I spent a half year in Blijdorp Zoo in Rotterdam accumulating cash to pay for graduate school. I have many happy memories, despite having a near-death experience in the workplace. I was hired a bit like a filler-in for a maternity leave except that the baby was the Werelds Grootste Aquarium Tentoonstelling - a huge new exhibition of tropical fish. The extra work was deemed to require an extra worker - me; who would do the grunt work while the permanent staff built aquariums. The centre-piece was the 30-meter-bak: a U-shaped aquarium for tropical-reef fish. It was a big engineering feat because 30m of glass enclosed 40 tonnes of water and required a substantial steel frame to raise the aquarium to eye-level. We needed to construct a reef: partly to provide some nooks and crannies for the fish and partly to save the punters from having to look through the water at other visitors on the far side of the aquarium. Someone had the bright idea of carving a rough template in 1m x 0.5m blocks of expanded polystyrene, plastering the slabs with concrete and covering them in coral-pink, green, beige and brown camouflage paint. The result looked convincing but when the tank was filled, the reef peeled off the floor in sections, turned turtle and bobbed to the surface. The density of polystyrene is much less than water: a 3cm thick coat of sand-and-cement isn't enough to compensate. The fall-back was to build the reef-wall from lumps of dull red lava, of which we had a heap from an earlier project. That worked out okay.
There were mishaps. One evening, one of the electricians dropped a hammer onto the floor of the tank cracking one of the 2cm-thick panes of glass. That had to be patched with a specially cut insert. It was a joy to watch the Surinamese-Dutch glazier confidently scoring the thick glass with his diamond cutter, tapping the the opposite side and then deftly cracking the glass along each line of the template. It fitted snugly into its silicon-glop mortar. One afternoon, two waitrons from the restaurant at the end of the exhibition hall were pushing a trolley laden with dirty plates across the building when they disappeared into the ground with a loud crash. Rotterdam is built on sand - formerly the sea-bed - which makes digging trenches for utilities particularly easy. But sand has very little cohesion and will wash away quickly in running water. It seemed that one of the many pipes that serviced the aquariums had developed a leak underground and this had eaten away the sand supporting the paving-flags of the floor. The concentrated weight of two people and 200 plates was too much for the residual structure and >!KARASH!<
As in all the countries bordering the North Sea, and elsewhere, the erosion of land by water is an occupational hazard in the Netherlands and they have a word for it - waterwolf. Waterwolf has been central to the development of the Zuiderzee which was a freshwater lake called Flevo Lacus in Roman times. The land was mostly peat from accumulations of sphagnum moss in the marshy margins of the lake and its rivers. The peat has some stickiness and supports a certain amount of plant life whose roots hold things together. But the peat overlies million-year-old sand. When the people turned from fishing and wild-fowling to trading and banking, the growing population's demand for peat for fuel rapidly outstripped supply and the edges of the lake fell into the water whenever there was a large spill of rain. Dramatic floods in 1282, 1287, 1362, 1421 extended the lake until the dunes separating it from the fury of the North Sea were beaten into submission and the Lake became a shallow bay full of salt-water. The Dutch have spend some billions of Euros over the succeeding years, especially in the 20thC, to reclaim the sea-bed for agriculture and dwellings. They will be severely pissed off with the rest of us when the sea levels overtop their dykes.