• A survey to National Hydrological Services by J. Fulford and S. Busaz has been conducted to find out what kind of equipment and from which manufacturer is used in the country to measure discharge. COMMENT: Only 14% of WMO members responded, mainly from western countries. According to the survey, mechanical instruments are used for over 70% of flow measurements.
• A paper on General Uncertainty Management (GUM) method by J. Fulford.
• An example of GUM in flow measurement by M. Muste
• Discussion papers on instrument specifications by P, J. McCurry

It was suggested that the GUM method should be recommended by WMO in estimating uncertainty. Until now there hasn't been one general and widely accepted method in estimating uncertainty. It was the idea of Climate and Water Department of the WMO to investigate and finally propose one general method and terminology. The GUM method is widely used and suitable for almost all uncertainty estimations. The basic principle is that it takes into account all sources of uncertainty, for example such as the experience level of the person conducting a measurement. The division of uncertainty sources differs from traditional way where sources of error are either random or systematic, so that now the error is defined either by statistical analysis (Type A) or other means (Type B).

The ISO representative pointed out that this method is widely used in their standards and recommended its use. There was a general understanding among the meeting participants that GUM is the way to proceed with estimating uncertainty.
It was proposed that WMO should recommended national hydrological services to let the manufacturers conduct the testing of their equipment in each country in an independent testing company to meet the individual national requirements. An estimation was given that such a test would cost something around 10 000 USD. Another proposal was that the industry should express the uncertainty of devices in a transparent and traceable way so that the declared accuracy of any device could be used as such in the uncertainty assessment procedure.

The vision of the CHy/WMO is to expand the uncertainty assessment procedure (GUM) to be recommended by all the WMO branches and eventually include the uncertainty assessment in modelling. Members of other branches were invited to take part in the meeting to hear about the GUM method and its applicability in all uncertainty assessment. Representatives from Climatology, and Argrology were present at the meeting.
 
It was agreed that the committee will try to produce a PC-software which can be used to estimate uncertainty in flow measurement. The idea is to provide an easy user interface so that everyone with basic computer skills could use it. The software could be then used either for comparing different measurement techniques and finding the most suitable for one's needs before purchasing the equipment, or for estimating the uncertainty for equipment already in use.

The message from the Management Committee towards industry was that the manufacturers should work through HMEI in establishing a common and general way how the uncertainty of equipment is expressed, so that one can easily compare for example sensor accuracy from different manufacturers. It was suggested by J. Fulford that the accuracy would be for example expressed in the measured units over the full declared operational range of the equipment with 95% confidence determined with a relevant distribution.
The meeting concentrated mostly on the second day in how to proceed from here. A working website is established and progress can be followed there.

Meeting Participants
Ms Zsuszsanna Buzás
Ministry of Environment and Water, Hungary

Ms Janice Fulford
Testing Section Chief, Hydrologic Instrumentation Facility, U.S. Geological Survey, USA

Mr P. J. McCurry
National Manager, Hydrometric Operations, Hydrometric Monitoring Division, Water Survey of Canada, Environment Canada, Canada

Dr Marian Muste
Research Engineer, IIHR - Hydroscience & Engineering, The University of Iowa, USA

Dr Paul J. Pilon
Engineering Advisor, International Joint Commission, Canada

Ms Jenny Pellaux
Technical Programme Manager & Technical Editor, ISO Central Secretariat, Switzerland

Dr Jürgen Skripalle (Representing HMEI)
Chief, Flow Division, SEBA Hydrometrie GmbH, Germany

Mr Bruce Summer
Executive Secretary, Association of HMEI, Switzerland

Prof. Gordon Young
President, IAHS, Canada

Mr Claudio Caponi
Chief, Capacity Building in Hydrology and Water Resources Office
Climate and Water Department, Switzerland

Mr. Risto Haimelin (Representing HMEI)
Application Specialist, Meteorology, Vaisalala OYJ, Finland

The WMO Report of this meeting is available here.