Environmental and Social Impact Assessment - Gibe III

Gibe III – Environmental and Social Impact Assessment 300 ENV R CS 002 C - A9003099
Table 5.26: Gibe III Dam Site – Extreme Flood Hydrographs
Elapsed Time 10000yrs PMF Elapsed Time 10000yrs PMF
[hr] [m 3 /s] [m 3 /s] [hr] [m 3 /s] [m 3 /s]
0 859 859 372 8103 13127
12 859 859 384 7781 12548
24 860 860 396 7374 11831
36 862 867 408 6859 10942
48 870 899 420 6257 9910
60 895 1001 432 5603 8793
72 964 1234 444 4938 7660
84 1115 1666 456 4300 6575
96 1390 2363 468 3716 5582
108 1828 3376 480 3203 4712
120 2455 4721 492 2765 3971
132 3278 6384 504 2401 3355
144 4279 8314 516 2104 2856
156 5418 10426 528 1867 2459
168 6621 12579 540 1679 2146
180 7782 14581 552 1531 1899
192 8794 16255 564 1414 1703
204 9593 17500 576 1322 1549
216 10153 18290 588 1248 1428
228 10481 18653 600 1190 1332
240 10606 18661 612 1143 1256
252 10578 18408 624 1105 1195
264 10445 17990 636 1074 1147
276 10247 17481 648 1050 1108
288 10011 16929 660 1030 1077
300 9756 16366 672 1014 1052
312 9492 15809 684 1000 1031
324 9224 15262 696 990 1015
336 8950 14721 708 981 1001
348 8670 14185 720 973 990
360 8389 13656 732 967 980
Peak flows determined in the two simulations equal respectively 10606 and 18661 m 3 /s both occurring after
10 days from the beginning of the storm. The peak of the excess rainfall happens after 6 days and
consequently the total lag time at Gibe III is 4 days. The whole flood events lasts about 30 days. After this
period the recession of the hydrograph is very modest.
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