 Hello, everyone. Welcome to NPTEL course on Rural Water Resource Management. This is week six and we are at lecture one. Let's see what we have seen in lecture five. We looked at in detail the groundwater hydrology components. We made sure that we understood the key hydrology components in the groundwater component and we then further progressed on finding the measurements and data where it can be available. We also looked at the role of groundwater in the overall hydrology. Now moving on, since we have looked at the groundwater as an important resource, we will look at the other resource which is very important, which is the surface water hydrology. So in this week, week six, we will be looking at the types of surface water storages, mostly in the rural regions because we are dealing with rural water resource in this course. We will also look at rural water bodies and lakes. We will look at methods for irrigation from the lakes. For example, how do you take water from rivers and lakes within the rural system? It's not only a running water, but also stored water, so ponds, lakes, etc., etc. And then there is a big concern on what is being happening in the current scenario. Most of the villagers are experiencing loss and conversion of lakes. We will look into why this phenomenon is happening, wherein we have disappearing of lakes, encroachments and conversion from rural to urban. Disappearing is also kind of rural to urban, but most of the time disappearing just means that the entire lake or water body is drained and then construction is built on top of it. Or like in Kerala, you have vegetation growing on it or agricultural crops. Encroachments is where you block the water so that you drain it indirectly. And rural to urban conversions is again like where the urban center is increasing in size and some villages on the boundary of the urban setting are losing the water bodies. Please understand that water bodies are government property and it has under no one's name. And so the boundaries are kind of very not stringent. There is no exact line because one day the water body would be big and then one day because of summer it will be small. So there is a demarcation. However, people don't know and they start to encroach it and abduct it saying that that is their land. This is the key reason why in Bangalore we have a lot of lakes that are lost. So let's dive into week six. First, why do we need surface water storage? We talk about groundwater storage. Yes, but there are specifics to why we need surface water storage. Let's look into detail the need of surface water structures. First, this image we saw in the early part of the course wherein we have a variation in rainfall. If you look at it, the rainfall is not the same across India and even within a village or within a district you can have a high rainfall zone and then shared with a no rainfall zone or a rainfall shadow zone. This leads to variations in rainfall and our skewness. What we call is how rainfall is less in one area and high in another area. So spatial variability is a phenomena which occurs because of the map you see here. It is not the same. Rainfall is not the same and if you make further more iso heights or lines of equal rainfall, you could see that there are some within a small village or within a small district also you will have variations in rainfall, spatial variability. Then we have a skewed rainfall pattern. What is skewed rainfall? It is not the same across every month because we are not in, for example, in these regions in the northeast, you do have rainfall almost every single day in the wettest part of the planet. But in most regions at least weekly you will have some rainfall, very little rainfall, etc. Hill stations. But most of the agriculturally active regions have a skewness which means 78% of the annual rainfall only happens in the monsoon months and that too between the peak monsoon. Here the peak monsoon is given as JJAS, we call it or June, July, August and September. This is kind of the overall average for India even though it shifts where you are. Most of the monsoon is at the peak monsoon where the annual India's annual rainfall happens 78%. Most 80% of the rainfall happens in JJAS. If you look at it, this is the average rainfall in millimeters monthly and you have Jan, Feb, March, almost very low rainfall pattern and then May whereas you have the summer and in some regions the summer extends until May but after May you have June, July, August, September. So here we say that every June 16 will have rain in Mumbai or in Maharashtra. That is the onset of the monsoon. But before we get the monsoon, the monsoon comes from Kerala. So here the monsoon is coming and while it rises here maybe a week later after the monsoon onset, we call onset is the coming in of monsoon. From there it can come here. So just a week more or less. That's why you see this variation but it's a beautiful probable redistribution, a bell curve, we call it normal distribution where you have more rainfall happening in a particular concentrated zone or concentrated months which raise from June, July, August and September. And then you have your winter post monsoon seasons rainfall. So if you look at it, there are some regions where there's zero rainfall but because across India there are some regions which also get rainfall in Jan and December, we have for example in Kerala region, in the northeast region, you do have rainfall across most of the time. You go to hill stations there is always rainfall, elevation, the elevation gradients. So the monthly average rainfall, this is from 1871-2016 so more than 100 years rainfall from IITM shows that this is the average pattern and there is this queerness. So because it is happening only in a concentrated time, you need to capture it so that you can use it for the remaining months. What do you mean by lean months? Lean is like how I'm lean or you have lean chicken thin. So in another word, what it means is these are the lean months where is less rainfall is happening. So if you say what is the average rainfall, okay, so maybe somewhere here you can draw a line below the average you will call lean or below average months and then this is the above average which is for sure during the peak rainfall season you will have above average rainfall. Moving on, we have to capture this rainfall so that we can use it for the lean months, both your summer spring for the monsoon and after the monsoon which is your winter season. So water needs to be stored and groundwater we saw in the previous week lecture it can be stored but the rate is very low. So it is very slow compared to the rainfall. The rainfall can happen for example 50 millimeters in a week but it cannot go that fast into the ground. Remember it has to go infiltration, percolation and then go to the groundwater aquifer. So that doesn't happen that fast. So that is why we are in need of surface water structures. It can protect and also reduce the damage during the floods and extreme events of climate change which are droughts and floods. Let's say drought, let's take an example. You have a drought which is a less rainfall year. So if you have a less rainfall year and you've already captured the previous year's rainfall in a storage system, surface storage system, we will look at what are the systems in the upcoming just this lecture but let's think like a tank. You're capturing the water from rainfall and river and storing it in a tank. That can be used for the lean season which is the right next the post monsoon season and also in a drought year. For example 2020 was a good rainfall year and then 2021 was a drought year. If you catch the rainfall in 2020 and conserve it you can use it in the 2021 drought year. So that is what a climate extreme drought how you can use rainfall from storage structures. How does it reduce damage in floods? Suppose you have a big flood coming through your river system and on the land and it just inundates the area. If you don't hold it at least in smaller quantities what happens is the water gets collected and comes downstream and floods more. So these structures actually hold this water for a particular period of time or until the volume is reached. For example a dam, let's say a dam it will just stop all the water and until the dam water is full. Suppose a dam was not there and there's a big flood all the water would come and flood the entire area. So this is how these surface storage structures help in a climate extreme and climate extreme also means drought and flood. So in both seasons it does help. It improves low water recharge. For example if it stores the water in the storage the water is stored then there is also infiltration and evaporation is happening. So the infiltration you cannot stop unless it is lined. Nined means you put cement on the bottom of the tank. Like for example a petrol tank you don't put nothing under the tank you have to put a lining so that petrol doesn't seep in swimming pool. You put a cement lining on the sides otherwise water will just get leaked into the aquifer. So we're talking about a natural system for agriculture where it stores the water and it can recharge. Suitable for areas with hard rock, terrain, non-porous soil because groundwater is needed and it takes a long time to recharge. So when you store this water and push it into the ground it can recharge slowly because you're also creating a potential head. When you have a dam or a storage the water level will rise and it creates enough energy to accelerate pushing the groundwater into the recharge. Provides a dependable source of water for local communities. If you look at the water storage structures like a dam or a small water lake, agricultural lake you could see that around the system around the storage structure there is a lively livelihood developed by the locals. For example fishing and it could be the drinking water supply for them and also agricultural means. So it is vital for the substance of rural livelihoods through agriculture and allied activities. When I say allied activities it includes fish, livestock, cattle, poultry anything that supports your agricultural livelihoods. And it also ensures drinking water security even though drinking water is less compared to the use of other units that I've described. Still it is very very important. So these structures could provide good drinking water source during the lean season which is drought or the high flood season. Let's take a look at the surface water storage structures in India. So the current storage as per MOSPE 2018 says that the reservoirs are around 2.93 million hectares. Tanks and ponds occupy 2.43 million hectares. Floodplain lakes and water bodies around 0.8 million hectares and brackish water is 1.15 million hectares. So this gives a good understanding that your reservoirs which is tanks and big storage structures occupy the most area in India followed by tanks and ponds. The floodplain and brackish are smaller however your tanks and ponds small tanks in villages and your rural ponds still occupy a good chunk of space. The current storage capacity in India is less than one-tenth of the annual rainfall. So if you compare this volume so this million hectares multiply the thickness and the volume total volume stored and then you compare it with the volume of rainfall we have it is not even one-tenth of the annual rainfall which means 90% of the rainfall is let to go into reverse water storage in groundwater and etc. Is it good or not that is a different question because you still need your rivers and lakes and streams to flow but is it all washed away into the oceans and seas is the question. Okay so that number we don't have exactly we need to calculate. So construction of new structures and restoration of old structures is very important because we are losing a lot of water into the oceans and rivers which can be captured for a water hungry nation like India where agriculture is predominantly using a lot of water and it is very very needed to have this water supply. Not only India but almost all South Asian countries are water hungry which means the population is increasing. There is a demand for water to sustain the livelihoods and demand for agricultural productivity. So all these countries are actually wanting more water. You cannot create water so you need to store and then capture as much as water is there and given the trans boundary natures and international issues in getting the water between countries it is always smart to at least use the water that you collect in rainfall. Capture it use it and then make sure you're not wasting too much water into the oceans and seas considering your agricultural needs. So let's continue looking at the large dams. So it is 5,334 large dams are in India as on 2019 and these large dams is one type of a surface water storage and it is the biggest. Okay everyone knows how a dam looks like. We'll have some images but dams have their own positives which are benefits of dams include flood production because it is a massive storage. It is a couple of feet high you know like it's not like you cannot just jump in and swim for days you know it's too big. So dams are pretty that's why you cannot allow you're not allowed to swim in a dam zone okay it's massive so it can actually capture the flood water and buffer act as a buffer which means a storage space where excess water can be put okay and it also increases your food production because you have an irrigated area. So once you store the water that water is released into the command area we call wherein water goes into the land for agriculture. It's supplied in the land for agriculture. If you look at the number of large dams so there is a difference between large dams check dams and small dams medium dams. So large dams are the biggest which are not only for irrigation but also for hydroelectric generation which accounts to almost 11 percent 10.5 percent of total power generation. So also India is in need of power right electricity because we are also pushing industrial development and we need a lot of power we have solar and etc but hydro electricity is also generated. So if you look at this you have the number of dams big dams large dams in India and it's not easy to to to make these dams right because before the British gave us independence when they were ruling us so you could see that not they built a big big dams and still operational but was slightly managed their motives were different they didn't want much for India's development but after India's independence that's when we started to push more on the large dam scenario and then because of the anti-benefits also or the issues with large dams there has been a slowdown and not much you can build. Also the lands are already occupied by large dams so let's look at some of the positives as I said food production is increased hydro electricity is increased flood control it can buffer the flood water and all this water can be piped into a water supply for example all the dams in Pune areas are catering to the drinking water supply of Mumbai because in a city of Mumbai you cannot afford to put a dam it's it's too expensive the land where it is the industrial capital of the country so where would you sorry the economic capital of the country where would you put all these you know dams you cannot so the water supply is taken from outside similar in Delhi you know water is taken from outside so this dams do help in drinking water supply not only for that region but for miles and kilometers away but there are a lot of issues if you look at dams there is a difference between naturally managed water and engineer dams are more engineered structures which means it is a kind of there to stop the natural movement and it's not accounting for the natural dependencies of water for example you have downstream you have e-flow which is the environment requirement of water so all this is not thoroughly taken up by large dams there are some issues time and cost overall that's a huge cost involved in time to build it just recently you would have noticed the Uttarakhand dam they built it in such large time and money but it just got washed away there are a lot of environmental impacts you have to clear the land there is a lot of people's livelihood displacement happens you have to clear the land take the people away relocate them all this happens because it's a huge area when you stop the water a huge area has to be flooded and that becomes a flood becomes your dam water correct you just stop the water one more thing is the size or not alone the size alone but also the environment factors as I said it has to cater to the movement of water so some environmental benefits are lost if you stop running water okay so these are mostly noted as the negatives of or issues of large dams by these authors given below so you could see that as I said most of the dams were did only after the independence but there is a question how did our ancestors do this if we know that dams were less during the British era and before that it was really really less 1900s so how did our ancestors kings and others who ruled before the Britishers how did they control this water so there is a lot of traditional water resources storages we call it surface water storage structures as SWSS it just in short to put it in the slides so there is multiple methods there is traditional there's nature based methods and there is engineered methods let's look at the traditional methods to understand how their ancestors did it so the first one we would look at is the Ahar pine system where flood water harvested through a small area demarcated in the villages and pines are the diversion channels which take the water into these small stores or storage regions as Ahar which is reservoirs with embankment so it's a small reservoir it's kind of a small dam but it is made with embankments not much cement used not much land is cleared so normally what the traditional ancestors did is to find a low lying area in the village and in that low lying area already water would have been stored so all they had to do is clear the land put embankments on the sides and then channelize the water so instead of water moving in every direction like for example like this moving in every direction into the Ahar they would just make sure that it is all pulled into one channel okay so this is how they manage this important capture the rainwater channelized it through these pines which are diversion channels and into Ahar and then they might have some blocks to stop the water for example like this and from that blocks after a particular height is reached people can use it for fish drinking livestock and also put smaller channels like this loose gate and then take the water into the villages into rural lands for example for agriculture johads is another similar type where smaller earthen buns to collect rainwater are done it's not as big as the Ahar pines and it's constructed in areas with high elevation in three sides and fourth side is protected by bun so for example you don't have a low lying area in the village what would you do so all you do like for example here all is elevation land you would pick an area where all these four elevations are high and the smallest elevation which is the smallest height land is used as a storage so we just build a small earthen bund burden bund is a structure like and earth is just mud, sand and stones it's not concrete so which means earthen ones still can do some recharge still can have some leakages which are good and so this bund actually stops the water from these high elevations and starts a pool so that pool of water can be used as a surface water storage. Moving on we also have another very important structure which is tanks in rural lakes so these are a demarcated simple land which is channelizing water into and storing the water so it's constructed across valleys to arrest the runoff so small small valleys you will have and all the runoff is arrested and put into it and around the area you will have mud or storm-based embankments so basically the ancestors just dug this area through hand and plows and stuff made a deeper thickness of like a bigger well and then all this water would come in and on the surrounding edges they made these embankments provides multitude of benefits such as irrigation flood control livelihood security groundwater recharge so because this is not lined which means no cement is at the bottom groundwater does recharge excuse me so therefore it provides multiple multiple benefits not only for irrigation not only for agricultural water use flood control as we saw livelihood for fish and then for food security etc and sanitation people used to be there and most importantly groundwater recharge however they are being abused they are not protected well if you look at it we will cover some issues of these tanks in the next class but you would notice that in the villages these tanks are not protected properly as long as the tanks we also have another a tank system called the cascade tank system so just visualize we had one tank so this is just one tank in the village think about placing small tanks and connecting those tanks so the ancestors are very smart they thought okay first let's make one tank and this tank could get it to the hamlets or the houses and villages around this tank but then it can water can still go to another tank so as one tank fills up it it goes through the channel and then fills another tank so only after number four fills up number three fills up and then number two fills up and then the bigger tank number one fills up and they built it along the tribute release also which is this line you see so the river is like kind of stopped and a big tank is made it's not a checker it is a big tank so water flows into the river and when water flows a big tank is first filled up and after the tank is filled up the next tank and the next tank until the bigger tank is done and once the bigger tank is full it goes into the massive river out into the system so all these are very very important and these are called cascading tanks so one tank is filled and then another tank is filled another time what we saw in the previous slide was an isolated tank we just had a channel and then the water was filling so what is the benefits of tank cascades it is a series of tanks it's not one tank so when you manage you have to manage all the tanks together to get good water in number one okay and then there is always surplus water is being taken from one tank to the other tank through downstream links okay so these are the downstream links where water would come the lowest tank may have higher storage which is the lowest rank or the lower elevation lower elevation tanks has more storage because it can take water from multiple resources and has the highest catchment area so this catchment area is the highest compared to this tank which is this is the catchment area the breach of upper tank may affect downstream tanks so that is why it is very important to manage and as I said in the previous slide most of these tanks are not well managed because we'll look at the reasons in the future class in this week there is no community participation there's no funds for it people don't take ownership so all these issues are there so there is a breach of upper tank and if that happens mostly all these tanks won't work well because all this water would come down and then we lose this land and then slowly this tank will also get broken because of this water coming in and slowly all these tanks would be eroded so after one tank breaks all these tanks other tanks slowly will break periodic maintenance of tanks and feeder channels are very important and even the transboundary tanks and transboundary connecting channels like the one in poshi have to be properly managed and periodically maintained otherwise a lot of issues can happen so there is a loss a lot of loss of these tank systems operational tank systems let's see some of the reasons and we'll also touch upon this in the upcoming lectures there is a decline of traditional systems surface water storage systems especially because of population and dependence increase when population increases people start to abuse and they take more than they want because of fear of others would take it for example here if you could see water was around here but then not proper maintenance you can see trees growing the rocks broken the stairs broken all of it so if you don't manage it and people are using it and so they should also manage it either the government or the local people land use land cover changes because you tend to abuse it you tend to encroach it these tank systems are gone the traditional systems are gone coming to disconnect and disuse as i said if those who are using are not going to take care of it we will lose the tanks we will lose the water bodies the ponds lack of maintenance and upkeeping there's no ownership there's no money set for these revival of these systems and people don't understand the connection with groundwater and also people have the access to individual groundwater so they have just started to abuse these systems they don't care about look how it's broken and once it's broken slowly it gets demolished and no one takes care of it so there is a need for revival of traditional SWSS especially because India has already 54 percent stress and it is going to increase pretty bad as per this report acute water stress is going to happen groundwater is already depleting and the increasing water trends as i said because of population and overuse lifestyle has changed everyone wants to wash their car using fresh water you know and which is not correct so when that happens you need more water to actually get into this lifestyle and there is increased frequency of extremism namely floods and droughts so there is a very very important aspect to conserve these structures capture more of this water before we lose it into the main ocean center and big rivers with this i'd like to conclude today's lecture i will see you in the next lecture thank you