locks in Seattle, which lower vessels from Lake Union to Puget Sound or raise them going the other direction. Puget Sound is always lower than Lake Union, even at high tide. Mitered lock gates hold back the waters of Lake Union like this: Puget Sound>....lock chamber.....>Lake Union, where > represents a pair of swinging lock gates. The higher water to the right of the gates holds them shut. Only when water is allowed to fill the chamber through another passageway can the gates swing open.

In Amsterdam, however, the canals could be either above or below the Zuiderzee side, depending on the tides. Therefore, two sets of lock gates, swinging in opposite directions, are required. High water on the right side requires this configuration: >. Low water on the right requires this: <. You can see one side of the gates in the photo here, recessed into the chamber wall. Each is hinged to swing in the opposite direction from the other.

In the early twentieth century a dike was placed across the Zuiderzee, isolating it from the North Sea. It was filled with fresh water from the Amstel, was renamed the IJsselmeer, and sees no tidal swings. The water level is equalized on each side of this lock and the gates are simply kept open.