Within the framework of the LIFE Tršca project, the ZRC SAZU Karst Research Institute is conducting continuous measurements of water level and water temperature at 10 different locations, which would not be possible without advanced instruments.
There are quite a few manufacturers on the market dedicated to production of instruments for hydrological observation, which offer a variety of options; from a wide range of measured parameters, battery operation, contactless reading to connectivity to the Internet network. Most of them can be set to the desired time interval for measurements, which are then automatically saved to memory.
Each environment has certain specificities, and karst environments (especially caves with an access to the groundwater; Figure 1) are characterized by very limited access to electricity or the Internet that enable the most modern methods of measurement and management. In most cases, we therefore rely on meters with their own power supply (battery) and memory, for which the measurement interval is set to such a range that the memory is not yet full and the battery is not empty at the next scheduled visit. Due to the rather demanding environment with pronounced fluctuations in water level, strong and turbulent water flow, the meters must also be robust and firmly mounted on the base.
Although the measuring points in the LIFE Tršca project are not located underground, they are also characterized with some limitations, such as inaccessibility for most of the year due to the presence of water. These measuring points can also be exposed to sediment displacement, the presence of (curious) animals and people, so we also opted for robust instruments with their own memory and battery, which we installed on a solid rock base. Where this was not available, we installed them on heavy concrete blocks (Figure 2).
The main observed water properties are the water level (calculated from pressure) and temperature. Such meters on the market have sensors for different depth ranges. The greater the possible measurement depth, the lower the resolution and accuracy. We have installed instruments with a range of up to 30 m depth, which means that they measure with a resolution of 0.3 cm and an accuracy of 1.5 cm. Temperature measurements have a resolution of 0.1 °C and an accuracy of 0.3 °C. As part of some past projects, we also established measurements of specific electrical conductivity, which observe the amounts of dissolved ions in water. Their measurement range is up to 2,500 µS/cm with a resolution of 1 µS/cm and an accuracy of 5 µS/cm. The instruments are started and data is transferred using a mobile phone or tablet via an application and a wireless connection (Figure 3). Since this does not require an internet network, this method is also suitable for the cave environment.
Installation of instruments and other visits for data transfer or maintenance of the measuring network is usually done in the summer period, when the lake windows are dry. This means that these instruments are also out of the water for some time and therefore they measure air pressure and air temperature. Figure 4 shows a short series of measurements from the Ajnce jame lake window – in the initial period the location is dry and shows pronounced temperature fluctuations, then the water level rises rapidly, and the temperature sensor observes water temperature without daily fluctuations.
We will publish more about water level measurements and the peculiarities of the lake windows in the coming years.
Article was prepared by the Karst Research Institute ZRC SAZU.
The implementation of extensive nature conservation projects exceeds the financial capacity of the local community, therefore Notranjska Park regularly applies for projects with the possibility of co-financing by the European Union.
The implementation of large-scale conservation projects exceeds the financial capabilities of the local community, therefore Notranjska Park regularly applies for projects with the possibility of co-financing from the European Union.
