Flow measurement

Flumes and weirs can have any shape or size. Two examples are:

Water management improvements can promote conservation and make best use of scarce water resources, but better management depends upon the ability to accurately measure and control the flow of water at important points in a river basin or irrigation system, such as head-works, canal bifurcations, off-take structures, and drainage collection points. Good water measurement systems enable accurate accounting of water use, and permit the available water to be supplied at optimum rates to the areas where it is intended to be used. To serve this need, the structures described in this manual play a key role. Their advantages are:

This broad-crested weir was retrofitted to measure the flow rate in the Lost River, Idaho. The WinFlume software can design and calibrate any size broad-crested weir (or long-throated flume) in any size natural channel or constructed canal.

The portable RBC-flume (Replogle-Bos-Clemmens) is often used to measure flow in small earthen channels. Construction drawings are available in the manual. Also. commercial firms offer several sizes of flumes. e.g. Royal Eijkelkamp offers stainless steel flumes up to 145 l/s.

  • A rating table can be calculated with an error of less than 2% of the listed discharge. The calculation can be made for any combination of prismatic throat and arbi­trarily shaped approach channel.
  • The required head loss over the weir or flume is minimal. This head-loss requirement can be estimated for any of these structures placed in an arbitrary channel.
  • Provided that the throat is horizontal in the direction of flow, a rating table can be computed using post-construction dimensions.  Thus, an accurate rating table can be produced even if the flume is not constructed to the designed dimensions.  The throat may also be re­shaped as needed according to changing site conditions, and a new rating table can be computed using the modified dimensions.
  • Under similar hydraulic and other boundary conditions, these are usually the most economical of all struc­tures for accurately measuring open channel flows, provided that conditions are such that a weir or flume is feasible.

The WinFlume 3.0 software can be downloaded from the USBR web site. The current version of the manual is:

Clemmens A.J., Wahl, T.L., M.G.Bos and J.A. Replogle 2001. Water measurement with Flumes and Weirs, Publication 58, International Institute for Land Reclamation and Improvement, Wageningen, pp. 382. Re-published in 2010, by Water Resources Publications LLC, Denver, USA.

A Chinese version of this manual will be published towards the end of 2020. Upon availability, a link will be given to the publisher.