Question

2. Design a trapezoidal channel to pass a discharge of 10m3/s and the channel will be excavated through rock by blasting. The topography in the area is such that a bottom slope of 1 in 4000 will be suitable. Assume that n = 0.030 and select a value for the side slope, Z, as 1 horizontal to 4 verticals. Sketch the diagram for all calculated dimensions.

Answer 1

solution Given Trapezoidal Channel discharge Q= 10 m3/see Bottom Slope 1 in 4000 S Yooo Manning's coefficient, n = 0.030 Side slope, z = liny Z st m For trapezoidal channel P Bottom width To Top width y depth B Area A = (Bt my y Perimeter, P = B+ 2y Jitma So, A = (B+44) y P = B+ 2y J1+ y2 = B+ 8.246y.

By Manning's formule (Mannings) I AR23 ghz R = Hydraulic radius n R = A ARB S2 10 = 1 0.030 loco Avdy)* (hod) 18.97 е 73 pZ putting the values of A & P. 513 18:57 = [(8+vyyy] (B+ 8.2469) 23 This can be solved by trial & & error metod. on putting different values of B8 g which will give an approximate value are, B = 3.52m. y=1.76m the combination I 08 I

T 17.6m y = 1.76m B-3.52 m Top width = B+ 8y =T y - 3.52 + 8 x 1.76 IT = 17.6m 2 2 y 2.49 Area = A= (B+vyJy = (3.52 +4 x170] X1.7 A-18.5856 m2 Perimeter, pa Brry Jitma P = 3.52 + 2x1.76 Jity P = 18.0333 m Hydraulic R = Mean depth 19.5856 - AA = 1.0306m 18.0333 R = 1.0306 m 3