sm_ch15

Water Resources Engineering

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15 – 1 Chapter 15 15.2.1. n = 0.014. Catchment Ground elevation (m) Area (km 2 ) Runoff coefficient Inlet time (min) 1.1 1.2 2.1 3.1 300 298 296 294.5 0.01 0.008 0.005 0.60 0.75 0.80 25 20 15 1.1 200 m 150 m 2.1 1.2 150 m 3.1 The solution for this problem is given in the following table. Figure P15.2.1 (b) has been used to determine the rainfall intensities. 1 2 3 4 5 6 7 8 9 10 Sewer Elevation (m) Length (m) Slope (m/m) Total drained area (km 2 ) Catchment Incremental area (km 2 ) C CA 6 CA 1.1 1.2 2.1 300 298 296 200 150 150 0.020 0.013 0.010 0.01 0.008 0.005 0.023 1.1 1.2 2.1 1.1 1.2 0.01 0.008 0.005 0.60 0.75 0.80 0.006 0.006 0.004 0.006 0.006 0.016 3.1 294.5 150 0.010 3.1 11 12 13 14 15 16 17 18 19 20 Inlet time (min) Upstream sewer flow time (min) t c (min) T d (min) i (mm/hr) Design discharge, Q p (m 3 /s) Computed diameter (m) Pipe size used (mm) Flow velocity (m/s) Sewer flow time (min) 25 20 15 25 20 Na Na Na 2.13 2.07 25 20 15 27.13 22.07 25 20 27.13 45.7 50.8 40.6 0.077 0.085 0.182 0.248 0.279 0.391 250 300 400 1.56 1.21 1.45 2.13 2.07 1.73
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15 – 2 15.2.2. n = 0.014. Catchment Ground elevation (m) Area (km 2 ) Runoff coefficient Inlet time (min) 1.1 1.2 2.1 3.1 300 298 296 294.5 0.01 0.008 0.005 0.60 0.75 0.80 25 20 15 1.1 200 m 150 m 2.1 1.2 150 m 3.1 The solution for this problem is given in the following table. Figure P15.2.1 (b) has been used to determine the rainfall intensities. 1 2 3 4 5 6 7 8 9 10 Sewer Elevation (m) Length (m) Slope (m/m) Total drained area (km 2 ) Catchment Incremental area (km 2 ) C CA 6 CA 1.1 1.2 2.1 300 298 296 200 150 150 0.020 0.013 0.010 0.01 0.008 0.005 0.023 1.1 1.2 2.1 1.1 1.2 0.01 0.008 0.005 0.60 0.75 0.80 0.006 0.006 0.004 0.006 0.006 0.016 3.1 294.5 150 0.010 3.1 11 12 13 14 15 16 17 18 19 20 Inlet time (min) Upstream sewer flow time (min) t c (min) T d (min) i (mm/hr) Design discharge, Q p (m 3 /s) Computed diameter (m) Pipe size used (mm) Flow velocity (m/s) Sewer flow time (min) 25 20 15 25 20 Na Na Na 2.01 1.76 25 20 15 27 21.8 25 20 27 69.85 81.28 68.58 0.117 0.137 0.307 0.291 0.334 0.476 300 350 500 1.66 1.42 1.57 2.01 1.76 1.60
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15 – 3 15.2.3. The IDF curve for Phoenix for T = 10 years is used for this problem. n = 0.014. A layout of the sewer system is shown below. 1 1000 ft 2 800 ft 3 (1) (2) (3) (4) (5) (6) (7) (8) (9) Pipe Slope (ft/ft) Length (ft) Drained area (ac) C CA 6 CA t c (min) i (in/hr) 1 – 2 2 – 3 0.005 0.006 1000 800 2 3 0.50 0.80 1.0 2.4 1.0 3.4 15 20 3.75 3.25 (10) (11) (12) (13) (14) (15) t d (min) Design discharge, Q p (ft 3 /s) Computed diameter (in) Pipe size used (in) Flow velocity (ft/s) Sewer flow time (min) 15 20.45 3.75 11.05 14.3 20.8 15 21 3.06 4.59 5.45 2.90 15.2.4. D 1 = 600 mm = 0.6 m, D 2 = 700 mm = 0.7 m, Q = 0.5 m 3 /s. 768 . 1 4 / (0.6) 5 . 0 A Q V 2 1 1 S m/s 299 . 1 4 / (0.7) 5 . 0 A Q V 2 2 2 For a sudden expansion, K = 1.0. Hence, ± ² ± ² 011 . 0 ) 81 . 9 ( 2 299 . 1 768 . 1 0 . 1 g 2 V V K H 2 2 2 1 e ³ » ¼ º « ¬ ª ³ m. 15.2.5. ) = 45 o , D = 500 mm = 0.5 m, Q = 0.45 m 3 /s, r/D = 2. g 2 V K H 2 b b 29 . 2 4 / (0.5) 45 . 0 A Q V 2 Since ) > 40 o , Figure 15.2.9 is used to determine K b . For ) = 45 o and r/D = 2, K b = 0.18.
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15 – 4 048 . 0 (9.81) 2 (2.29) 0.18 H 2 b m 15.2.6. Q L = 30 cfs, Q u = 50 cfs, Q o = 80 cfs, D L = 30 in = 2.5 ft, D u = 42 in = 3.5 in, D o = 48 in = 4 ft Outfall pressure line elevation = 475.7 ft Top of Manhole elevation = 476.0 ft Bottom of Manhole elevation = 470.15 ft Manhole diameter = 48 in = 4 ft. Step 1) Outfall pressure line elevation given as 475.7 ft Step 2) Velocity head at outfall: 63 . 0 4 / (4) 80 ) 2 . 32 ( 2 1 A Q 2g 1 g 2 V 2 2 o 2 o ¸ ¸ ¹ · ¨ ¨ © § ¸ ¹ · ¨ © § S ft Step 3) Compute the ratios: 625 . 0 80 50 Q Q o u 875 . 0 4 5 . 3 D D o u 625 . 0
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sm_ch15 - 15 1 Chapter 15 15.2.1. n = 0.014. Catchment 1.1...

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