WHO GIVES A SINK? – 3D GEOLOGICAL MODELLING AND GEOPHYSICAL INVESTIGATIONS OF THE SINKHOLE PRONE CITY OF RIPON, UK

Ripon is a historic cathedral city and market town located in North Yorkshire, UK. It is the only city in the UK enforcing classified planning zones based on the potential for subsidence caused by bedrock dissolution. The underlying geology comprises Permian limestone, marls and gypsum, all capped by superficial deposits. It is the rapid rate of dissolution of the gypsum (CaSO₄ 2H₂O) that enables karst features to form and evolve on human timescales. Following a collapse that formed a sinkhole in the garden of a property on Magdalens Road, Ripon, in November 2016, the British Geological Survey (BGS), funded by a Natural Environment Research Council (NERC) urgency grant, initiated a programme of research. Monitoring began on a depression feature forming in a nearby recreation area that had been reported by residents to have increased in dimensions. A geophysical survey was undertaken utilising integrated ground-based LiDAR imaging with geophysical techniques (Williams et al. 2020).

Alongside this work, a 3D geological ground model was built to provide the wider geological context. The Ripon 3D geological model was one of the first applied geological models to be piloted in the BGS Groundhog Geological Software. Initially created using GSI3D (Geological Surveying and Investigation in 3 Dimensions), (Mathers et al. 2011), the original data was imported into Groundhog, testing the interoperable capabilities of the software (Wood et al, 2015).

Setting the sinkhole and the geophysical surveys in a spatial 3D context, it may be possible to allow interpretations to be made with respect to the processes associated with the formation of sinkhole geohazards. BGS, as the UK’s premier provider of objective and public-good geoscientific data, works with the local community, councils, and geotechnical consultants to communicate a better understanding of where sinkhole hazards may occur. The model will become a useful and integral part of planning and geological investigations and will be made open-to-use for all BGS stakeholders.

A. Keith Turner was passionate about 3D geological modelling, especially for visualisation and geohazard mitigation. On one of his many working trips to the UK, Keith visited Ripon as part of a field trip hosted by BGS - a true gentleman - always offering his umbrella when the rain came down sideways!