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CIVE 445 - ENGINEERING HYDROLOGY
SPRING 2008 - MIDTERM 2 - SOLUTION
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To convolute the 2-hr unit hydrograph with the effective storm pattern defined at intervals of 3 hr, it is necessary to change the unit
hydrograph duration to 3 hr. We use the S-hydrograph method to change the 2-hr UH to 3-hr UH.
To calculate the flood hydrograph, for 6 cm, it is 6 times; for 12 cm, it is 12 times (lagged 3 hr).
| Time | 2-hr UH | 2-hr SH
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Lagged 3 hr | 3-hr UH | 6×UH | 12×UH
(lagged 3 hr) | Flood
hydrograph
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| (hr) | (mm/hr) | mm/h
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(ha) | (m3/s) | (m3/s) | (m3/s) | (m3/s)
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0 | 0 | 0 |
0 | 0.00 | 0 | 0 | 0
| 1 | 5 | 5 |
0 | 3.33 | 20 | 0 | 20
| 2 | 15 | 15 |
0 | 10.00 | 60 | 0 | 60
| 3 | 30 | 35 |
0 | 23.33 | 140 | 0 | 140
| 4 | 60 | 75 |
5 | 46.67 | 280 | 40 | 320
| 5 | 70 | 105 |
15 | 60.00 | 360 | 120 | 480
| 6 | 60 | 135 |
35 | 66.67 | 400 | 280 | 680
| 7 | 55 | 160 |
75 | 56.67 | 340 | 560 | 900
| 8 | 45 | 180 |
105 | 50.00 | 300 | 720 | 1020
| 9 | 35 | 195 |
135 | 40.00 | 240 | 800 | 1040
| 10 | 25 | 205 |
160 | 30.00 | 180 | 680 | 860
| 11 | 15 | 210 |
180 | 20.00 | 120 | 600 | 720
| 12 | 5 | 210 |
195 | 10.00 | 60 | 480 | 540
| 13 | 0 | 210 |
205 | 3.33 | 20 | 360 | 380
| 14 | 0 | 210 |
210 | 0.00 | 0 | 240 | 240
| 15 | 0 | 210 |
210 | 0.00 | 0 | 120 | 120
| 16 | 0 | 210 |
210 | 0.00 | 0 | 40 | 40
| 17 | 0 | 210 |
210 | 0.00 | 0 | 0 | 0
| ∑ | 420 | - |
- | 420.00 | 2520
[= 420×6] | 5040
[= 420×12] | 7560
[= 420×18]
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Problem 3
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