GC: n

CT: A structure, used to dam up a stream or river, over which the water flows, is called a weir. The conditions of flow, in the case of a weir, are practically the same as those of a rectangular notch. That is why, a notch is, sometimes, called as a weir and vice versa.
The only difference between a notch and a weir is that the notch of a small size and the weir is of a bigger one. Moreover, a notch is usually made in a plate, whereas a notch is made of masonry or concrete.

S: CODECOGS – http://www.codecogs.com/library/engineering/fluid_mechanics/weirs/index.php (last access: 30 December 2014)

N: 1. Old English wer “dam, fence, enclosure,” especially one for catching fish (related to werian “dam up”), from Proto-Germanic wer-jon-, from PIE wer- “to cover, shut”.
2. It is not used to store water but to retard flow and raise the upstream water level to permit diversions and perhaps to measure the rate of flow.

S: 1. OED – http://www.etymonline.com/index.php?allowed_in_frame=0&search=weir&searchmode=none (last access: 30 December 2014). 2. GDT.

SYN:
S:

CR: cofferdam, dam, flume, reservoir , water hammer.