JDC Electronic SA EasyFlow User Manual
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MADD
Technologies sàrl
–
Avenue des Sports 42 – CH-1400 Yverdon-les-Bains – Switzerland
Tel: +41 24 445 31 16 – Fax: +41 24 445 21 23 – Email: [email protected] – www.madd.ch
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The device EasyFlow uses the tracer dilution method to determine the stream flow of the measured
watercourse.
Principle
The main principle of this method consists to inject into a watercourse a concentrated solution of tracer.
Downstream, at a distance large enough from the injection point for a good mix with the river water, the tracer
concentration is measured during the passage of the tracer could. This dilution is a function of flow rate,
assumed constant along the section concerned during the measurement time.
The following conditions are necessary for the application of the dilution method:
• The flow of the river should remain roughly constant during the measurement;
• The tracer must pass totally through the gauging sector;
• At the measuring point, the mixture should be such that at each point of the section of the river must
spend the same amount of tracer.
According to the above conditions, this method is especially adapted in case of low depths, very high speed or in
presence of turbulences that does not guarantee a stable speed, like rivers or streams. As against, it is not
suitable for measuring flow in concrete channels which does not permit the mixing of the water.
Cooking salt as tracer
The cooking salt, sodium chloride (NaCl), is an ideal tracer: it is very easy to find, cheap and has a high degree of
dilution in water. Furthermore, it is not harmful to the fauna and flora at the concentrations used and it is few
absorbed by vegetation and materials of the bed of the river. Finally, it is very easy to measure its concentration
with a conductivity probe.
In this case, the operator injects into the river a known mass of salt
M
diluted in a volume of water of the river.
Downstream, is placed a conductivity probe that will measure the electrical conductivity of water throughout
the duration
T
of passage of the cloud of salt. A linear relationship exists between the conductivity of water and
dissolved salt concentration. The concentration curve can therefore be deduced in function of time
C
t
. The flow
Q
is then obtained by integrating the concentration over time:
Q
: flow of the water course [l/s]
M
: mass of the injected tracer [mg]
C
t
: water salinity at time t [mg/l]
C
0
: basic water salinity [mg/l]
T
: duration of gauging [s]