 I am Dr. Siddhisth Kumar Kashi, professor in civil engineering, Valshan Institute of Technology, Sulapur presenting a topic from reservoir planning. The topic is estimating reservoir capacity of a dam reservoir. Learning outcomes of this session. At the end of this session, the students will be able to describe how storage capacity of a dam reservoir changes with elevation of water surface. And the students will be able to calculate storage capacity of a reservoir using contour map of a particular reservoir site. Who are we? Firstly, we will have idea of a river valley development. Then we will see few views of a typical dam reservoir. Then we will see a typical contour map. And thereafter we will have a look on to formally for estimating reservoir capacity. And then one small numerical example to estimate the reservoir capacity. Now, this is a typical river valley development plan for Damodar. This is a catchment area or the watershed area of Damodar river. And you will find that dams are constructed in this valley at certain locations such that every dam gets a certain catchment. At the same time, a good reservoir is formed. So, when we construct a barrier across a river and when a pool of water is formed, that is called as a reservoir. You know that reservoirs are used for human consumption and industrial use. Also for irrigation, also for hydropower, also for hydropower plants. We also construct dams as flood control dams and we also construct dams and form reservoirs for the immunity use. This may include for boating, water sports, fishing, sightseeing and so on. This is full reservoir level. This is the storage which is used at the time of flood control level. And this is the searcher storage. It matches with the highest flood level. This is the conservation storage which is used for satisfying the demands let it be for irrigation, let it be for hydropower and so on. And below this dead storage level, whatever the storage is there that is called as a dead storage. So, in this way, the storage zones are important for us. Dead storage, this is a live storage, this is the flood control storage and the searcher. Now, here you can see the Terry Dam from India. So, a barrier which is constructed across the river is called as a dam and a pool of water which is formed that is called as a reservoir. So, here you can imagine this is the well-known Terry Dam which is constructed as an earth dam. Over 250 meters is the height of the dam. And this is a reservoir which is formed. Now, here you observe that the water level is quite low and one more picture I will show you. Here you find the dam is almost full and water is passing over the spillway which is constructed at the end of this particular dam. So, here you can see a reservoir which is having water level very less and then here you can see a reservoir which is almost full. So, you can imagine at every level the storage capacity will be different. This is a Kona Dam and its reservoir from Maharashtra state. This figure will show you that the periphery of this particular pool of water reservoir follows a contour line and this principle we are going to use whenever we go for estimating storage capacity of reservoirs. Now, capacity of a reservoir. Dam are constructed for water supply, irrigation, hydro power. A contour map is used to estimate capacity of a reservoir which is formed by a dam. As we discussed the periphery of still water body always follows a contour and all the contours are closed lines within the reservoir area. So, if we find out the areas enclosed by contours say at level 1, A1, A2, A3 and AN and which are spaced vertically at a contour interval say D meters then it is possible to estimate capacity of a reservoir by adopting certain formulae. Now, this picture will give you the idea about reservoir water elevation and reservoir capacity. So, this is a dam and this is a reservoir. So, water level may be here, water level may be here, water level may be here and may be here. It means water level goes on varying. So, you can imagine here that this is a contour line say matching with this level. A3 is matching with H3. Area A2 enclosed is matching with H2. Area A1 is matching with H1. So, you can imagine this point if you transfer here or this point if you transfer here or this point if you transfer here. This will give you idea about the contours which are enclosed. By using planimeter one can find out these areas. It means submerged areas at different elevations. So, here we will go for two small questions. The storage created on upstream side of a river by construction of a dam is technically known as a reservoir or a tank or lake or none of these. Second question, the area covered by a reservoir water at a particular level is known as Subvergence area, catchment area, watershed area or none of the above. Here are the answers. The storage created upstream side of a river by dam is called as a reservoir, not a lake, not a tank. The area covered by the reservoir water at a particular level is known as a Subvergence area. Now, let us see how one can compute the volume of water. The first very simple rule is a trapezoidal rule. According to this rule, volume by trapezoidal formula V is d by 2, d is the distance between two successive vertical distance between two successive contours into bracket first area plus last area plus two times sum of areas of other. It means V is equal to d by 2 into bracket a1 plus aN plus two times a2 plus a3 up to aN minus 1. There is one more formula which is called as a prison model formula. This formula is better than the formula which we have discussed. That is the trapezoidal rule. The volume V is equal to d by 3 into a1 plus aN plus four times a2 plus a4 plus aN minus 1 plus two times a3 plus a5 plus aN minus 2. That is volume is given by contour interval divided by 3 into area enclosed by first contour plus area enclosed by last contour plus four times sum of areas enclosed by even contours and two times sum of areas enclosed by odd contours. This formula is applicable when there are odd number of sections. If the number of sections are even, the end section is treated separately. The volume of the remaining section is calculated in the usual manner by trapezoidal formula and then it is added to that. This is an example where given the contour elevations and area enclosed in hectare meters 100, 105, 110, 115, 120, 125 and these are the areas enclosed in hectares. Here we adopt the prison model formula. D by 3 into a1 plus a5 plus four times the even and two times the odd areas. When you do this, you get this 120. Here we adopted up to 120 meter. The section from 120 meter to 125 meter is calculated here by using a trapezoidal rule that is D by 2 into a5 plus a6. It gives you additional capacity of 130 hectares. In first step, what we calculated here is up to 120 meter and in second step we calculated volume from 120 meter to 125 meter. We get this 383.33 hectare meter as an area. In summary, you understood from this video how storage capacity of a dam reservoir changes with elevation of water surface. Now you can calculate storage capacity of a reservoir using control map of a particular reservoir site. These are the references used. Thank you.