Data from a distance
With manual monitoring of water quality and flow rate often presenting challenges, Rosa Richards examines some of the remote monitoring options that have emerged
The announcement that England is set to run short of water within 25 years made the headlines in March 2019. As freshwater resources become scarcer, accurate measurement of water quantity and quality is more critical than ever. Flooding events also cause water quantity and quality issues, causing damage and public health issues – as seen in the catastrophic flooding in Mozambique resulting from Cyclone Idai in March 2019.
Monitoring the quality and flow rate of water bodies is necessary in order to meet regulations and protect ecological health, human health and the environment. However, effective manual monitoring is often impractical. High river flows during flooding events, for example, can make manual monitoring too dangerous. In addition, budgets for environmental monitoring may be tight. Fortunately, remote and autonomous methods for monitoring water bodies can offer safe, cost effective and efficient alternatives.
“Remote sensing using satellites is especially useful for monitoring lakes in areas that are inaccessible for ground sampling”
Satellite images used to be too crude to be useful for environmental monitoring purposes, with pixels corresponding to 300m2 groundcover, but resolution now goes down to pixels of 10m2. “The resolution of images from the second generation of European satellites is now detailed enough to provide useful optical data to environmental agencies,” says Dr Bill Brierley, CEO of the F
reshwater Biological Association. “Another benefit is that satellites revisit the UK every one to five days, which is much more frequent than manual sampling by environment protection agencies.”
A Natural Environment Research Council project evaluated the use of satellite remote sensing for regulation and monitoring of inland water quality in the UK. Dr Claire Neil of the University of Stirling assessed algorithms for inferring valuable water quality parameters from satellite images using reflectance data; she found that satellite data could be used to accurately predict the quantity of chlorophyll a (a surrogate measurement of algal biomass in water) present in Scottish lochs when compared to actual water samples.
The University of Stirling is currently developing a method for using satellite images to classify water bodies according to the European Water Framework Directive, which could be used across Europe. The next step will be to add in other common water quality parameters using publicly available data sets from the Google Earth Engine. Maps can then be produced to monitor water quality using satellite images. This can help with environmental regulation, and also boost early detection of quality issues in drinking water reservoirs. Satellite images can also be used to identify where samples should be taken on the ground, so that water quality can be investigated further and pollution sources located.
Of course, satellite imagery has limitations: a satellite pass-over can only take useful images on a cloud-free day. At Loch Leven in Scotland, for example, there were only 95 days in one year when satellite images could be taken. However, this is a much bigger dataset than the 12 samples that were taken by the Scottish Environmental Protection Agency (SEPA) that year. Additionally, thousands of lakes can be monitor
ed in one satellite pass-over, whereas only 60 lakes are manually monitored by SEPA, and remote sensing using satellites is especially useful for monitoring lakes in areas that are inaccessible for ground sampling.
Another benefit is the fact that a satellite can obtain a picture of the water quality across the whole lake, rather than just one spot sample from one location. This equates to millions of satellite ‘water samples’ per year – far more than the 720 manual samples per lake per year taken by SEPA. Satellite monitoring could thus help environmental protection agencies deliver more for less at a time when environmental regulation budgets are tight.
Satellite imagery can even be used to monitor river flow rate; Professor Fujita Ichiro at Kobe University has developed a piece of software that can measure flow rate using image analysis. This could be used for flood risk management.
“When ARC-boats are used, data can be collected by two people 15 times more efficiently than by a manned boat”
“Remote sensing methods offer a much safer way to measure fast-flowing rivers,” says Andy Roberts, technical specialist at the Environment Agency. “Methods have advanced a long way since the old days of sending out a manned boat in dangerous conditions to measure river flows, or sending staff to a gauging weir, which itself can become flooded when we experience extreme events. We now use remote control ARC-boats with integrated acoustic Doppler current profilers (ADCP), among other methods.”
An ADCP sends out sound beams to measure river flows and map the river profile. When ARC-boats are used, data can be collected by two people 15 times more efficiently than by a manned boat – two people can cover six sites in one day (three sites per person per day), whereas five people manning one boat for one day for one site (0.2 sites per person per day). ARC-boats also achieve better results at difficult sites.
River flow monitoring is used not just for managing flood risks, but also for managing a host of other issues, including droughts, water supply, discharges from industry, ecology and environment, infrastructure planning, design and protection, agriculture, house building and climate change research.
Even more advanced than remote control vehicles are autonomous aquatic vehicles (AVs), which can be programmed to run repeatable missions for a series of data, even at sites with difficult access. There is an investment cost, but AVs pay for themselves over time as field resources can be reduced – an AV can feasibly be deployed by just one person, and this can be done outside of normal working hours if needed. The AV can even be left unsupervised to navigate a water body
on a pre-programmed course and create a detailed profile before being picked up later.
An aquatic AV can collect various types of data: bathymetric data, hydrometric data, environmental water quality, industrial water quality and side scan sonar, depending on the sensors on board. This data has a wide range of applications, such as bathymetry surveys, flow/velocity/discharge, habitats surveys, reservoir management, bathing water monitoring, combined sewer overflows, unlicensed industrial discharges, pollution tracking and tracing, dredging and construction, commercial aquaculture, thermal discharge and saline intrusion into a freshwater body.
A joint India-UK research project is evaluating the use of water quality sensors to indicate aquatic ecological health in India. A fluorescence sensor can be used to detect the processing activity in water, distinguishing peaks of fluorescence associated with microbial activity in order to measure the presence of the amino acid tryptophan. The project is deploying, adapting and networking sensors along the Hooghly River in urban Kolkata, India, to undertake catchment-scale monitoring of freshwater systems.
Researchers at the University of the West of England (UWE) propose that measuring aquatic fluorescence organic matter in situ and in real time, alongside other water quality parameters in a multi-parameter probe, will enable them to monitor microbial activity and help infer the overall ecosystem health of the water.
Professor Darren Reynolds of UWE is leading the UK consortium of the research project. “Our initial scoping studies showed a good correlation between the level of tryptophan measured with a fluorimeter compared with biological water quality indicators like thermotolerant faecal coliform (TTC) bacteria and E. coli measured in lab tests,” he says. “We are confident about building on these findings to develop a method for potentially monitoring freshwater ecosystem health.”
A method for inferring how well our aquatic freshwater ecosystems are functioning is needed if we are to better manage the freshwater needed for human life, as well as identify the presence of pathogenic bacteria that could require extra water treatment. There is no doubt that managing our water resources is a global issue, and many new technologies are enabling us to do so more effectively than ever before.
Rosa Richards is an independent environmental consultant specialising in water policy and monitoring, a freelance science writer and programme manager of the Sensors for Water Interest Group (SWIG)