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Determine the ordinates of 12 hr unit hydrograph
written 7.9 years ago by gravatar for teamques10 teamques10 ★ 68k •   modified 7.9 years ago

The ordinates of a 4hr unit hydrograph are given below. Determine the ordinates of 12 hr unit hydrograph.

Time (hour) 0 4 8 12 16 20 24 28 32 36 40 44
Ordinates in m3/s 0 24 28 159 184 151 103 64 36 17 6 0

Mumbai University > Civil Engineering > Sem 7 > Irrigation Engineering

Marks: 9M

Year: Dec 2015
irrigation engineering
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written 7.9 years ago by gravatar for teamques10 teamques10 ★ 68k

Given $T_0 = 4hrs.$

$t_0 = 12 hrs.$

Since $t_0$ is an integral multiple of $T_0 (i.e. t_0 = 3T_0)$, the desired hydrograph can be obtained by taking the sum of the ordinates of three unit hydrographs of 4-hours duration, each lagging from the other by 4-hours, and dividing the sum by 3.

Time 4 hrs unit hydrograph Offset unit hydrograph Offset unit hydrograph Sum Ordinates of 12 hrs. unit hydrograph
(1) (2) (3) (4) (5)=(2)+(3)+(4) (5)/3
0 0   0 0
4 24 0   24 8
8 84 24 0 108 36
12 159 84 24 267 89
16 184 159 84 427 142.3
20 151 184 159 494 164.6
24 103 151 184 438 146
28 64 103 151 318 106
32 36 64 103 203 67.6
36 `17 36 64 117 39
40 6 17 36 59 19.6
44 0 6 17 23 7.6
48   0 6 6 2
52     0 0 0

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