Research is currently being carried out in the Hessenhau Cave, located in southern Germany. With a depth of 144 metres (472 ft), it is the deepest known cave in the Swabian Alps. A permanent stream flows through the cave, hydrologically linking it to other cave systems in the region and making it a key site for karst and groundwater research.
Artificial access to the Hessenhau Cave was created in 2005, after strong airflow was detected — a clear indication of underground connections to other caves. Although speleologists have not yet found a physical connection to the nearby Blauhöhle cave system, tracer studies conducted in May 2012 provided clear evidence of a hydraulic connection between the two systems. It is suspected that the Hessenhau Cave extends up to 7 kilometres north, potentially reaching as far as Laichingen.
A unique characteristic of the cave is its pronounced air circulation, driven by temperature differences and atmospheric pressure fluctuations. Hessenhau is the only known cave in Germany exhibiting barometric pressure effects, making it of particular scientific interest.
Conducting discharge measurements deep underground is physically demanding and technically challenging. Accessing the lower sections of the cave requires long descents under difficult conditions, combined with moisture, low temperatures, and uneven terrain.
In this environment, measurement equipment must be lightweight, compact, and robust, while still delivering reliable and precise discharge data. Traditional instruments with moving parts are at higher risk of damage and are less suitable for such demanding conditions.
To measure discharge at various locations within the cave, researchers used the OTT MF pro electromagnetic current meter. Despite the challenging access to the deepest parts of the cave, the lightweight yet rugged design of the MF pro proved ideal for underground use.
Discharge measurements were carried out using the classical multi‑point method, with flow velocity and immersion depth recorded automatically at several verticals. Once velocity measurements were completed, the MF pro calculated discharge directly in the handheld unit, fully compliant with international USGS and ISO standards.
After the fieldwork, the handheld was connected via USB to a PC or laptop, allowing easy data download and further analysis in the office.
The use of the OTT MF pro enabled reliable discharge measurements even under extreme cave conditions. Its advantages proved particularly valuable for speleological and hydrological research:
The successful use of the OTT MF pro in the Hessenhau Cave demonstrates its suitability for challenging and unconventional measurement locations, supporting advanced research into underground water systems.
Video and images from the project were provided courtesy of ARGE Blaukarst, the working group formed by speleologists from southern Germany to coordinate excavation activities in the Hessenhau doline. Special thanks go to Mr Uwe Krüger (video) and Mr Andreas Schober (photos) for their support.
For current information on the excavation activities and research progress, visit: www.blauhoehle.de
(Source: Wikipedia – Blauhöhle)