CEN/TC 318 - Hydrometry

This document provides guidance on the collation of the measurements required for the management of siltation at river structures. These include structures used by water supply utilities, other major water abstractors, HEP producers, and for flow measurement by environmental protection agencies.
The document is also intended for use when a redundant structure is being removed, or when modifications to a structure are being made to facilitate fish migration or for river restoration. This is to ensure that the impacts of these changes are adequately monitored and recorded.
The document covers the provision of routine measurements, and the checks and requirements that need to be made by the operator so that specific basic information is collated and made readily available. This information is used to inform decision-making by environment management agencies that authorise flushing, sediment clearance or sedimentation removal. This is to ensure minimal environmental impacts, and to compliance with existing environmental legislation.

Non-catching type gauges are the emerging class of in situ precipitation measurement instruments. For these instruments, rigorous testing and calibration are more challenging than for traditional gauges. Hydrometeors’ characteristics like particle size, shape, fall velocity and density need to be reproduced in a controlled environment to provide the reference precipitation, instead of the equivalent water flow used for catching-type gauges. They are generally calibrated by the manufacturers using internal procedures developed for the specific technology employed. No agreed methodology exists, and the adopted procedures are rarely traceable to internationally recognized standards. This document describes calibration and accuracy issues of non-catching instruments used for liquid/solid atmospheric precipitation measurement. An overview of the existing models of non-catching type instruments is included, together with an overview and a description of their working principles and the adopted calibration procedures. The literature and technical manuals disclosed by manufacturers are summarized and discussed, while current limitations and metrological requirements are identified.

This document specifies general requirements, minimum performance requirements and test procedures for open channel instrumentation used to determine either volumetric flow-rate and/or total volume passed of waters in artificial open channels. It covers the following technology categories:
- Level sensors with associated electronics designed to be used with a conventional gauging structure. (The requirements and test procedures for gauging structures, such as weirs and flumes, are excluded. The stage discharge characteristics for many of these structures are established and published in national and international standards).
- Water velocity sensors.
- Integrated velocity area instruments comprising level and velocity sensors that may be separate or combined in a single assembly.
- Velocity sensors that determine the mean water velocity through a channel.
It is recognized that for some OCIs, certain tests cannot be carried out.

This document specifies general requirements, minimum performance requirements and test procedures for instrumentation used to measure either volumetric flow-rate and/or total volume passed of water in closed conduits. It covers all closed conduit instrument (CCI) technologies intended to operate in closed pressurized pipes and partially filled pipes. Requirements are expressed in volumetric units which may be converted to mass using the density of the water.
It is recognized that for some CCIs certain tests cannot be carried out.
The data obtained from the testing of CCIs in accordance with the requirements of the Measuring Instruments Directive [1] or EN ISO 4064-1 [2] can be used to meet, in part, the requirements specified in this document. However, for the avoidance of doubt, compliance with the requirements of this document does not equate to compliance with the requirements of the Measuring Instruments Directive or EN ISO 4064-1.

This document defines the requirements for on-site measurements of snow depth and depth of snowfall. This document provides guidance on manual and automatic measuring techniques, and information about sources of errors and measurement uncertainty.

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 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 Technical Report (TR) provides guidance to assist with the planning and design of Hydrometric networks, to ensure a better understanding of the water cycle, and that any data are observed and collated in an effective and appropriate manner. The TR is intended for use when:-
• a new network is being planned and designed;
• the nature, value and extent of an existing network is being reviewed;
• a redundant network is being decommissioned or modified.
This is to ensure that the impacts of these changes are considered objectively, and all changes are adequately monitored and recorded.
This TR covers all aspects that are considered pertinent to the evaluation. The information will be used to inform the decision-making process employed by the network’s owners and operators. The objective nature of the review will ensure that all influential factors, both beneficial and otherwise, are considered. This will ensure that primary and potential alternative uses of the network are considered. It will also ensure compliance with any extant environmental legislation.

This document considers liquid atmospheric precipitation and defines the procedures and equipment to perform laboratory and field tests, in steady-state conditions, for the calibration, check and metrological confirmation of liquid precipitation measurement instruments. It provides a classification of catching-type measurement instruments based on their laboratory performance. The classification does not relate to the physical principle used for the measurement, nor does it refer to the technical characteristics of the instrument assembly, but is solely based on the instrument calibration. Attribution of a given class to an instrument is not intended as a high/low ranking of its quality but rather as a quantitative standardized method to declare the achievable measurement accuracy in order to provide guidance on the suitability for a particular purpose, while meeting the user’s requirements.

This document gives recommendations for the management of observed hydrometric data, including raw data and other data as well as statistics derived from these observations. Although the principles of data management can be applied to all hydrometric observations, particular focus is placed on measurements of precipitation, water level (including stage), volume and discharge in open channels.
NOTE   The range of sites where water levels, and sometimes flow, are measured includes lakes, reservoirs, rivers, canals, tidal waters, sewers, wells, and boreholes.
The document covers metadata associated with hydrometric data, including recommendations for the production and management of descriptive, analytical and statistical material relating to sites where and measuring techniques, by which hydrometric data are collected. The recommendations of this document can be applied to some forms of data directly derived from observational records (for example, summary time series of monthly mean river flows). While not primarily designed for the management of data resulting from more complex numerical models or spatially aggregated data sets (for example, remotely-sensed data), many of the recommendations are applicable for such types of data.
This document does not cover the field collection of data or its transmission, but focuses on the management of data once they have been received in a hydrometric information management system.

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 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 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.

This Technical Report defines the requirements for manual measurements of SWE over land, see ice and glaciers, under natural environmental conditions, and shows methods for calculating the spatial distribution of the data. It includes measurements with snow tubes, core drills and density cutters.

This Technical Report describes a method for calibrating rainfall intensity (RI) gauges and the measurement requirements to obtain accurate and compatible data sets from hydro-meteorological networks, as a forerunner to the development of full hydro-meteorological data collection standards.
This Technical Report deals exclusively with catching-type RI gauges (see Clause 3). It concentrates on the generic calibration, performance checking and estimation of uncertainties for RI gauges. It does not cover specific gauge measurement principles, technical characteristics and technology adopted in the design of RI gauges.

This European Standard specifies the design of a reference raingauge pit. The reference raingauge pit is designed for the liquid precipitation only. The specified details of the pit and the grating, are purposely kept to a minimum in order to allow each raingauge operator latitude in their construction and to suit local conditions.

This Technical Report defines the requirements for the use of snow mass registration devices for measurement of SWE under natural environmental conditions. It includes weighing and pressure measuring methods.

This standard covers the semantics (meaning) of data exchanged between data producers, users and databanks, independently from the software device and the formats used to exchange the files.
It provides a consistent set of terms defining selected objects and their related attributes.
The standard is not applicable to:
   data describing domestic uses (drinking water, waste water) or qualitative aspects ;
   real time data or data calculated from models;
   all the various characteristics on the organizations exchanging data concerned;
   debimetric measures.

This document considers atmospheric precipitation and defines the procedures and equipment to perform laboratory and field tests, in steady-state conditions, for the calibration, check and metrological confirmation of non-catching precipitation measurement instruments.
It provides a classification of non-catching measurement instruments based on their laboratory performance. The classification does not relate to the physical principle used for the measurement, nor does it refer to the technical characteristics of the instrument assembly but is solely based on the instrument calibration.
Attribution of a given class to an instrument is not intended as a high/low ranking of its quality but rather as a quantitative standardized method to declare the achievable measurement accuracy to provide guidance on the suitability for a particular purpose, while meeting the user’s requirements.

ISO/TS 25377:2007 provides an understanding of the nature of measurement uncertainty and its significance in estimating the quality of a measurement or a determination in hydrometry. It is applicable to flow measurements in natural and man-made channels. Rainfall measurements are not covered.

ISO 4373:2008 specifies the functional requirements of instrumentation for measuring the level of water surface (stage), primarily for the purpose of determining flow rates. An informative annex provides guidance on the types of water level measurement devices currently available and the measurement uncertainty associated with them.

ISO 772:2011 gives terms, definitions and symbols used in standards in the field of hydrometry.

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.

Gives terms, definitions and symbols in the English and French language used in the scope of hydrometric determinations.

This Standard specifies the design of a reference raingauge pit. The specified details of the pit and the grating, are purposely kept to a minimum in order to allow each raingauge operator latitude in their construction and to suit local conditions.

This European Prestandard specifies the operational requirements, calibration and maintenance of propeller-type devices for the measurement of flow velocities in open channels. The requirements of the calibration facility are laid down. The result of calibration is the relationship between water velocity and rate of revolution of the propeller.
This European Prestandard does not define the form of the signal produced by the equipment or the signal receiving equipment.