 Hello, welcome to NPTEL Rural Water Resource Management course week four lecture three. In this week, we are focusing on groundwater hydrology. The past two lectures, we looked at what constitutes groundwater hydrology. We also looked at the concept of aquifers, then unconsolidated versus consolidated, unconfined versus confined and saturated versus unsaturated. So we've seen different phases of aquifers, different phases where groundwater can exist, what drives the groundwater storage and what drives the groundwater flow, especially potential difference. So in the following lectures, we would like to see how groundwater is recharged and then discharged or pumped out, used, etc. So now you have a better idea of managing the groundwater resource if we know about the recharge and discharge. Let's start with groundwater recharge. So the recharge area, which you see on the top of the land is going to be the predominant where you have water coming in. Yeah, water comes through streams and rivers but it's much less compared to precipitation induced. So if you visualize yourself as a water droplet, you will come infiltrate and then get into the first unsaturated then saturated zone. Once you get into the saturated zone, and you have a confining bed becomes an unconfined. Remember, I was saying that you don't just have to have one confined aquifer that can be multiple. You can only have one unconfined aquifer, they can't be unconfined after suddenly after a confined aquifer. So only when you dig it up, yeah, if you dig up a well and you have open water coming in, then it is unconfined, but it won't call it as an aquifer because it is at a longer time and space. You clearly see here where you have an unconfined layer because you have a confining bed, impervious bed, or aquitar, all these terms we discussed. So recharge water comes in and it takes days. So let's say if you have a rainfall within a couple of days you will see it coming into your pump well. So the well is where water gets stored, you could see the water level rise so you know that recharge is happening because of the rainfall. If you put a well here, you can also monitor the level rise when water is flowing in the stream. So that also gives you an idea about water level rise due to recharge from water from the spring. Springs can also give water to stream. So coming back, let's look at this angle only for now. So rainfall comes in, recharges your groundwater and flows into your wells, it takes a couple of days, anywhere from a day to a week. Then you have further away, further away water can come into due to precipitation, infiltration and then go into your wells which will take years. Depending where your aquifer is stored, depending where the point of water access is there, the water will have to move a long term, a long term and distance. And groundwater flow is very, very slow. So please look at this, because it is slow it will take years and why is it slow? Because there's a lot of obstacles on there, solid materials are there. So water has to go around it, connected through another pore, those kind of things. And if there's already water, it's less with the high potential, I'm saying then water movements are balanced out. So it takes anywhere from years, in the unconfined aquifers. So anywhere you can start from a days to years. For example, in the Ganges Basin, you could see it within a days, the wells start to recharge when there's good water flowing in the river and also good rainfall. It may not be the same in Central India, it will take some more days to see the groundwater rising up. And then somewhere in the drier regions, you would see years. Let's get into the confined unit. Now here comes the lag, the delay. So water can come, but when it sees the confining bed or the impervious bed, it cannot directly come into and recharge. It takes long, long time. Okay, long time the water has to sit on top of the surface slowly infiltrate or water comes from a longer distance. Okay, distance can also increase the time the water takes to come into the aquifer. So I'm looking at confined aquifer one, this is confined aquifer two. Okay, for the confined aquifer, water can come from a very far distance and then move slowly, slowly, slowly into this aquifer. Or water can come from the unconfined but stay there for a long time and then infiltrate, penetrate through the impervious layer. Whatever it is impervious, there's still some leaks. Okay, it's not 100% impervious layer, it's not a steel put so that it just stops your water. It's a stone, it's a rock. So some weathering can happen, so water can move through. Okay, and that takes centuries, hundreds of years for the water to come there. So that is how long water takes from the surface to come into that aquifer. Then you have the next confined aquifer, which is at a much lower depth. And it has two confining units to jump. So water has to come, go to the unconfined aquifer, then jump your confining bed which means infiltrate, come into the confined aquifer. Here it can move faster because it has four spaces so it can move much faster and then it goes into the confining bed again. Now, again it has to infiltrate, wait, slow down and then get into the confined aquifer. This takes a millennia which means a thousand years. So see how the same water can go from days recharge to years recharge and also from centuries to millennia. So it is very important to understand the time groundwater takes to recharge and this I hope has clarified to understand that part so that we can put better rules and regulations for using the water. For example, if you have a pump in the unconfined aquifer, you're okay that even if you dry it out, for example, I'm pumping all the water out. And after a rain, the water can be recharged in a day, couple of days a week or max by years. Within one or two years, good rainfall, water levels will come up. So if you see right now, all the areas in India are getting good rainfall, so all the groundwater levels are recording high. But if your well is in the confined aquifer one and you pump out all the water, so for it to refill again, for it to come back to the original level it could take centuries, not one but multiple centuries. So you are actually taking your future generations water or the water that has been given to you by past generations for you to save and to use wisely. If you pull it out within 10 years, five years, which is happening right now due to agricultural expansion, people doing two rotation crops, three rotation crops in an area where only one rotation of a crop should be done. If you're too much using the water groundwater resource, you actually are taking from the past and the future groundwater demand. So it is as a much more important to conserve the groundwater. Now coming, if you have a well so deep, so in some parts in the drier regions you can see wells going to 400 feet, 600 feet. What is that mean, so you are actually tapping the very deep confined units. Once you take the water, it's gone, you're not going to wait for another 1000 years to come. And that is where people abandoned the wells, same here. If you have a well here, the water is taken out, and you see you wait for a couple of years the water doesn't come, people just move on, they say okay it's unburdened well, I'm going to go for another area and put another well. Same here, if you pump out all the water then it goes on, but that is not sustainable, because you use some water which was there for over a century. So it is as and more important to conserve groundwater. I hope this actually brings in a lot of sensitization on using of groundwater, understanding how deep your well is, so your depth of the well can actually give you a rough estimate of your aquifer. So if you're tapping groundwater, let's say within 30 meters, you're well and good, you say okay 13 meters, it should be an unconfined aquifer, technically the soil profile is there, water can come in, okay well and good. And this without talking about pollution. But then when you have your confined, when your well is further deep end, when you push your well deeper, then you're taking water from deeper confined unit. And once your water level is coming down, which is which means you're using the water, the water was running out, it is an alarming well, alarming that you need to start recharging start doing some other practices to bring the water well back. Back to a sustainable level. Okay, so please understand that it is not the same recharge rate across differs and it differs at a big massive difference. Years, days, millennia centuries. So you should not be using what water you took for a century to recharge within a year or two. So as we can serve. Moving on. You can have days and years also in the same unconfined unit, but more importantly considering the centuries and millennia water is important. No water discharge. Now we are in a groundwater discharge slide where we talk about pumping or water from the ground water aquifer and that act is called discharge discharge can be of two types. One is forced discharge when you put a pump and pull it out to energy or manual labor etc. Or by naturally, no water can discharge into a system or out of the system. Your presentation happens your recharge happens you have the aquifer form your water table is there. Then you start to pull water out through your pump for agriculture for domestic use for livelihoods industry be it any any use you want, but you are pulling it down. Once you pull, you could see that the water table is not the same and water table doesn't go down like this. First, it goes as a cone of depression, which means around the radial area of the valley. Suddenly the water level will come down because all the recharge that was happening evenly evenly has created even water table, but your localized pumping is pumping at one point. Even though there is recharge happening on the sides, because of this pumping all the water will go in as a cone of depression. So once you have a cone of depression, this is the worst part. If you have a cone of depression, then the water table which was almost stationary because of the same potential now starts to flow to your wells. So you're not actually pulling water from a different distance, but by the act of pulling you create a cone of depression. And once you create a cone of depression, there's a potential difference between this water table and the water table here. So the water table here and the cone of depression here, there is a potential difference, high potential, low potential. And because of that water will go naturally to the well. So you don't have to pump with more energy. So this is where farmers are losing it. They think, sir, if it is recharging faster as I pump, then there's a lot of water. No. Because the cone of depression is forcing the water to come in. Think about you have a glass of water, you're putting a straw and you're taking water out. Initially you have to have less energy, but when you go down further, you have to spend more energy to bring the water out. Because there's no water coming in. If it is pouring in more and more water, then it's the same. But here, because there is a potential of a cone of depression, because water is not, it's not a river underneath. You still have soil and materials in the aquifer. So that is where the cone of depression forms. If it is a river you pull, then the whole water table will go like this. This visualizes you drinking water from a straw in a cup. If you drink, it goes like this, the water level. It doesn't go like a cone of depression because it is pure new water. Here, because of your sediments, solid materials, only the water is released. That's why you see it still is brown. After you take the water out, it becomes brown, just no water. So the cone of depression is kind of concerning because it actually pulls water from around your area into the well for easy access of your water. So the water level doesn't increase, but the water coming into the well increases. And you keep on pumping and discharging. So here's where, if your pumping cost is very low. If it is supplied by an alternative energy, which is very low, for example, solar pumps and other things. What can happen is if you do not have concern of pumping for the energy, then too much water can be used, too much water can be extracted. So it's always important to meter your pumps, understand how much water you're using, only use what water you need for your crops and then stop. Otherwise this cone of depression will go bigger and bigger. Another groundwater discharge diagram, again, you can pull water from your groundwater aquifer. And also you could reverse the sign of your stream network. So initially the stream was getting groundwater from here. So it was a gaining stream. But because you're pulling and because of the cone of depression, you have been pulling the water from the stream, which is a surface body into the ground. Then it becomes a groundwater and then back into the well. So the well is now pumping it out. So the groundwater flow diagram is given, infiltration happens, leave the contamination that's not in this course. But evaporation, losses, et cetera, et cetera, water comes in, goes into your pump because of your pumping. And then you have a cone of depression and because of that depression, a high potential, low potential gradient is formed and the volume of water is now pulled. So where does the water quality come into the picture? Because if you have a contaminated source, for example, a landfill or a septic tank which is broken and a lot of waste, solid waste is here. And it is standing there because of our high water potential. But when you pump too much and the cone of depression is formed, then you actually start pulling the contaminated water, which was initially not moving. So it is always important not to put groundwater wells near contaminated sites, sewage lines, and then over pump it. So if you over pump it, the cone of depression forms, and even though the polluted water did not want to move initially, because of this cone of depression, it starts to move. Then you have an influence recharge and influence discharge. So what we saw in the initial stage is if you just pump and the water table comes down, there's no influenced discharge. But when a cone of depression is formed, there is a influence discharge. So water level after pumping is here. It recovers. So water recovers, but still the cone of depression is there. And your initial water was here. But because you pulled the water out, you could see. So now let's take two wells in tandem. And this is where the well monitoring I was talking about of representative analysis, et cetera, et cetera. So you have a well here. Let's call it well A and then well B. Well A is used for your irrigation for applying water to the crops. So you put a pump, you pump the water out and you apply the water. And then what happens, the water falls on the surface and you're irrigating. But meanwhile, you are creating a cone of depression. There is a well B, which is a little bit farther away and no pumping is happening. There is no pumping here. So what happens? Watch closely that when you're pumping in well A, the cone of depression is formed and the actual water level from your well B is falling. So now visualize this as two farmers. This farmer is an ethical farmer who says, no, I don't want to grow crops in the summer because there was not a good rainfall. I'm not going to use groundwater. But this greedy farmer says, no, I want to use groundwater all the groundwater and then grow. He, she is not only using their groundwater, but also the water levels up here. So even though this farmer farmer B did not put a groundwater pump and use the water, his water levels is also coming down. So here's where a communal source of water, which was for the community for general public has become one person's property because they put in a pump. They did not talk to others. They start sucking all the water out because of the corner depression. And because of this, there is a induced discharge. Water level comes down. That is a discharge. It is induced because of the pumping from a different way. Here we can say pumping in observation, but hypothetically, it can be two farmers nearby each other and pumping a lot. So think about even houses. You can have a flat system and apartment and right next to it a single house. The single house can have a well and they can take water. There is very less, you know, maybe five people are using it for drinking, but the flat apartments need is big. So if they pull too much water, they would eventually pull the water off the neighbor also. So this is the important part about induced discharge. What could be the induced recharge? Same as you have water discharge being induced because of the pumping. If there is a recharge happening here, it would recharge more here because of the corner depression. Why would water go into a place where there's high potential? It wants to go into the low potential and where there is more space. So because of this pumping induced recharge can also happen. We also looked at the natural discharge and recharge, which is again, we'll have to go through it because of the terms of recharge and discharge. You have the gaining stream versus the losing stream in the gaining stream, which is on the top. A river is flowing through a good forest area and the water table is at a much higher level because of the forest. There's good soil and good soil can have more water infiltrate and keep. And so the water level is high. It can come down into the stream. So that is a gaining river, the river gains. So that is a recharge from the groundwater, but the groundwater is discharging into the stream. As a stream, it is getting water. So it is recharged by the groundwater. As a groundwater, I'm losing my water to the stream. So the groundwater is discharging into the stream. The other diagram when we saw a losing stream here, it is natural recharge, not discharge because groundwater is not going to the stream. On the other hand, the stream is giving water to the groundwater because the stream is at a high potential compared to the groundwater, which is at a low potential. So this act of getting more water by the groundwater through the stream through a losing stream is natural recharge. So if you have pumps here, then it becomes induced. Here we are only talking about natural process. Once you put an engineered process inside, then a lot of induced processes can happen. In this lecture, we have seen about the recharge and discharge mechanisms. We have seen the timeline that takes for these mechanisms. Anywhere starting from days to years in an unconfined unit, a consolidated unit, which is much more down deeper. So if you have unconsolidated units or unsaturated units, water can move within days to years. Whereas if you go beyond a confining unit, an impervious unit, then it can take years, multiple years, centuries, and then furthermore, another layer, impervious layer can take you millennia. So it is kind of very important to understand the recharge process and the time it takes. It is a slow process because of the presence of sediments, rock, and other materials. Once you know the recharge process at the time as per se, then you could look at induced processes because of pumping and induced discharge because of pumping. And also we saw that in this lecture, your groundwater, which you claim because you're putting your well and say, no, it is my water. It is not just your water, but the water of the surrounding area also. So just because I'm not putting a well in my field doesn't mean you can take my groundwater. Because groundwater is a communal source. Maybe the farmer did not have money, cannot afford it. And that is where in the Rural Water Resource Management course, we'll be looking at how to pool farmers to better manage this resource. In one of my field works as a project scientist, we looked at mobilizing farmers, sensitizing them saying, not all farmers can have pumps, not all farmers can have tractors. So can we work together to conserve the groundwater? For example, if seven farmers say, okay, you take the groundwater, I won't manage my land. I will not manage my land, I put cement on my land. Will the other three grid groundwater they won't? Because he or she has to give the land for recharge. So that is very important. Again, here, if this farmer is not pumping, but still he's recharging the groundwater. So this farmer, which is farmer A, is taking all the water from farmer B and his hard work, his or her hard work in recharging the groundwater. So this is the concept which needs to be driven for Rural Water Resource Management to make them understand it is not one person's utility groundwater. It is a communal source or a social common source for everyone. And also the management has to be common. With this, I would like to stop about groundwater recharge, discharge, communal use, etc. Let's see what is available for the next lecture. Thank you.