Protecting nature with detailed and non-intrusive geophysics investigations

Matt Stringellow is associate director at RSK Geophysics and a Chartered Geologist

The aim of a geophysics survey is to provide a comprehensive guide on any risks in the ground ahead of an intrusive investigation. While utilities lines or built hazards generally follow a predictable pattern, nature often does not, so GPR and other non-intrusive methods have often been used to inform the ground conditions. But more and more, we recognise that the non-intrusive aspect of geophysics surveys is perfect for new and innovative uses where nature and ecology are concerned.

Currently, there is no specific law that states that geophysics must be used at any given time, but it is recommended in the Construction Industry Research and Information Association (CIRIA) good practice guide. Geophysical investigations typically provide greater data coverage of a site and are often more cost-effective compared to using only intrusive investigations, as they can reduce risks and potential costs when dealing with unknown ground conditions.

Often, geophysics is called to use only upon the discovery of unforeseen hazards or ground conditions, by which point damage may have already occurred, potentially leading to fines and delays.

Proactively using geophysics by comparison, especially when dealing with nature, can provide non-destructive, full-site coverage to inform further work without the associated risks. In fact, geophysics is well used in archaeology, as it can heavily reduce the amount of trenching required. Bringing this proactive approach to construction, development and ecology will bring similar benefits.

Of course, there are situations when it may not be possible to achieve the same results – clay soils or made ground can be particularly difficult for GPR because clay is conductive and attenuates the radar signal, while the granular make-up of worked soils can cause scattering, reducing signal strength relative to the background noise. Nonetheless, near-surface geophysics offers a range of tools for use in non-invasive ground investigations that are often underutilised.

One of the more practised uses of GPR in nature is for finding underground animal burrows and tree roots. The technology has been used to find everything from rabbit burrows to water vole burrow systems, a project that featured on BBC’s Springwatch, although in practice its main application has been in mapping badger sett systems on railway, waterway and highway infrastructure.

If embankments are sufficiently burrowed into, there is a risk of collapse. In fact, there are some 100,000 sites on UK railways alone that are affected by burrowing animals. Badgers are protected under the Protection of Badgers Act 1992, and work that disturbs badgers occupying a sett is illegal. In these situations, GPR is often the only solution to help locate the extents of the underground burrows.

Because GPR is non-invasive, there is no need for excavations or ground disturbances to map a tree root system or badger sett network. This is particularly important when dealing with nature, which can otherwise be harmed by intrusive excavations. Trees, for example, bring us multiple benefits, from increased biodiversity, health and wellbeing to reducing urban temperatures in the face of climate change. Therefore, we need to protect them as much as we can.

This is important for any developments or ground works, especially in the vicinity of protected trees, where there is a requirement to not disturb or damage them. GPR is a very versatile technology and, as well as mapping burrow systems, it can be used to locate tree roots in the ground. Tree roots are analogous to water-filled pipes and can be mapped in the same way we would deploy the technology to find utilities on brownfield land.

More recently, GPR has been successfully used to survey hidden palaeochannels as part of river restoration works by the Environment Agency and Affinity Water. A recent project located near Amersham in the Chilterns saw a 2km section of the River Misbourne – one of the UK’s rare chalk streams – mapped. GPR was able to find the buried palaeochannel winding its way across a series of fields so that the river channel could be renaturalised and returned to its old course, restoring the flow, connecting it to its natural water table and improving the ecology and amenity value of the river.

In the UK, 97% of rivers have been modified and blocked by weirs, dams, locks, channels and other structures to suit our needs, with enormous damage to wildlife. In the future, we can see geophysics assisting in reversing some of that damage by revealing features such as former channels and hidden engineered structures.

Geophysical technology such as GPR is in use daily, but its applications are wide-ranging, with more uses being found all the time. New instruments with multiple antenna arrays will provide an even greater insight into the underground. The more we use geophysics technology, the more we find innovative ways to utilise it and see beneath the ground to inform our next steps on a project for development or restoration.

It should be seen as the first part of a ground investigation, especially when working with nature and sensitive ecology, where it can provide key habitat information that is needed by ecologists and planners alike.

• Matt Stringellow is associate director at RSK Geophysics and a Chartered Geologist

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