 Welcome to this lecture number 20. This is the lecture in which the following topics will be covered that is we will start with this induced recharge which is basically a spillover from the previous lecture and we will move on to waste water recharge for reuse and followed by water spreading. Now we will go to the first topic of this lecture that is induced recharge. So basically this induced recharge is a recharge which has been induced artificially due to creating a difference in the water level. So unlike in most of the water the artificial ground water recharge schemes wherein the ground water is, the surface water is transported near to the well or other subsurface storage facility thereby the water is made to infiltrate, the surface water is made to infiltrate and get stored in the subsurface storage facilities. And here the same thing, the purpose is the same but this recharge is induced by say lowering of the water table. So thereby a head is created and this creation of head will induce the hydraulic gradient and thereby the artificial ground water recharge. So here, so I can if you write this one the meaning of this induced recharge we can write that it is the recharge induced artificially by creating a head difference by lowering the water table, water table strobe piezometric surface and thereby creating a hydraulic gradient which will induce the recharge into the subsurface storage facilities. So unlike the commonly employed artificial ground water so which you have been abbreviated in abbreviating as AGWR schemes so there is no physically, physical transport of the surface water in the vicinity of a subsurface storage facility. So this is the major difference between the induced recharge and the artificially, artificial ground water recharge. So here it is induced because of the head difference. So this head difference is a major cause which results in the establishment of hydraulic gradient which will induce the recharge into the, this one and now we will see some of the typical induced schematic diagrams of typical induced recharge schemes and so typical schematic diagrams of induced recharge schemes. So firstly let us see there is a suppose this is a the ground surface and here let us say this is a river and here so this is the water surface and there is one and here let us say this is the water surface and in this case say that is say the river water surface is lower than the water table maybe due to say excessive pumping of water from the, so this is the water table so this is river and because of this lower water level in the river so what happens is the water is the ground water enters the river through bed as well as banks. So basically here you can note down so this is just to write a so the river having water level lower than the water table. So this river having a water level lower than the water table will establish hydraulic gradient and that hydraulic gradient brings about the induced recharge into this one and so that is the this one and so the next so next we will so here you can say next we will and here in this one say let us say suppose in this vicinity of this this is the ground level and so and here just in the vicinity of the river so there is a well and so this is a pumping well and this pumping well so here you can say this is the screen or the slotted casing and because of the screen and this is the water table or the water surface in the river and then so it is so this is the original water table and here what happens is while on the other side there is a recharge and here what happens is so the because of the pumping of water through the well and so here you can say so this is a that is natural flow pattern which is this top figure and b is the flow pattern with a pumping well so here what happens is had when the pumping well is not there so then so everywhere so through this bed as well as banks so there is a recharge into the river and whereas this when the pumping well is drilled in the vicinity of the river so what happens is the water surface in the pumping well is slightly much below the water surface in the river so therefore what happens is towards the well so the flow gets reversed so initially it was the flow was into the river so on both sides that is on the left side as well as the right side so now after the pumping well has been drilled so what happens is towards the pumping well so the flow is from the river into the well whereas away from the pumping well the flow is into the river so therefore this is an example of this is a typical schematic diagram for this induced recharge scheme sorry so this is just a scheme and now we will see little bit about of course so here what happens is so this is a typical example and so there could be various other reasons wherein there is an establishment of hydraulic gradient and then so because of this establishment of the creation of hydraulic gradient so the recharge that is the induced recharge starts so this will go to the next topic that is on waste water recharge for reuse so here this is so with the awareness in the about the water use efficiency so this there have been many schemes which have come up in the recent past wherein the waste water is used for various waste water is reused for various purposes and through this recharge so basically here we can say so it is a method of reusing waste water through recharge for purposes like irrigation to overland flow recharge well so these are some of the purposes so wherein so this waste water is reused and here so this is the waste water irrigation so this is quite common and here so let me just so first let us consider that is the land application of waste water for reuse through irrigation so that is a waste water reuse through recharge for irrigation so here suppose this is the so these are the plants which need irrigation and these are the root zone of the plants and this is the general ground level with some slope here and so here so this is the root zone so these are all the crop and so here through this so this is vapor transpiration and so this is so this waste water is so waste water is reused for irrigation either by that is spraying so which has been indicated by this kinds of arrow or by surface application so this surface application has been indicated by so this kinds of arrow so by employing any of these methods either spraying from the top or by surface application so we can reuse the waste water and thereby reduce the water demand and on irrigation because we all know that this irrigation requires the highest amount of water this is highest water requirement is for irrigation so by using this waste water reusing this waste water we are slightly minimizing the water requirement for irrigation and here what happens is whether we use whether we employ the that is spraying or the surface spreading of this waste water so it will infiltrate into the root zone of the crop and thereby so it will provide the necessary irrigation for the plants for which form the crop and thereby so this we make use we rather we take care of two problems one is we will reduce the load on the of waste water in the sewerage system or waste water system and then secondly we will also reduce the irrigation water requirement of crops and so in doing this we make use of the that is the storage which we can create in the root zone of the plants which form the crop and so next we will go to that is the waste water waste water reuse through overland flow so here so in this case suppose there is a more sloping ground say this is a ground level slope greater than 2 percent and less than say 4 percent or so so that is say slope of 2 to 4 percent and here say suppose the this one so there are the various say crops are there so here what you do is so there is a percolation so there is a so this waste water is sprayed through a sprinkler so this is a sprinkler for spraying waste water and thereby so here sheet flow or overland flow is created so this is obviously so these are the so this is the so this is sheet flow that is overland flow and of course there is also some percolation of so this is a percolation and this case here this so you may also collect this so this is for runoff collection so like this so this waste water can be reused in sloping lands so thereby what happens is by either applying generally through this one and of course so here we can also show so this is so this is evapotranspiration so this is ET so this is a second method of waste water reuse and of course in this case also so what happens is so once the waste water is this is generally here you can generally sprinkler is adopted for spraying waste water so in sloping lands so suppose we employ this sprinkler for spraying the waste water so then what happens is and the larger this one is waste water is created and then so part of it percolates and part of it very small portion or some portion may also flow as a sheet flow and thereby so the waste water is recharged and the same in the previously whatever was happening in case of irrigation that means reduction in the water demand for irrigation as well as reduction in the load on the sewage system so both purposes are achieved simultaneously and that is this one and then third is that is say this is the waste water reuse through recharge wells so in this case what happens is waste water is allowed to recharge wherein there are a number of filtering layers to screen as many pollutants from the waste water as possible so therefore it is substantially filtered waste water is allowed to get stored in a recharge well so here we can a typical diagram can show say suppose this is a suppose this is a recharge well and of course here I am showing this as a an open well and so this is the waste water and so typically so different kinds of so this filter beds are employed and so here we can maybe another and in this case so this is the recharge well I am sorry this is the this is the ground level so this is the waste water and so this waste water gets filtered through this so these are the series of filter beds to substantially remove the most of the pollutants in the this waste water and then eventually what happens is so this is so the waste water is allowed to recharge into this recharge well so like this we can ensure that this waste water is actually because what happens is generally this waste water flow is a very regular flow because of the municipal water use which is obviously the all human beings do need water on a regular basis irrespective of the season for carrying out the daily activities so therefore waste water is generated and if this waste water is properly filtered and then allowed to recharge into a recharge well so then of course and again so it will provide a constant supply of water for the recharge well and then again so it can further be purified and then in many cases it has been brought to the level of this even portable standards also of course there is an attitude problem is there and if this attitude problem is also over this taken care of so then this waste water this treated waste water so it can be used significantly to meet the water requirements and so now we will go to the other this one that is this water spreading the last topic of today's lecture is on water spreading so in this here what is done is so this waste water is allowed to spread and waste water after successive filtration layers of filtration is allowed to spread on the surface wherein eventually gets infiltrated thereby bringing about artificial groundwater recharge that is AGWR so this is water spreading even though it is the we call it water spreading so it can be either waste water or even say that is rain water waste water here and let me write this as rain water so after successive layers of filtration is allowed to spread on the surface thereby so it is this artificial groundwater recharge is achieved so this is regarding the this one and obviously so this is but only thing is so the precaution to be taken so precaution needs to be taken to prevent this mosquitoes and other vectors from breeding so it is a very important one so that precaution has to be taken so that so this water spreading does not increase or does not create the new menace of vector or mosquitoes and thereby it is it will cause more problems and so we will also that is so with this we will come to the end of this chapter on artificial groundwater recharge and of course so this artificial groundwater recharge is very this one that especially in the scenario of climate change so this artificial groundwater recharge is very necessary these days and as we all I would like to take this opportunity to bring it to the notice that the human dependence on water of course this was this was dealt in one of the earlier lectures water so it starts with rain water then moves on to river water and then so this is a so rain water so then this is a river water and then moves on to so this is a ground water then moves on to ground water so therefore so here so this artificial this groundwater recharge schemes so what they do is and here this is either through rain water so the water is allowed to filter and that is infiltrate and thereby create a thereby fill the subsurface reservoirs and so so this is a artificial groundwater recharge brings about the necessary water security which is very important which is very important especially in the context of climate change wherein the frequency of floods and droughts is significantly increasing in most of the places on earth as well as there is a gradual decrease in the number of rainy days at a place in many locations so this these rainy days so here a rainy day is a day with a minimum daily precipitation of 2.5 mm so this is the one and of course so this so the so to design this any artificial groundwater recharge schemes so various factors such as the amount of rainfall as well as the infiltration as well as the desired water table depth the range of water table depth all these factors need to be considered and so how much this one and of course here I would also this bring about bring to the notice of one very effective technique which is which can recharge the that is the unconfined aquifer at the top as well as the confined aquifer at the bottom and so that I would like to mention here so this is it is known as the relief well so basically so this relief well is a facility that is a well having screens along all the aquifers it is a facility wherein so this artificial groundwater recharge for all the aquifers is achieved in stages starting from the lowest aquifer through through successive filtration of rainwater so here I would like to bring about this one so a relief well is so basically here so this relief well is something like this so here if this is the just let me consider here so there is a filter bed and so here so here the water enters and thereby and afterwards so this is the impervious layer so this is the unconfined aquifer so this is confined aquifer one and this is confined aquifer two and so on and here so wherever this is there so the so there is a strainer with perforations so here what happens is so once the water enters through the this one so next the flow is into these aquifers similarly here also the flow is into the aquifers so this is also a very important facility for relief well and then here so this is the graded filter bed so with this I will come to the end of this chapter and so this completes four modules and the remaining four modules will be dealt by my colleague Professor Anirvanthar thank you.