Ground­wa­ter is the main source of wa­ter in li­mes­tone en­vi­ron­ments. These re­sources are of­ten of good qua­li­ty and in suf­fi­cient quan­ti­ty, but the dif­fi­cul­ty lies in their ac­ces­si­bi­li­ty. Lo­ca­ting and si­zing wa­ter pro­duc­tion fa­ci­li­ties to match needs with avai­lable re­sources re­quires prior know­ledge of the en­vi­ron­ment and tar­ge­ted in­ves­ti­ga­tions. SISKA pro­vides so­lu­tions for re­sear­ching, ex­ploi­ting, ma­na­ging and pro­tec­ting ground­wa­ter in li­mes­tone en­vi­ron­ments.

Karst plays a spe­cial role in the pro­blem of na­tu­ral ha­zards. SISKA has de­ve­lo­ped in­ves­ti­ga­tion me­thods for as­ses­sing and map­ping the fol­lo­wing na­tu­ral ha­zards:

Col­lapses oc­cur re­gu­lar­ly in kars­tic re­gions. By stu­dying these phe­no­me­na through concrete cases, we can pre­dict the condi­tions that lead to these events. As a re­sult, col­lapse risk maps can be pro­du­ced.

In karst, run-off is es­sen­tial­ly un­der­ground and the­re­fore in­vi­sible. Ho­we­ver, the un­der­ground wa­ter table can so­me­times reach the sur­face, floo­ding areas that are nor­mal­ly dry, and pro­du­cing sud­den and si­gni­fi­cant in­creases in ri­ver flow. Thanks to the mo­dels de­ve­lo­ped by the SISKA (KARSYS, Karst­MOD), it is pos­sible to fo­re­cast floods and ri­ver flows and pro­duce flood ha­zard maps tai­lo­red to the spe­ci­fic cha­rac­te­ris­tics of karst.

The SISKA sup­ports ci­vil en­gi­nee­ring pro­jects in kars­tic re­gions and pro­poses so­lu­tions to prevent pro­blems of sta­bi­li­ty, wa­ter in­gress and grey wa­ter in­fil­tra­tion.

The SISKA is fre­quent­ly com­mis­sio­ned to sup­port sur­face de­ve­lop­ment pro­jects (mo­tor­ways, wind farms) or the construc­tion of un­der­ground struc­tures (tun­nels, gal­le­ries, etc.). Through its re­search and de­ve­lop­ment ac­ti­vi­ties, the SISKA has de­ve­lo­ped me­thods for iden­ti­fying and re­me­dying the pro­blems po­sed by construc­tion in kars­tic en­vi­ron­ments. The Kars­tA­LEA me­thod, the re­sult of col­la­bo­ra­tion with the Fe­de­ral Roads Of­fice (FEDRO), is an illus­tra­tion of the prac­ti­cal me­thods de­ve­lo­ped by the ins­ti­tute.

The SISKA spe­cia­lises in un­der­ground mea­su­re­ments and do­cu­men­ta­tion.

The SISKA is fre­quent­ly in­vol­ved in the pro­duc­tion of un­der­ground mo­dels to help un­ders­tand, de­ve­lop and ex­ploit un­der­ground geo­lo­gi­cal and hy­dro­geo­lo­gi­cal as­pects. Va­rious tools can be pro­po­sed for the lo­ca­tion, to­po­gra­phy or 3D ac­qui­si­tion of un­der­ground voids. There are ma­ny examples of ap­pli­ca­tions:

• De­si­gning un­der­ground de­ve­lop­ments: tou­rist in­fra­struc­tures, laying pipes, etc. or sur­face de­ve­lop­ments in­ter­ac­ting with the sub­soil;
• Plan­ning for the ex­ploi­ta­tion stra­te­gy of un­der­ground de­po­sits (e.g. salt mines) or for the as­sess­ment of back­fill ca­pa­ci­ties;
• Do­cu­men­ta­tion of his­to­ric un­der­ground struc­tures, etc.

The SISKA al­so has a great deal of ex­pe­rience in the ins­tru­men­ta­tion of phe­no­me­na in un­der­ground en­vi­ron­ments, par­ti­cu­lar­ly in the context of mo­ni­to­ring ground­wa­ter qua­li­ty, the qua­li­ty of the un­der­ground at­mos­phere or tre­mors du­ring de­ve­lop­ment work.

Karst re­gions are in­crea­sin­gly concer­ned with the de­ve­lop­ment of in­fra­struc­ture for the pro­duc­tion of re­ne­wable ener­gy, main­ly hy­droe­lec­tric, geo­ther­mal and wind po­wer. The SISKA as­sists de­ve­lo­pers with re­ne­wable ener­gy pro­jects in these re­gions.

Karst ground­wa­ter of­fers some po­ten­tial for ge­ne­ra­ting elec­tri­ci­ty. Ho­we­ver, such ex­ploi­ta­tion is not wi­thout risk to the en­vi­ron­ment, and the risks must be as­ses­sed by spe­cia­lists.
The SISKA is ac­tive in this field, pro­vi­ding sup­port for pro­jects and car­rying out im­pact stu­dies. We are in a po­si­tion to make a diag­no­sis at the pre-pro­ject stage to see whe­ther the pro­ject has a chance of suc­cess and what adap­ta­tions would be ne­ces­sa­ry to com­ply with the va­rious laws and prac­ti­cal ins­truc­tions re­la­ting to pro­jects in karst.

The ins­tal­la­tion of wind tur­bines in kars­tic en­vi­ron­ments must be sub­ject to spe­ci­fic sup­port in terms of en­vi­ron­men­tal im­pact and, conver­se­ly, the risks of sta­bi­li­ty for the struc­ture.

The heat pro­pa­ga­tion me­cha­nisms in karst sub­soils are ve­ry dif­ferent from those in other geo­lo­gi­cal en­vi­ron­ments. Ex­ploi­ta­tion pro­jects of­ten re­quire adap­ta­tion and spe­cia­li­sed sup­port. The SISKA has tools and ex­pe­rience in this field, and works in col­la­bo­ra­tion with the Centre for Hy­dro­geo­lo­gy and Geo­ther­mal Ener­gy at the Uni­ver­si­ty of Neu­châ­tel, which is a re­co­gni­sed centre of ex­per­tise.

Caves and kars­tic land­scapes are the re­sult of the dis­so­lu­tion of li­mes­tone in rain­wa­ter. In some cases, dis­so­lu­tion can re­sult from other causes (e.g. deep gas up­wel­ling). Un­ders­tan­ding how caves are for­med is of ob­vious in­ter­est to the ca­ver ex­plo­ring them. Ho­we­ver, pre­dic­ting the pre­sence of an un­der­ground void is al­so im­por­tant in­for­ma­tion for an en­gi­neer buil­ding a tun­nel or a hy­dro­geo­lo­gist col­lec­ting wa­ter.

Se­ve­ral nu­me­ri­cal mo­dels of spe­leo­ge­ne­sis have been de­ve­lo­ped over the last 35 years. They have taught us a great deal about the prin­ciples, rates of for­ma­tion and broad out­lines of the geo­me­try of un­der­ground gal­le­ry net­works. Ho­we­ver, the cha­rac­te­ri­sa­tion of the ground pa­ra­me­ters that feed these mo­dels is com­pa­ra­ti­ve­ly late. The SISKA's re­search is the­re­fore hel­ping to pro­vide field da­ta, re­present it and com­pare it with the re­sults of si­mu­la­tion mo­dels.

Karst struc­tures clear­ly do not de­ve­lop ran­dom­ly. We have iden­ti­fied the ge­ne­ral cha­rac­te­ris­tics and can sketch out the areas that are po­ten­tial­ly the most kars­ti­fied. Ho­we­ver, if we are to ge­ne­rate rea­lis­tic net­works, there is still work to be done for fu­ture ge­ne­ra­tions...

Our work main­ly concerns :

• The spa­tial dis­tri­bu­tion of kars­tic conduits (concept of in­cep­tion ho­ri­zons)
• The ge­ne­sis of kars­tic net­works in the epi­phrea­tic zone (loops)
• The laye­ring of kars­tic net­works (spe­leo­ge­ne­tic phases)

At present, they are concen­tra­ting main­ly on pre­dic­ting the (pro­ba­bi­lis­tic) po­si­tion of ducts and on cha­rac­te­ri­sing them (size, shape, filling, wa­ter, etc.).

Al­though at first sight a high­ly aca­de­mic sub­ject, a de­tai­led un­ders­tan­ding of the un­der­ground cli­mate is im­por­tant for the ma­na­ge­ment of ar­chaeo­lo­gi­cal, or­nate and tou­rist caves, and even for cer­tain spe­leo­lo­gi­cal pro­jects. It is al­so im­por­tant for un­ders­tan­ding the ther­mal cha­rac­te­ris­tics of kars­tic mas­sifs, and hence the ins­tal­la­tion of geo­ther­mal probes, or for ex­plai­ning the pre­sence of a na­tu­ral gla­cier. Fi­nal­ly, it is ne­ces­sa­ry to in­ter­pret the va­ria­tions ob­ser­ved in the growth of sta­lag­mites and to pro­duce pa­laeo­cli­ma­tic re­cons­truc­tions.

Cur­rent pro­jects:

• Ca­ve­Seds
• Ana­ly­sis of the in­ter­ac­tions bet­ween ven­ti­la­tion, CO2 le­vels and wa­ter che­mis­try in the Mi­landre cave
• Long-term mo­ni­to­ring of se­ve­ral na­tu­ral gla­ciers in the Ju­ra

Past pro­jects:

• Ther­mo­karst
• Stu­dy of na­tu­ral gla­ciers in the Ju­ra
• Ana­ly­sis of the cli­mate in the Las­caux cave
• Stu­dy of the ther­mal pro­per­ties of kars­tic mas­sifs
• As­sess­ment of the ther­mal po­ten­tial of kars­tic mas­sifs
• Ar­ti­fi­cial ven­ti­la­tion test in a kars­tic ca­vi­ty (Mi­landre)

Iso­la­ted from ex­ter­nal ero­sion pro­cesses, caves pre­serve se­di­men­ta­ry se­quences span­ning hun­dreds of thou­sands or even mil­lions of years. The stu­dy of these de­po­sits, whe­ther de­tri­tal se­di­ments (i.e. la­mi­nites, pebbles) or spe­leo­thems (i.e. sta­lag­mites), pro­vides va­luable in­for­ma­tion on cli­ma­tic and en­vi­ron­men­tal changes over time. From gla­cial cycles to sea­so­nal fluc­tua­tions, cave se­di­ments pro­vide va­luable in­for­ma­tion about our past en­vi­ron­ment.
In ad­di­tion to da­ting these se­di­ments, the SISKA is stu­dying their mi­ne­ra­lo­gi­cal (cal­cite, ara­go­nite, quartz, etc.), geo­che­mi­cal (Mg, Sr, Ba, S, etc.) and iso­to­pic (d18O, d13C, etc.) si­gna­tures, as well as their fau­nal (mi­croin­ver­te­brates, bones) and bo­ta­ni­cal (pol­lens) content.

See al­so our ex­per­tise in ar­chaeo­zoo­lo­gy.

Cli­ma­tic condi­tions have ma­ny in­fluences on karst. Among these, the SISKA is main­ly as­ses­sing the ef­fect of cli­mate change on the fol­lo­wing ele­ments.

• In­fil­tra­tion of wa­ter in­to the sub­soil or re­charge of aqui­fers. This has a di­rect in­fluence on the quan­ti­ty of ground­wa­ter avai­lable. It is the re­sult of a de­li­cate ba­lance bet­ween cli­ma­tic fac­tors (rain­fall, tem­pe­ra­ture, etc.) and bio­pe­do­lo­gi­cal fac­tors (ve­ge­ta­tion and soil).
• The pre­ci­pi­ta­tion of cal­cite in sta­lag­mites is par­ti­cu­lar­ly re­le­vant to pa­laeo­cli­ma­tic re­cons­truc­tion. The layers of cal­cite de­po­si­ted in sta­lag­mites re­cord the cli­ma­tic condi­tions pre­vai­ling at the time of their de­po­si­tion, in a si­mi­lar way to the rings on the trunk of a tree.
• The dis­so­lu­tion of li­mes­tone plays a role in slo­wing down glo­bal war­ming. In­deed, it has been shown that glo­bal war­ming in­creases bio­lo­gi­cal ac­ti­vi­ty in soils, lea­ding to an in­crease in the soil's CO2 content. Wa­ter in­fil­tra­ting the soil the­re­fore dis­solves more CO2, which in turn al­lows it to dis­solve more li­mes­tone. The re­sult is that for each ad­di­tio­nal mo­le­cule of li­mes­tone dis­sol­ved, one mo­le­cule has been re­mo­ved from the soil, and the­re­fore from the earth's at­mos­phere. This re­mo­val of CO2 could ex­plain a large part of what spe­cia­lists call the "car­bon sink", i.e. the fact that at­mos­phe­ric CO2 is in­crea­sing less qui­ck­ly than mo­del es­ti­mates.