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Old English wer "dam, fence, enclosure," especially one for catching fish (related to werian "dam up"), from Proto-Germanic *warjanan (cf. Old Norse ver, Old Frisian and Middle Dutch were, Dutch weer, Old High German wari, German Wehr "defense, protection," Gothic warjan "to defend, protect"), from PIE *wer- "to cover, shut" (cf. Sanskrit vatah "enclosure," vrnoti "covers, wraps, shuts;" Lithuanian uzveriu "to shut, to close;" Old Persian *pari-varaka "protective;" Latin (op)erire "to cover;" Old Church Slavonic vora "sealed, closed," vreti "shut;" Old Irish feronn "field," properly "enclosed land").
any control or barrier placed in an open channel to permit measurement of water discharge. The latter may be computed from a formula expressing the discharge in terms of crest length of the weir, depth of flow above the weir, weir geometry, and other factors. A variety of weirs have been used in streams, the so-called sharp-crested and trapezoidal forms being relatively common; but broad-crested, triangular, and contracted weirs are also favoured in certain circumstances. Spillways, controls, and embankments designed to permit discharge measurements are simply different kinds of broad-crested weirs