Skip to main content

Cutthroat Flume Settling

One requirement for a Cutthroat flume to accurately measure flow is that the converging floor be set level from front-to-back and from side-to-side. However, because of the material weight, the unreinforced nature of natural channels, long-term consolidation of the foundation soils, and general installation errors, the flume may be installed off level or may experience settlement over time.  When this happens, the standard flow equations will no longer accuracy indicate the true flow rate of the flume.

Investigations by Colorado State University have resulted in the development of a generalized correction for Cutthroat flumes that have experienced settling.

The true or measured discharge (Qm) may be determined by: 

general Cutthroat flume settlement equation

Where (with level measurements taken on the LEFT side of the flume looking downstream):

correcting for Cutthroat flume throat width by length

Cutthroat Settling Defined

A negative lateral (crest) slope is when the RIGHT side of the flume, looking downstream, is lower than the flume-floor centerline.  A positive lateral slope is where the LEFT side is lower than the flume-floor centerline.

cutthroat flume lateral settlement diagram

A negative longitudinal slope is where the flume entrance is LOWER than the exit of the flume.  A positive longitudinal slope is where the flume entrance is HIGHER than the exit of the flume.

Terms and Coefficients

terms used to determine corrections for Cutthroat flume settling

terms used to determine Cutthroat flume settling

These corrections were determined to be applicable for:

  • Cutthroat flumes from 18" L x 8" W to 108" L x 24" W in size (although researches state their belief that the procedure should be applicable to a wide range of Rectangular Cutthroat flumes)
  • Lateral slopes of -6% to 4%
  • Longitudinal slopes of -6% to 4%

 


Sources:  Revising the Cutthroat Flume Settlement Rating Adjustment Procedure, Rating Adjustment for Settlement of Cutthroat Flumes