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H Flume Design

As a group, H flumes are broken into three distinct classes:

HS: low flows

(0.00016 to 0.803 cfs)

H:  medium flows

(0.004 to 84.0 cfs)

HL:  high flows

(0.005 to 116 cfs)

 

While similar in layout, the flumes are only dimensionally similar to other flumes in their class.  

For a given height (D = flume depth):  

  • HS flumes are the narrowest (1.05D) and average length (1.5 D)
  • H flumes average in width (1.90 D) and short length (1.35 D)
  • HL flumes the widest (3.20 D) and average length (1.5 D)

The v-shaped discharge of the H flume means that is has little resistance to downstream submergence.  As a result, H flumes have very small submergence ratios (HS / H 25%, HL 30%) and should always be designed for free-spilling discharge.  Should an H flume become submerged, a complex equation must be used to correct the indicated flow rate.

One drawback of the H flume design is its relatively short length – with the primary point of measurement (Ha) close to the inlet of the flume.  For applications where the flow approaching a H flume needs additional conditioning before it reaches the flume or where the flume is being adapted to measure piped flow, long, rectangular approach sections have been developed.

Approach sections are usually 3 to 5 times the maximum anticipated head (Hmax) in length.  As a default, Hmax is usually assumed to be the flume’s depth.  

For example:  a 1.0-foot H flume would have an approach 3 to 5-feet long (3-5D).

Note that when using H flumes with approach sections on flow streams is a high solids content (or larger solids), sedimentation may occur in the approach section. Here, sloped floors have been used to direct the flow to one side of the flume, with minimal change in flow accuracy.

Also, unlike the flume itself, strict dimensional accuracy in construction the approach section is not required so long as the flow is fully directed into the flume.

H Flume Dimensions

The dimensions for the HS / H / HL flumes are presented in two primary publications:

While the dimensions for approach sections was presented in:

HS / H / HL FLUME MASTER DIMENSIONS