One advantage that the Cutthroat Flume has always had over other short-throated flume like the Parshall or Trapezoidal was the ability to develop intermediate width flumes for one of the four standard lengths.
But what if the standard lengths don’t yield a Cutthroat flume that fits the application? The answer: a custom Cutthroat flume!
A set of “unified discharge” calibrations were developed by Skogerboe for Cutthroat flumes so that it is not necessary to select one of the 24 standard sizes.
So long as the custom Cutthroat flume conforms to the standard layout, a custom flume can be developed:
- Flat floor
- “No length” throat
- Inlet contraction ratio of 3:1
- Outlet contraction ratio of 6:1
- 0.1 < W/L < 0.4, W = width, L = length
- Length is between 18-inches [45.72 cm] and 108-inches [274.3 cm]
Merkley presents five equations derived from regression analysis performed on Skogerboe's graphic results; the result of which is that both free-flow and submerged flow can be determined for custom Cutthroat flumes conforming to the above.
Free-Flow Equation for Custom Cuthroat Flumes
Submerged-Flow Equation for Custom Cuthroat Flumes
When compared to the parameters of the 24 standard Cutthroat flume sizes, the above equations have a maximum difference of less than 2%.