Instead of putting in a vertical obstruction, as with a weir, a flume consists of a constriction in the channel width. This constriction causesthe water level to change, and that water level in the constriction can be correlated with flow rate. The diagram at the right shows a top view of a venturi flume and a top view and side view of a Parshall Flume. A venturi flume has no bumps or dips in the floor of the channel. The Parshall Flume has the specific shape shown for its floor. The Parshall Flume has very specific dimensions for any channel width. There are equations and tables available, giving flow rate through the flume as a function of head (water height) above the bottom of the flume at a specific location. Parshall Flumes are widely used to measure wastewater flow rates in wastewater treatment plants. See the article, The Parshall Flume for Open Channel Flow Measurement for more detailed information about the Parshall flume.