ISO/TC 113 - Hydrometry

This document specifies the functional requirements of instrumentation for measuring the level of water surface (stage), primarily for the purpose of determining flow rates. This document is supplemented by Annex A, which provides guidance on the types of automatic water level measurement devices currently available and the measurement uncertainty associated with them. The manually operated measuring devices are described in Annex B. This document is applicable to both contact and non-contact methods of measurement. The non-contact methods are not in direct material contact with the water surface but measure the height of the water level with ultrasonic or electromagnetic waves.

This document defines terms and symbols used in standards in the field of hydrometry.

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 specifies the functional requirements and characteristics of the different types of suspended-sediment samplers used for collecting water-sediment mixtures from streams, rivers, lakes and reservoirs. This document does not include equipment for collecting samples in closed conduits and wastewater discharges. NOTE The units of measurement used in this document are SI units.

This document specifies the typical requirements of instrumentation for measuring liquid precipitation, primarily for the purpose of hydrological and meteorological observation. This document is applicable to both non-recording and recording catching-type precipitation gauges for the measurement of liquid precipitation. This document covers design criteria for the gauges and elements to be considered in their construction. This document does not include specification, design and installation conditions. NOTE Since the measurement of solid precipitation is outside the scope, the disadvantages of solid precipitation apply to all gauges listed in Annex A. The measurement of solid precipitation and associated disadvantages are well documented in Reference [1].

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 a calibration method for mechanical type, electromagnetic type and acoustic type hydrometric current-meters used for point velocity measurement of flowing water. The method requires towing the instrument through still water in a straight open tank. It includes measuring apparatus, the calibration procedure, the method of presenting the results and the uncertainties associated with the method.

This document provides an understanding of the nature of measurement uncertainty and its significance in estimating the "quality" of a measurement or a determination in hydrometry. This document is applicable to flow measurements in natural and man-made channels. Rainfall measurements are not covered.

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 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.

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 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/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 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 6420:2016 specifies methods of determining the position of hydrometric boats based on satellite navigation systems and/or with respect to known points on the banks of rivers, estuaries or lakes. It applies to electronic positioning equipment and conventional surveying techniques.

The application of geophysical methods is an evolving science that can address a variety of objectives in groundwater investigations. However, because the successful application of geophysical methods depends on the available technology, logistics, and expertise of the investigator, there can be no single set of field procedures or approaches prescribed for all cases. ISO/TR 21414:2016 provides guidelines that are useful for conducting geophysical surveys for a variety of objectives (including environmental aspects), within the limits of modern-day instrumentation and interpretive techniques, are provided. The more commonly used field techniques and practices are described, with an emphasis on electrical resistivity, electromagnetic, and seismic refraction techniques as these are widely used in groundwater exploration. Theoretical aspects and details of interpretational procedures are referred to only in a general way. For full details, reference is intended to be made to specialized texts listed in the Bibliography.

ISO 24155:2016 specifies the technical requirements that should be considered in designing and operating hydrometric data transmission systems (HDTS) and also the necessary functions of those systems. The scope of HDTS is shown in Annex A.

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/TR 11651:2015 describes a method for estimation/prediction of sediment deposition within and upstream of a reservoir using numerical simulation techniques through one-dimensional flow and sediment transport equations. Numerical simulation models for predicting sediment distribution are applicable for reservoirs, where the length of the reservoir greatly exceeds the depth and width and the reservoir has a significant through flow. ISO/TR 11651:2015 includes the theoretical basis and fundamental assumptions of the technique and provides a summary of some numerical methods used to solve the unsteady flow and sediment transport equations. Also provided are details on the application of the model, including data requirements, procedures for model calibration, validation, testing, applications and identification of uncertainties associated with the method. This Technical Report does not provide sufficient information for the development of a computer program for solving the equations, but rather is based on the assumption that an adequately documented computer program is available.

ISO/TR 9212:2015 reviews the current status of direct and indirect bedload-measurement techniques. The methods are mainly based on grain size distribution of the bedload, channel width, depth, and velocity of flow. This Technical Report outlines and explains several methods for direct and indirect measurement of bedload in streams, including various types of sampling devices. The purposes of measuring bedload-transport rates are to a) increase the accuracy of estimating total sediment load in rivers and deposition in reservoirs, b) gain knowledge of bedload transport that cannot be completely measured by conventional suspended-sediment collection methods, c) provide data to calibrate or verify theoretical transport models, and d) provide information needed in the design of river diversion and entrainment structures. NOTE The units of measurement used in this Technical Report are SI units.

ISO 4375:2014 defines the requirements for equipment, anchorage, supports and accessories for cableway systems for use in stream gauging. Systems which are operated either entirely from the river bank or from a suspended personnel carriage (also called a "cable car") are discussed. Should the cableway installation be required to be certified as lifting equipment, other standards or regulations may apply. ISO 4375:2014 is only applicable to the cableway systems to be used for hydrometric measurements.

ISO/TR 13973:2014 provides details of methods aimed at augmentation of ground water resources by modifying the natural movement of surface water as a general guide. This Technical Report does not cover the process of deciding and planning artificial recharge

ISO 11657:2014 specifies methods for determination of the concentrations and particle-size distributions of suspended sediment in streams and canals by surrogate techniques. ISO 11657:2014 covers brief description of the operating principle of each method and details of some of the instruments available.

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 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.

This International Standard describes methods for the measurement of temporal and spatial changes in reservoir capacities due to sediment deposition.

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 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 23211:2009 provides information about the functional requirements of instrumentation for measuring the water level in a well using automated pressure transducer methods. ISO/TR 23211:2009 provides guidance for the proper selection, installation and operation of submersible pressure transducers and data loggers for the collection of hydrologic data, primarily for the collection of water-level data from wells. Basic principles, measurement needs and considerations for operating submersible pressure transducers are described and the systematic errors inherent in their use are discussed. Standard operational procedures for data collection and data processing, as well as applications of transducers for specific types of hydrologic investigations are included. Basic concepts regarding the physics of pressure and the mechanics of measuring pressure are presented, along with information on the electronics used to make and record these measurements. Guidelines for transducer calibration, proper use and quality assurance of data also are presented. Ground water field applications of pressure transducer systems are discussed, as are common problems that may corrupt data, along with suggestions for field repairs. An informative annex provides guidance on the types of pressure transducers commonly used for water-level measurement and the measurement uncertainty associated with them.

ISO 3454:2008 specifies the functional requirements of the equipment, excluding bankside cableway systems, used in the measurement of liquid flow in open channels for sounding (by direct method), and suspending the measuring equipment (for example, current-meter or sediment sampler) at the point of measurement.

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.

ISO 1088:2007 provides a standard basis for the collection and processing of data for the determination of the uncertainties in measurements of discharge in open channels by velocity-area methods using current meters. To determine the discharge in open channels by the velocity-area method, components of the flow (velocity, depth and breadth) need to be measured. The component measurements are combined to compute the total discharge. The total uncertainty in the computed discharge is a combination of the uncertainties in the measured components. ISO 1088:2007 is intended to be applied to velocity-area methods that involve measurement of point velocities at a relatively small number of discrete depths and transverse positions in the flow cross-section, as described in ISO 748. It is not intended to be applied to measurements made by Acoustic Doppler Velocity Profilers (ADVP) or other instruments that produce essentially continuous velocity profiles of the flow field.

ISO 4366:2007 provides information concerning the principles of operation, selection and performance criteria for echo sounders used in depth measurements for open-channel flow (and related) measurements. The use of standard terminology is promoted.

ISO 2537:2007 specifies the operational requirements, construction, calibration, and maintenance of rotating-element devices for the measurement of flow velocities in open channels.

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 %.

ISO 21413:2005 develops procedures and prescribes the minimum accuracy required of water-level measurements made in wells using graduated steel tapes, electric tapes and air lines. Procedures and accuracy requirements for measuring water levels in a flowing well are also included, as are procedures required to establish a permanent measuring point. ISO 21413:2005 discusses the advantages and limitations of each method and requirements for recording the data. ISO 21413:2005 does not include methods that use automated electrical or mechanical means to measure and record water levels.

ISO 9825:2005 deals specifically with the measurement of discharge in large rivers and the measurement of rivers in flood. It also describes the relevant field measurements when it becomes necessary to use indirect methods of estimating discharge.

ISO 4365:2005 specifies methods for determining the concentration, particle-size distribution and relative density of sediment in streams and canals. The detailed methods of analysis are given for the following: determination of the suspended sediment concentration by evaporation and filtration; particle-size analysis of suspended sediment; determination of the bed-load and bed material sediment; determination of the relative density of sediment; determination of particle-size distribution characteristics.

ISO 14686:2003 describes the factors to be considered and the measurements to be made when designing and performing a pumping test, in addition to a set of guidelines for field practice to take account of the diversity of objectives, aquifers, groundwater conditions, available technology and legal contexts. The standard specifies the fundamental components required of any pumping test. It also indicates how they may be varied to take account of particular local conditions. It deals with the usual types of pumping test carried out for water-supply purposes, in which water is abstracted from the entire screened, perforated or unlined interval(s) of a well.

ISO 4363:2002 specifies conventional and simplified methods for the measurement of cross-sectional mean suspended sediment mass concentration and mean particle size distribution. The conventional method is used for routine measurements in periods of stable or slowly varied flow. The simplified method is mainly used for sediment measurements for the purpose of observing the variation process of sediment transport and can be performed under difficult conditions. Empirical relationships are established between the cross-sectional mean suspended sediment mass concentrations and mean particle size distributions measured by conventional and simplified methods. The methods specified in ISO 4363:2002 are applicable to suspended sediment measurements at hydrological stations.

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 Technical Report is a summary of best practice for those involved in geophysical borehole logging for hydrogeological purposes. It describes the factors that need to be considered and the measurements that are required to be made when logging boreholes. There can, however, be no definite "standard" logging procedure because of great diversity of objectives, ground-water conditions and available technology. Geophysical logging of boreholes is an evolving science, continually adopting new and different techniques. Every application poses a range of problems and is likely to require a particular set of logs to gain maximum information. This Technical Report therefore provides information on field practice with the objective of how variations in measured parameters may be useful to take account of particular local conditions. It deals with the usual types of logging carried out for delineation of aquifer boundaries; mapping aquifer geometry; assessing the chemical quality and quantity of ground water; water-supply purposes; landfill investigations and contamination studies; borehole construction and conditions; and subsurface lithological information. Applications not specifically considered in this Technical Report include mineral and hydrocarbon evaluation and geotechnical and structural engineering investigations. However, this Technical Report may be a source of general information for any borehole geophysical logging effort. NOTE Interpretation of the data collected during logging is referred to in this Technical Report only in a general way. For full details of the analysis and interpretation of geophysical logs, reference should be made to specialized texts. Examples of such texts are included in the Bibliography.

This International Standard deals with the method and techniques for the sampling of suspended sediment and estimation of sediment transport rates in natural and man-made channels influenced by tidal action.

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.