Monday, June 04, 2007

The Delta Works and Zierikzee, Holland

I'll leave it to Case to explain the Delta Works. While I enjoyed the tour very much -- including the history leading up to this project -- I believe you will better appreciate this engineering marvel from an engineer's perspective.
From Case: The Delta Works is a huge dike project that protects the lowlands of south Holland from winter flooding. Massive movable "doors" between the roadway piers (see photo) regulate tidal flows into the estuaries, and river outflows from three of Europe's largest waterways (Rhine, Meuse, & Scheldt).

The project was initially planned for 1948, but was delayed due to budget. (In the years following WWII, Holland wasn't exactly flush with cash.) Then the winter storms of 1953 blew in, breaking previous tidal records, cresting then breaching the dikes, and flooding the south of Holland. Over 1800 people drowned, and 300,000 were displaced. Budget or not, the Dutch realized they had to move ahead with the project or risk repeated disasters.

This huge endeavor is now an integral episode in the story of how the Dutch wrested their land from the sea. On the tour, we didn't hear a word about which bureaucrat or engineer was "responsible" for the decisions that left Holland susceptible to those winter storms. I wonder what history will record about the aftermath of Hurricane Katrina in New Orleans. Endless finger-pointing? Or a more productive response?

The main structural element spanning the piers is the triangular concrete "beam" (seen in cross-section) to which the roadway and moveable barrier elements are anchored.

Here, our tour guide leads us through just one of the sub-triangles of a span.

It was fascinating to learn how the project was planned and carried out, and how it continues to this day. Initially, the inland "seas" it created were to be freshwater lakes. However, as the the first segment across the Haringvliet was completed, ecologists were just elucidating the consequences of such a move. Thus, only the Haringvliet was kept fresh, while the rest of the estuaries remain brackish and tidal. Next year, the barriers will be opened, and even Haringvliet will be returned to its "natural" state, in hopes of recovering the salmon run (among other things).
A single -- but very much larger -- barrier protects the shipping harbors of Rotterdam. The salinity in that area is now tightly controlled, saving shipping companies millions in costs for corrosion.
Not surprisingly, the Dutch hydraulic engineers in the 1950s & 60s were not planning for global warming. Few of Holland's dikes are high enough for the peak sea levels and river flows we may see in the future. Consequently, the engineers and accountants are back at work. According to a documentary we saw on TV, the new plan is to purposely breach selected dikes and flood the adjacent lowlands in high-water emergencies. This will relieve the risk to more critical locations. People with homes or property in the flooded lands will be reimbursed, realizing a net savings over the cost of revamping the national dike system. (I guess the accountants are winning...)
If you squint (as we did), you might spot many kites and windsurfers in the distance. (Brrr... I'll stick with more tropical climes and breezes when I try these activities.)

Iconic Dutch sailing ships enter the Zierikzee's old harbor via the iconic drawbridge. The Dutch fellow in the foreground is (obviously) not iconic.
These Dutch sailing vessels employed retractable "side-boards" instead of keels, enabling them to negotiate both the sea and Holland's shallower canals.

Over the centuries, these homes along Zierikzee's harbor have settled and now appear to be leaning on each other for support. In this picture, the white house leans forward, while the the brick one is falling backward. It is hard to capture with a camera, but to us the line of homes looked like a detachment of dozy sentries, falling asleep on each others' shoulders.

No comments: