Cutthroat flume
The Cutthroat flume is a class of flow measurement flume developed during 1966/1967 that is used to measure the flow of surface waters, sewage flows, and industrial discharges. Like other flumes, the Cutthroat flume is a fixed hydraulic structure. Using vertical sidewalls throughout, the flume accelerates flow through a contraction of sidewalls until the flow reaches the "throat" of the flume, where the flow is then expanded. Unlike the Parshall flume, the Cutthroat flume lacks a parallel-walled throat section and maintains a flat floor throughout the flume. The design of the Cutthroat flume is standardized but not  covered by a national or international standard (unlike the Parshall flume). The flumes are not patented and the discharge tables are not copyright protected. A total of 16 standard sizes of Cutthroat flumes have been developed, covering flow ranges from 0.3536 gpm [0.0223 L/s] to 54,801 gpm [3,458 L/s]. Free-flow equation. Under free-flow conditions the depth of water at specified location upstream of the flume throat can be converted to a rate of flow. The free-flow discharge can be summarized as Where Both “K” and “n” vary by flume length alone. Table 1 Submergence. Submergence  transitions for Cutthroat flumes varies by flume length: The submergence transition values for Cutthroat flumes are generally better than those for similarly sized Parshall flumes – an advantage in flat gradient channels where downstream hydraulics may increase the submergence ratio in the flume. Unlike the Parshall flume, the secondary point of measurement, Hb, in the Cutthroat flume is located away from the throat section, making the determination of the level relatively easy. Development. The Cutthroat flume was developed during the 1966-67s at the Utah Water Research Laboratory, Utah State, Logan, Utah by Skogerboe, Hyatt, Anderson, and Eggleston. The result of  these efforts was a flume that is simple in form and construction and that is well suited for use in flat gradient (low slope) applications. Design. Cutthroat flumes lack a parallel-wall throat section (hence the name) and has a flat-bottom to allow for installation in flat gradient channels. From the top, the Cutthroat flume has an hourglass look similar to the Parshall flume, with which it is sometimes confused. The walls of a Cutthroat flume are vertical, like Parshall and HS / H / HL flumes. The approach section walls contract uniformly at a 3:1 ratio, while the discharge section  walls expand at a 6:1 ratio. The point at with the approach and discharge section walls meet is termed the “throat” of the Cutthroat flume. The primary point of measurement, Ha, occurs at a point upstream of the flume throat and can be determined by the equation Where "L" is flume length. The secondary point of measurement, Hb, occurs at a point downstream of the flume throat and can be determined by the equation Where "L" is flume length. Standard sizes. Four standard lengths of the Cutthroat flume have been developed, with four throat widths for each length. Below are  the standard flume lengths with their respective standard throat widths. For a given length, Cutthroat flumes of intermediate throat widths can be developed without the need for laboratory testing. Where Installation. As with the Parshall flume, the initial applications for Cutthroat flumes were envisioned to be measuring flows in irrigation channels and other surface waters. Again, like the Parshall flume, the Cutthroat flume has proven to be applicable to a range of open channel flows including: