ISO/TC 113/SC 2 - Flow measurement structures

This document specifies methods for the measurement of the flow of water in open channels under steady flow conditions using triangular profile weirs. The flow conditions considered are steady flows which are uniquely dependent on the upstream head and non-modular (drowned) flows which depend on downstream as well as upstream levels.

This document gives guidelines for selecting a particular type of flow measuring structure for measuring liquid flow in an open channel. It describes how the individual structures function in simple non-technical terms, and sets out the factors and parameters to take into account in order to make an informed decision on which type of structure to use. Values of the relevant parameters describing the limitations and uncertainty involved in the use of these structures are given in this document. More definitive details of a particular type of structure are given in the individual standards listed in Table 1, which cover each type of structure.

ISO 18481:2017 specifies a method for the estimation of the sub-critical flow of clear water in a smooth, essentially horizontal channel (or a gently sloping channel), abruptly discontinued at bottom by a hydraulic structure, with a vertical drop and discharging freely. Such an overfall forms a control section and offers a means for the estimation of flow using the end depth measurement method. A wide variety of channel cross-sections with overfall have been studied, but only those which have received general acceptance after adequate research and testing, and therefore do not require in situ calibration, are considered. This document covers channels with the following types of cross-sections: a) rectangular with confined and unconfined nappe; b) trapezoidal; c) triangular; d) circular; e) parabolic. The flow at the brink is curvilinear; therefore, the measured depth at the drop is not equal to the critical depth as computed by the principle based on assumption of parallel flow. However, the end depth and the critical depth (as in the case of the assumption of parallel flow) have unique relation, which is used to estimate the flow through these structures.

ISO 1438:2017 defines the requirements for the use of rectangular and triangular (V-notch) thin-plate weirs for the measurement of flow of clear water in open channels under free flow conditions. It includes the requirements for the use of full-width rectangular thin-plate weirs in submerged (drowned) flow conditions.

ISO/TR 19234:2016 specifies the requirements for the integration of baffles on the downstream face of triangular profile flow measurement structures to aid the passage of fish.

ISO 29606:2015 specifies requirements for the integration of fishpasses with flow measurement structures. It identifies those fishpasses which have satisfactory hydrometric calibration data and gives methods for computing combined flows and uncertainties. NOTE Flow measurement structures and fishpasses have inherently different hydraulic performance criteria. Flow measurement structures perform better with uniform flow patterns; conversely, fish passage performance is improved by the variability of the flow conditions that allow fish and other aquatic inhabitants to select the passage conditions that best meet their mode of movement. This International Standard does not suggest that the fishpasses discussed are the preferred methods of fish passage or that they are good enough that passage performance can be sacrificed to obtain a single structure that meets both the fish passage and flow measurement requirements.

ISO 4359:2013 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. The water level downstream of the structure is low enough to have no influence upon its performance. ISO 4359:2013 is applicable to three commonly used types of flumes, covering a wide range of applications, namely rectangular-throated, trapezoidal-throated and U-throated. 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.

ISO 4377:2012 describes the methods of measurement of flow in rivers and artificial channels under steady or slowly varying conditions using flat-V weirs

ISO 3846:2008 lays down requirements for the use of rectangular broad-crested weirs for the accurate measurement of flow of clear water in open channels under free flow conditions.

This International Standard specifies methods for the determination of discharge in open channels in steady flow conditions using vertical underflow gates on a flat horizontal floor between vertical side walls under modular or non-modular conditions.

This International Standard specifies the methods of measurement of flow in rivers and artificial channels, using any combination of standard weirs and/or flumes in a compound structure. For guidance on the selection of weirs and/or flumes, refer to ISO 8368. All structures can be operated in the modular flow range, but only a limited number of structures can be used in the drowned (non-modular) flow range (see clause 4). Compound weirs improve the quality of discharge measurements at low stages. The characteristics of velocity distribution are described annex A. Structures standardized for operation in the drowned (non-modular) flow range and the method of computation of flow are described in annex B. Methods and examples of flow measurement calculations are given in annex C. Compound flow-measuring structures without divide piers need in situ or model calibrations and are not covered by this International Standard.

This International Standard specifies a method of steady-flow measurement in open channels using a trapezoidal broad-crested weir under modular and non-modular conditions. Consideration is given to the use of the weir in both rectangular and trapezoidal channels. Limitations to the use of the weir are given in 7.6 and 8.6.

Specifies methods for the measurement of the flow of water in open channels under steady flow conditions. The flow conditions considered are free flow, which is dependent on the upstream head only, and drowned flow, which depends on both upstream and downstream water levels.

Specifies methods of liquid flow measurement in open channels (particularly in irrigation canals) under steady or slowly varying flow conditions. The flumes used are designed to operate under both free-flow and submergence conditions.

Deals with the measurement of flow in rivers and artificial channels. The flow conditions considered are limited to steady flows which are uniquely dependent on the upstream head. Drowned flows, which depend on downstream as well as upstream levels, are not covered. Cancels and replaces the first edition (ISO 4374 :1982), of which it constitutes a technical revision.

Specifies a method for the measurement of subcritical flow in small rivers and artificial channels using V-shaped broad-crested weirs. Covers also selection of site and installation conditions, measurement of head, discharge equations and errors in flow measurement and contains three annexes.

ISO 26906:2009 specifies requirements for the integration of fishpasses with flow measurement structures. It identifies those fishpasses which have satisfactory hydrometric calibration data and gives methods for computing combined flows and uncertainties. NOTE Measurement structures and fishpasses have inherently different hydraulic performance criteria. Water measurement structures perform better with uniform flow patterns; conversely, fish passage performance is improved by the variability of the flow conditions that allow fish and other aquatic inhabitants to select the passage conditions that best meet their mode of movement. ISO 26906:2009 does not suggest that the fishpasses discussed are the preferred methods of passage or that they are good enough that passage performance can be sacrificed to obtain a single structure that does both.

ISO 1438:2008 defines the requirements for the use of rectangular and triangular (V-notch) thin-plate weirs for the measurement of flow of clear water in open channels under free flow conditions. It includes the requirements for the use of full-width rectangular thin-plate weirs in submerged (drowned) flow conditions.

ISO 4360:2008 specifies methods for the measurement of the flow of water in open channels under steady flow conditions using triangular profile weirs. The flow conditions considered are steady flows which are uniquely dependent on the upstream head and drowned flows which depend on downstream as well as upstream levels.

ISO 4377:2002 describes the methods of measurement of flow in rivers and artificial channels under steady or slowly varying conditions using flat-V weirs. It also gives guidance on acceptable velocity distribution.

Deals with the measurement of flow in rivers and artificial channels using flat-V weirs under steady or slowly varying flow conditions. The standard flat-V weir is a control structure, the crest of which takes the form of a shallow "V" when viewed in the direction of flow.

Specifies the requirements for the use of the given appliances for the measurement of flow of clear water in open channels under free flow conditions. Cancels and replaces the first edition (ISO 3846 : 1977), of which it constitutes a technical revision.

Specifies methods for the measurement of the flow of water in open channels under steady flow conditions using triangular profile weirs. The flow conditions considered are steady flows which are uniquely dependent on the upstream head and drowned flows which depend on downstream as well as upstream levels.

Specifies a method for the estimation of subcritical flow of clear water in smooth, essentially horizontal, straight open channels with a vertical drop and discharging freely. Gentle positive slopes not greater than 1 in 2000 are admissible. Covers channels with the following types of cross-section, the nappe being confined: a) trapezoidal; b) triangular; c) parabolic; d) circular.

Deals with 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. An annex gives the guidelines for the selection of weirs and flumes for the measurement of the discharge of water in open channels.

Specifies methods for the measurement of water flow in open channels using rectangular and triangular-notch (V-notch) thin-plate weirs. The flow conditions considered are limited to steady, free and fully ventilated discharge. Recommended discharge coefficients are applicable to water only in the approximate range of temperatures from 5 to 30 °C.

Specifies a method for the estimation of sub-critical flow of clear water in smooth, straight, rectangular prismatic open channels with a vertical drop and discharging freely. Using the measured depth at the end, the flow in rectangular channels (horizontal or sloping) with confined nappe and unconfined nappe may be estimated.