CIVIL WORKS GUIDELINES FOR MICRO-HYDROPOWER IN NEPAL
145
TABLE A3 Prediction coefficients for long term average monthly flows
MONTH
CONSTANT
POWER, AREA OF POWER, AREA OF BASIN POWER OF MONSOON
COEFFICIENT
BASIN (KM2)
BELOW 5000 M+1 (KM2) WETNESS INDEX
January
C
0.01423
A1
0
A2
0.9777
A3
0
February
0.01219
0
0.9766
0
March
0.009988
0
0.9948
0
April
0.007974
0
1.0435
0
May
0.008434
0
1.0898
0
June
0.006943
0.9968
0
0.2610
July
0.02123
0
1.0093
0.2523
August
0.02548
0
0.9963
0.2620
September
0.01677
0
0.9894
0.2878
October
0.009724
0
0.9880
0.2508
November
0.001760
0.9605
0
0.3910
December
0.001485
0.9536
0
0.3607
Note : unit of flow are m3/s
2 Ascertain if there are significant upstream abstractions,
attempt to quantify them and add this amount to the
measured flow.
3 Establish in which hydrological region the catchment lies,
from Figure A2. Divide the measured flow by the non-
dimensional hydrograph ordinate (Table A4) for the
appropriate month and region. If the flow measurement
was conducted at the beginning or the end of the month, it
may be necessary to interpolate between the two relevant
ordinates from Table A4. The result represents the mean
April flow to be expected in that catchment.
4 Take the April flow calculated in step 3 and multiply it by
each non-dimensional ordinate from Table A4. The result
is the hydrograph of mean monthly flows.
5 It is useful to compare the hydrograph calculated in step 4
with the appropriate regional hydrograph depicted among
Figures A4 to A10. To do this, divide each ordinate of the
catchment hydrograph by the catchment area. Normally,
the calculated hydrograph will correspond to the regional
hydrograph within the limits indicated. The limits may be
used as a rough guide to the reliability of flow in the
catchment. If the hydrograph lies outside the limits then it
is not typical, due perhaps to unusual land use or a typical
detail of topography and geology.