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a barrier across which a stream of water flows; in hydraulic engineering an overflow is called a spillway, with water flowing freely over its crest. In order to guide the flow, rectangular openings bounded on the sides by abutments or intermediate walls (piers) are made in the crest. A distinction is made among overflows with narrow or broad ramps and with an ogee section built to match the coordinates of a freely falling stream and having maximum carrying capacity. An ogee-section overflow can be of the vacuum type (if the pres-sure on the ramp beneath the stream is less than atmospheric pressure) or the nonvacuum type (if the pressure is greater than atmospheric pressure). Overflows used in laboratory and hydrometric work to measure water flow rate are called meter overflows.