No need for sink holes to wreck con­fi­dence in Ripon

The hole that opened up un­der a Ripon house this week left home­own­ers with a sink­ing feel­ing. Should they be wor­ried? Sharon Dale re­ports.

Yorkshire Post - Property - - PROPERTY -

SEN­SA­TIONAL pic­tures of a house in Ripon be­ing swal­lowed by the earth and ripped asun­der have left home­own­ers ques­tion­ing the sta­bil­ity of the ground be­neath their foun­da­tions.

The 25ft wide sink hole, which opened up on Mon­day, has prompted fran­tic Googling and crash cour­ses in ge­ol­ogy via Wikipedia.

What’s clear is that sus­tained mon­soon-style rain­fall is the most likely cat­a­lyst. There is usu­ally an aver­age of two sink holes a year in the UK and there have been six so far in 2014, in­clud­ing a 15ft wide chasm in High Wy­combe that con­sumed a car.

In some ar­eas of Ripon, there is a Per­mian layer of gyp­sum deep un­der­ground that is apt to dis­solve when del­uged by seep­ing ground­wa­ter and over­loaded un­der­ground rivers, known as aquifers.

The is­sue of gyp­sum dis­so­lu­tion has been on ge­ol­o­gists’ radar for years and the Bri­tish Ge­o­log­i­cal Sur­vey has re­ported on the nat­u­ral phe­nom­e­non.

Paul Hil­dreth, of the York­shire Ge­o­log­i­cal So­ci­ety, says: “As gyp­sum is sol­u­ble, given lots of time, any in­crease in rain­fall is al­most cer­tainly go­ing to cause faster so­lu­tion. How­ever, hu­man ac­tiv­ity has a part to play in ac­cel­er­at­ing this prob­lem.

“The ef­fi­ciency of ur­ban ar­eas to trans­port wa­ter through Tar­ma­cadam sur­faces and drainage sys­tems may di­rect faster flows and greater vol­umes to spe­cific ar­eas and make these hot spots more prone to the so­lu­tion of gyp­sum. Added to that, the weight of build­ings in sus­cep­ti­ble ar­eas will con­trib­ute to ground fail­ure and sub­se­quent col­lapse.” He adds: “Gyp­sum-bear­ing rocks, such as the ones at Ripon, oc­cur in a nar­row belt from Durham to Not­ting­hamshire but their thick­ness and pu­rity varies. It has been recorded that as well as be­ing close to the sur­face, the beds at Ripon are also strongly con­torted which could make them more prone to so­lu­tion than neigh­bour­ing ar­eas.”

In 2005, a lec­ture by Prof. Anthony Cooper of the Bri­tish Ge­o­log­i­cal Sur­vey, re­vealed that the gyp­sum prob­lems in the Ripon area were so se­vere that “spe­cial plan­ning reg­u­la­tions are en­forced for de­vel­op­ment.”

Har­ro­gate Coun­cil has long in­sisted that all plan­ning ap­pli­ca­tions in gyp­sum af­fected ar­eas are sup­ported by a ground sta­bil­ity re­port. That doesn’t ap­ply to older prop­er­ties, of course, so how con­cerned should home­own­ers be about the pos­si­bil­ity of sub­si­dence?

Char­tered sur­veyor Jon Char­ters-Reid, who is keen to put a stop to the panic, says: “Frankly, you have more chance of win­ning the lot­tery or be­ing hit by a fall­ing piano than your house fall­ing into a sink hole. They are very rare, so much so that in­sur­ers see them as an act of God.”

He adds that al­though ge­o­log­i­cal maps show gyp­sum de­posits run­ning through Ripon, that doesn’t mean property is at risk.

“Some of the houses have stood for hun­dreds of years and they’re still stand­ing. What hap­pened this week is a freak oc­cur­rence due to freak weather con­di­tions.

“We’ve had some of the heav­i­est rain­fall for 200 years and that has had a knock on ef­fect caus­ing flood­ing and also caus­ing gyp­sum to dis­solve.”

Jon, who is based in York, sug­gests that prospec­tive buy­ers in­vest in a com­pre­hen­sive property sur­vey from a lo­cal in­de­pen­dent sur­veyor who knows the area well.

The sur­veys cost from £300. If there are con­cerns about ground sta­bil­ity then a thor­ough ge­o­log­i­cal re­port is a good in­vest­ment. It should cost around £200. In­sur­a­bil­ity should also be checked to make sure there is cover avail­able and at what cost.

Tak­ing the DIY ap­proach and fret­ting over ge­o­log­i­cal maps and sci­en­tific data you’ve found on the in­ter­net is point­less, says Jon.

“You might see that there is gyp­sum un­der or close to a property and panic when there is ab­so­lutely no need. It’s the same with flood maps. They as­sume a worst case sce­nario. Some vil­lages have been placed in flood plains on the maps when they have never flooded and are not likely to.

“Per­son­ally, I am not at all con­cerned about sink holes.

“I think we should be far more wor­ried about the ef­fects of frack­ing in this coun­try, where we have a lot of aquifers. There is a lot of un­cer­tainty about what could hap­pen.”

Es­tate agent Andrew Bead­nall, of Bead­nall Co­p­ley, which has a branch in Ripon, is wor­ried that the me­dia storm could af­fect Ripon’s soar­ing pop­u­lar­ity. The small city has be­come in­creas­ingly at­trac­tive to buy­ers, who are keen to be close to the gram­mar school and to live in a pretty, his­toric area with its own cathe­dral, a Booth’s su­per­mar­ket and fan­tas­tic links to beau­ti­ful coun­try­side and to the A1M.

“Ripon is in­cred­i­bly pop­u­lar. At the mo­ment we are sell­ing prop­er­ties as soon as they come on the mar­ket but I am con­cerned that the sensationalism sur­round­ing the sink hole will af­fect con­fi­dence,” says Andrew. “There is ab­so­lutely no need for panic. You re­ally do have more chance of win­ning mil­lions on the lot­tery than be­ing af­fected by a sink hole.”

BY GE­ORGE: This Ge­or­gian town­house is in a con­ser­va­tion area close to York city cen­tre and has views of the Min­ster. The pe­riod fea­tures have been ren­o­vated and re­stored. It was one of a pair of houses that had been carved up into flats, but now is a...

DON’T PANIC: The house in Ripon which col­lapsed into a sink hole. But the chances of your property be­ing sim­i­larly af­fected are very re­mote.

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