48 CIVIL WORKS GUIDELINES FOR MICRO-HYDROPOWER IN NEPAL
TABLE 4.1 Roughness coefficient and allowable maximum velocity
See note below for advice on channels where the water depth is less than one metre.
CHANNEL TYPE
Earth channel
DESCRIPTION
Clay, with stones and sand, after ageing
n
0.020
MAX.
VELOCITY(M/S)
0.8
Gravelly or sandy loams, maintained with minimum vegetation
0.030
0.4
Lined with coarse stones, maintained with minimum vegetation
0.040
1.0
For canals less than 1 metre deep, use the equation in Note 4.1 for n e.g.:
Vegetated (useful to stabilise soil); water depth 0.7 m
0.050
0.8
water depth 0.3 m
0.070
0.8
Heavily overgrown, water depth 0.3 metres
0.150
1.0
Rock cut
Smooth and uniform
0.035
1.5
Jagged and irregular
0.045
1.5
Very jagged and irregular
0.060
1.5
Masonry and
Stone masonry in mud mortar, dry stone masonry
0.035
1.0
concrete
Stone masonry in cement mortar using rounded stones
0.030
1:4 cement sand mortar
1.5
1:3 cement sand mortar
2.5
Stone masonry in cement mortar using split stones (dressed)
0.020
1:4 cement sand mortar
2.0
1:3 cement sand mortar x
3.0
with 1:2 pointing
5.0
Concrete (according to finish)
0.013 - 0.017
1:3:6 plain concrete
1.5
1:2:4 plain concrete
2.0
1:1.5:3 reinforced concrete
3.0
1:1:2 reinforced concrete
5.0
Cement plaster
0.013
3.0
1:3
1:2 5.0
Wooden canals Planed, well-jointed boards
0.011
3.0
Unplaned boards
0.012
3.0
Older wooden canals
0.015
3.0
Metal canals
All types
0.020
3.0
Mountain streams Dominant bed material :
Gravel (up to 60 mm)
0.03
Cobbles (up to 200 mm)
0.04
Boulders (up to 600 mm)
0.05
Note 4.1 Roughness effect for shallow channels
Large boulders (> 600 mm)
0.07