 Hello, I am Dr. Satish Kumar Kashi, Professor Department of Civil Engineering, Balchan Institute of Technology, Sulapur presenting a topic, application of unit hydrograph for deriving unit hydrographs of different duration, learning outcome. At end of the session students will be able to derive unit hydrographs of different durations using unit hydrographs of given duration, unit hydrographs of different durations. Now, these are necessary under conditions where log of adequate data is there in development of unit hydrograph, a D our unit hydrograph is used to develop unit hydrograph of different durations say that is N times D, it means 2 times D, 3 times D also it means we have suppose 2 our unit hydrograph that is 2 multiplied by 3 times that is 3 into to 6. So, we will be able to derive say 6 our unit hydrograph by using 2 our unit hydrograph. There are 2 methods available, first method is method of superposition and second method is the S corp method. In this small presentation we will be dealing with the method of superposition. Now, what is method of superposition? If a D our unit hydrograph is available it means say we have 2 our unit hydrograph available and it is desired to develop unit hydrograph of N times D, N can be 2, N can be 3, N can be 4 then it is easily accomplished by superposing N unit hydrographs with each graph separated from previous on the previous on by D ours. Example will clarify the things. Now, suppose we have D equal to 2, 2 our unit hydrograph. 2 our unit hydrograph means what? Whenever there is 1 centimeter rainfall excess in 2 hours, in 2 hours there is 1 centimeter rainfall excess. This intensity of rainfall was 0.5 centimeter per hour it trained here for 1 hour it accumulated half centimeter, in second hour it again accumulated 0.5 centimeter totaling to 1 centimeter. So, this was 1 centimeter rainfall excess in 2 hours and due to that effect of that rainfall over a specific catchment was to produce a hydrograph in this way which has a base of say 9 hours and these are the ordinates which are produced by rainfall in a particular stream flow at 1 time 1 hour this is the ordinate at time 2 hour this is the ordinate so peaking time is at 3 hours say the rainfall say the stream flow is about say 450 meter cube per second and so on. Now, this particular 2 hour in hydrograph we are going to use further. Now, change the unit hydrograph duration consider 1 hour unit hydrograph and add lag to unit hydrographs by 1 hour sum and divide it by 2 resulting 2 hour unit hydrograph. It means this is 1 hour unit hydrograph this is another 1 hour unit hydrograph lagged by 1 hour. So, what we will have to do we will have to add the ordinates and divide those by 2 and that will result in 2 hour unit hydrograph. Now, we will take a question select appropriate answer a 3 hour unit hydrograph differs from 6 hour unit hydrograph for any catchment options are 4 both the time of rise and the peak ordinate for the former that is 3 hour unit hydrograph are less than that for the latter that is 6 hour unit hydrograph. Second option both the time of rise and peak ordinates of the former are greater than that of the latter. Third the time of rise for 3 hour unit hydrograph is less but peak ordinate is greater for the former that is 3 hour as compared to the latter that is 6 hour unit hydrograph. Option D is the time of rise is greater but the peak ordinate is less for the former as compared to that of the latter. The answer is see the time of rise is less but peak ordinate is greater for the former it means for a 3 hour unit hydrograph we find that 1 centimeter rainfall takes place in 3 hours only that is why rise will be more for 3 hour unit hydrograph as compared to 6 hour unit hydrograph why because in second case 1 centimeter rainfall takes place in long 6 hours that is why as time is more obviously you will find the rise is lesser for 6 hours and rise will be more for 3 hours and you will find the ordinate is greater for the former because more rainfall in less time so you will find ordinate will be greater for 3 hour unit hydrograph as compared to 6 hour unit hydrograph so this gives us the idea about how hydrographs differ now here let us have example given the ordinates of 4 hour unit hydrograph as below dry the ordinates of tell our unit hydrograph from the same catchment so time our 0 4 8 12 16 20 going up to 44 and ordinates of 4 hour unit hydrograph are this 0 meter cube per second 20 meter cube per second 80 meter cube per second it means due to 1 centimeter rainfall spread over entire catchment in 4 hours of course 1 centimeter rainfall excess in 4 hours at the outlet of the catchment we are getting these discharges varying with the time so this time we are showing 0 4 8 12 16 20 24 28 32 and so and then we are given these ordinates of 4 hour unit hydrograph right now we are doing calculations for 12 hour unit hydrograph from 4 hour unit hydrograph means we are given 4 hour unit hydrograph ordinates and we want to derive 12 hour unit hydrograph ordinates it means time is 3 times so here what we are doing in figure I will show the first 4 hour unit hydrograph start from 0 and goes up to 44 hours it will be followed by another 4 hour unit hydrograph we will start from 4 going this way with these ordinates and go up to 48 in third part we will start from 8 and go in this way so these were lag by 4 hours so this is lag by 4 hours second 4 hour unit hydrograph this is lag by 8 hours the third unit hydrograph and then we are adding these ordinates horizontally to get direct runoff hydrograph of 3 centimeter rainfall excess 1 due to this second centimeter due to this and third centimeter due to this that is 3 centimeter rainfall excess and this is the resulting hydrograph so this was 3 centimeter rainfall excess so we need to divide these accumulated ordinates again by 3 to get the ordinates of 12 hour unit hydrograph so these were the ordinates of 12 hour rainfall event with 3 centimeter rainfall excess obviously we need to divide those by 3 to get ordinates of 12 hour unit hydrograph in meter cube per second so in this way by knowing ordinates of 4 hour unit hydrograph we have calculated ordinates of 12 hour unit hydrograph which was the objective of this particular lecture so you will find that when we sum the ordinates of these 3 4 hour unit hydrograph lag by 4 hours this is a total f is equal to a plus b plus c direct runoff hydrograph of 3 centimeter and when we divide it by 3 we get the 12 hour unit hydrograph dividing this ordinate by 3 and obviously it is due to 1 centimeter rainfall excess over 12 hours over 12 hours so in this way we constructed 12 hour unit hydrograph from 4 hour unit hydrograph these are the references and thank you.