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News Release from: Editorial: letters to the Processingtalk Editor | Subject: Hydrometry
Edited by the Processingtalk Editorial Team on 26 February 2007

'World Hydrometry Today'

''World Hydrometry Today - and concerns for the future'' by Dr Reg Herschy of the BSI Committee on Hydrometry: a keynote presentation from the Sontek/YSI 2007 International Water Resources Forum

The term 'Hydrometry' comes from the Greek hydor meaning 'water' and metra meaning 'measurement'; literally 'water measurement' The science is not new and indeed a chair in hydrometry, or professorship, was founded as long ago as 1694 at the University of Bologna in Italy - and earlier, in 1674 Pierre Perrault carried out pioneering hydrometric work in the Upper Seine Basin that was a major step in the development of hydrometry

The beginnings of hydrometry, however, are lost in history and the subject as old as the records of Nile floods before 3000 BC and irrigation in China in 2000 BC.

In Britain Frontinus (AD 35 - 103) the Roman governor became Rome's water engineer.

The term is often used synonymously with 'hydrology', and although in the past 'hydrometrician' was commonly used for one employed in applied hydrology, the term is, however, clumsy in English usage and the broad term hydrologist has become accepted to describe someone engaged in the measurement of any part of the water (hydrological) cycle.

And of course there is also a unique relationship between hydrology and hydraulics and connections between the more specialised branches of hydrology, namely hydrogeology, climatology, ecology, geomorphology, hydrometeorology, glaciology and limnology.

Although in the nineteen - fifties and later, hydrometry was considered to mean 'streamflow measurement', today hydrometry covers the whole water cycle.

The Global Water Cycle contains the components that make up the world's water resources and these components require to be measured by, and to, universally acceptable methods.

The ISO definition of Hydrometry is "the measurement of the components of the water cycle".

But this (ISO) definition does not appear in any of the recognised English dictionaries.

For example the Oxford and Webster's give 'the art or operation of using the hydrometer' (the hydrometer being 'an instrument for measuring specific gravity').

Hydrometric data, especially streamflow data, are the fundamental basis for the management of water resources.

However, today to meet present day economic needs, unless modern computing facilities are available, the collection , transmission and processing of streamflow data are substantially labour intensive and routine and therefore may not be considered cost effective by management.

For this reason, measuring methods such as the ADCP have been introduced to hydrometry.

GLOBAL WATER.

A number of efforts have been made to assess global water reserves but there are substantial differences between these assessments with the possibilities of large uncertainties and consequently little reliability can be placed on them until as such time more precise hydrometric measurements of the water cycle are available, but this will require a larger coverage not only of streamflow stations but also of precipitation stations.

Nevertheless, the present figures indicate that of the total water in the water cycle, only about 0.6% is available for use as fresh water of which about 99% is groundwater and 1% surface water (0.594% and 0.006% respectively of the total water).

In Europe, two-thirds of the population rely on groundwater and in the US about 25% of the domestic supply is from groundwater.

In Austria, for example, nearly 100% of the domestic water supply is from groundwater.

Unfortunately, hydrometric data has to be collected from a hostile environment and in all weather conditions throughout the year.

The data is of a routine nature, the work may not be scientifically exciting, much of it cannot be used immediately, some can only be used later for research purposes, some can be used for monitoring purposes and flood data can perhaps be used immediately and in real time.

So data collection and archiving is a slow, dedicated, long term process and the longer the record the more important the data become.

Therefore, we sometimes hear from governments that it is necessary to reduce network stations because of rising costs.

Nevertheless, no matter how much scientific and practical considerations are given to network design requirements, there is hardly one country satisfied with its network of hydrometric stations for the performance of their water resources management duties.

There are great gaps worldwide especially where the data is manifestly required such as Africa, but also in China, Russia and India to name just a few.

It seems clear that deficiencies in the hydrometric networks are not being addressed and over the last ten years investment has decreased, especially in developing countries where the need is most critical.

Also, a decline in station data has been observed by the WMO Global Runoff Data Centre (GRDC) in Koblenz between 1990 and 2000, where information from some 150 countries are stored.

In fact it is a shocking state of affairs when many countries are reported to be less able to assess their water resources than they were 20 years ago.

And this is in spite of the fact that demand for water is rising more rapidly than at any time in history.

More than 200 river systems draining half of the planet's area, are shared by two or more countries and over-pumping of groundwater aquifers that stretch under political borders inject international politics into the management of water scarcity.

The reliance on transboundary rivers can lead to tension between countries especially where total water availability in the upstream country is less than in the downstream country.

In Europe alone some 20 countries depend on other countries for more than 10% of their water resources with five countries relying on over 75% of their resources coming from abroad via rivers (The Netherlands, Hungary, Moldova, Romania and Luxembourg).

There are instances where international water rights can lead to tension and subsequent conflict.

The most serious situation presently causing concern are the international rivers of the Middle East.

The great rivers Euphrates and Tigris feed Turkey, Iran, Iraq and Syria.

With the construction of the Ataturk Dam, Turkey now controls the water of the Euphrates.

There is an agreement to share the waters of the Tigris and Euphrates based of course on hydrometric flow measurement data.

Yet other examples are the Danube flowing through European countries and the Ganges and Brahmaputra from India to Bangladesh.

Measurement of river flow to international standards in these circumstances is crucial to international agreements.

However it is clear that there are not sufficient streamflow stations to meet these demands.

Hydrometric data have provided the focus for international collaboration and cooperation which helps modern tensions and provide a fair basis for peaceful co-existence.

CLIMATE CHANGE.

The effect of possible global warming and consequent climate change on the components of the water cycle is not yet proven and and long term compelling (climate-driven) trends in streamflow remain elusive across most of the Globe.

With some notable exceptions (mostly in Europe and the US), few streamflow stations have long enough records to characterise the historical variability in flow regimes.

An improved understanding of this variable is essential if signals associated with global warming are to be detected and quantified.

However considerable research has been undertaken in this field by the IPCC (Intergovernment Panel on Climate Change).

Two important elements for hydrometry to address are rainfall and streamflow, but reliable forecasts of regional climate change in these elements are as yet unavailable.

Climate change, however, can be expected to lead to changes in precipitation and streamflow.

Water supply in arid and semi-arid regions is very sensitive to small changes in rainfall and evaporation although the latter may be reduced because of increased CO2 concentrations.

In the runoff scenario it is believed that a doubling of CO2 might increase river flows in the US and Australian rivers by between 40 and 80%.

Such estimates of runoff extremes, if confirmed, would require careful streamflow monitoring as well as considerable modification in the design of water related structures and statistical calculations for flood control works and their conveyance capacity.

Monitoring of streamflow information is most critically needed when CHANGE is occurring and to detect change benchmark stations are needed.

Hydrometric standard methods are available with over eighty ISO international standards, the following being examples: Measuring structures; Current meter methods; Stage Discharge Relations; ADCP method; Uncertainties.

Unfortunately some countries are either unaware of these standards or are not following them.

However, the need for training and development of appropriate professional competence for hydrometric personnel is necessary.

Worldwide we need to capture more extreme events that need skill and commitment (and, on occasions, an acceptance that a good estimate is better than nothing at all).

UNCERTAINTIES.

Hydrometric data measurements today should always be presented with an estimated uncertainty value.

Data presented without an uncertainty are considered incomplete.

Considerable investigation into uncertainties has been been carried out during the past 30 years, or so, in addressing this problem particularly with regard to streamflow measurements although not as much investigation has been carried out into other components of the water cycle.

Indeed most streamflow single discharge measurements taken daily worldwide do not include an estimate of the uncertainty of the measurement.

Yet ISO Standards are available showing how this can and should be estimated.

PRECIPITATION STATIONS.

Precipitation appears to be a bigger problem than streamflow measurement in respect of both accuracy and world coverage.

Snow is still not being measured satisfactorily, if at all, and in rainfall measurement catch decreases as gauge height increases.

In fact, worldwide, there is a significant percentage under estimation of rainfall measurement, in some cases by as much as 90% (Newfoundland).

In Europe the underestimate varies by up to 60% and in the US by up to 50%.

There are some 54 different types of raingauge in 136 countries representing 90% of the land area.

The orifices vary from 7 to 1000 sq cm and their heights vary from 0.2 to 2 m.

It is clear that general rainfall data are not compatible and hardly suitable to study trends or to compute norms nor to study climate change effects.

Weather satellites and radar options are far from being the answer.

However, there are many examples of good rainfall measurement practice worldwide, for example UK, US, NZ and many others.

Finally, hydrometry is blessed with dedicated professional scientists and technicians worldwide.

Somewhere in the world, at any moment in time, a measurement is being made.

That measurement is unique.

The conditions will never again be exactly identical.

It will be another important component of the Global Water Cycle.

* Dr Reg Herschy is the Chairman of the British Standards Institution Technical Committee on Hydrometry, and was previously Senior Hydrologist for the UK Environment Agency: this paper was presented at the recent Sontek/YSI 2007 International Water Resources Forum and Conference in Barcelona, see http://www.processingtalk.com/news/soe/soe100.html.

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