 Hello everyone, welcome to NPTEL course on groundwater hydrology and management. This is week 6 lecture 4. In this course we are looking at more importantly groundwater as a component, how it recharges discharges and then management. How we break in this course is until week 6 you look at most of the important concepts of groundwater then we will jump into managing the groundwater resource. On that note we have been looking at the groundwater recharge and discharge properties in this week's lecture. In the past couple of days lecture we have looked at the last three lectures we have looked at groundwater recharge concepts, how is it recharging, what are the different methods to recharge and how to estimate. Let's move on and look at some more estimation methods. Ground on recharge from seepage, why is this very important? This forms a very important task in environments where there is a water body because a water body can influence the groundwater movement both recharge and discharge. So in this term we are going to look at recharge and as I said in the previous lecture just before the end of the lecture I mentioned that recharge and discharge are happening through similar monitoring process which is the water level. At what time line it happens may be different, what is driving the recharge or discharge may be different but monitoring is almost same because you are going to use a similar methods. Here the physics that drives it is just opposite. For example in a recharge water goes in and discharge water comes out. You push water in that is recharged, you pump water out that is discharged. Similarly in a natural environment where there is a water body and a high elevation land with groundwater table, water table would flow into the stream, river, network, whatever you call it, lakes, ponds, etc. and that is groundwater recharge into the stream but it is a discharge for the groundwater. In this lecture we are looking at groundwater recharge. So let's take this example where you have a land which is also at high elevation however the water table is at a low elevation compared to the stream. So when water comes in the stream it tends to flow down and recharge your aquifer. So to prevent this think of this as a canal to prevent this in regions like Gujarat they put lining which is cement to prevent the water to recharge into the ground. They don't want it they won't take it to the farm which is also why they built the canal. So now coming back depending on the use you can make a canal recharge or just take the water. Now let's look at the recharge concept. So water is seeping into the groundwater table, you can see here water is seeping into it. It is not infiltration it is not percolation it is seepage because infiltration percolation happens in the medium where there is four spaces and then the water has to push through those medium and calm. Whereas in seepage it is water that is pushing water at a good table look at it there is a good water level and then it pushes itself it seeps leaks into the groundwater that is groundwater recharge through seepage. So let's see how we can measure it. This is a method as given by Monty and Winter and promoted in the USGS book. So USGS has a manual for all these different different things for recharge estimation discharge estimation for rainfall etc and most are used in Indian terms with slight modifications. So let's look at how recharge is estimated through seepage. So this is your sediment surface or your stream bed okay right here on the stream bed you will put the meter in and here the meter is like a pipe with a screen interval of three centimeters and that is where water can move in or out okay. So in this example your potentiometric surface or the groundwater head is at a higher elevation compared to the surface so it is this example okay and what happens is because of the potential difference because water wants to flow from high to low potential water would seep in from groundwater and then come out and join your surface water and this can be monitored through the pipe here and the pipe has some meters which actually monitors how fast water is seeping through okay and the manometer is a meter which is also looking at how fast the suction happens the suction or how fast the water moves through this tube and a reading is given for the velocity of water discharge of water etc. So these seepage meters are kind of expensive and doesn't give you the right picture all the time why because it depends on where you put it in the land so you can put it here you can get a different seepage you can put it on this point you can get a different seepage because the rocks and bed rocks are not the same everywhere so that is why in most terms it is just simple enough to estimate it rather than putting a meter and estimating the rare data more or less it gives a different flavor the easier way to look at it is you have a river flowing okay a river flowing and you take a discharge measurement how much water comes in the river at point A and take a reading at point B okay you have two discharge now QA QB if QA is equal to QB there is no recharge there's no discharge which means the water is not losing water is not gaining however if A is less than B that means water is losing into the ground which is discharge of the stream water into the ground which is a recharge for us so that is the case where you have A is less than B okay and the subtraction of B minus A okay B minus A would give you the actual water which is gained in the stream because of ground water coming into the river this is a discharge if you want to recharge A is greater than B okay if A is greater than B what is happening water is losing into the ground water which means groundwater is getting recharged so A minus B is the total volume lost by the river but gained by the groundwater and that gaining is groundwater recharge okay for groundwater discharge how do you do let's take a system where the water is coming in groundwater is giving water into the river so A is less than B or B is greater than A B minus A is the net volume of water recharged because of this length on a non-rainy day so all these equations should apply on a no rainy day because the rain is happening and water is just picking up because of rain so you need to take it in a non-raining day okay so here we are we can estimate the actual groundwater recharge just looking at two sections in the river and making see the connection of how the water is recharging or discharging the groundwater activity again a lot of people don't actually do these they just estimate it because it's a lot of data it's not one point data you have to take multiple data what they do they go on the riverbed they look at the river's material the riverbed material and then they estimate a value and the other easiest way which is really in some ways is okay is they say for example this is the river they say water groundwater is giving into in this location and groundwater is giving out into this location which means Q A or here let's say G for groundwater so G A which comes into the river is equal to G B which leaves the river so G A is equal to G B no changes the river is now gaining or losing in the long run which is a good estimate one would say so you can see how estimations and assumptions can make your life easy in terms of groundwater recharge and you're not that particular about groundwater recharge happening along the river because your lands are away from the river or your house for the water level is away so it's more on how you want to use your recharge however so now here comes the tricky part what if no data is there no meters no money for meters no time and no budget which is money put on the meters if nothing is there what happens this is a concerning part which is crippling a lot of places because India is the most highest groundwater user in the world however if you look at monitoring per centimeter area of your map or let's say per kilometer area it is not much it's very less compared to the other countries that are actually monitoring groundwater pretty well so here's where we are in this situation what if no data exists and again think about only four months we are monitoring what if no data exists no meters are there in some locations and budget is less to augment or add meters what do you do if you simply GSE has given you that option also that you can simply estimate the recharge from rainfall because rainfall for sure you'll have and these satellite products have given you a lot of rainfall data for a lot of years at least 1857 till date so around 150 years of data you have for rainfall and you know the soil material the rock material because those don't change you can use the GSI geological survey of India maps all these are in my slides please go and look at these maps and when I'm teaching the groundwater data I will show you how to take rainfall data so what you will do is you can see that your recharge happens as a function of your rainfall so this is a simple uh logical uh hypothesis given by geese geese says your rainfall is what is recharging of groundwater let's put a percentage a percentage of the rainfall goes in and based on the physical setting of the aquifer the land surface the land cover etc and the rainfall you can estimate how much is your recharge again let's do this exercise they have divided India into two major hard rock formations rock formations one is hard rock and the other is aloe vera aloe vera takes around 20 to 30 percent of the land whereas the remaining is mostly hard rock aquifers so the aloe vera are mostly in the river delta regions belts etc ganges those regions have aloe vera sediments and formations and of that indo gangetic has the major formations because it is big and the river flows every day every year so it brings a lot of sediments and still it's a young river because it flows it cuts through and also brings a lot of sediments which form the aloe vera aquifers so they say that if there is rainfall say for example 100 mm rainfall 22 percent of that is your recharge in the previous example we looked at infiltration if you don't know the rock material it is going to be very hard so you have to know the rock material which is found by the map if you all you have to know is the location for example if I say Mumbai or Chennai I go to the map I look at the aloe vera or hard rock area type what is the rock type and then I look at the rainfall and then I can estimate it in the last lecture we looked at what is the infiltration rate infiltration rate is different recharge is different because infiltration is the water going into the ground and then plants take it soil take it and then still further water has to move down so you see that infiltration percentage from rainfall is much bigger than your recharge from rainfall because recharge groundwater still has to move further and after plant uptake soil uptake etc so let's look at some examples so you have the indo-ganzitic and inland areas suppose 100 mm rainfall so for example in the indo-ganzitic you have 1500 mm rainfall 22 percent of that the recommend value is recharging into the groundwater so if you have your rainfall as millimeters you can have your recharge is also millimeters so 100 mm rainfall gives you 22 millimeters of recharge what happens to the rest it goes as ET and surface runoff then you have the east coast and west coast as I said along the east and west you have a lot of rivers actually flowing out and those are alluvial aquifers like Kaveri the Penar on the east coast on the west coast you have Narmalathapthi and other rivers the hard rock are the central part of India and you could see that there is a lot of these multiple types whether whether granite granulite vascular whether basalt let's try etc and depending on the rock type there is a fracture percentage all this has been done by GSI and other studies across the world and they have estimated how much infiltration happens and how much of that goes further in the groundwater recharge and this is the value okay so 11 percent of the rainfall eight percent of the rainfall etc so now I'm giving you the volume but what is the time that is hard to do so I can say I give you 100 mm rainfall in an alluvial aquifer you get 22 mm as recharge but is it going to happen the next day the rainfall happens no because it is a process which takes slow slow time to go in so it is better to say annual annually Kolkata in the Ganges Belsen gets 100 mm rainfall for example it takes much more and it gets around 22 percent of the annual rainfall which is 22 millimeters of rain of recharge from rainfall in a year so that is a good way to tell you cannot say that tomorrow there is rain the day after tomorrow it will be recharged no so if I take 100 mm rainfall today today I'm getting 100 mm rainfall which is like a flood does that mean tomorrow I'll get 88 percent as runoff and 22 percent which is 22 mm in my groundwater recharge not it will take some more time okay so please think this out and when you discuss this with others make sure there's a time aspect and the time no one can tell only you would be able to estimate it but again at the end of the day they want annual recharge if you look at the last lecture I gave the groundwater board has given you recharge annually okay so take annually that is fine but for understanding the physical process you need to understand that it is not a daily process it takes time and the last part I would like to say after we did the estimations through water budgets through your meters see page meters etc and water flow fluctuations the last part is models multiple models that can easily estimate your groundwater recharge based on the driving factors which is your land use man cover your rainfall the type of aquifer or the type of rocks or ale etc and those can be taken from these open source models so the link I'm giving here in the bottom if you just go there all these models are already there and you can click on the title and it goes into the model where you can learn it for free okay so it is very important that these models have their own positives and negatives you can look at the rate and there are multiple models for a single parameter which is groundwater recharge please understand that it is because of the changes in the modeling world because the computers have become faster the data has become more accessible you see more models coming up every a couple of years once so you have around 1988 there's a model and then there's some new models in 2002 etc so you have to read about these models the suitability for your research area and then you pick and choose your research model now someone can ask me which is the best model as a faculty what do you teach I would say the best model for groundwater as an open source and widely used as mod flow it runs on Darcy's law which we have already explained and it is a very simple model less data intensive however it has been very successful in getting groundwater estimates across the world not only in US or India wherever the groundwater extraction is happening but most of the studies have used mod flow whereas some have actually gone out or outdated etc some of the models so what is a recharge estimation model not a groundwater model but it is a very good surface water model so surface water you have rainfall converting to runoff and then infiltration after infiltration it goes into recharge where mod flow comes in mod FL OW this one so there is also a good model but mod flow is widely known as a very good model it's a 3D model also we will see some of these models how to set it up etc in the class so now we have looked at recharge estimates and how to do recharge etc what are the different methods and then we came to models but the important question is is net groundwater recharge enough okay what is your net groundwater recharge so this is your time on your x-axis and then you are on y-axis you have your h which is hydraulic head okay let's do jan to december normally you do water here which means at least here in monsoon starts in june so i'll do june to june but let's do calendar because most of you would like to have calendar here so the water would start around here and then come down during your summer and then rise up during your monsoon and then come back to the same value okay so if this is happening the the downfall of the water level is because of discharge and pumping etc and then your recharge happens because of monsoon okay what is net net is not only the groundwater recharge happening through your rainfall but also the c-page dams etc and you have to also calculate your water used because that is also being taken for from your net groundwater recharge correct it has been taken for your agriculture but it is taken from a recharged well so that is what net recharge is so you have to take it from here so from here the recharge is happening you cannot say that oh no no i'll start here because i don't take into consider the water i used for agriculture etc so you have to take from this and also include the water that you have taken out for recharge and groundwater irrigation etc it is very important to understand that net groundwater recharge is it enough is it stable is the question and as you would know as we spoke the groundwater use has always been increasing in India so definitely the groundwater recharge is not enough it is going down the rainfall patterns have changed the climate patterns have changed and then the monsoon level which is before your monsoon before your monsoon which is from your peak monsoon to your next monsoon the water that you have used in summertime if you look at it it is a drastic condition most regions are red in comparisons from 2014 to 2016 the index is the same the colors are the same so what it means is those areas which were green having healthy groundwater levels of 2 to 5 so within 2 to 5 meters you'll have groundwater all those are changing into yellow and pink and red which is not sustainable in the long run so it is very important to do more groundwater recharge so here's the question is it possible to do more groundwater recharge because the rainfall patterns are changing naturally it is not going to be enough okay and that is why there are a lot of schemes just look at the central part of India yeah this red part where Afghanistan and Punjab and other regions you have a lot of groundwater use a lot of agricultural activities but look at central India so where the hard rock aquifers are so much water used and that is why it shows a big drop in the pre-monsoon level so the net recharge is not enough okay or you're using more water even though the rainfall is same you made me using too much of water so the net recharge is not enough and as I said the climate changed within even couple of years you're seeing the groundwater available for irrigation is being unsustainably used and your rainfall is giving less into the recharge because faster rainfall is coming flash floods are coming so all this has to be accounted for in the groundwater management let's look at the situation of the number of blocks that have been turned as critical or semi-critical over exploited means you are exploiting more than 100 percent of the groundwater that is recharge okay and critical is somewhere around your 100 percent 70 to 100 percent and 70 percent semi-critical below that it is safe so what do you recommend now so in India is it safe yes because of the water level if you look at India level it what it was it was 62 percent okay of 433 billion cubic meters you're using 245 billion cubic meters as per cgwb it is outdated but it's okay it is a 62 percent use of groundwater in the country which is fine and they said okay it is safe however if you look at certain blocks it is really bad and it is in the over exploited condition and that is why it is important to artificially recharge groundwater I'll continue with these methods in the next class but let me give you an introduction to what is artificial recharge as the name suggests artificial means it is not natural meaning it will take more time for the groundwater to go in within a natural setting and that cannot be sustained for the life forms agriculture in the current India you need to push methods that can augment groundwater and increase groundwater recharge and luckily the GEC the groundwater estimation committee and the groundwater board the central groundwater board have made these kind of very useful documents with live examples you could see here pictures of examples from study areas on how you could increase the groundwater recharge using artificial means anything you construct on land is artificial because it is not natural recharge okay in the next class I will start with the introduction of natural recharge versus artificial recharge and then we'll look at some examples and wrap up v6 with this I'd control today's lecture thank you