 Hello everyone. Welcome to rural water resource management NPTF course. This is week seven. We are covering the syllabus as given in the website and if there's any questions feel free to check the TA through the group. Let's do the recap of week six and link to week seven. In week six we looked at surface water hydrology equation and also how surface water is being stored across India with some special focus on rural water surface storage structures. These structures are predominantly used for rural water irrigation schemes or programs. Some of them are run by the government. Some of them are run by the state agencies and some with local punch islands, etc. There are some ad hoc surface water hydrology structures which are made by the individuals, maybe legal or not, but these are kind of obstructing the flow and holding it for their personal use. What we saw that is if surface water hydrology is developed like this through ponds and command areas, there could be some issues in the downstream farmers community. So for example, we have upstream farmers. They can store the water in lakes, dams, ponds, manmade ponds, etc. However, if it is not released eventually to downstream communities, then there is a risk of having a downstream starvation for water. So it has to be balanced, not only for farmers, but also for other living things which constitute the ecosystem. And we looked upon ecosystem services concept. Moving on, let's come to the week seven where we combine the previous week lectures like for example groundwater precipitation, etc. into the hydrological water balance and see where the understanding takes us. We also jump into the conceptual model framework wherein you use your hydrological water balance understanding, then you collect data reflecting your water balance and you input them in conceptual models to understand the performance of different structures to understand the need of water, which is the demand side, and to understand the supply side scenario. This gives insights for better managing by having alternative methods for demand side management and for supply side management. With this introduction, let's do a recap of your hydrological cycle with groundwater and hydrology for surface water. You have different types of surface runoff based on your precipitation input. So you have precipitation, which can go as overland flow into the rivers, lakes, or streams. This becomes your discharge. Then you can have water to go into the soil profile and then come out as subsurface flow. Then you can have deeper groundwater infiltration as groundwater and come out as base flow. So all of these come back to one point where you can monitor and measure it as discharge. Moving on, let's look at the distribution of rainfall components in India. So like breaking the rainfall. So this is an attempt to do a water balance, but let's go through the exercise from Lagunath's book 2006. So the annual rainfall over the entire country for which the author has taken a timeframe is 370 million hectares meters. Evaporation loss at one third of the item above. So one third is also kind of empirical, but it could be based on statistical information, which is giving you 123. So one third of 370 is 123. Then runoff from rainfall in rivers also could be an empirical estimate, not a discharge estimate because not all data is coming together. So this is an entire India scale. So these kind of assumptions kind of smoothens out. It is not noisy to create a big disturbance, but it can smooth out. We'll see how it is. So runoff from rainfall in rivers is 167, which is what? The remaining component. So if you add both, what do we get? You get 0, 9, 2, 9. So there's evaporation loss, there's a runoff loss and you have an annual rainfall. So what are the other components? C-page into subsoil for which the remaining water can go into the groundwater. So you have 290 units of water, which goes, one third of it goes as evaporation loss. And then there's another fraction, which goes as runoff loss and the remaining 80 goes as C-page into soil. How did we call it as infiltration? Okay. So there are other aspects as I said, interception losses, there could be soil evaporation, plant evaporation, animal drinking it. But all those kind of are negligible when compared to these big, big units of evaporation and runoff. So for an India scale, they have taken it as an average. Water absorbed in top soil. So off the 80, now we're going to break the 80. Okay. So here we stop and now we go into the ground. C-page is going into the ground infiltration. Water absorbed in top soils, i.e. contribution to soil moisture. So when water moves through gravity, the first part of your soil is going to get the water and it can increase the soil moisture. Then you have your groundwater component under the soil moisture. Remember, soil moisture is the component where it supplies water to the plants. And whereas the further movement of groundwater or water through the soil profile would be eventually contributing to groundwater flow and groundwater change. So now we've been divided. So 43 goes to approximately 43, approximately 50% goes to water in the soil. So it is not going to release it. Another field capacity concept that we looked at in previous lectures. So where in water is going to be held by the soil. The remaining what happens through percolation, it goes down further into the recharge into groundwater. So which is just basically 4 minus 5. The C-page minus the water stored in the top soil. Now this component is full. 80 has been divided into soil moisture component and your deep groundwater component. Ground water that can be economically extracted from the present drilling technology at 60% of item 7, which means all the water cannot be extracted out. As I've been telling in the groundwater hydrology concept slides, you cannot extract all the groundwater out because some would be going into the deep, deep aquifers. Some the energy is too expensive to even extract. And some water would be attached to the materials of the soil or the rock. So assuming at 60% efficiency, we're going to remove the water. So 60% of item 7, which is 45 is 27. Present utilization of groundwater at 50% of item 8. So not all the water which is extracted or which could be economically extracted. Please move the word economically. You cannot spend a lakh rupees on water to irrigate a field which is going to be 50,000 rupees profit. You understand the concept. So economically, it has to be viable for the farmer or they will try it and then they just abandon. So let's assume an estimation of 50% of item 8 that could be used for groundwater. So available groundwater for further exploitation and utilization is another 50%. So not all groundwater can be used. And off the groundwater, only 50%, 60% can be economically used, but out of the 60%, 50% is present current, the current status of utilization. The remaining 50% can be utilized by further exploration, utilization, improved pumping efficiency, economic cost, etc, etc. So this can be evaluated only if you have all the parameters on the top. For example, I want to start with groundwater. I say no, I want to understand what is number 10. You cannot come to number 10 without going through one, two, three, four. You cannot say 30% of the rainfall can come into groundwater. Let's jump into groundwater because it might be misleading. So for your plot scale, you have to go through the cycle of hydrology to fit in the numbers as much as possible. If you don't know, then you have to discuss it and make sure it is negligible to remove it. For example, interception loss is not put here. You can club it into evapotranspiration and remove it. Let's get back to this slide. So let's take a hypothetical field. In a hypothetical field, you should know the input of the water coming in. Let's remove the lakeside. You're not going to look at the lake, you're not looking at the stream, only your field. So from here up to the overland flow. This is number one, two, three. So you should know the precipitation level, which is coming in, which is why people are striving to say we need more rainfall gauges. We need to understand the rainfall variation. So you need more rainfall gauges to catch the precipitation rate. Then as I said, you won't have proper estimation of interception loss or we can say whatever water is intercepted falls down back into the land. For example, we have a short crop like spinach and spinach leaves are brought, water falls on the spinach, but it can drip down. So assuming that this interception loss is negligible. So we are going to not estimate it. Knowing your soil profile, you could estimate the infiltration and your runoff. So only two components. Now precipitation is falling. It is dividing into infiltration versus runoff. And the infiltration is going to give you some evaporation and transpiration loss because you have plants. The plants have a consumption rate. We looked at this in the FAO method. We looked at KC value. So the plant will just take the water and evaporate it. Okay. Evapotranspirator. So transpiration also occurs. So ET is the term. So we started with precipitation. We went to seepage. We went to evapotranspiration. What is not being used goes to runoff. So every land has a runoff potential based on the land use land cover. For example, if it is a cement row, 100% rainfall would go into your runoff. Maybe 98% because 2% can be vetted and evaporated. So there's no transpiration. There's no seepage. Let's say 98% goes into runoff. Where it would be 100%. If rainfall falls on an open water body, let's say river, ocean, lake, all of that goes into the runoff. There's no seepage. There's nothing. It just goes into the water, which is actually a runoff. So like this, based on your feed area where you want to do the conceptual model or the water management practice, you should be identifying the parameters that are more important and you should neglect those you cannot feel it is important. And or if there's no sufficient data, you have to market that there's no sufficient data. Let's go through the field exercise now. So precipitation eye monitor. Then knowing the land use land cover, let's say I have an agricultural field, 70% of the water is infiltrated. 30% is gone as runoff, for example, for that particular crop. So 30% I know. The remaining 70% goes into seepage and out of the seepage, some part goes into evapotranspiration, most of them. So now the seepage is then or infiltrated water is then allocated into two compartments. One is your soil moisture and then the other is your groundwater. Soil moisture holding capacity is taken from your SR value. If you remember, it is your serve specific retention and specific yield values. So if you know your specific yield, you can know your porosity, you can know your specific retention. So the amount of water that is held up by the soil can be estimated and then multiply to get the volume. So now you have the groundwater. All the groundwater, how much water can you take out? And that depends on your economic analysis and you can say approximately 30%, 50%. You do not know about the groundwater aquifer. Let's say I don't know about my groundwater aquifer. A good estimate is 20% is lost. Okay, so that is what this author has also done. It's a beautifully set up equation, which equates out. So if you add all these relevant features, it should come to 370. There should not be extra than 370. You get my point. But when you use pump groundwater, there might be some old water that is present. Same way, your soil moisture can have some old water, which is also evaporative transpiring. So somewhere you need to adjust these values to come to the exact PPT or the precipitation that has entered into the soil. It is necessary to relate all those into one equation. Don't you think so? So because somewhere you say out of 370, one-third, then out of one-third, I'm taking subtracting to get the seepage. So it is necessary to collate them into one equation so that a user can go to the feed and use that equation to populate it for his or her own study area. And that can be done only when you arrest a size for your analysis. So before that, what is your unit of analysis? I've been telling in my previous example that I would like to do it for my feed. So I won't talk about the lakes. I will not talk about the rivers. I would only focus on my land, which is a one-acre plot of sugarcane, for example. Or I like turmeric. So I'd be putting turmeric. So coming back, that size has to be first set up before you get into your water balance concept. In the previous example, what was the water balance done for? It was done for India. So India, the whole boundary, was taken as a unit of analysis. So you're free to take as much or big or small size depending on the availability of your data. So let's come back to this discussion. We have different hydrological terms for unit of analysis. Normally we don't do plot scale. We don't say, I'm going to do India scale at all. There is a hydrological unit of analysis and it is called watershed size, basin size or catchment. I will explain them now. So what is a catchment? It is a small watershed and a watershed could be basin, which is a large watershed. So you see the size could be different depending on which notes you use. In India, sometimes you say Ganges basin, which is a big watershed. And within that, you can have smaller watershed, Koshy watershed, for example. Koshy watershed leads into the Ganges basin. So you can have it. So this can be interchanged in the US. So that's why I've kept two different formats. One is a watershed can be bigger than your basin or your large watershed can be called as a basin. So let's define each term. The size can come later. Catchment, what is a catchment? If you look at the term and this is good that all these terms have the meaning within them. Catchment, what does it mean? Catch. So you catch rainfall. So this is a catchment. The name is given because rainfall is coming and I catch the rainfall. I catch it and it is a small size because it doesn't give the water out. It holds it within the area. It is called a catchment. So your land, your plot can be looked at as a small catchment. Where do we use it in hydrological terms? We use a dam catchment area. So when you want to construct a dam or you discuss a dam's potential, you put a dam and above that or upstream of that is called the catchment command area. And all the water catching in that will come to your dam. So it's catching. Now coming to watershed. Let's use the Indian term. So in India, catchment is the smallest, then is the watershed and then it's the base, this one. So what is a watershed? Let's break the name, watershed. A shed is not a shed that you put for your scooter or your car but shed means giving off. A tree sheds the leaves. So there's a tree and during autumn season or fall season we call it sheds the leaves. It falls down and then new leaves come up. And that is called shedding. So now combine watershed. So it catches the water and sheds it. It gives it out and that is a true concept in land. What happens is, let's say for this figure, this is the state of Missouri, you have water coming into the land. The land catches the water because it is made up of smaller watershed which is also called a catchment. So water is first caught in a catchment and then it sheds. So it brings all the small catchments together, all the water comes to one point and then it sheds it out which means it gives out the water. The same thing is happening here. You have water from the small watershed. It catches the water and then gives it out. Let's take the Ganges. The Ganges has smaller, smaller catchments. All the catchments give water for Ganges to flow and the Ganges is flowing. If it is not flowing, it is not a watershed. So water is let go of the system. So naturally, waters will flow from high potential to low potential and because of that, it is called a watershed. It's not storing the water. It's leaving the water. So watershed is taken from that concept. So watershed is something that catches the water and combines it to one point or concentrates the water to one point and from there, it leaves it. I hope you remember when we discussed about the fern shape watershed, elongated watershed, leaf shape watershed. What does it do? It takes the water and then puts it in the stream channels and brings it to one point out as discharge. When we discussed about discharge, we discussed about this watershed concept. Now coming to basin. What is a basin? Everyone has a basin in their house. You have a kitchen basin. You have a sink basin in your washroom. So something that catches the water, catches it, doesn't spill it out within the boundary of the basin and goes into the drainage. So here you can look at basin as a large scale catching land. It catches the water and it also sheds like a watershed. So the shedding part is still there. The Ganges basin is there. It takes all the water from starting from Tibet flowing into Nepal and then India then goes into Bangladesh and then sheds it into the ocean through the sea. Goes to Bay of Bengal and then the Indian Ocean. So all this is shed from a point where the rainfall occurs or precipitation occurs and then it goes through a small watershed which is called a catchment. Normally catchments keep the water but if it is connected together it becomes a large watershed and as the name suggests watershed will shed the water and so watershed all combined to a big basin and then comes out. Cauvery basin, Krishna basin, Ganges basin. We go to the western countries watershed is bigger. The basin is small. So you can discuss that where you are but for our class let's keep basin as a big and how do you know by going to government reports and how do they call the Ganges? The Ganges is a river and the river basin not a river watershed. The Khoshi which is a tributary to the Ganges can be called as a sub basin or a watershed. So sub basin is also another term that is being used which is also a smaller watershed than the basin. It's not the catchment. So catchment is always the same. Catchment is the smallest. So now we have the unit of analysis. It could be a catchment, it could be a watershed, it could be a basin. It could be a plot depending on where you are. If you want to do your farm, it is a plot. That's why we say river basins, sub basins, village and regional watersheds, sub watersheds and catchments. So sub word can be used for small size basin, sub basin and then watershed, sub watershed and then catchments. It doesn't differ when you interchange in models. You should understand what you put as a watershed but the same process is there. Catch the water, stores it and if it is combined together it sheds the water. So let's come to the hydrological water balance. We had the hydrological components. Most of them we have discussed in class in the previous lectures. Let's do the basic hydrological water balance equation which is the objective of the lecture. It follows the basic continuity equation as storage is mass in minus mass out. What is the basic continuity say? That if you have a mass which is coming in and you have a mass which is going out. The storage, what remains in your storage is your mass in minus mass out. If your mass in and mass out are same, it is zero. Your storage is zero. So you're not saving anything. Think like a bank account if you have 100 rupees coming in and you're taking 100 rupees there's no storage. If you have 100 rupees coming in and you take 80 rupees, 20 rupees is your storage. So that is the basic continuity equation. So a water balance equation can be kept as simple as possible or as complex as possible depending on the number of variables. For hydrology, we put it as the following. It is input is equal to output plus storage. You can rearrange it to bring it out the real meaning. Why do we put input in one side? So we actually rearrange the storage mass in minus mass out. So we keep the storage on the side. We take the negative in front of the mass out to the other side which is the output and then you get input is equal to output plus storage. So that we have a better understanding of the input which is your precipitation. So precipitation is equal to output which is your losses plus storage. So now all this combined to your input. Remember the example we saw 370 is the total rainfall units and that if you add all the other components it should come to 370. So now let's discuss the water balance equation which I pulled out based on these estimations. So your del S which is your storage or your change in storage. In some books it is called change in storage because it is a changing term and some books are just S, which is storage. It's equal to P which is your precipitation. You can take it from here plus Qn minus Q out which is your surface water coming in minus your surface water going out minus your Et plus groundwater in minus groundwater out. So let's look at this equation here. Your storage here also is your mass in or your volume in which is precipitation. Okay and your Q in is also your precipitation coming in or your mass coming in your groundwater in is a positive because it is coming into the system minus mass out which is all your outputs. So Q out is a loss. So that is a minus sign minus Et evapotranspiration is a loss. So you take it out as a loss and then you also have G out which is another negative you take it out because it is leaving the system. So all that is coming into the system is a positive if you have storage on one side the water that is coming into your system will have a prefix positive. So P, Q in, G in are positives groundwater in. So let's say this is my storage structure and I'm trying to see how much storage is changing your precipitation is positive it is coming from the top your Q in the river is discharging so Q in is positive Q out is negative so somewhere another way the water is leaking out okay so this is groundwater let's take this work yeah so water may be flowing out to the ocean so that is Q out minus Et evaporation is happening plant is taking so Et is loss the arrow mark is up plus G in groundwater is coming into the lake so it is a positive and G out is negative because groundwater is losing to the system. So you could actually visualize this equation as I've done now in this image I always use this image because most of the components are reflected and if I don't have that problem I can strike it up you say strike it also negligible or zero good so why is this important for water management this question should always lag because this is a water resource management course and it is very important to understand why we learn these concepts. So if I know the storage change and if I know the key dominant losses in my system can I better manage my resource that is the idea. So better management scenarios can be produced from your water balance exercise supply side management which is your water coming in because precipitation is the same even before or after the management I'm saying but now you can store the precipitation and give it as a storage you can store the precipitation as in a river and then bring it as Q in okay that is a supply side also you could arrest your Q out so how much water leaves your system you can close it let's take a plot in my plot if I have water coming in if I make buns across the plot then all the water stays right I'm arresting the water from going out so Q out is zero Q in I'll have a higher potential water coming in through a pipe so I can put more water in so supply side I'm managing understanding water availability knowing the precipitation cutting down the losses I now know better how much water is available for plants storage requirements so if there is excess water even all these buns I've created but water is overflowing from my plot or my area of watershed what do I need to do I need to arrest the water how do I arrest it by increasing storage structures one such storage structures is a check that we're discussing this in future but check downs are good to catch the water and store it in your local area you can have rainwater harvesting systems to push more groundwater storage by pushing rainwater into the rainwater harvesting then goes into your groundwater storage and then green infrastructure where they could slow down the water so that your plot can have more water so think about your equation again going back so here you have increased your Q in by supplying more water you have decreased your Q out in the supply side by raising buns and preventing the water from going out or having a storage structure you have also increased your groundwater in okay by recharging and then using it again and reduce the groundwater out so that is your supply side management okay better supply systems which is your pumps your drip irrigation those kind of things you could evolve now knowing that you have X amount of water so now if you know your water you can have better supply systems let's do the demand side management but I also wanted to mention that in your supply system you can have a drip you can also have a channelized water only for some parts you can arrest the top of your land you've seen strawberry farms they put plastic sheet in the empty land so along the plants there's a hole water is taken but on the other part of the land there's a plastic sheet which prevents the water from evaporation which means your E part in the ET is slashed down so all this is better supply and management systems another management system which is important is your demand side management if I know that the water is not enough based on my equation can I not reduce the transpiration which is a loss how do I reduce the transpiration yes by changing the type of crop okay because crops transparent your plants and animals and trees transpire so how do you reduce it by changing the type of crop or plant better options for crops can be given diversification of crops or also area that the crop is going to take can be controlling cropping acreage the better options could also include better types of crops for example if you have rice there are some less water intensive rice that you could use for growing your crops crop diversification means changing it totally for example I have a plot I have water coming in for my sugar cane now I know that my groundwater is less so groundwater in component is going to go less my storage is going down so what do I do I change it for this year I say no I'm going to diversify my crop I'm not going to put sugar cane I'm going to put turmeric so then or millets then I grow a much more different crop with less water requirement thereby increasing my storage for the next sugar cane crop so it's about long-term vision not short-term this vision if you're just showing no no I want to get my sugar cane this year then you boom you do it but your water is gone so you have to be very careful about it then you have controlled cropping acreage knowing the water now you could tell how much water acreage crop can be used so if I have 1,000 millimeters of total storage then I can choose an ET crop which is much much lesser than 1,000 so then the acreage can be increased better crop irrigation facilities which is also a supply site and a demand site management with example drip irrigation those kind of things so you have to pick a crop which is suited for drip irrigation that's why I'm putting it in the demand side in the supply side every crop can be used for drip irrigation but in the demand side you have to pick a crop for suitable drip irrigation methods and analysis you could look at climate change trends okay and understand from your water balance are you following the current trends or have you taken future trends and scenarios in your analysis like as I said long-term vision to take them in your analysis and thought about your storage which can change in the years to come so in the current trends I only know the current rainfall pattern my current rainfall pattern I put in my water balance equation I estimate what is the ET what is the losses then I pick a crop also use future trends and scenarios and then pick a precipitation and based on that you now play with your storage play with your groundwater in groundwater out Q in Q out to arrive at which crop can be grown for optimum ET your ET should not go above then the water you have which is your precipitation and so today we have covered a very broad topic of the need of a water balance equation given what a water balance means the name water balance can be differently given as water budgets water mass balance and a hydrological balance you have multiple other names this is all based on the continuity equation of storage is equals to mass in minus mass out and we have also seen how we could use it for a India scale example from the book and also a short pilot scale or field scale analysis by the equations we did and we also saw how that understanding can be used for better management in the demand side and supply side we also thought about trend analysis given the climate change projections and trends how can you better manage water so with this I would like to conclude today's lecture on water balance components I look forward to the next discussion in the next class which would go further in developing these water balance equations and developing the conceptual model at different scale sizes which could aid your analysis until then see you thank you