Water level - capacitive (Odyssey)

Parameter to be measured:

Water level

Method:

Capacitive

Equipment:

Odyssey

Advantages:

Cheap
Logging of 64k of data
Logger start by starting start time
The lack of an outer shroud makes it easy to transport the probes
Available in different lengths
Available with 2 sizes of brass weights
The probe fits exactly on a 32 mm (ID) PVC pipe
You can replace the batteries yourself
Log-interval can be event-controlled
Very good support from the company (prompt answering emails).

Disadvantages:

Each sensor needs to be calibrated:

"median measurement error that ranged from 11 to 288 mm using the bucket calibration method and 12 to 81 mm using the PVC pipe calibration method" (Larson and Runyan, 2009)

the sensor is not compensated for temperature or electrical conductivity.
manufacture state the accuracy to be -+ 5mm, but in practice it tends to be -+1cm.
temperature dependency: "tests in water temperatures of 0°C - 20°C have shown a variation (under estimation) of approximately 5mm" (manufacture statement).
electrical conductivity dependency:
- "If the conductivity of the water is above 5000µS/cm the sensor is largely unaffected by fluctuations in conductivity whereby large changes result in very small variations in the recorded data" (manufacture statement).
- "We suggest these probes only be used in water higher in conductivity than 4150 μS/cm" (Larson and Runyan, 2009).
- Larson and Runyan (2009) tested the influence of EC on the measurement by changing the EC. Here are the results (see study for details):
  - EC variations: from 590 μS/cm to 1600 μS/cm --> "observed" water level variations: 40 mm
  - EC variations: from 705 μS/cm to 1000 μS/cm --> "observed" water level variations: 15 mm
  - EC variations: from 670 μS/cm to 1200 μS/cm --> "observed" water level variations: 24 mm
  - EC variations: from 210 μS/cm to 620 μS/cm --> "observed" water level variations: 153 mm
  - EC variations: from 175 μS/cm to 1950 μS/cm --> "observed" water level variations: 240 mm

What to watch out for:

Don’t damage the wire.

Problems/Questions:

After 2 years of use, two of my loggers would no longer connect to the computer. All others still worked fined.
One of my loggers would only record data for a few seconds. Restarting the logger and letting it run until the storage was full seemed to take care of this.
How do temperature/electrical conductivity influence the measurement.

Price:

between 120 and 150 EURO (2010, Germany) depending on the length

Links

Projects that used the above equipment:

TERENO

Other related web sites:

References

Bachmaier, S., Weiler, M., Troch, P. (2012): Intercomparing hillslope hydrological dynamics: Spatio-temporal variability and vegetation cover effects. WATER RESOURCES RESEARCH, VOL. 48, W05537, DOI: 10.1029/2011WR011196.
Bachmair, S., Weiler, M. (2012): Hillslope characteristics as controls of subsurface flow variability. Hydrol. Earth Syst. Sci., 16, 3699–3715, DOI: 10.5194/hess-16-3699-2012.
Larson, P. and Runyan, C. (2009): Evaluation of a Capacitance Water Level Recorder and Calibration Methods in an Urban Environment, CUERE Technical Memo 2009/003