ISO 5002:2013 pdf download.Flow measurement structures -Rectangular, trapezoidal and U-shaped flumes.
ISO 5002 specifies methods for the measurement of flow in rivers and artificial channels under steady or slowly varying flow conditions, using certain types of standing-wave, or critical-depth, flumes.
A wide variety of flumes has been developed, but only those which have received general acceptance after adequate research and field testing, and which therefore do not require in situ calibration, are considered.
The flow conditions considered are uniquely dependent on the upstream head, i.e. subcritical flow must exist upstream of the flume, after which the flow accelerates through the contraction and passes through its critical depth (see Figure 1). The water level downstream of the structure is low enough to have no influence upon its performance.
This International Standard is applicable to three commonly used types of flumes, covering a wide range of applications, namely rectangular-throated, trapezoidal-throated and U-throated. Typical field installations are shown in Figure 2. Site conditions are important and Figure 3 shows acceptable velocity profiles in the approach channel.
Detailed illustrations of the three types offlumes covered by this International Standard are given as follows:
a) rectangular-throated (see Figure 4)
b) trapezoidal-throated (see Figure 5)
c) U-throated, i.e. round-bottomed (see Figure 6).
It is not applicable to a form of flume referred to in the literature — sometimes called a “Venturi” flume
— in which the flow remains subcritical throughout.
NOTE This form is based on the same principle as a Venturi meter used within a closed conduit system and relies upon gauging the head at two locations and the application of Bernoulli’s energy equation.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 772, Hydrometry — Vocabulary and symbols
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 772 apply.
5.2 Because the flume design is based on critical flow, this International Standard is largely based on fundamental hydraulic theory, without the need for the large-scale volumetric testing that has been used to derive the coefficients for other forms of flow measurement structure. In order to obtain critical flow within the throat of the flume, the following conditions shall be satisfied.
a) The throat of the flume shall be long enough for the flow to be virtually parallel with the flume invert, so that hydrostatic pressure conditions occur at the control section.
b) The entrance to the flume throat shall be shaped so that there are virtually no energy losses between the point where the head is gauged and the point where critical flow occurs.
c) The flume throat shall constrict the channel severely enough to raise the energy level in the throat sufficiently high above the energy level downstream to ensure that the flume is “modular”.
5.3 Figure 2 shows examples of flow in rectangular-throated, trapezoidal-throated and U-throated flumes. The choice of flume type from these three depends upon several factors, such as the range of discharge to be measured, the accuracy required, the head available and whether or not the flow carries sediment that is liable to accrete. The graphs in Annex A give the user of this International Standard a means of quickly comparing the idealized performance of a range of flume designs, to aid a preliminary choice of the size and form of flume needed to deliver the required discharge capacity and stage—discharge relationship.ISO 5002 pdf download.