 Hello everyone, welcome to NPTEL course on rural water resource management. This is week six, lecture two. In week six, we are looking at surface water structures and storages for rural water resource management. We are looking at the types of structures that can be made and also the size and is a traditional new natural or nature based or engineering based. From historic times, there has been no rural lakes and tanks and what they have been doing is they have been silently helping a lot of farmers, locals in capturing the rain water and then using it during the lean season. We saw that how rainfall is queued, which means there is more rainfall during the monsoon months of JJAS during July, August and September, but during the other months there is considerably very low rainfall. So there is a need to build and monitor these tanks so that we have more water for the lean season. So one of the prominent type of surface water storage system in India is rural lakes and tanks. You see multiple images on the right where they have set up these systems and mostly farmers and women use it for livelihood support and domestic water use drinking for example. It is one of the prominent types in India, especially in rural villages and part of traditional wisdom is used while constructing and maintaining these structures and most of it is done by local communities in India and they span to more than 2000 years. So if you see the first image here, there's a lot of scriptures about these tanks and how they evolved. If you notice that in villages there will be a tank and then around the tank or near the tank there will be a temple. So normally they will say that this is a water so don't pollute it and that is why they had placed all these religious structures near the temple so that people don't misuse the water. It is for domestic use wherein you can take and use the water for drinking, bathing, etc. but make sure you're not polluting the water because the God idols and other things also would be bathed with the same water if it is a temple tank. So the idea is same, you would capture the water, you store the water and make sure you manage it using local participation because it is the local swath to use the water. It is very prominent in the south part of India because of the hard rock terrain wherein recharge is really less sometimes and sometimes the water just hits the land and runs away because of slope and also low infiltration values. So it is very important in this regions and they've played a very prominent part and suppose multitude of benefits, for example irrigation which is for agriculture, water supply, flood control as I explained in the previous lecture, it captures the water and stores it in the tanks for flood and most importantly groundwater recharge. Domestic use is one of the dominant uses, you can see women on the bottom collecting the water and taking it to the house for drinking and other uses. Let's see how they are constructed. This is mostly a methodology of how they construct. So on your right, you have a map of a tank irrigation system. So a tank can also be for irrigation, a tank can be for temple as I said or domestic use, but the same construction method is used. So first they have to look at the catchment area. So where rainfall will be capturing to be drained into the tank and depending on the area and the rainfall volume, you should be able to consider as storage. You cannot put a very small storage for large area and large volume because it will just break the tank. On the other hand, you cannot put too big also because land you cannot just evacuate all the land and then all the water which comes in just evaporates. Because what happens is you're spreading the water thin and when you do that water can evaporate. So catchment area is first determined and watershed area is determined. And then what you do is you have to look at supply channels and how water is going to be brought from these catchment areas into the tank. So you demarket a catchment area, you demarket a tank area. And for the tank area, you have to make the supply channels. The supply channels can be earthen, which is made by mud. You dig and then put mud on the sides or it can be lined through cement and concrete, which is really expensive. But if you want to arrest the groundwater recharge, you don't want the water to go in the groundwater recharge here, but here it's okay. Then normally people line it because by the time the water comes, it's gone. Then you have a tank bund, which is protecting the tank area. Otherwise, that is actually the tank, right? Otherwise the tank, if the bund area is not there, what would just come and flow on all other sides? That is also made by earthen, stone and concrete. Normally it is made by stone and earthen, big, big stones are put and then mud in size and so it just is made like a big wall, you could see. And some concrete lining on top of it can be also used. So all these methods can be used or a combination of the method can also be used, earthen, stone and concrete. Then we have the plantation area where it is the area, the trees and shrubs and bushes that actually protect the tank. Most importantly, it gives shade so that evaporation doesn't happen rapidly. And also it protects sediment and other things from infiltrating in or flowing into the tank because it acts like a wind buffer. So it's just a windshield where all the impurities can be blocked so that it doesn't get into the tank, paper, plastic, whatever it is. So it will be like a buffer which controls, captures these impurities from getting into the water spread area. It could be a village forest, a small plantation also is accepted. Then we have the water spread area where the water in the tank area. So this is the actual tank area where the water is put and the volume is created. Then for the tank, you have an irrigated area or a command area. So this is the catchment area where water is caught. And this is the area where the water is going to be used for irrigation. That is called the irrigated area or the command area. So water is taken and from sluices and other channels, water is being channelized to the irrigation plots. Small, small land where water has to be applied. These water can be taken through this channel. It doesn't only stop there, okay? It is not only just for irrigation and domestic use. So let's see the other uses of tanks. Most importantly, the water spread area of the tank can be used as a perennial and a non-perennial source. Perennial means it is always there, water. A non-perennial because sometimes it evaporates. So in the perennial season, it is good that everyone knows that, okay, I don't have water in my well. But for sure the tank will have water, they will go and fetch water from the tank, okay? The other is non-perennial use is when you have certain times in the year when you know the water is there. So you could go and use it for your domestic and other uses. As we said, it's supposed multitude. For example, livestock breeding. You can see a woman and men taking their livestock, which is cattle goat sheep and then there to drink water to feed. The grasses are there because of the water so they can feed and wash them, clean them, et cetera. Cloth washing and other things are also being done. You can see here women come there. So it is like a kind of a meeting for them every day. You know, in the morning they finish breakfast. They cook the lunch and maybe then they take the clothes in the bucket and then they walk towards, all of them walk towards the tank and then they wash it and then bring the clothes, wash clothes. It is also used for spiritual religious uses. As I said, most of these tanks would have a temple with them and where the temple festivities would happen in the tank water. It is for groundwater recharge. It is an indirect recharge because you're ponding the water for irrigation and domestic use, but also there's a loss which goes into the ground and that loss is a groundwater recharge. It also improves microclimatic conditions because it gives a cool temperature when you go near the tanks because of the evaporation. So that gives a microclimate, which means a different small level climate which is suited. Maybe for example, raring livestock, certain kind of crops, et cetera. Let's see how water flows into tanks. I said to me, there is a catchment area and then you put all these other channels and also runoff can also come. So the first important thing is, yes, channelized water can come but also runoff can come into the tanks which is just your water hitting on the surface. It cannot infiltrate most of it. So most of it will just flow as runoff. So that runoff from the catchment can go into the tank. So this is your tank and you have water coming in from the tank. There is also direct rainfall. Rainfall just on top can come into the tank. So that is one of the inflows to the tank. And depending on the water spread area, you can have a large area of influence where the rainwater is coming in. Then there is channels, as I said earlier. So this is where how a tank is normally built. You have the runoff coming into the tank, rainfall capturing in the tank. There is some groundwater loss and then evaporation loss but the water can be used later for irrigation. The other aspect is seepage. Seepage is the either loss of water from the tank to the groundwater or groundwater into the tank which is a discharge from the groundwater and seeping into the tank. The seepage from groundwater storage or shallow wells where in surface water, groundwater interactions occur and the one way is where the tank can lose water as you see here, but most of the times it also gains water. It can gain water because it is actually sitting in a low lying area and so the groundwater can come in and store. There are some locations where groundwater neither comes in nor stores because it just goes in and then the same volume comes out. So it doesn't affect the volume of the lake. In this example, the tank or the water storage gains water. Here it loses water, here there is no change. Let's look at the outflows. So what do you do with excess water from the tank? So the tank is full. What happens is you have to release it and that is released by channels as I showed in the earlier diagram also. You have a channel that releases water into the irrigated area's crops or it can be through veers and sluices, a gate which we just opened and then water would flow. And outflows doesn't only relate to water that we control. It is also the water that is lost from the system. We have to be very careful about how much water is lost because in a hydrological water balance, the losses are also called outflows, okay? So excess water is released through channels. That could be a genuine, we know about the outflow. We remove it, we let the water go, but there are other losses. For example, evaporation. It depends on the radiation. It depends on the ambient air temperature and how much water vapor is there. So there's a lot of evaporation happens. There is seepage to groundwater as I showed in the earlier diagram, groundwater can also take water out from the tanks. And then there is a controlled release using sluice and gates. So always control it. And there is an overflow. What is the difference between a controlled gate is where you manually control it or automatically control it? Whereas a flue or a overflow veer. What is a overflow veer is? It is just a stop like this. So once water comes up, it has to flow through. There's no opening. There's no nothing needed. It just flows through. We'll show you some examples of these. And there are a lot of multiple uses of the channel. So the tank doesn't stop just when the water is released. So along the water channel, along where the water is released, there's multiple benefits. For example, command areas irrigated with the help of these channels and sluice and gates. You see here how water is flowing from a tank or a lake. And then each place they'll put a small inlet outlet and they can release the water inside. So normally farmers decide from themselves. They talk to each other. For example, this is Farmer A. This is Farmer B. And this is Farmer C. What they'll do is they'll wait for the water. And then when the water comes, maybe A will open it here. Water will come and then flood irrigation. This is called or phallog irrigation. So it just comes in on the top and then irrigates the field. Then water, this guy, number B, Farmer B would say, okay, I'll also open after you done. And then this field fills up and then see fills up. Sometimes it is done on rotation. Sometimes it is done as per need. But they have a good understanding of how much water is going to come and who gets it first, et cetera. So that is a good aspect. Then we have flood irrigation with the help of feeder channels. So this is the main channel. And then you have another feeder channel, small channels that take water from the main channel. So for example, the water can go here and there could be another channel that can take another source into a different location. Maintenance of stock water for livestock breeding. So sometimes these channel waters can actually put in a small storage. So this channel can also lead to a small storage, not as big as a dam or a tank, but a small, very small storage for livestock, like chicken, those kind of rearing. And most of the time you would also see that you have, excuse me, you have fish also growing coming into these channels and the fish can also be growing along with the rice and paddy. Vietnam, they have this very good agricultural system where fish is also red with the rice. And then groundwater recharge does occur along all the channels. So you see here, this is an earthen channel. There is no lining, there is no concrete. So water can easily recharge. And then this is less expensive because you just have to dig and then use the same mud, same the soil on the sides to make a bun. So use of lakes doesn't stop here. Use of lakes of surface water storage systems don't stop just for irrigation, just for domestic. There are a lot of multiple things that it contributes which are very important for the overall picture. For example, ecosystem services. Let's define ecosystem. Ecosystem is the interaction between the biotic, which is your agriculture, human, all the life forms, et cetera, fungus, worms. So it is an interaction between the biotic and the abiotic. So biotic is all your biological living organisms and abiotic is a non-living things like rocks, soil, those kind of things. So there is a beautiful interaction between them. For example, the soil has to be wet for the fungus to grow. If you say, no soil, I don't give water, I only give water for the fungus, it doesn't grow. Okay, so there is a beautiful coexistence, a system and the word ecosystem, that is how the word ecosystem is coined. So use of lakes can be understood under four types of ecosystem services as per millennia, ecosystem assessment, provisioning, regulating, cultural and supporting. Let's see some examples of how these rural lakes, rural tanks, rural water storage, surface water storage can help, okay? So let's see provisioning, provisioning food. Food like for example, production of fish, wild game, fruits and grains. So basically you can just grow using this water, you can grow your crops, you can set it to a small tank and from the small tank you can rare fish. So if you go to Nepal kind of regions, they have this fish farms. So what they do is they channelize this water into small tanks, like a small swimming pool for the fish and then they grow the fish inside and then they sell it for food. So it comes under the food, production of fish, wild game, foods and grains. Not all fish is for food, right? So there are some fish and that comes under the ecosystem services. Then there is freshwater storage and retention for domestic, industrial and agricultural use, as I mentioned. I also didn't mention much of industry because not much industrial demand is there in the rural water from these tanks. Maybe like cottage industries, they can take this water for small, small activities. But other than that, there's very limited use for industry because agriculture itself is an industry. So when you combine agriculture as an industry, then it's just one more agriculture industry. Then you have fiber and fuel, a production of logs, fuel, wood, peat, fodder. These are the biotic systems that are grown using it, not directly for food, but for fiber, paper and our cloths, cotton, et cetera, and also for fuel, for cooking, all those things. So you can have the food, like for example, I can have the water for fish, but I need to cook it, right? I cannot just eat it raw. So what you do is you have to have the ecosystem to survive and give you firewood. And that wood is grown using this water also, biochemical extraction of medicines and other materials from biota. So that can also happen. There's a lot of chemical reactions, biological reactions, which can lead to some medicines, et cetera. So genetic materials and genes, for instance, to plants, pathogens, ornamental species, et cetera. So there are some things that you can specifically grow using these. Wetlands and small tanks and ecosystem services. Then you have regulating, climate regulation. As I said, it gives you a microclimate. And it's also a source of a sink for greenhouse gases. Local temperature can be regulated, precipitation can be caught, all those things can be happening in a tank or a surface water storage system. Wetlands is kind of a rural surface water storage, where water can come and it also has some growing stuff inside it already. Okay. But those, these examples that are given by MEA can also be used most of it for the tanks. So as I said, when you go near a tank or a good water storage system, small surface water storage system, the temperature is different. And you see the buffer around it, there's a lot of forest and plantations growing. Okay. So water purification and wastewater retention. So because water is held in that, you can actually, you know, make sure that, okay, if it is too much polluted, you don't open the water to drain to the irrigation land. You just hold it and then do something else with the water, right? You can evaporate it and then don't release it to the groundwater also. Erosion regulation, because you stop the water, so the sediments would stop, okay? So it will fall down and those sediment would not be going down in the irrigation channels. So you will have to evacuate the sediments. So that is the maintenance part of these surface water storage systems and wetlands where you have to take off the sediments, take off the eroded sediments. And by slowing down the water, you also prevent the water from eroding further downstream because when water goes fast, it starts to eat up the sands of the sides and under the bed. But when it stops in these storage structures or slows down, then sediments fall. More importantly, because it's slowing down, it doesn't take off more erosion on the way, okay? Natural hazard regulation flood control has been already discussed in this class. Storm protection is given through these systems. Pollination habitat for pollinators, bees, okay? So if you look at bees and other insects, they normally go around these lakes because of these good water resource and cooling time climate. A lot of flowers will be there. So there's a lot of pollination that happens. Cultural, spiritual and inspirational, source of inspiration, marriages, attached beliefs are attached to this water bodies. If you see all these water bodies have a good religious connection which is held on through centuries and traditions, okay? So it's not about a particular religion, but it is about how they've taken it through the tradition and how they lived along with this water bodies. It is a source of inspiration because when you go there, aesthetically, you feel calm, you feel natural, so those kinds of things. The creational, some people, for example, Coimbatore, I've seen some village big tanks, they use it for boating also, so people go on creational activities. You should not be polluting it, but you can just use a boat. You can just, and those boats are non-electric, non-diesel, it has to be manned power, so you have to pedal it, okay? Because if you have too much of this fuel coming in, it leaks from the boat into the lake. So if you go to Kerala, for example, all these motor boats have a negative impact on the water quality because the oil, the petrol, diesel, whatever they use leaks into the system. Whereas in the, for example, Ooty, and now if you go, you see these pedal boats where it doesn't pollute the system. You cannot go long, but it's for recreational, right? So it's still okay. And aesthetic, as I said, aesthetic means it's pleasing to the eyes. It is beautiful, so it gives you a calm feeling when you see these water. People go there and sit and then have a coffee or snack or something. So a good aesthetic value is built educational because opportunities for formal and informal teaching training can happen there. A lot of information about the ecosystem services, food production, climate, everything. So these stands can serve as a teaching material. Most importantly, it supports a lot of natural processes, soil formation, sediment retention, accumulation of organic matter. All this is driven by water and because you are regulating the water, you're slowing down the water, it supports in your natural process of soil formation. Nutrient cycling, it is very, very important because storage, it stores the nutrients within the system. It can recharge the nutrients, recycle it. And also because of the sediments, all the nutrients would be attached to the sediments and those sediments can come along with your water body release channels. For example, nutrients are coming in the field or in other aspects and sediments are there. So sediments attach, nutrients attach themselves to sediment and then it flows in the water and while it flows in the water, it can get accumulated in the tank or it can be released to different parts. So a lot of nutrient cycling aspects are held in these water storage structures, especially wetlands would have all tick marks for other types of storage structures. It is limited application, but still I could say that it can be applied for all these systems as we saw in the examples I gave in the class. So with this, I think we have covered the rural water storage types, how they are constructed on the land in terms of what do you need? You need elevation difference, you need a smaller area and that area if it is beneficial, if it is a low lying area, the elevation should be low. So that water can come in there and you erect the buns around it and then you demarcate a command area where the area gives you the volume of water that comes into the system and you can play. So this is a supply side management. When it comes to water management, I'll just introduce this concept but we'll get into this in detail. It is a supply side management, which means water is a supply and since water resources are low, if you don't have the tanks, the rainfall is very low as I showed in the previous class. So rainfall is like this. So the supply is limited only to this region. So these months. So what you do is you increase the supply by having a storage. So all the months mostly will get the water. So it is a supply side scenario and also you release the water from the tank through channels to different areas and you pick and choose which areas to supply. So it is a supply side management. For example, there was only two river streams and a tank here on the water was stored, nothing else. But here, this land is good fertile, but it didn't get water. So all you do is you put a channel from your tank to the land and that land now gets water. So you are augmenting, you're creating a supply. First you are creating a storage, which is a supply. Then you are distributing the supply to a region where there's no water. And so you are increasing the supply scenario. So all this is very doable by even a small tank in the village. Mostly it doesn't happen because of the funds and people not coming together to do it out of ownership. So now slowly with these classes and lectures, I hope you could take the message across and then engage with more people to build these kind of systems. I'll see you in the next class.