 Welcome everybody to the NPTEL course on rural water resource management week three. In the last lecture, we looked at groundwater as a hydrological component. Groundwater storage and groundwater induced base flow. So we looked into the some properties of groundwater and in today's lecture, we'll see how groundwater has been managed or monitored across India. Because it is a important resource for rural water management, we will be spending one more extra lecture on groundwater. Let's start with groundwater monitoring and measurements. As I said previously, the central groundwater board in short called CGWB is the authority for groundwater monitoring and measurements in India. This is a central government agency. On top of this, every state has their own monitoring and measurement agencies for groundwater. Mostly it will be with the PWD, which is the public water department or irrigation department, etc. So they will have their own wells or they have in collaboration with farmers, they will have a monitoring network where they look at water depletion. They monitor the water levels at regular intervals and have access to these wells. Let's look at the central government program. So it is based on physical monitoring by observation wells. It's not modeling, they don't assume, but they actually measure, which is very important for groundwater monitoring. The central groundwater board is the official monitoring agency as I mentioned and has a total of 32,730 wells as per the latest report in 2020. So and the location of the wells is given in the figure here wherein you see a lot of wells along the most important states for agriculture. Some less number of wells in Rajasthan because of the desaturated area or very semi-arid air conditions, not much groundwater, etc. And you don't see wells in the hilly regions. So if you remember the lecture from previous week and also the couple of lectures before this, we mentioned that for groundwater to be available, you should have a soil plus a weather material. If it is purely rock as you can find in the hilly regions, you won't have that much groundwater. So it is not that important to monitor regularly in these regions. So along the borders, you don't see much groundwater monitoring, but if you see in Central India and wherever there's good agriculture activities, you see a good spread of monitoring wells. Around 16,375 wells are for shallow aquifers. Please understand the difference as we explained earlier. A shallow aquifer would be from the top of the land surface up to a confining layer, impervious layer. After the impervious layer, you do have another aquifer, which could be your deeper aquifer. So that is monitored by pysomics, around 6,355 pysomics for accessing deep wells. So what is the difference between these two? The dug wells are mostly in shallow, which is approximately 30 meters. And you would normally measure it with a tape or you would have automatic measuring device. But for pysometers, which is a tube, which goes very deep into the ground, more than 30 meters. So in some regions, you say that groundwater is at 300 meters. So in Chennai, I would remember people complaining that the groundwater level has fallen to very, very low levels, like around 300, 250 meters, et cetera. So at that level, you cannot have a tape and a measure. So you would have an automatic monitoring device. And that setup is called a pysometer, a pysometer, which is one which goes down in. So now we understood that the government is actually monitoring both shallow aquifers. Most of the wells is tapping into the aquifers. Let's see how you would put in, let's differentiate between the shallow monitoring wells and the deep monitors. So this image is from the courtesy of British Georgia Survey, where they've done a lot of work in Nepal and bordering regions of India on assessing groundwater. How they would do it is almost common across. So let's look at different methods. So the first one is just a normal, long, deep well. So this could be your pysometer where you would put in a bore well and a pysometer at the bottom. And it is screened along the well, which means water can come in through all areas into the well. And you would actually measure the water level from here. Sometimes you don't need to go deep as the bedrock, but still here you could see the fractures present and water is present. So it is okay to measure into the very fractured network. Then you have a short well, which is for mostly your dug wells. So the 15,000 plus 16,000 plus wells that we saw in the previous slide is mostly of this nature. And then you have the difference between them. You could see clearly that it is measuring the shallow aquifers, the water is moving from left to right and into your streams. You could see that the other well is also screened from that same level from the water table, but goes throughout the aquifer until the bedrock, which is here. Then you have a nested single bore well. So this is a very important phenomenon because you would like to see at a single point how the shallow aquifer responds and how the deep aquifer responds. Because in this example, you have it isolated, so you have a deep aquifer monitoring and then you have a shallow aquifer monitoring. But in this diagram, what you see is a nested. Nested means together nested. So in a nested configuration, you have around the three different wells monitoring the same aquifer, very, very close. That is what is called nested so that you capture the same aquifer dynamics. So you have here, it's going into the shallow aquifer, the first well. The second well would be going into a somewhat between the shallow and the deep aquifer. And then the third well is going to a deep aquifer. So at a single point, you are measuring three different aquifers at the same location. This would give you a better understanding of how the shallow and the deep aquifers react to pumping. For some instances, when you pump too much shallow water, the deep aquifer is also suffering because there is less recharge happening. And then you have clustered separate bore wells. So similar to nested but clustered and a little bit separate. So you have it spaced out evenly to measure water and also the pollutants how they move. So these wells can also be used for water quality assessments because they can take a sample out. For water levels, you don't need a sample. We just put a meter in or a tape in and measure. We'll come to the devices later. But for water quality, you would take a sample out and then take it to the lab or do in situ water quality measurements. Then you have a multi-level well wherein you could actually take water from different depths by openings at different levels. This is mostly for a water quality assessment where you would stop and then take a sample here from the seepage. So when water is coming in from the side, you would take a sample and then go down, take another sample, take another sample. So these are for the water quality but I'm showing it mostly for also water levels. So you now have a difference of opinion between how you would monitor a dug well which is a shallow well which is using a single well monitoring well. Then you can also monitor a deep well or a nested or a clustered well. So what are the different methods that we could use for measuring on water level and how are they collected? So for measuring wells, you could have basically a steel tape with measurements and you put in a steel tape inside the well. The chalk would be washed away by water and when you pull it out, you know where the chalk has been washed away. So that would give you the depth from the top, how deep the aquifer is or the water level is. Then you have similarly an electric tape, same method but it gives you a light bulb or a sound when it touches the water because the electrical connection is made. Pressure transducers are put in piezometers where piezometer is a well which goes deep. As I said, pressure transducers is an instrument where it can actually record a pressure difference between because of the height of the water and when there's a change in water, it would record the change in pressure on the instrument. It is a very sensitive instrument which means it can easily capture even small changes in ground water level and it is one of the best methods to use but it is a little bit expensive. An acoustic probe, ultrasonic, etc. use the sound wave properties to go in and come out to tell the water levels from the well and floats, poppers, airlines, etc. So floats and poppers are same like it just floats on the water and then you make an electrical connection, etc. So these are for non-flowing wells which means a well which is, yes, it recharges so it flows into the well but then it is stationary. It doesn't move up and down when you see the water. So because at a very quick instance, you cannot put the chalk in and take and then say it is moving, the water is moving. So you will have to wait till the water stabilizes. So that is what we call non-flowing wells. So water can recharge. Let's say it recharges in the night. In the morning when you come and see, the water will be at a particular level. You take it and measure it out. So to be consistent, it is always good to measure the water level at the same time every day. So for example, every month you want to take a sample. You go on the first day of the month. The first day of the month, you should go at exactly the same time. Let's say 6 o'clock in the morning, you go to 6 o'clock and take the measurement so that it is comparable. Then you have the flowing wells where you have a well like the artesian well. So the artesian well is a well where even without pumping, the water will come out. Why will it come out? Because of the principle I told earlier, water flows from high potential to low potential, high pressure to low pressure. So this water inside the aquifer, the confined aquifer or the deep aquifer is under tremendous pressure because of the mass on top of it. So it will be pushing the water down. It has pressure. It cannot go anywhere, the water because underneath is also an impervious surface. So the water is under tremendous pressure and when you put in a well, just a bore, a hole inside, what happens is you will see water just gushing out because outside atmospheric pressure is much lower than the pressure inside. So the water will come out until the pressure inside the confined aquifer is equalized. So how do you measure flowing well in that? Same transducer, pressure transducer can be put in because it is very accurate and quickly measured and a manometer or a pressure gauge on top of the well where it measures the water or the pressure difference. So in most cases, you would be using as the central water board, etc., you'll be using a tape method. So this is the tape method, an electric water level tape method, pretty expensive for the technology. And what you do is you would lower this probe. You could lower this probe and this is a meter which has the markings of SI units, which is and then you would leverage it in. So you would see me putting the meter into the groundwater level, groundwater wells in both the cases. And then when it goes in and the probe touches the water, the connection is made. So there is one wire which goes on this side and another wire on the other side. Those are not connected. So the two wires are not connected. But when the probe is also connected to these two wires and the probe touches water, water makes the connection between the two wires and then you hear a beep or a light. So the beep sound or light will come around here and you will stop lowering the probe and that level you would read off from your meter. So that is basically how you would measure groundwater level. Please understand that from the base of the well. So if this is the land, this is the well you would measure from here going down. So it is a depth to water level. Then you'll have to convert it back to height of water level. So from here you know zero, you would estimate the water level by just knowing the distance from the top to the water level. So for example, let's do an exercise. From here the water base is zero and you know that the well is at 50 meters and the water is at 10 meter depth. So what would you do? You would subtract 10, 10 from 50 to get 40 meters. So from zero the water level is at 40 meters and that is how you establish a head. In the groundwater class I'd go through again on these exact same methods. But here it is good to understand how you collect groundwater level data. So now we have collected the data. So what does Central Ground Water Board do? They collect four times a year and these are the months or seasons they collect pre-monsoon. So somewhere in the peak of summer June or I would say May. Then you have another collection during the peak of your monsoon. Here it is August and the monsoon after the monsoon has one or two months. So let's say it stops in September. You can take it in October and then November, December, January for the winter. So approximately three months in between they take a sample. So this depth to water level gives a lot of inferences. So here they don't do the head which I told earlier. They do a simple depth to water level. So basically lower the meter and from the ground how deep is your groundwater level. Let's see what this exercise is taking the pre-monsoon or the peak summer. So you have the depth to water levels in meters below ground level. So meters below ground level, MGL, that's the unit, MBGL, meters below ground level or you might see MGL also. What you find here is less than two, two to five, the coloring is the same. So I've read it out from here and 10 to 20, 20 to 40 and greater than 40 meters. So anything greater than 40 meters is pretty deep. So they would say that it is pretty red in color, which means kind of dangerous. Whereas less than two is okay. It's a good number. In the summer season here in the pre-monsoon level, you would see that most of the hilly regions are still okay in the blue and green color. I would say the coloring scheme is really good, how they've picked up the colors for the levels because it tells a warning signal. So here blue and green means good water. Water is blue in color. So when you see blue and green color, that means the water levels are healthy. So here along these regions, it is healthy. The hilly areas, they don't collect water levels, as I mentioned, because it is very hard to drill down and get the water. So there's no point of setting the water levels there. Not much is being done. And then along the border. So you would see that wherever the western guards is, the water levels are pretty okay compared to the central and the eastern part, northeastern part. So along Rajasthan and Gujarat and central India, the water levels are pretty bad in terms of depth, which is really concerning because as the depth increases, you have to supply more energy to take the water. And as the depth increases, the water quality changes and the time of recharge also changes. So it takes longer time for the water from a deep aquifer to recharge. So it is very important to understand this map of pre-Monson water levels, the summer. So once you understand this, then we have your summer is gone. The monsoon comes in June, July, August. So you have the peak, August, monsoon month. And you could see that most of central India is turning into blue and western guards, Maharashtra, where we are from, the water levels are pretty healthy along the western guards. After the western guards, you could see it is not that good. This is because of when the precipitation I taught you, it is because of the orographic effort. The rainfall picks up on one side of the western guards, whereas on the other side, it is totally dry. So what you see here is the central India is now turning into blue in terms of healthy water levels. So water levels within two meters from the ground, whereas the Rajasthan part and other parts are still really, really bad in terms of groundwater, but it's turning slightly into pink from dark red and red into pink. And then you have the southern region where tremendous agriculture activity is happening. Still, you do have less groundwater, but also it's because the monsoon is not the same. So most of India gets the monsoon by June, July, whereas this part gets it later and we will see it in the next images. And this is the post-monsoon map, mostly around September, November. And you could see that most of these regions, which were blue, have turned into healthy in terms of the is yellow, whereas two to five is green. So somewhere it is still okay to be pumped. So from two to five meters, they're pumping the groundwater. The water levels are not fluctuating much. And now you see slowly the southern part of India also turns green. So there is a lag between the precipitation that occurs on the Western Ghaz and Central India. And then one or two months later, Tamil Nadu, Kerala, Andhra, Karnataka gets their rainfall, gets a share of rainfall. So you see that water levels have actually stabilized in most of India except your Rajasthan and Gujarat regions. And then in the winter season, January, again, the water level slowly starts to deplete. It could be because of water use or also because the water would be slowly going into base flow, the groundwater, and the base flow goes into the rivers, rivers goes into the oceans and seas. So the water continues to move. And this understanding is very important that it's not like water will just stay there, groundwater. So some, up to some level it stays. But once it goes beyond the level, it will start moving to the zero level, which is the sea and ocean. So what do we see here? If the pre-monsoon, which is the pre-monsoon of 2019, is the same or similar from the pre-monsoon in 2020, then it is okay, because every year you kind of take the water and put it back during the precipitation. But if it is not the same, imagine like a bank account. So you have a bank account, you have money before four months, you take some money and during the precipitation peak season, which is a monsoon, you put back some more money. And if the first year of analysis and second year of analysis are the same, the water levels are same, you are okay. It's sustainable, we would call. Most, relatively it is sustainable because whatever water you use, the precipitation is putting it back into the groundwater aquifer. So you're fine. But that is not the case because what is happening is slowly it comes slow. So let's say if it was 10 meters in pre-monsoon conditions in the next year it becomes 11 meters and slowly the depth to the water level is increasing. And that is why you see more and more of these blocks converting into red color. Red color is pretty bad in terms of depth to water level. So now the exercise has been done. So they got four times a year and then they estimate how much water recharges. If you know the rainfall and if you know how much level, the water level has increased, for example from 10 meters it has increased 5 meters. For example, here you had all these regions around 10 to 20 meters of groundwater. And later after the pre-monsoon, post-monsoon it has come to green color, which is 2 to 5 meters. So by that you need to understand that the recharges happen. So if the water use is equal to your water you put in, it is safe and semi-critical. And if you almost come close to the water use is almost equal, you become critical because you need some water for the ecosystem services and rivers, as I mentioned. But then when it goes above your groundwater available, for example, your extraction is more than your recharge, groundwater recharge, than it is an over-exploited state. So the groundwater mapping committees of India through the Central Water Board, etc. So they have actually put in a plan to map aquifers. So because unlike your surface water, aquifers and groundwater do not have a watershed boundary. They do not follow an administrative boundary. A dam can be put in a state and you can make sure that the water doesn't go to another state by channelizing the water. But you cannot do that for groundwater. Rivers can be stopped by checkdams, but you cannot do that for groundwater. So that is why they have been doing an aquifer mapping. So you can see here where they're mapping. And how did they pick these locations? Because they know how many use the Central Ground Water Board and understanding where the safe semi-critical and critical blocks are, they have colored it red for over-exploited blocks. So if groundwater is more abstracted than the recharge, then it is an over-exploited. So those are the blocks they want to map the aquifer so that they could do some water management plans, groundwater management plans. So this is where we need to be careful in understanding how many areas have been demarcated. So for example, total over-exploitation in critical blocks are 1,288 of which the aquifer mapping and some management activities are going around in 1,127 blocks. The priority areas are in eight states, including Rajasthan, Gujarat, etc., and other areas around 212. So in the eight states, you have 915 blocks. So in other areas, you have 212 blocks. For example, in Tamil Nadu, Kerala, there are some blocks that are there monitoring. So these are the areas for prioritized aquifer mapping. They want to map the boundaries of the groundwater storage and by mapping, they have now a better idea to put in structures or control the demand of water by saying you cannot pump more than this volume or you cannot use a particular crop. For example, if it is sugarcane or banana, you cannot use groundwater. So that kind of regulations they can put once they have the aquifer mapped the boundaries and they have this map of where the critical blocks are. So almost Rajasthan, Gujarat, Punjab, all these regions are under the scanner for better water management. And also, people are slowly understanding that if the groundwater is being depleted beyond a point, then your river flow is also reduced. And because of that, your surface water irrigation or the water you use from the rivers and dams for irrigation also is questioned. It reduces. So that is where slowly farmers and every agency is putting more focus on mapping the groundwater, reducing the use of groundwater and also managing better recharge techniques for groundwater. With this, we are covering the groundwater sector. And in the next lecture, I will go through the recap of for this week in some more examples. And we will conclude the hydrological.