Many people ask: “Are Water Level Meters still required on projects where data loggers are being deployed?” “If a constant and stable water level value is being provided why would I need a manual water level measurement?”
Due diligence requirements on many projects may require a secondary verification of the data. If relying solely on submersible datalogger readings, you will be unaware of any drift experienced by the transducer, as well as any variation in the deployment depth which may occur over time.
When initially installed, in order for your collected data to be relatable, you need to establish a common reference datum. In many cases this can be the ground surface, the top of the casing or even sea level if multiple locations are being compared. The submersible data logger will monitor the water above its deployment location but does not relate this value to any reference point. A deployment depth must be known to calculate the depth to water level. While most datalogger software has incorporated this functionality it is not always a static value.
There are multiple factors which can affect the deployment depth of a data logger.
- Many types of cable or wire on which these units are deployed can stretch.
- When initially deployed and the level calculated the cable may have not been fully extended or may have been caught on something thereby temporarily shortening the cable.
- Seasonal changes to the surrounding area can result in the ground shifting or the casing being moved.
- Any seismic activity in the area can also cause topographical changes.
- The person responsible for affixing the cable to the casing may have not done it in the location expected when the information was input into the software to calculate the depth to water.
- The cable length may have been measured incorrectly or from the incorrect location.
The employment of a Water Level Meter measurement can correct for all these shortcomings.
A measurement of depth of water “R” should be taken by your datalogger device at the same time.
The sum of these two values will give the accurate depth of deployment.
If you need to reference your water level to some other geodata point such as sea level, you will still need these measurements plus the elevation of the reference point used for the static water level reading.
When your data is downloaded the depth of deployment will be used in the calculation of your Depth to Groundwater.
Periodically, during the monitoring project, the depth of deployment can be verified by re-measuring the depth to water and comparing it with the calculated value.
Once your data has been graphed, superimposing your water level meter readings on your calculated measurements will instantly show any drift experienced and allow you to correct for this change.
If you require a single water level measurement, sometimes it is more quicker and more efficient to just take a measurement with a Water Level Meter rather than downloaded a data logger and performing the required calculations.
To optimize your time having a Water Level Meter at your disposal is always a great idea.