Groundwater level logging comes of age

November 15, 2011

To say that groundwater is vital is understating its importance. Groundwater accounts for almost 70% of the world’s freshwater supply and as rivers and lakes tend to be supported by groundwater it is no exaggeration to say that almost all the water used in agriculture, industry and for drinking is, or has been, groundwater at some point.

It is easy to relate the impact of groundwater on our environment but less so the effect on our economy. Water has long been recognised as a major source of wealth and agriculture is made possible due to the abundant use of water and, historically, towns and cities around the world have been built on the banks of rivers.

There are many reasons why it is important to monitor groundwater levels: for consistency of supply, protection of the environment from extremes like floods and droughts and also to monitor groundwater quality for pollutants. Rising groundwater can bring pollution problems to the surface, flushing it into local rivers and waterways, affecting wildlife and impacting on the water supply. Rising groundwater can also lead to flooding which is estimated to cost the UK around £2.2 billion every year. We spend around £800 million per annum on defences and even with these flood defences in place it costs the economy an average of £1,400 million in damages, so monitoring groundwater is environmentally, economically and politically important.

Water level logging techniques have developed over the years and the data collected from this activity shapes almost everything we do when it comes to water security, commercial and domestic design and planning, so it is vital that the data collected is consistent and correct.

Water level logging with a dip meter or water level meter measures the depth of water in wells, boreholes and standpipes at a moment in time. These instruments are accurate, reliable, easy to use and collect data from up to 1000m, and some have a bottom sensor to measure the depth of the well being monitored. However they are not intended for continuous use hence the water level data logger was born.

A data logger is an electronic device that records data at predetermined intervals, based on a digital processor they are generally small, battery powered, portable and equipped with an internal memory for data storage. Water level loggers interface with computers and utilize software logger to view and analyse the collected information.

Water level data loggers record water level, temperature, conductivity and other parameters automatically 24 hours a day, seven days a week. Upon activation a water level logger will typically be deployed and left unattended to measure and record information for the duration of a monitoring period. This allows for a comprehensive and accurate picture of the groundwater being monitored. We have known of water level loggers deployed in the field, successfully collecting data for more than six years.

These smart and easy to use data loggers have changed over the years to become far more reliable and accurate and some now have the option of telemetry. Originally however, a water level logger was placed down-well and readings regularly collected on site directly from the instrument. Historically these were stand-alone level logging devices with large onboard memories capable of storing data collected over many days or months of unattended recording. The data was collected and typically recorded at a specific date and time to produce a sequence of events. Today level loggers range from simple single-channel input devices to complex multi-channel instruments that allow for many computations and alarms based on predetermined conditions. The newest water level loggers can populate web pages, allowing numerous people to monitor a system remotely.

Most water level loggers have to work in field conditions that dictate that they must be extremely robust and reliable as they need to operate for long periods nonstop with little or no human supervision, and may be installed in harsh or remote locations, so it is imperative that as long as they have power, they will not fail to log data for any reason. Manufacturers go to great lengths to ensure that their water level loggers can be depended upon. In addition there are now water level loggers manufactured with ceramic casings to allow for accurate logging in more corrosive conditions to monitor saltwater intrusion, injected wastewater and contaminated waste from chemical or landfill sites for example. Even in these conditions you can expect a typical accuracy of +/- 0.05% and a memory for 48,000 measurements and to sample at variable intervals of between 0.5 seconds to 99 hours.

See the example below of a water level logging system set-up using various methods of communication including Read-Out Units, Onsite Data Store and cable links to a PC/Laptop. Additionally there is the telemetry option using a Well Modem linked to the water level logger via a cable.

Most groundwater level logging systems can be added to a complete data acquisition system that may include a rain gauge, soil/MCT sensor, weather station, evaporation ring and telemetry system as seen in the second illustration.

For more information regarding one of the most well respected names in water level logging technology, with tens of thousands of units in place worldwide – Diver® by Schlumberger Water Services call Van Walt on +44 (0)1428 661 660 or email john.bolton@vanwalt.com.

Tracey Daley