The correct answer is All the aboveExplanation:Orifices: Orifice is a small opening of any cross section (rectangular, circular, or triangular etc) on the side or bottom of the tank. Notches:A notch is a device used for measuring rate of flow of liquid through a small channel or tank. It can be defined as an opening in the side of a tank or a small channel in such a way that the liquid surface in the tank or channel is below the top edge of the opening. Notch is generally made up of metallic plate. Weirs:A concrete or masonry structure, placed in an open channel over which the flow occurs. Weir is normally made up of Concrete or masonry structure. Parshall flume:Parshall flumes are devices for the measurement of flow of water in open channels when depth of flow is less i. e. , head drop is very small, the volume of flow is less and channel bed slope is less. The flume consists a converging section with a level floor and walls converges towards the throat section, a throat section with a downward sloping floor and parallel walls, and a diverging section with an upward sloping floor and diverging walls towards the outlet. The size of flume is determined by the width of its throat. Meter gates:Meter gates have been used for controlling and measuring irrigation flowThese gates are basically modified, submerged, variable area orifices (slide gates) at the upstream end of a length of smooth or corrugated pip.