 Professor, Department of Civil Engineering, WIT, Solapur. Topic for today's session, estimation of discharge of a sewer line. At the end of this session, student will be able to estimate discharge of sewer line. There are following types of sewer line, pipe sewer. It is also called as house sewer, lateral sewer, sub-main sewer, main sewer, and outfall sewer. In this diagram, all the types of sewer are there. You can see house sewer. It is directly connected to house. It carries the sewage away from the building. It is a pipe which is carrying sewage away from the building. And this is lateral sewer. Lateral sewer, all these are the lateral sewer. All these are the lateral sewer. Lateral sewer receives the sewage directly from the house. And it is connected to house sewer. Then through lateral sewer, sewer get collected in a sub-main sewer. See here, sub-main sewer you can see. Sub-main sewer is also called as branch sewer. Then through sub-main sewer, sewer get collected in a main sewer. Main sewer, it is also called as a trunk sewer. Then at last, all the sewage of entire city collected in an outfall sewer. It is a larger sewer which collects all the sewage from the area. And then it disposes it at the disposal point or at the point where we want to dispose it. Total waste water flow. Total waste water flow can be divided into two components. Dry weather flow, it is also called as DWF and wet weather flow. It is also called as WWF. Dry weather flow is nothing but the sanitary sewage. In that there will be no rain water. It depends upon rate of water supply per capita per day. Rain growth, type of area serve, infiltration of ground water and etc. Wet weather flow is nothing but the strong water flow. It depends upon catchment area, ground slope, types of area, rainfall duration, climatic condition etc. For estimating strong water flow for sewer design, following two methods are commonly used. Rational method and empirical formula. When the draining area is less than 400 hectare, then use rational method. And when draining water area is more than 400 hectare, then use empirical formula. Let's see first rational formula. It is q is equal to k into ai ri, where a is the catchment area, i is the impermeability factor, ri is the intensity of rainfall, q is the runoff or discharge and k is the constant which permit the expression of factor ai and r in convenient unit. For example, convenient unit like keep q in meter cube per second, keep area in hectare and keep rainfall intensity in mm per hour. Let us find k. So, q is equal to ai ri is the basic formula. In that formula, we have area in hectare, so multiply it with 10 to the power 4 that is the relation between hectare and meter square. In i, it is just impermeability factor, no need of unit conversion and ri convert that in initially it is in meter per second, convert that meter per second in mm per hour. So, this is all unit conversion 1000 into 3600. So, by simplifying it, q is equal to 1 upon 360 ai ri. So, that 1 upon 360, it is nothing but the key. So, our formula of discharge is q is equal to 1 upon 360 ai ri in that q should be in meter cube per second, area should be in hectare and ri should be in mm per hour. Now, you pause video here and you find the expression for the strom that is q for the convenient unit q in liter per second, keep discharge in liter per second, area in hectare and intensity of rainfall in cm per hour and do the unit conversion and find out the key. Here is the answer. q is in liter per second, area is in hectare and ri is in cm per hour. So, unit conversion will be as follow, q is equal to 10 to the power 4 for conversion of meter square in hectare into i into ri for cm per hour you multiply with 100 in and 3600 and this 1000 is for conversion of meter cube to liter. So, it will come 250 by 9 into ai ri. So, that 250 by 9 is nothing but the key or it is approximately we can write q is equal to 28 ai ri. So, here 250 by 9 or 28 are the value of key. So, you remember the convenient unit for the this two equation. Take one example, a certain district of a city has projected population of 50,000 receding over an area 40 hectares. Find the design discharge for the sewer line for the following data. Rate of water supply 200 liter per capita per day, average impermeability coefficient for the entire area 0.3 and rainfall intensity 1.45 centimeter per hour. The sewer line is to be designed for the flow equivalent to the wet weather flow plus twice the dry weather flow. Assume that 75 percent of water supply reaches in sewer as wastewater. First list of the given data, here it is given population 50,000 area 40 hectare. Rate of water supply 200 liter per capita per day. Ai that is impermeability factor for entire catchment area it is in given 0.3, ri is equal to 1.45 and sewage flow is given that 75 percent of rate of water supply. So, 75 percent of 200 is 150 liter per capita per day. So, per head there is a supply of 150 liter per day, calculate the dry weather flow. So, for 50,000 of population it is 50,000 into 150 and convert it is in second so multiply it 24 into 60 into 60 divided by 3600. So, dry weather flow is 86.8 liter per second. Wet weather flow is here we have discharge in liter per second so obviously we have to use the formula 28 ai ri. So, 28 area is in hectare 40, i is 0.3 and ri is 1.45 centimeter per hour. So, wet weather flow is 487.2 liter per second. So, we have here dry weather flow and wet weather flow and design discharge is given that is twice dry weather flow plus wet weather flow. So, you put in a formula 2 into 86.8 plus 487.2 the discharge will come 661 liter per second. So, like this we have calculated discharge. These are my references. Thank you very much.