Discharge - Velocity profiler (Sontek IQ)
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Parameter to be measured:
Discharge (velocity profiles, water stage, temperature)
Method:
ultrasonic Doppler profiling in 4 slant beams, stage measurement via pressure and vertical beam
Equipment:
Sontek IQ device, cable + adaptors (needs external power supply, optional logger)
Advantages:
- continuous monitoring of discharge where not clear h-Q-exists
- useful for conditions of reverse flow and backwater effects
- velocity profiles along 4 beams up to 5 m depth
- small and lightweight
- data storage in device or on external logger
Disadvantages:
- unsuitable for conditions with bedload or siltation
- For slow/stagnant water, velocity measurements are problematic (noisy, negative bias)
- measurements needs movement of particles (or fish!). Below SNR of 10 dB, data seems to be erroneous (e.g. with stagnant water).
- For *relatively* sudden and intense changes in velocity, unrealistic velocity and depth readings may occur.
- depth measurement is prone to error: beams may underestimate (beam interference, fish) or overestimate (multiple path echos). Strangely, depth measurements via pressure are corrected with faulty beam data, not vice versa.
- Per default and IQ Standard, the conversion of beam velocity data to mean beam velocity seems to use some power law, which is faulty in case of unusual velocity profiles.
Fix this by selecting "Recalculate Flow" (works only if all single profile have been recorded, ie. Sontek Plus, see below).
What to watch out for:
- IQ comes in three flavours: Standard, Plus and Pipe (?). The former two seem to be physically identically and vary only in price and the way the software interprets the data. The Standard can be upgraded to Plus for ~3500 € or with some creativity.
- Sensor burial by sedimentation
- maximum water depth differs between Standard, Plus and Pipe
- minimum water depth for Standard/Plus according to manual is 8 cm. We found 10 cm to be the minimum for our application of the Plus.
Problems/Questions:
- exact usage of the beams for velocity calculation is intransparent; often, only forward and backward beam seem to be used.
Price:
3700 / 8000 € for Standard/Plus (Germany, 2013)
Links
Projects that used the above equipment:
Other related web sites: