Weir

An overflow structure built across an open channel to raise the upstream water level and/or to measure the flow of water. A measuring or gaging weir is calibrated for depth of flow over the crest. A weir generally consists of a rectangular, trapezoidal, triangular, or other shaped notch, located in a vertical, thin plate over which water flows. The height of water above the weir crest is used to determine the rate of flow. See Cipolletti weir, rectangular weir, and v-notch weir. Other types of weirs include broad-crested weir, sharp-crested weir, drowned weir or submerged weir. See contracted weir and suppressed weir.

1. A low dam or wall built across a stream to raise the upstream water level, termed fixed-crest weir when uncontrolled. 2. A structure built across a stream or channel for the purpose of measuring flow, sometimes called a measuring weir or gauging weir. Types of weirs include broad-crested, sharp-crested, drowned, and submerged.

(a) A low dam built across a stream to raise the upstream water level (fixed-crest weir when uncontrolled); (b) A structure built across a stream or channel for the purpose of measuring flow (measuring or gaging weir); (c) A structure built into a levee or river bank that allows water to flow from the main river channel into a bypass channel during time of high flows.

In hydrologic terms,

(a) A low dam built across a stream to raise the upstream water level (fixed-crest weir when uncontrolled);

(b) A structure built across a stream or channel for the purpose of measuring flow (measuring or gaging weir).