 Hello everyone. Welcome to NPTEL course on rural water resources. This is week 9, lecture 2. In this week, we are looking at how to manage rural water resources using engineered infrastructure. The whole idea is we have been seeing that rural water issues are there, lot of water is mismanaged and infrastructures are absent to capture excess runoff or aid groundwater recharge. On that note, in the last lecture we looked at the largest infrastructure that could be possible which are large dams and irrigation networks. In today's lecture, we'll be looking at the smaller brother of the dam. Hopefully it is not much different but just the size is different. Let's take a look. So we are looking at check dams for this lecture. What you see here is you can see people walking on the check dams whereas in the large irrigation project I mentioned, you cannot walk on top. There is really security issues that you cannot even go near to that wall of the dam, the storage structure of the dam whereas here you see people happily walking on top and going around. So this is more like a localized small size dam and those are called check dams and there are multiple multiple designs. First let's look at the check dam but before that I would like to also talk about the areas that are above and below the dam, the area above the dam is called the catchment area whereas below it is called the command area where the water is going to be given. So this is your dam be it check dam or large dam and then you have a catchment area on top. This is where the water is caught and then stored so that you can release the water later. Even though it says check dams and reservoir, those terms are kind of used and misused in literature but reservoirs are larger dams and check dams which are placed on the top you could see are smaller dams. Each check dam will have its own command area, very small command area at the bottom and catchment area on the top. Let's use different colors. So where the water is going to be caught is called the catchment area. So this is the catchment area, check dam. For the big dam, this is the catchment area. So it is that area above that point where water will drain and come into the storage. Then water is used below the dam for irrigation. So that is a small more smaller area or it depends on the crop etc. I'm just drawing because of the space but it could be any design, any shape whereas the catchment area is normally a watershed shape, fern leaf or a leaf shape. So the command area is where the water is released and given for irrigation through canals, river networks and other water bodies. So let's look at the specifics of check dams. Again there's a lot of government assets, books on these, I'll give you the links. Please go ahead and look at it because these are very, very important for rural water resource management. Not only for groundwater, not only for surface water but it gives a holistic picture of capturing water, storing water and then slowly releasing it through the downstream communities. What is a check dam? It is an engineered structure across the stream network. It is not parallel perpendicular to the flow of the stream, river etc. If it becomes a large river then it becomes a dam. So just think about the size, you're not concentrating on a big river, maybe small, small rivers and river networks, stream networks, it is possible. These are also low cost, you don't need to clear the land. How does it differ from a dam? Check dams are smaller in length and built across secondary stream networks while dams are considered major rivers. As I mentioned, major please underline. If you go to the Ganges River, those who are from that area, you would see the river is around more than a kilometer width. How do you build a check dam? You cannot and that is where water is being stored in big, big dams and then released in the South Cauvery and other stuff. Less downstream impact compared to the dam. Luckily I have a figure which has both the large dam and the small dam, check dam in one image. You could see the sea is a check dam and this is the large dam. What it says is there is less downstream impact. When you block water, when you're blocking the water, downstream there is no water. As a result, you are kind of stopping the water which is due downstream and then storing it in your large dams. Whereas the check dam, yes you're storing water, however the volume is very small. So sometimes water fills and then over goes and then goes to the next check dam or downstream. You could see that is what is happening here. Okay, so the water is coming and then there's a check dam, oops, there's a storage and then it goes down, another storage and then goes down. So you're not actually drying down this area, whereas in a dam, this area would be totally dry, no water where this dam is being filled up. There are uses for it. They want to create the level up so that they can draw hydropower. It's called maintaining a head or an elevation of the water so that when water falls it can be used for your hydropower. Whereas check dams normally you don't use for hydropower. It is mostly for water recharge, irrigation, lift irrigation, etc. It is less costly, small size therefore less costly. You don't have to clear the land. So all this land would have been cleared because the water is inundating the area. So let's think about it for a second. You have all this as a forested area, okay? Before the dam was constructed, all this was a forested area. And then what you do is when you make the dam, this water front would be inundated, which means water would be filling up. When water fills up, those land cannot have any vegetation. It suffocates, the plants will suffocate and die. So it is better to clear them off and then make it more storage. Like you take out the soil, take out the rock so that water can be stored. So basically you clear the land, take out the soil and rock so that water can store more volume. Whereas in check dam, you don't do that. You just make maybe you clear the sides a little bit so that the bank is stable. You could see they have done some work here. And then you also deepen this part. So deepening a little bit to store water, otherwise it doesn't make sense to have a check dam in a high elevation. So this is also a decentralized versus a centralized approach. Whereas a decentralized means it is not one dam for everyone. So that is the large irrigation project, a centralized approach, centralized heating, centralized AC we call. So an air conditioner, which is for the entire floor, it's called centralized air conditioning, theater, a movie theater, for example. But when you call decentralized, then the hallway need not be aced, but you have each room in the office, each in a floor, each room can have air conditioner, its own small air conditioner that is decentralized. So here what we say in the dam is the large dam would store all the water and then release it to many, many acres of land, that is centralized approach. In a decentralized, every small acre would have its own check dam and that water will be used only for that acre. So as I said in the drawing, this area, the command area, which is going to be here, all the area would be given the water from the centralized dam. Whereas in the check dam, it's only this small area which will get benefit, this small area which will get benefit. So you could see that instead of putting one dam and having all the area irrigated by one dam, you're breaking it into smaller pieces and giving it a small area of influence. Now, this is easier to maintain because people power, etc., is easier if you have a decentralized for water. Otherwise, the controlling agent would be sitting on one end of the watershed, whereas people are fighting for water on the other end. So that distance is a big problem. Check dams and associated benefits. Let's look at the check dams and their benefits. Does not require relocation of people. As I said, when the big dam is filling up, all the areas on the side, the houses have to be removed because the water will be full. And so in the check dam, nothing, you just have to clear the sides and then the in-stream. Does not require clearing of land. You're not going to clear the land and then make the dam. Less considerable negative impact. Negative is more subjective and it depends on who uses it. But here overall, negative is less in a check dam because you don't clear the ecosystem. You don't clear the forest or vegetation. So the birds, animals, everything still remains. Whereas in a big dam, all of those have to be cleared. Community-based solutions, check dams are community-based. As I said, decentralized means it has less water, less number of people benefiting. But those people would be happy to maintain the check dams. Easier to manage due to the size. Again, the size is very, very small compared to large dams. And that gives them a very good way of managing it, more freedom and less people. For example, for large dam, you need a big agency to maintain it. Whereas a check dam, every week, one house can maintain it. They just go and check. So like here you could see, they're just checking the dam, the wall on the sides, etc. And most probably everyone will be using it for the daily activities also like washing, bathing, fishing. Whereas in a large dam, you don't see those kind of activities. Localized benefits, the benefits are visual. You can see it, local people would enjoy and they then understand that they should manage it. Whereas in a large irrigation dam, you don't know how, for example, in Pune, water is being poured and it can be sent to Mumbai for use. Would Mumbai people know about these dams and the areas they may not know? Whereas if it is a check dam, a smaller tank, for example, that is a decentralized, a small tank within Mumbai and people are getting water from that, they would know about the tank. So that is where localized benefits help in getting ownership and also benefits of the water to the people. This is a decentralized approach. I have spoken a lot about this. So I would move on. Let's look at the operations of check dams. Stores runoff in smaller volumes. Let's quickly look at what did we say has runoff? You have precipitation on a land. Some precipitation is happening, part of it goes in as infiltration, part of it goes as percolation into the ground water aquifers. Plans uptake is there. Whatever remains, which is a big amount, will go as runoff. In most systems, runoff is the biggest component of the rainfall. When you rainfall into different compartments, your runoff is the biggest factor because all the others processes is much slower than the rainfall rate. Whereas runoff is much faster. It can be faster than the rainfall, thereby giving you ease of movement of water. Water wants to move. It doesn't want to stay in one location because of law of physics. It has to flow from high to low potential. Agent recharging radially the groundwater aquifers in the vicinity of the check dams. What it needs here is the check dams. For example, you have a river and then you put a check dam. There is a check dam. Radially, the influence of the check dam is felt in the groundwater. This is radially. It depends on how the aquifer is, what type of rock, soil, water content, etc. But most probably the lateral movement of recharge from the check dam, water would be moving and actually contributing to groundwater recharge. Most probably it will. Why? Because initially the river was flowing. The water level may be at the same level of the groundwater. But now, because you are pointing it up, the level rises in the check dam. And because of the level rise, the water is at a high potential compared to the groundwater, which is at a low potential. So, water would move from the check dam into the groundwater. But also, all these would depend on is there space for the water to move? Is it empty, unsaturated, etc. Agent increasing soil moisture near the check dam. Because it is recharging to the groundwater, in the process, the soil moisture also gets recharged. So, initially it is the soil moisture depending on the depth of groundwater recharge. Or if it is moving in the seepage, in the depth of the groundwater, it can move in the soil moisture profile because of plant uptake, etc. Mostly built by local agencies on a log. It is very, very low compared to the irrigation dams wherein you don't have to have lot of rules and regulations except some permissions are needed. So, the local agencies can build these check dams after they get some clearances. You don't have to have big, for example, economic clearances, impact assessments that you need in the irrigation dams. For small check dams, normally it is the people who have to talk to the low downstream communities. And also to the people who actually manage the water body, CWC, PWD, those kind of agencies, and then get permission and do it on a lower budget. As I said, it gives you the freedom to use any material you want. It could be done by wood, it could be done by bricks, sandstone, mud, rocks. So the budget is low. You don't have to worry about it. Whereas in a dam, large dam, it has to have the dam clearances, safety inspections, the thickness of the wall should be appropriate. So there's a lot of issues because once it breaks, all the downstream communities are washed away. Whereas in a check dam, not much disaster happens. You don't see disasters by check dam failure. You see that in the large dam failures. Maintenance is not built into the budgets. As we looked at the issues before this class in the last week, the major issue is people don't maintain it. So it concerns. It's a big concern because it is your property in terms of it is a property. You are the major stakeholder. You're the major benefactor. Why are you not maintaining it is the question. So we've looked at multiple answers to this question. Most importantly, they don't know that if they're allowed to manage the water, manage the check dam because the flowing river, they never managed. And that they know that that is their water, they go and take it etc. But they don't manage the river. It was a natural system. It just flows and then suddenly one day the river will wake up and she thinks I should move in a different direction. It will move in a different direction like the Ganges. But check dam is like a structure and it involves money. Even though it is low budget for villages, it might be a big budget. So that is where the maintenance is not built into the budgets may lead to sanitation upstream of the check dams. So where the check dam is there, for example, there's a check dam right in this point. When water is blocked, then this area can also have sedimentation. This we can see in the large dam also. So the physics doesn't change between the size of the dam. So you have water flowing and then a dam which is actually stopping your water because your water is flowing in this way, for example. And then it goes like this. When it comes to this part, the water slows down. So all the sediments and rocks and pebbles that it carries is deposited before the check dam. This is a common thing because the velocity was enough to carry it. Now the velocity is slow, so the materials drop. So materials drop down here. And that leads to sedimentation. Once this is not clear, then water will go over the check dam. There's no point of storing the water. So that is what nature is. You can try to stop it and curb it, but if you don't maintain and accept the power of nature, she will just run through your check dam or large dam anything. So you have to be very careful about nature. Mainly to less downstream flow and associated impacts on agriculture and aquatic life. Even though you are making a small section of water storage, still it is a water. So you have to accept that yes, down people would have lesser water than before. And the impact could be on agriculture and aquatic life. For example, the fish. The fish need flowing water to lay eggs. And if it is not there, then it is a problem. Insects, all these things are tied in the ecosystem. So it is better to understand and then build these check dams. Anyway, any non-natural infrastructure will have impact on agriculture and nature. Anything. Your road, for example, has to have an impact on the land and the nature. Any engineered product will have an impact. That is why if you see tribals, they don't, they practice agriculture and associated things in one piece of land. Then they move to another land. They don't own the land. They'll just go to another land and then they start agriculture. So the old land will recuperate or bounce back into a forest. So this we don't do because we are engineering the land. So still there is less downstream flow that comes down. So you have to be careful. In the previous figure, we saw that there is, here you could see that if everyone is stopping the water in the up check dams, then what do want to come down into the reservoir? Slowly, I'm saying, if one check dam is 1000 liters, just for example, I'm saying, and your big dam is 50,000 liters. You build 50 tanks, 50 check dams above the major dam or the dam. You won't get any litter of water in the dam because you're already de-centrally holding the water and only less water would come down into the reservoir. For example, only this area rainfall will contribute to the water, whereas all the other check dams are big and storing the water. So this understanding is needed to talk to communities about dams, any dams, large or small check dam. The only positive is it is less, much, much less compared to a large dam. But if you can share the profit, make some aspects for aquatic life and agriculture, then it is a very good method to store water and use it for lean season, non-monsoon season, agriculture. As I said, these check dams have been proved worthy in many, many areas. However, you have to do considerable estimations of the properties before you assess if they work. Check dams, as I said, have been highly beneficial in many Indian religions, in fact, across the world. Many people have seen rivers getting back to life because of check dams because initially the water would flow through the river and gone. Only three months the water would be in the river. But now since you slow down the river water through check dam, you are seeing the water flow annually, every day, the year it will flow. This brings a lot of happiness to the people around because they used to see this water flow every day. So the Narmada, Dabti and all these rivers in the northeast and north regions were used to flow fully. There's a river called Vahegai in Madurai, which used to flow every single day. If you go there, it is like a kilometer width, more than a kilometer. But then now there's no water because things have changed, climate change, etc. Water abuse, capacities, etc. But now if the water is slowly, slowly released into Vahegai, it will start to flow again. What are the benefits of the check dam? As I said, there are many benefits. Let's look at some. Irrigation scheme is a big hit in the check dams because you're storing the water, you're creating upon thickness of water at the check dam. And now you can put a pump and remove it for agriculture because recharge groundwater can take time, whereas this kind of activity can at once take the water and prevent evaporation laws, recharge laws and apply it to the field. There is some energy component needed because you are using a pump, but farmers have the money to do it if they want to have a product, an agricultural productivity. The most important thing you need to understand here is, can you do this in a flowing water? Yes, but we don't know if actually the water would be there throughout. Whereas in a check dam, you pond the water and you see the water, okay, I have this much volume of water, now I can pump it up. So you know how to better control the pumps and also irrigation area, whereas in a running thing, you cannot. Now this is the NM Sadguru Foundation, which is an NGO in Daho, Gujarat. I've been there multiple times to see the wonderful work they do. They bring communities together, these land were not agriculture productivity at all. There was no water, very less rainfall and water doesn't flow from check dam to the land because the land is high elevation, the check dam is low elevation. So you need a pump water up, which is highly energy intensive. One farmer cannot do it, but if the community joins together, that's what this foundation has shown, if the community joins together, then they can collectively work to pump the water and spread it for agriculture. So look at this, 10 community lift irrigation schemes were installed in one year. That's pretty big. What they do is they pump the water, bring it to a central location and from there, they channelize it to different farmers. And from here also, they can pump to different elevations. But most importantly, this storage can be used to send water to each and every field. NM Sadguru Foundation is in Daho, Gujarat. Please look at this link if you would like to get in touch. They have good training programs for people who are interested and they can take it up. It's an NGO, so it's not for profit. Lift irrigation from a check dam. So this is how the schematic works. You have the water in the check dam. You have a pump house as you've seen in this diagram. This is the pump house. And then you pump it into a reservoir or a smaller tank where water is stored. And from there, you disperse it to the field. So there is some power and cost for lifting the water, the pipes, etc. But this NGO would give money for 10 years and then later, they say, okay, I will build it. You manage it. The farmers should manage it and then if you want, you can increase the area of acreage. 401 community lift irrigation schemes are executed. And this is how, as I said, the distribution point, these are called. So from one check dam, the water goes to this distribution point and every farmer can now manage the water. Also, it's making it easy for the farmers to get the water. And this has also been done by the Government of India schemes, especially the MG Nerega. Under the MG Nerega, there is the NRM, Natural Resource Management. And under the NRM, there is a lot of budget for water resources, almost 75% of NRM budget. Then what do they do is mostly they do check dams. You can see here, they do small, small ponds which are not connected to a river or a street. Farm ponds and ponds are not connected. So along the river, the biggest investment is a check dam where they stop the water and then from there, they spread the water. If you look at budgets also, compared to ponds and farm ponds, check dams are pretty expensive compared because ponds and farm ponds are small. There's no machinery involved, etc. Whereas check dams are running water. Then you have dug wells and bankments, etc. So there's lots and lots of assets we call them. These are each one of our assets have been created because of the positive impact on the farmer's livelihood, total livelihood. It's also used for drinking, for washing, bathing. All I said, the check dams store the water. People go there for fishing, take water for drinking or cleaning the vessels. In rivers and stuff, you would see in villages, it's the same water for everything. They boil it, maybe they filter it. But at the end of the day, the water is good for them. They've been doing this for a lot, lot of years, a lot of generations, I would say. The impurities are very less. So here you could see in Maharashtra, where the locations are and some locations like Latur has less, but others have a lot of check dams. So the benefits of check dams have been studied very, very explicitly and detailed in many, many literature. Let's look at this study. This study used remote sensing to look at, has the check dam improved the condition of soil water and the groundwater recharge? This was in a location in Gujarat, same Tahore location. And you could see that the number of check dams increased from 1990 to 2015, so from 0 to or P to 52. And then all these areas are the basin boundaries where the check dams are placed. And you could see that in a year where the rainfall is comparable, same rainfall, 1991, 2017, the rainfall is almost the same. But you could see that the NDWI, which is an indicator of water in the soil, is higher in 2017 after the installation of 52 check dams. You could see here all these areas are turning into yellow. And if it is positive, high number of positive means it is more water is available. You could see all the red is converting into yellow or orange. And these pockets are coming up where water is there. So there is a radius of influence, but overall these check dams have improved the water because from here they take the water out and recharge the entire area. There is lift. So with this, I would conclude today's lecture. We looked about check dams and how they are useful. I will meet you in the next lecture with another Engineer Infrastructure for Rural Water Management. Thank you.