WEBVTT Kind: captions Language: en 00:00:04.480 --> 00:00:10.960 so after this very interesting overview of what  is water on earth i will focus on on groundwater   00:00:12.080 --> 00:00:20.880 and why explaining you what is groundwater for  several reasons groundwater plays an important   00:00:20.880 --> 00:00:29.520 role of course we are here in Evian and about  100 percent of bottled water is coming from   00:00:29.520 --> 00:00:35.920 ground water but as Ghislain said as potable  water, drinking water is very small amount   00:00:37.360 --> 00:00:42.160 of course bottled water is very small  amount but for instance also in France   00:00:42.720 --> 00:00:49.120 60% of tap water is also groundwater and this  is the same in most countries of the world   00:00:50.560 --> 00:00:57.440 and groundwater is also used for several  other uses like agriculture and these   00:00:57.440 --> 00:01:05.360 industrial uses and as Ghislain said agriculture  is the biggest water use in the world 00:01:08.000 --> 00:01:14.400 and of course for hydration, well-being,  food production, economic development etc   00:01:16.080 --> 00:01:22.800 and the second point why i do explain what is  groundwater is that because this water resource   00:01:22.800 --> 00:01:29.200 is mostly unknown by the public and i would  say that you are the public today at least   00:01:30.240 --> 00:01:37.280 so if i was asking you this question what is  groundwater here in the room or in the street   00:01:37.280 --> 00:01:44.240 in Evian or in paris or i don't know what could  be the main the main answers first of all some   00:01:44.240 --> 00:01:52.880 people would speak about siphons you know that may  explain that you've got water in a well somewhere   00:01:53.760 --> 00:02:00.960 and this water may came from very far away and  get down and came up by a mysterious process   00:02:02.720 --> 00:02:09.360 some other people maybe here in Evian would tell  us that this groundwater comes from the Alpes   00:02:10.320 --> 00:02:16.400 and even from the Mont Blanc because this is the  highest peak in the Alpes so here we are in Evian   00:02:16.400 --> 00:02:22.400 80 kilometers from the Mont Blanc it might be  credible even if it is not the case but i was   00:02:22.400 --> 00:02:29.440 working in Avignon near the mediterranean sea and  most people were saying the same so it's false and   00:02:29.440 --> 00:02:35.200 probably in your country if you ask somebody they  will tell you it comes from the rocky mountains   00:02:35.200 --> 00:02:43.360 from the Andes and and so on people would also  speak about dozers you know these guys that know   00:02:43.360 --> 00:02:51.280 how to look for water and some other people maybe  a little bit more informed we'll speak about caves   00:02:52.800 --> 00:02:56.720 stalagmites speleologists and underground rivers 00:02:59.200 --> 00:03:06.080 and surely you have some other image we  can debate of that after my speech but   00:03:06.880 --> 00:03:15.440 in fact there is a science of groundwater which  is groundwater hydrology or hydrogeology and there   00:03:15.440 --> 00:03:22.720 are some hydrogeologists and which are not dowsers  and you've got two specimens in the room today 00:03:24.960 --> 00:03:30.080 and these guys they can be scientists because  it's a science and as you they are publishing   00:03:30.080 --> 00:03:36.720 some papers and they can also also be  practitioners applying this science day   00:03:36.720 --> 00:03:41.840 to days to solve practical problems and  i would say that myself i am in between   00:03:43.840 --> 00:03:51.360 and so now if we go to hydrogeology or groundwater  hydrogeology we've got a proverb in France which   00:03:51.360 --> 00:03:59.840 is that the tree often hide the forest which means  if i apply it to groundwater is the fact that   00:04:00.480 --> 00:04:07.760 most groundwater doesn't flow in  underground rivers it's only a few   00:04:07.760 --> 00:04:15.840 percent most of groundwater flows in very very  small voids, in pores or interstices of the rocks 00:04:18.080 --> 00:04:26.480 and so and second point this groundwater flow in  all the rocks and not in rivers so if i take the   00:04:26.480 --> 00:04:33.440 example of France maybe you recognize France even  if with the colors it's a geological map of France   00:04:34.720 --> 00:04:37.600 we are somewhere here near the Geneva lake   00:04:38.160 --> 00:04:43.920 and to begin i take the example of  the Paris basin the Paris region   00:04:45.360 --> 00:04:52.160 if we look at the Paris region and make a  cross-section from the east to the north-west   00:04:53.280 --> 00:05:02.480 we will see that these different colors in fact  here they represent a pile of geological layers   00:05:03.520 --> 00:05:14.160 okay and so if you look at water infiltrating here  in the place where this layer is at the surface   00:05:14.880 --> 00:05:21.280 then the water will flow along this layer  and get out at the west of the region   00:05:22.880 --> 00:05:30.640 and if we get more in details you see here on  this picture that you've got surface water rivers   00:05:30.640 --> 00:05:39.600 so the sand river and the main affluence from the  sun river but if we look at water flow in the blue   00:05:39.600 --> 00:05:46.960 layer i was speaking about then you will see that  the water flow is not at all following any river   00:05:46.960 --> 00:05:54.240 it is flowing in the wall rock so this is a  huge difference because it means that you can   00:05:55.200 --> 00:06:02.960 drill a well here or here or here and if the blue  layers contain groundwater then you will be able   00:06:02.960 --> 00:06:09.360 to have this water and you don't need  to drill only along a river which has   00:06:09.360 --> 00:06:18.000 no sense so this is the first and very important  difference now let's focus in Evian and i will   00:06:19.040 --> 00:06:27.200 take several examples in avion in order to link  these concepts with the place you are in Evian   00:06:27.200 --> 00:06:32.560 the most of the rocks in which the Evian  natural mineral water is flowing is sunned   00:06:33.360 --> 00:06:38.320 which means that the water is flowing  in between these very small grains 00:06:42.480 --> 00:06:51.680 and these sands they were deposited by  glaciers so we must go back in the past   00:06:53.040 --> 00:07:01.040 and maybe you can see this picture this is the  Geneva lake this is your jura mountain that you   00:07:01.040 --> 00:07:07.440 can see on the other side of the lake and if  you instead of being here at the royal hotel   00:07:08.400 --> 00:07:12.640 you were in the Alpes which  are a little bit farther about   00:07:13.280 --> 00:07:22.000 15 kilometers from here the landscape you have  today is that one but the landscape we had about   00:07:22.000 --> 00:07:30.240 20 000 years ago was a bit different because  this huge valley you've got there was totally   00:07:30.240 --> 00:07:37.280 filled with ice because it was the climate was  a bit more colder than today it was glacial time   00:07:38.400 --> 00:07:46.880 that explained that the rocks we've got in Evian  were deposited by such glaciers at that time   00:07:47.920 --> 00:07:52.720 most of the northern part of Europe north  America and so on was covered by glaciers   00:07:53.280 --> 00:07:58.240 and most of the Alpes you see this white  color were also covered by glaciers   00:07:59.280 --> 00:08:06.320 so here in Evian the process that created the  rocks in which the water is flowing is glaciers   00:08:06.880 --> 00:08:16.160 and these rocks for us are quite young it's  only 10 000 or 100 000 years old it's very   00:08:16.160 --> 00:08:22.800 young if you compare to the age of the earth  which is billion years, four billion years 00:08:25.200 --> 00:08:31.040 then if we go more in detail again  we are there at the royal hotel   00:08:32.160 --> 00:08:39.600 and as i did in the paris basin we will  look at a cross section here from the hotel   00:08:39.600 --> 00:08:47.040 to the peaks of the alps in order to look at this  plateau which is a place where water infiltrates   00:08:47.600 --> 00:08:54.000 where the groundwater infiltrates and so  if we look at it this is a lake this is   00:08:54.640 --> 00:09:00.080 the surface of the of the earth the topographic  surface and again here's a royal hotel   00:09:01.360 --> 00:09:09.200 and you can see i won't get into detail but that  the underground is made of complex rocks and   00:09:09.200 --> 00:09:18.800 all the rocks that above this limit were deposited  by this glacier and now if we look on how it works   00:09:19.760 --> 00:09:25.360 as Ghislain said you've got rainfall  in that region hopefully not today but   00:09:25.360 --> 00:09:32.080 last week we had rainfall as Ghislain said  part of this rainfall which is green water   00:09:33.760 --> 00:09:42.240 is going back to the atmosphere as we are in a  cool climate here it's about 50 percent and then   00:09:43.920 --> 00:09:50.640 due to the geology here we've got a layer  of impervious rocks which means that   00:09:50.640 --> 00:09:58.240 on that area we are able to identify that most  of the rain water which is not evapotranspirated   00:09:58.240 --> 00:10:03.840 is running off at the surface of the soil  which means it feeds some streams and so on   00:10:04.800 --> 00:10:13.200 and in this part here on the plateau part  of the water can infiltrate into the ground   00:10:14.880 --> 00:10:24.400 and then it will go deeper and deeper  and flow out at the spring you may visit   00:10:24.400 --> 00:10:30.240 in the center of the city of Evian okay  so you see that here we reconstruct   00:10:31.040 --> 00:10:38.400 by geological data studies and so on the travel  of the groundwater the journey of the groundwater 00:10:40.640 --> 00:10:48.400 and if we continue you see that this place here  where water can infiltrate this is what we call   00:10:48.400 --> 00:11:03.280 the recharge area the place where rainfall can  infiltrate into the ground and by studying this   00:11:03.280 --> 00:11:13.840 region we can also identify the contours the  limit of this recharge area and so the size   00:11:15.680 --> 00:11:21.440 and from that we are able to compute what  i would call budgets groundwater budgets 00:11:24.560 --> 00:11:29.600 rainfall is about 1000 liters per square meter   00:11:31.120 --> 00:11:38.960 evapotranspiration as i told you is about 50  percent runoff about 35 and then we know that   00:11:38.960 --> 00:11:48.480 aquifer recharge is only about 15 percent here in  Evian but however as the watershed is quite large   00:11:49.040 --> 00:11:59.920 about 30 square kilometers then we've got a  flux of water not a stock a flux of a billions   00:11:59.920 --> 00:12:07.520 liter per year that we can use for bottling so  this is how we as hydrogeologists we compute   00:12:08.240 --> 00:12:18.240 such budgets another point is that if we  look if you look at the label of the bottle   00:12:19.600 --> 00:12:27.760 you may see some small numbers on it you know this  is the ions which are dissolved in the water how   00:12:27.760 --> 00:12:35.600 do these ions appear in fact it's a bit i would  say rather simple it's what we call water rock   00:12:35.600 --> 00:12:43.360 interactions during its journey the water has time  to exchange to dissolve a little bit the rocks 00:12:45.520 --> 00:12:51.840 from rocks are composed of minerals  which are composed of chemical elements   00:12:53.040 --> 00:12:59.440 and then you will find these chemical  elements in the water and this is a   00:13:00.000 --> 00:13:08.560 discipline a sub-discipline or a sub-science of  hydrogeology that we call hydrochemistry which is   00:13:08.560 --> 00:13:16.080 from the composition or from the mineral  dissolved in the water you are able to reconstruct   00:13:16.080 --> 00:13:23.680 the journey of the water and the types of  rocks the water meet during this journey i   00:13:23.680 --> 00:13:29.200 do it simple but we can get more in detail much  more in detail that only with these elements 00:13:32.160 --> 00:13:40.080 and for this journey it takes time  because water has difficulties to flow   00:13:40.080 --> 00:13:47.840 inside these rocks and most groundwater takes  a long a very long time to travel in the rocks   00:13:48.560 --> 00:13:55.680 if i give you the example of Evian you may see in  the advertisement that it is more than 15 years in   00:13:55.680 --> 00:14:04.720 fact from scientific data we know that it is about  45 years from the top of the plateau to the spring 00:14:08.960 --> 00:14:15.600 another point i'm sure you observe that is  the fact that this water cycle either for   00:14:15.600 --> 00:14:24.240 surface and groundwater is due to the solar  energy because this is the solar energy that   00:14:24.240 --> 00:14:32.960 enables water to evaporate get elevation in  the clouds and then fall down on the ground   00:14:33.920 --> 00:14:39.360 and once it is on the soil then it is  the weight of the water which means   00:14:39.360 --> 00:14:44.640 the gravity that enables the water  to flow into the rocks and get out   00:14:45.920 --> 00:14:53.200 so if you cut the sun no more water cycle on earth  there will be probably other consequences but 00:14:56.080 --> 00:15:02.480 another point is that as Ghislain  said very well the vegetation   00:15:02.480 --> 00:15:09.360 is triggering this water cycle because  globally Ghislain told us that about 50 percent   00:15:09.360 --> 00:15:13.360 of the water on earth of the rain  water is coming from the vegetation 00:15:16.960 --> 00:15:23.520 and another important point is also the fact  that most of the water you can see in the rivers   00:15:24.480 --> 00:15:31.520 is also i would say groundwater again as an  example the picture of Evian i told you about   00:15:31.520 --> 00:15:37.440 the spring which is the outlet of the aquifer the  place where the water is flowing out of course in   00:15:37.440 --> 00:15:46.560 Evian this water was going to the lake there was  not really a river but if we consider other places   00:15:48.080 --> 00:15:54.160 you can have some springs feeding rivers  and when you look at the river which is   00:15:54.160 --> 00:16:03.360 flowing even during the summer even after weeks or  months with no rainfall it means that this river   00:16:03.360 --> 00:16:11.440 is feed by lots of small streams along its  course and so each time you see a river   00:16:12.880 --> 00:16:18.560 flowing during the dry season most of the time it  is due to the fact that it is fed by groundwater   00:16:19.680 --> 00:16:28.720 so rivers are also mostly groundwater during the  dry season with important consequences of course 00:16:31.280 --> 00:16:39.280 then two last points before ending this  speech which is how we manage this groundwater   00:16:39.280 --> 00:16:42.720 you already saw that i was speaking  about the groundwater budget   00:16:43.760 --> 00:16:54.000 and we can make the image of a bank you are  you have a banker and you can consider that   00:16:54.000 --> 00:17:00.160 the water which is stored in the rock the  stock is the capital you have put at the bank   00:17:01.200 --> 00:17:10.640 and what is coming from the rain year after year  it's the interest that the bank can serve for this   00:17:10.640 --> 00:17:18.640 capital and then you've got some needs or some  expenses this is what you pump in the aquifer okay   00:17:20.480 --> 00:17:27.440 and then you can have various scenarios but if you  look at the evolution of your capital with time   00:17:27.440 --> 00:17:37.440 over years the capital is there and then the first  year you will have interest and water use in red   00:17:38.400 --> 00:17:46.560 you see that if water use is less than  interest it's nice because the year after   00:17:46.560 --> 00:17:52.960 you still have the same capital or the same water  in the storage it's a little bit different from   00:17:52.960 --> 00:17:59.200 the bank because in the bank you can accumulate  the interest but in most aquifers what you   00:17:59.200 --> 00:18:05.280 don't use is flowing out to rivers as i said  a few minutes ago feeding ecosystems and so on 00:18:07.600 --> 00:18:17.040 but if you are one year with lower interest which  means lower water then the interest of having this   00:18:17.040 --> 00:18:23.440 capital is that you can still use what you need  but at the end of the year you will have less   00:18:23.440 --> 00:18:31.680 water in your in your stock but it's not a problem  because the storage is huge okay so this is a very   00:18:31.680 --> 00:18:36.960 important point of groundwater is that you've  got this storage and that you can play with it   00:18:38.080 --> 00:18:48.240 maybe you've got the same scenarios a year after  but if the year after you've got more rainfall   00:18:48.240 --> 00:18:57.600 than your water needs then you will reconstitute  your storage in the aquifer so it means that if   00:18:58.240 --> 00:19:07.280 on average you use less than the recharge you make  a sustainable groundwater management okay and you   00:19:07.280 --> 00:19:16.400 can rely on the storage to pass the bad years with  no not so much rainfall this is a huge advantage 00:19:18.960 --> 00:19:24.880 other advantages of groundwater inertia  it's the fact that it's a low cost ground   00:19:24.880 --> 00:19:29.840 water resource because you can drill a well  here in your farm in your house and so on 00:19:32.720 --> 00:19:36.080 and for instance it enabled for instance in India   00:19:37.040 --> 00:19:46.320 farmers to be able to sustain the food needs of  a big country like India with millions of wealth 00:19:48.400 --> 00:19:56.640 but there is a huge drawback about this issue and  the drawback as Ghislain said is over exploitation   00:19:58.240 --> 00:20:08.960 if on average every year you use more water in  red than the recharge then you would deplete   00:20:08.960 --> 00:20:16.080 your storage and after several years you will  have no more water in the aquifer which means that   00:20:16.080 --> 00:20:21.120 you use this water for an economic for  well-being and so on but it won't last   00:20:21.920 --> 00:20:27.600 so this is a really very important issue  which means that groundwater must be   00:20:28.720 --> 00:20:33.840 managed at the scale of the  watershed knowing the water budget 00:20:36.400 --> 00:20:39.520 and if i again take the example of India 00:20:41.680 --> 00:20:46.560 most of wealth most of aquifer  in India are over exploited   00:20:46.560 --> 00:20:53.040 which means that this green revolution will  probably not be able to last in the future 00:20:55.440 --> 00:21:02.240 but of course just 20 seconds thank  you but of course as i told we've got   00:21:02.240 --> 00:21:09.200 tools to manage groundwater and for instance we  we are able to simulate the behavior of aquifers   00:21:09.200 --> 00:21:13.920 and simulate various scenarios in order  to sustainable manage these aquifers   00:21:15.600 --> 00:21:24.480 so uh as a conclusion and to to stop on this issue  of of groundwater i would say that groundwater   00:21:24.480 --> 00:21:30.160 have lots of advantages they have got i would say  drawback but this is probably not the good word   00:21:30.880 --> 00:21:40.320 but it means that today we are facing climate  change but as gila said the most of over   00:21:40.320 --> 00:21:47.440 exploited aquifers are today overexploited it's  an issue and it is not related to climate change   00:21:48.160 --> 00:21:56.400 and we have the tools to manage that so my  conclusion is we don't need to say that it will   00:21:56.400 --> 00:22:01.840 change in the future we need to act in the future  but for over exploitation we need to act now 00:22:07.440 --> 00:22:12.720 thank you you