荷兰新近建成造价近10亿马克的移动式防洪大坝。这座大坝从空中俯视很像是两座平放的埃菲尔铁塔,仰卧在莱茵河最后一段通航河段“尼文水道”的南北两岸。两条巨大的铁臂长250m,接近埃菲尔铁塔的高度,重量超过1.4万 t。其上端通过世界上最大的万向球(直径10m)固定在地面上,下端是两条弓形空心钢墙,长214m,厚15m。如果该市周围的水位 The Netherlands has recently built a mobile flood control dam at a cost of nearly 1 billion marks. The dam looks down from the sky like two Eiffel Towers placed flat on the north and south sides of the “Rhine Waterway”, the last navigable section of the Rhine. Two huge iron arm length 250m, close to the height of the Eiffel Tower, weighing over 14,000 t. Its upper end is fixed to the ground by the largest universal ball (diameter 10m) in the world. The lower end is made of two bow-shaped hollow steel walls with a length of 214m and a thickness of 15m. If the water level around the city