146 CIVIL WORKS GUIDELINES FOR MICRO-HYDROPOWER IN NEPAL
TABLE A4 Non-dimensional regional hydrographs
MONTH
January
February
March
April
May
June
July
August
September
October
November
December
1
2.40
1.80
1.30
1.00
2.30
6.00
14.50
25.00
16.50
8.00
4.10
3.10
2
2.24
1.70
1.33
1.00
1.21
7.27
18.18
27.27
20.91
9.09
3.94
3.03
REGION
34
2.71
2.59
1.88
1.88
1.38
1.38
1.00
1.00
1.88
2.19
3.13
3.75
13.54
6.89
25.00
27.27
20.83
20.91
10.42
6.89
5.00
5.00
3.75
3.44
5
2.42
1.82
1.36
1.00
0.91
2.73
11.21
13.94
10.00
6.52
4.55
3.33
6
2.03
1.62
1.27
1.00
2.57
6.08
24.32
33.78
27.03
6.08
3.38
2.57
7
3.30
2.20
1.40
1.00
3.50
6.00
14.00
35.00
24.00
12.00
7.50
5.00
A3 Design example
Catchment name
Catchment location
Hydrological region
Basin area
Area below 5000 m
Area below 3000 m
Monsoon wetness index
Month of gauging
Flow measured
Solu Khola
Solukhumbu
3
330 km2
308.5 km2
97.7 km2
1500
April
2.8 m3/s
Figure A1 shows the catchment map.
A 3.1 WECS/DHM PROCEDURE
a) Flood flows
RETURN PERIOD (YRS)
INSTANTANEOUS FLOOD
DISCHARGE (M3/S)
2 106
5 175
10 228
20 283
50 362
100 426
example:
Q2 = 1.8767 (97.7+1)0.8783 = 106m3/s
Q100 = 14.63 (97.7+1)0.7342 = 426m3/s
Q100
=
e [1n106+2.054
1n(426/106)
2.326
]=
326m3/s
b) Flow duration curve
PROBABILITY OF
EXCEEDENCE (%)
DISCHARGE (M3/S)
0 98.45
5 59.33
20 32.62
40 9.47
60 4.58
80 3.00
95 2.03
100 1.78
example:
InQ5%
= -3.4978 + 0.9814 ln (308.5 + l) + 0.2670 In 15OO
= 4.083 Q5 = e4083 = 59.33
InQ5%
= - 5.9543 + 1.0070 ln (330) + 0.3231 In 15OO
= 2.248 Q40 = e2.248 = 9.47
InQ95%
Q100%
= - 5.4716 + 1.0776 ln (308.5 + l)
= 0.708 Q95 = e0.708 = 2.03
= [-0.O9892 + 0.08149 x (308.5 + 1)]2 = 1.78