Groundwater depth measurements (often called bore hole monitoring) help in the management of the important groundwater resource on which we depend for many purposes. In particular groundwater resources may be used up through agriculture or mining operations.
Instruments can easily measure the amount of water that resides in our groundwater so we can manage the resource better. Measurements can deepen our understanding of the factors that influence groundwater recharge and lead to more effective water management.
Groundwater depth is measured with a small diameter sensor deep in an observation bore hole. Water depth can be measured with a pressure sensor lowered down the bore hole and immersed in the water. This is call hydrostatic depth method.
Alternatively a standard float-and-pulley sensor system with a small (50mm or 100mm) float and a pulley at the top of the bore hole can also be used to measure depth.
The hydrostatic depth method is widely used as it is convenient to install, however all pressure sensors have some drift which needs to be considered. The float and pulley method is less convenient, especially in narrow diameter bore holes of 100mm, however it is very accurate and is not subject to drift.
Unidata offers the 6542 Hydrostatic Water Depth and Temperature Probe which uses the hydrostatic pressure of water to measure water depths in various environments.
These systems are typically installed in existing bores, perhaps with a diameter of 100 to 200mm and a depth of 5 to 50 meters, with a bore head cap, often in a valve box / enclosure or some other form of bore head arrangement.
A data logger / RTU / NRL needs to be added at the top of the bore for data to be recorded and telemetered to a central location on a regular, perhaps 4 hourly basis.
There are generally two types of customers for these systems:
• A government authority which measures the groundwater levels for water table history generally.
• A mining or oil and gas company which has some mining or drilling activity in the area and has a need to ensure there is no change to the groundwater during their mining or drilling processes for compliance reasons.
The data collected can then be viewed, limits checked and alarms set in the event of a sudden change in the ground water level. The data can then be passed to a statistical groundwater analysis software package for groundwater modelling purposes.
Unidata offers the 3001M Borehole Logger that is designed for use in boreholes of 100mm internal diameter and above. It can be configured to use ether Cellular, LoRa, Iridium or Microsatellite networks as its method of sending sensor data from the field to the Neon Server. A wide range of sensor types are supported, for
example, analog sensors, frequency counters, digital inputs as well as Modbus and SDI-12. Sensors are connected to the logger via pluggable terminal blocks, SQL connector or a custom specified connector, allowing for easy removal of the logger if servicing is required.
