Presentation on theme: "Sewer Hydraulics Gravity flow: full flow Gravity flow: Partial flow"— Presentation transcript:
1 Sewer Hydraulics Gravity flow: full flow Gravity flow: Partial flow Pressure flow: full flowLhHGLHGLHGLS= HGL = slope of the sewerR =Ap/PpS= h/L = slope of the HGLR=D/4S= HGL = slope of the sewerR = Af/Pf = D/4
2 Manning equationMany formulas are used to solve the flow parameters in sewers were discussed in the hydraulic course. The most used formula for sanitary sewers is Manning equation:R = Hydraulic radius (Area/ wetted parameter)S = slope.n = manning coefficient.D = pipe diameter.Q = flow rate.Note: Equation 1 is used for calculating the velocity in pipes either flowing full or partially full. Equation 2 same for flow rate.Vƒ = velocity flowing fullVP = velocity flowing partiallyNote: Equations 3 and 4 are the same as Equation 1, but they are written using the subscript (ƒ) and (P), to indicate flowing full and partially full, respectively:
3 In sanitary sewers the flow is not constant; consequently the depth of flow is varying as mentioned above. In this case it is difficult to find the hydraulic radius to apply Manning’s equation. For partially full pipe the following relations are applied:DӨdDd = partial flow depth.R = Hydraulic radius (P = partial, ƒ = full)Ө = flow angle in degrees.Maximum capacity of the pipe when d/D = 0.95A = Flow area.Maximum velocity in the pipe occurs at d/D=0.81Өd
4 Example 1Find the diameter of the pipe required to carry a design flow of m3/s when flowing partially, d/D = , slope = 0.4%, n = use the relations of partial flow.SolutiondDӨ
5 It is noticed that it is quite long procedure to go through the above calculations for each pipe in the system of large numbers of pipes. The alternative procedure is to use the nomographs of Mannings equation and the partial flow curves.
6 Example 2Find the diameter of the pipe required to carry a design flow of m3/s when flowing partially, d/D = , slope = 0.4%, n = using the nomographs and partial flow curves .Solution