Unlike stream monitoring or rainfall, groundwater monitoring has always been a bit of a “dark art” for many people.  Depth to water measurements may only be done intermittently and infrequently (e.g.annually).  Depending on the site and requirements for that bore, this may not tell us what is actually happening with the groundwater.

Manual SWL measurement

Low Frequency Monitoring

The first chart below shows actual data from a bore that has been monitored since 2009.  The readings for January and July are shown. Biannual measurement is common in many groundwater monitoring programs .

The standing water level (SWL) in the bore appeared to be stable until Jan 2012 then it appears that the bore level is fluctuating significantly.

Monthly monitoring

The chart below shows monthly data for the same bore.  4T was, in fact, monitoring the bore each month, and the monthly data shows the variability that is actually occurring in the groundwater level.

Monthly monitoring
Monthly SWL readings from the same bore show high variability as the bore is pumped for use.  The bore recovers well after each pumping cycle to a stable SWL.

Monthly SWL readings from the same bore show high variability as the bore is pumped for use.  The bore recovers well after each pumping cycle to a stable SWL.

The hidden story

The smaller dataset in the first chart disguises a significant amount of variability in the SWL.  From 2009 until 2012, the level appears to be very stable, raising no cause for concern.  It is not until July 2012 that there is any indication of variability.  

In this particular instance, we know that the SWL variability is due to the bore being pumped – it is a production bore – so there was no cause for alarm because it recovers to a stable SWL following each pumping cycle.  

In the first chart, the readings in July 2012, January 2014 and January 2015 just happened to coincide with dates that the bore was being pumped.

Continuous monitoring

The use of continuous, in-situ loggers is a cost-effective and accurate means of overcoming the data deficit that comes with intermittent monitoring.  The logger can be programmed to record SWL at any time interval required. (If you need your SWL recorded every second – that’s possible!), so it provides very detailed data and highlights any small fluctuations.  

Data download

Loggers can be;

• configured to transmit data in real time. This data can be viewed on-line, and even connected to alarms set to trigger at a given groundwater level, or
• downloaded manually to a computer – either during a periodic site visit or when the monitoring period has ended and the logger is removed.

The chart below shows SWL data from a bore logger that was set to monitor at 6 hourly intervals, giving a very accurate and transparent picture of what is actually happening in the bore.  

This data also shows that there appears to be a trend of dropping water level (SWL) since July 2012.

Data from an in-situ bore logger recording at 6 hourly intervals tells an accurate and transparent story about the state of the groundwater bore.

Tools of the Trade

Manual SWL readings are taken using an electronic ‘dipper tape’ (left photo).  This sends an audible signal when it contacts water.  There are different length tapes and types available and 4T can assist with selection and operation.

Continuous loggers (right photo) are small enough to fit most bores, and are generally very robust and reliable. However, 4T has encountered some problems in high-salinity (high EC) environments.

The selection of tools to measure SWL depends on your objectives , budget and what resolution of data is required.  4T can assist with selection of the right tool for the job.