Bell Environmental supplying environmental monitoring equipment, field hydrometry products and remote telemetry systems and this includes water loggers. However, there are a number of considerations to be made when selecting the right application for any given situation. Both here and at Geotechnica Bell Environmental's guide to selecting the correct model should help people to choose the most appropriate water logger and make sure that it works efficiently, requires little maintenance and provides the best accuracy for their application.
What will my water depth be?
When selecting a water level logger one of the first things any user will need to know is the water level at the monitoring location(s). To determine this a knowledge of the potential change in level at each location will need to be known. For example, if you have 100m of water in a borehole, but the change will only be 5m a 100m range water level logger is not necessarily needed. Potentially a 10m range model would be sufficient in this example. If, however, the variation in level would be greater, for example, 80m, then a large range water level logger would be required.
What accuracy do I need?
After determining the range of the water level logger the next thing to consider is the required accuracy. The lower the range of the water level logger the greater the accuracy. For example, the 9m rugged Troll 100 logger has an accuracy of +/-9mm. However, in comparison, the 76m version has an accuracy of +/-76mm. For monitoring a surface water application, which typically has lower levels, we would highly recommend using a model with a lower level range to provide the best possible accuracy.
Will the water be potential saline/acidic?
The potential salinity and acidity of the water are very important to consider when choosing a water level logger. If the application is likely to be acidic or saline users should look to consider certain materials for the water level logger. For highly saline or acidic applications a titanium bodied product would be recommended, with a ceramic pressure sensor to ensure the unit is not corroded or damaged as these materials offer high levels of resistance. In the case of a clean water application stainless steel or titanium products can be used.
Is the area been monitored likely to flood?
Determining if the location is likely to flood is crucial and can be the difference between having a system which works accurately and a system becoming damaged. In applications which could be prone to flooding, it would be recommended that an absolute (non-vented) water level logger be used. The reason for selecting the absolute version simply comes down the way the sensor works. With a vented system there is a breather tube, with a desiccant connected to the top of the sensor cable. If this desiccant and breather were to become submerged there is potential for water ingress into the water level logger and potential damage to the sensor. As absolute water level loggers are completely sealed there is no risk of water ingress via a vent tube, therefore are ideal for potential flood applications
Vented or absolute
It may be the case that the points above have highlighted key aspects of an application, which in turn have confirmed the model needed. If not, then an overview of both the key advantages and disadvantages of both a vented and absolute water logger should help further.
Barometric compensation calculations
When looking for the highest level of accuracy then the vented option would be recommended. In most cases, this will also be more accurate than an absolute system. An example of this is shallow applications, as the vented tube directly transmits barometric data to the water level logger pressure transducer. With an absolute sensor, both the inaccuracies of the water level logger and the barometric logger would need to be considered. However, in deep monitoring applications or those with a greater level variation it may be advantageous to use an absolute sensor. This is because as the measurement of individual barometric data alongside level data allows the user to determine the barometric efficiency.
What budget do I have?
Cost is another factor, typically absolute water level loggers are lower in cost, especially when monitoring with multiple sensors in one location, as a single barometric logger can be used to compensate multiple water level loggers. Costs could be comparable to monitoring a single point, however, this would be determined by the cable lengths. As well as purchase cost, the maintenance of absolute water level loggers is a lot less as there is not desiccant or breather tube to protect from water ingress.
