Minimum
gradient
This is important only at locations where surface drainage is important. Camber will take care of the lateral drainage .but the longitudinal drainage along the side drains require some slope for smooth flow of water .therefore minimum gradient is provided for drainage purpose and it depends on rain fall, type of soil and other site conditions. A minimum of 1 in 500 may be sufficient for concrete drain and 1 in 200 for open soil drains are found to give satisfactory performance.
This is important only at locations where surface drainage is important. Camber will take care of the lateral drainage .but the longitudinal drainage along the side drains require some slope for smooth flow of water .therefore minimum gradient is provided for drainage purpose and it depends on rain fall, type of soil and other site conditions. A minimum of 1 in 500 may be sufficient for concrete drain and 1 in 200 for open soil drains are found to give satisfactory performance.
|
Terrain
|
Ruling
gradient
|
Limiting
gradient
|
Experimental
gradient
|
|
Plain or
rolling
|
3.3 per
cent
(1 in
30)
|
5 per
cent
(1 in
20)
|
6.7 per
cent
(1 in
15)
|
|
Mountainous
terrain, and steep terrain having elevation more than 3,000 m above the mean
sea level
|
5 per
cent
(1 in
20)
|
6 per
cent
(1 in
16.7)
|
7 per
cent
(1 in
14.3)
|
|
Steep terrain
upto 3,000 m height above mean sea level
|
6 per
cent
(1 in
16.7 )
|
7
Percent
( 1 in
14.3 )
|
8
Percent
( 1 in
2.5 )
|
Suppose the
road is with zero gradient passing through level land and open side drains are
provided with a gradient of say 1 in 300. It may then be necessary to deepen
the downstream end of the drain by about 3.3 m for one kilometre length of
road. This course is not possible from practical considerations. Hence it is
desirable to have a certain minimum gradient on roads from drainage point of
view, provided topography favours this. The minimum gradient would depend on
rain-fall, run-off , type of soil, topography and site conditions.
A minimum
gradient of about 1 in 500 may be sufficient to drain water in concrete drains
and gutter , but on inferior surfaces of drains a slope of 1 in 200 or 0.5
percent may be needed where as on kutcha open drains ( soil drains ) steeper
slopes up to 1 in 100 or 1.0 percent may be needed.
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