Although the day started off gloomy and wet by the time of Geoinvestigate’s slot at two in the afternoon it had turned into a pleasant sunny day, perfect for filming. The shoot lasted the afternoon. Earlier the film crew had been recording the impact of sinkholes at a local golf course – not always a bad thing it would seem as sinkholes can provide useful natural features and scenery providing of course they don’t themselves pose ground stability hazards to golfers or the club house.
The shoot with Geoinvestigate outside the Town’s former Auction Mart site reviewed the impact of sinkholes on both the existing housing stock and new development in Ripon and how buildings should be investigated and safeguarded from future sinkhole events. The use of mobile caravan parks in the Town as an alternative to standard housing which may be at risk of cracking and demolition from sinkholes was discussed.
The recent sinkhole collapse of 2014 on Magdelans Close near to the film location (120m to the SE) and the sudden collapse of 2016 on Magdelans Road (250m S) where Frances O’Neill narrowly escaped falling into a deep hole were mentioned as well as the “notional” sinkhole design spans of 3.5m (the size of a patio door) up to 5m currently used to safeguard new building in the Town whereas in reality sinkhole collapses of 10m to 15m diameter are not untypical, the most recent in 2016 being 10m diameter x 5m deep.
Following the November 2016 Magdelans Road collapse Landmark carried out a retrospective risk analysis indentifying a 250m “high risk” area extending from this focus including much of the former Auction Mart site.
Proposals in 2016 to evacuate a new residential caravan park development at the Auction Mart occupied by elderly and senior Towns folk and remove or crane out caravans which might be affected by future subsidence were considered. This scheme relies on the ground subsiding slowly and progressively sagging allowing occupants plenty of time to leave their home prior to removal of their caravan to a safer part of the site. However this ground behaviour model has been turned on its head by the subsequent sudden large sinkhole collapse at Magdelans Road.
The recent event at Magdelans Road near to the proposed caravan park suggests that the earlier ground behaviour model on which the both the safety and feasibility of the caravan park development is based namely slow ground subsidence may be a fundamentally flawed and dangerous assumption in this and also other parts of Ripon. The perception that such an ill conceived safety plan might have on the public mindset as well as the recommendation that residents of the park should not be allowed to buy their own caravan homes but lease from a management company was also reviewed.
The Towns current “responsive” strategy to dealing with the impact of new sinkhole events on the Towns existing housing stock was also raised during filming. In Geoinvestigate’s opinion it is no longer acceptable to do little or nothing and just wait for the next sinkhole event which can be expected every two or three years – or perhaps longer if we’re lucky. When a new event occurs the current investigative MO seems to be – attend site, send up drones, take pics, update sinkhole maps, publish news articles and give interviews. Geoinvestigate believes the time is long overdue to adopt a more proactive strategy in dealing with Ripon’s never ending sinkhole problem. Geoinvestigate’s suggestion was that an ongoing programme of investigative drilling was required steadily working through the Towns existing buildings and homes starting with those at higher risk.
Following the 10 November 2016 sinkhole collapse at Magdelans Road the BGS at the beginning of this year were awarded an URGENT NERC grant for 52K to investigate the use of geophysical methods on the sinkhole geology of Ripon.
In Geoinvestigate’s opinion it is still to be shown that geophysical and microgravity surveys can provide reliable results in the built-up areas of the Town such as Magdelans Road and currently drilling continues to provide the only reliable method of quickly locating large holes beneath houses and gardens. Perhaps the outcome of the BGS’s current research will change this. It’s the big holes which are the most worrying and according to BGS they are lurking below Ripon waiting to be found or reveal themselves as subsidence or sudden collapse.
While concerns have been raised about the safety of drilling and that drill holes might (there is no conclusive evidence as yet), if badly constructed seed future sinkhole events it is Geoinvestigate’s opinion that new, cheaper and safer micro-hole probing technology or “Microdrilling” could be used safely in the Town to overcome this concern. For this reason Geoinvestigate recently developed their new high speed sinkhole probing machine, Microdrill. Geoinvestigate told Channel 5 that Microdrill offers a safer way of investigating Ripon’s sinkhole problems before they occur. In Geoinvestigate’s opinion it was no longer acceptable to continue burying heads in the sand and sitting on our hands just waiting for the next collapse in the Town. The next time around we may not be so lucky and someone could get hurt. Frances O’Neills close shave with the Magdelans Road sinkhole was a wake up call.
The recent proposal in the Town to drill using a “Down The Hole Hammer” raised concern. Geoinvestigate told Channel 5 that “You’re asking for trouble looking for sinkholes on potentially unstable ground using a hammer drill which creates mini-shock waves and releases large amounts of pressurised gas into a potentially already unstable situation”
Geoinvestigate were asked if Ripon really could claim to be “The Sinkhole Capital of Britain”. “Well The British Geological Survey have said Ripon lies in one of the most susceptible areas of the UK for sinkholes because of its Permian gypsum deposits, which can dissolve more quickly than surrounding limestone. So we assume this is where this title has come from. Where else in the UK do you have the same magnitude of recurring major natural ground instability mixed with built-up areas and human occupation”.
With regard to what perhaps might appear to some to be a fatalistic or accepting outlook by many in the Town to living with sinkhole hazard it was Geoinvestigate’s opinion that this could change if there was a very serious incident in the future or if banks and building societies decided as they have done recently with mine shaft hazard to look less favourably on lending in the Town. Only time will tell.
After the wrap Geoinvestigate enjoyed talking to Boomerang TV about the nuts and bolts of putting together a TV programme and with envy about the crews visit next week to film Florida’s sinkholes. Don’t be fooled they told us its hard work making movies even in Florida Ha Ha ! Watch out for Gators we told them as we left.