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Discharge Measurement Deep Within a Cave

Research is currently being conducted in the Hessenhau cave, located in southern Germany. The cave is the deepest known within the Swabian Alps at 144m (472 ft) and has a stream running through it that connects it to other caves within the area.

Discharge measurements were taken in different parts of the cave with the OTT MF pro electromagnetic current meter.

Reaching the bottom of the cave for discharge measurements was difficult but the lightweight yet rugged design of the OTT MF pro performed well.

Watch the MF pro Cave Discharge Video

Video and pictures appear courtesy of the ARGE Blaukarst. We thank in particular Mr. Uwe Krüger (video) and Mr. Andreas Schober (pictures) for their support.

Handheld electromagnetic stream flow meter with automatic discharge calculation

OTT MF pro - Water Flow Meter

Handheld electromagnetic water flow meter with automatic discharge calculation

The OTT MF Pro is a user-friendly, low maintenance electromagnetic current meter for cost-efficient in-stream discharge measurement.

  • Spot
  • Electro-magnetic
  • Flow velocity and water depth
  • Low maintenance magnetic - inductive probe with level measurement for reliable flow measurements. Works well in low flow and turbulent conditions, cross - sections with weed growth and pollution. Applicable in streams and conduits.
  • 0 … 6 m/s
  • ± 2% of measured value ± 0.015 m/s ( 0 … 3 m/s ) and ± 4% of measured value ± 0.015 m/s ( 3 … 5 m/s )
  • In 2005, artificial access to the Hessenhau-cave was created after strong airflow was identified in the cave, indicating connection to other caves. 
  • The two speleologists researching  the two cave systems could not find a connection between the Hessenhau-cave and the Blauhöhle cave system so far, however tracer studies in May 2012 delivered evidence of a hydraulic connection between the two caves.
  • There are speculations that the Hessenhau-cave stretches out 7 km to the north, possibly as far as Laichingen.
  • A remarkable characteristic of the Hessenhau Cave is that the strong air flow (ventilation) in the cave is caused by temperature differences and air pressure fluctuations. The Hessenhau cave is the only cave in Germany for which the phenomenon of barometric pressure occurs (caused by air pressure fluctuations).
  • For coordinating and implementing the excavation activities in the Hessenhau doline, speleologists from Southern Germany formed the working group "ARGE Blaukarst".
  • For current information from the ARGE Blaukarst regarding the excavations and the situation in the Hessenhau doline go to:

[Source WIKI:]

  • Discharge measurements in the cave were carried out with the OTT MF pro electromagnetic current meter
  • The discharge is determined using the classical method of measuring at several vertical points, with velocity of flow and immersion depth being recorded automatically.
  • As soon as the velocity measurement is finished, discharge is calculated according to international standards USGS / ISO by the software directly in the handheld.
  • Later in the office, the handheld can be connected via USB to a  laptop or a PC to download data comfortably for further evaluation. 


  • Compact size, easy to handle and light-weight
  • No moving mechanical parts: no risk of damaging during transport and in rough operating conditions.
  • User-friendly handheld: light and water-protected enclosure (IP67); with graphical easy-to-read color display.
  • Applicable in shallow waters
  • Measurement is possible from 0 m/s: ideal for use even in lowest velocities.
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