Not in use anymore but still alive.
Close to the airfield of Reinheim is this weir. It is probably related to the Reinheimer Teich, but it's function is unclear. The "Teich", kind of small lake, is North of this weir and the direction of the water is towards the Teich. So what was this weir stopping the water to flow into the Teich for? The land South of the weir was wet enough. Weird.
Another funny thing is the word weir. It sounds almost like the German Wehr, same meaning, and both words are so different than the Dutch word "stuw", also meaning the same. Although German and Dutch are usually closer to each other than German and English. Both are close to the Dutch "weer".
The Dutch "stuw" is related to the German "Stau", and the English "stow".
Superfluous knowledge. But I like words. Εν ἀρχῇ ἦν ὁ λόγος.