CIVIL WORKS GUIDELINES FOR MICRO-HYDROPOWER IN NEPAL
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these rivers provide more flexibility. For example, it is possible
to use more permanent river control structures such as concrete
or masonry weirs and river training walls.
3.4 Intake types
3.4.1 DESCRIPTION
Types of intake structure are chiefly distinguished by the method
used to divert water from the river. In micro-hydropower, mainly
two types of intake are used which are as follows:
Side intake
Bottom intake
Apart from the above types, an innovative intake called
“Coanda intake” has also been field tested in a micro-hydro
scheme in the UK. This is discussed in Chapter 10
(Innovations).
3.4.2 SELECTION CRITERIA
Table 3.2 aids the choice between side and bottom intakes
for given conditions.
TABLE 3.2 Selection criteria for side and bottom intake
SELECTION CRITERIA
SIDE INTAKE
Amount of water:
Favourable site selection necessary
(outside of a bend, or an artificial bend
by groins) if the amount of diverted
water is greater than 50% of the
water supplied.
Gradient of river:
• very high (i > 10%)
to high (10% > i > l%)
Favourable: maintenance free
operation of the intake structure
should be ensured as far as possible.
BOTTOM INTAKE
The bottom screen draws off the
river water up to the capacity
limit of the screen (i.e. all river
flow if screen is large enough).
Favourable for very high gradient;
can be maintenance-free,
if properly designed.
• mean gradient
(1% > i > 0.01%)
Plan of river:
• straight
• winding
• branched
Suspended sediment
concentration:
• high
• low
Bed load transport:
• strong
• weak
Favourable
Possible
Very favourable if the river channel is
stable; when arranged on the outside
bend.
Unfavourable; damming of the river
is required.
Unfavourable if i < 10%.
Unfavourable: fine bed load
into the initial headrace canal
results in difficulty in flushing.
Very favourable, as bottom
screen is uniformly loaded.
Unfavourable, as bottom screen
is not uniformly loaded.
Unfavourable.
Suitable in combination with very
efficient settling basin.
Well suited
Less suitable,
Well suited
Suitable as long as sufficient amount of
water remains in the river for flushing.
Well suited
Less suitable
Well suited