ISO/TC 113/SC 1 - Velocity area methods

This document specifies methods for determining the velocity and cross-sectional area of water flowing in open channels and for calculating the discharge employing point velocity measurement devices. It is applicable to methods using rotating-element current meters, acoustic doppler velocimeters (ADVs), acoustic doppler current profiler (ADCP) stationary method, surface velocity measurement including floats and other surface velocity systems. Although some general procedures are discussed, this document does not describe in detail how to use or deploy these systems. NOTE For detailed procedures, refer to guidelines from instrument manufacturers and the appropriate public agencies.

This document gives guidelines for the use of boat-mounted acoustic Doppler current profilers (ADCPs) for determining flow in open channels. It describes a number of methods of deploying ADCPs to determine flow. Although, in some cases, these measurements are intended to determine the stage-discharge relationship of a gauging station, this document deals only with single determination of discharge. ADCPs can be used to measure a variety of parameters, such as current or stream flow, water velocity fields, and channel bathymetry. As a potential application, an idea of bedload discharge can be obtained applying the bottom track velocity, while suspended sediment flow can be obtained applying the acoustic backscatter and the sonar equation. This document is generic in form and contains no operational details specific to particular ADCP makes and models.

This document specifies methods of determining the stage?discharge relationship for gauging stations. It specifies an accuracy for defining the stage?discharge relationship based on a sufficient number of discharge measurements, complete with corresponding stage measurements. This document considers stable and unstable channels and includes brief descriptions of the effects on the stage?discharge relationship of the transition from inbank to overbank flows, shifting controls, variable backwater and hysteresis. Methods of determining discharge for twin-gauge stations, ultrasonic velocity-measurement stations and other complex rating curves are not described in detail. NOTE These types of rating curves are described separately in other International Standards, Technical Specifications and Technical Reports, which are listed in the Bibliography.

This document specifies a method of determining discharge in open channels from observations of the surface slope and cross-sectional area of the channel. It is applicable to use under special conditions when direct measurement of discharge by typically more accurate methods, such as the velocity-area method, is not possible. Generally, the method can be used to determine discharge a) for a peak flow that left high-water marks along the stream banks, b) for a peak flow that left marks on a series of water-level gauges or where peak stages were recorded by that series of gauges, and c) for flow observed at the time of determining gauge heights from a series of gauges. The method is commonly used to undertake the extension of stage?discharge relationships above the highest gauged flows. It does not apply to determining discharges in tidal reaches.

ISO/TR 9210:2017 provides guidelines for discharge measurements in meandering and braided rivers, and from bridges, following the provisions of ISO 748.

ISO 9123:2017 specifies methods for determining stage-fall-discharge relationships for a stream reach where variable backwater occurs either intermittently or continuously. Two gauging stations, a base reference gauge and an auxiliary gauge are required for gauge height measurements. A number of discharge measurements are required in order to calibrate the rating to the accuracy required by this document. The preparation of rating curves is not described in detail in this document. NOTE For a more detailed description of preparing rating curves, see the methods described in ISO 1100‑2.

ISO 6416 describes the establishment and operation of an ultrasonic (transit-time) gauging station for the continuous measurement of discharge in a river, an open channel or a closed conduit. It also describes the basic principles on which the method is based, the operation and performance of associated instrumentation and procedures for commissioning. It is limited to the "transit time of ultrasonic pulses" technique, and is not applicable to systems that make use of the "Doppler shift" or "correlation" or "level-to-flow" techniques. ISO 6416 is not applicable to measurement in rivers with ice. NOTE ISO 6416 focuses on open channel flow measurement. IEC 60041 covers the use of the technique for full pipe flow measurement.

ISO 18365:2013 gives requirements for the establishment and operation of a gauging station for the measurement of stage, or stage and discharge, of a lake, reservoir, river or canal or other artificial open channel. It also describes how a gauging station utilising one of the measurement methods listed should be operated and maintained. Requirements are provided for stage only measurement stations, stage-discharge stations and direct-discharge measurement stations in natural channels, as well as for stage-discharge stations with artificial structures. Additionally, some requirements are given for measurements under difficult conditions, such as under ice conditions.

ISO 2425:2010 provides a summary of recommended methods for the determination of liquid flow in tidal channels, special consideration being given to those techniques that are either unique to or particularly appropriate for application under tidal conditions, including treatment of uncertainties. Reference is also made, where appropriate, to methods for the determination of flow in non-tidal channels, but attention is drawn to their limitations with respect to practicality and/or uncertainty. ISO 2425:2010 does not describe alternative methods, such as the use of weirs, flumes, dilution gauging, salt velocity and floats, although they might be suitable under certain conditions, especially where the effect of tides only impedes and does not stop or reverse the passage of stream flow. These methods are described in detail in other International Standards. ISO 2425:2010 specifies two types of technique: techniques for single measurements of tidal flow; techniques for continuous measurement of tidal flow. Annex A specifies the cubature method of measurement. Annex B specifies methods for the determination of flow under tidal conditions, and Annex C gives an example of the computation for a single vertical. Similar computations are possible for other verticals. Annex D describes the determination of tidal flow using an acoustic Doppler velocity meter.

ISO 15769:2010 provides guidelines on the principles of operation and the selection and use of Doppler-based and echo correlation velocity meters for continuous-flow gauging. ISO 15769:2010 is applicable to channel flow determination in open channels and partially filled pipes using one or more meters located at fixed points in the cross-section.

ISO/TR 9824:2007 provides a synopsis of the methods of flow gauging that can be deployed in closed conduits flowing part full, i.e. with a free open water surface. This Technical Report provides a brief description of each method with particular reference to other International Standards where appropriate, the attributes and limitations of each technique, possible levels of uncertainty in the flow determinations and specific equipment requirements. The uncertainties quoted herein are expanded uncertainties with a coverage factor of 2 and an approximate confidence level of 95 %.

This Technical Specification gives guidelines for the design, selection and use of electromagnetic current meters used to determine point velocity for the purpose of measuring flow in an open channel using the velocity area method. NOTE The electromagnetic current meter is acceptable as a device for making point determinations of velocity for the purposes of open channel flow determination by the velocity area method, using the multiple point velocity sampling technique described in ISO 748 (see reference [1] in the Bibliography).

This Technical Report deals with the use of boat-mounted acoustic Doppler current profilers (ADCPs) for determining flow in open channels without ice cover. It describes a number of methods of deploying ADCPs to determine flow. Although, in some cases, these measurements are intended to determine the stage-discharge relationship of a gauging station, this Technical Report deals only with single determination of discharge. The term ADCP has been adopted as a generic term for a technology that is manufactured by various companies worldwide. They are also called acoustic Doppler velocity profilers (ADVPs) or acoustic Doppler profilers (ADPs). ADCPs can be used to measure a variety of parameters, such as current or stream flow, water velocity fields, channel bathymetry and estimation of sediment concentration from acoustic backscatter. This Technical Report is generic in form and contains no operational details specific to particular ADCP makes and models. Accordingly, to use this document effectively, it is essential that users are familiar with the terminology and functions of their own ADCP equipment.

ISO 1100-2:2010 specifies methods of determining the stage-discharge relationship for a gauging station. A sufficient number of discharge measurements, complete with corresponding stage measurements, are required to define a stage-discharge relationship to the accuracy required by ISO 1100-2. Stable and unstable channels are considered, including brief descriptions of the effects on the stage-discharge relationship of shifting controls, variable backwater and hysteresis. Methods of determining discharge for twin-gauge stations, ultrasonic velocity-measurement stations, electromagnetic velocity-measurement stations and other complex rating curves are not described in detail. These types of rating curve are described separately in other International Standards, Technical Specifications and Technical Reports, which are listed in ISO 1100-2.

ISO 748:2007 specifies methods for determining the velocity and cross‑sectional area of water flowing in open channels without ice cover, and for computing the discharge therefrom. ISO 748:2007 covers methods of employing current‑meters or floats to measure the velocities. It deals only with single measurements of the discharge; the continuous recording of discharges over a period of time is covered in ISO 1100-1 and ISO 1100-2.

ISO 6416:2004 describes the establishment and operation of an ultrasonic (transit-time) gauging station for the continuous measurement of discharge in a river, an open channel or a closed conduit. It also describes the basic principles on which the method is based, the operation and performance of associated instrumentation and procedures for commissioning. It is limited to the transit time of ultrasonic pulses technique, and is not applicable to systems that make use of the Doppler shift or correlation orlevel-to-flow techniques. ISO 6416:2004 is not applicable to measurement in rivers with ice.

ISO 9213:2004 specifies procedures for the establishment and operation of a gauging station, equipped with an electromagnetic flow meter, in an open channel or a closed conduit with a free water surface. ISO 9213:2004 is applicable to configurations where an artificial magnetic field is generated through which the entire body of water flows. The induced voltage is sensed in such a way that all elements of the moving water contribute. The equipment described normally requires an electrical mains power supply. ISO 9213:2004 is not applicable to devices sampling only part of the flowing body of water (e.g. velocity meters) or to flow meters which operate by using the Earth's magnetic field.

Deals with the establishment and operation of a gauging station for the measurement of stage oder discharge, or both, of a lake, reservoir, river or artificial open channel. Replaces the first edition.

Deals specifically with the measurement of discharge in large rivers and the measurement of flood flows. Also describes the relevant field measurements when it becomes necessary to use indirect methods of estimating discharge.

Describes the establishment and operation of an ultrasonic gauging station for the measurement of discharge in a river, an open channel, or a closed conduit with a free water surface. Is limited to the "time of travel of acoustic pulses" technique. Annex A describes the determination of flow direction.

Specifies procedures for the establishment and operation of a gauging station, equipped with an electromagnetic flow-meter, in an open channel or a closed conduit with a free water surface. The field of application is limited to sites where the magnetic field is generated by an electromagnetic coil which traverses the full channel width. Does not apply to flow-meters which operate by using the Earth's magnetic field.

The method is suitable for use under somewhat special conditions when direct measurement of discharge by more accurate methods is not possible. It can be used with reasonable accuracy in open channels having stable boundaries, bed and sides (e.g. rock), in lined channels and in channels with relatively coarse material. In other cases it is subject to large uncertainties, and it is not suitable for use in very large channels, channels with very flat surface slopes and high sediment load or channnels having significant curvature.

Specifies methods for determining stage-fall-discharge relations for a stream reach where variable backwater occurs either intermittently or continuously. Two gauging stations, a base reference gauge and an auxiliary gauge are required for stage measurements. A number of discharge measurements are required in order to calibrate the rating to the accuracy required by this Technical Report.

Summarizes the results of investigations of the total error in measurements of flow by velocity-area methods. Describes the procedure used and types of errors (section one), and gives recommendation for the collection of data for investigations of errors (section two) with a view to supplementing the information given in ISO 1088.