The H flume is a class of flumes developed by the Soil Conservation Service (USDA) to measure runoff from catchments and experimental plots. 

Really more of combination between a flume and a weir, the H flume provides excellent low flow handling, solids passage, and a wide turndown ratio.

H Flume Flow Equations

The flow equations, however, can be troublesome to work with as the flow is governed by three separate flow regimes:  low, transitional, and main.  For typical applications, the need to transition from one equation to another as the level in the flume rises and falls becomes needlessly cumbersome.

To simplify flow calculations, Bos developed a single, standard, best-fit equation for the data:

Bos’ equation requires only three dimensionless constants for each flume size and the level at the point of measurement. The equation is useful over the full range of flows.

For a further discussion of H flume flow equations, visit the H Flume Flow Characteristics portion of this site.

H Flume Flow Tables

Instead of using flow equations, it is often easier for the operator in the field to use  flow tables.

When using H flume flow tables it is important to remember that the tables are calculated to the TOP OF THE FLUME.  Unlike other flumes, there is no freeboard or reserve head height in the H flume flow tables. 

In practice, a freeboard of 1/6 of the flume’s depth is recommended in the event that waves, turbulence, or undercalculation of the maximum flows occur.  Without this buffer, the flow could overtop the flume.