CIVIL WORKS GUIDELINES FOR MICRO-HYDROPOWER IN NEPAL
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Steep river gradient and steep slopes along both river banks.
High degree of continuing erosion and sediment transport.
Smaller streams of steep and unstable nature with a bouldery
alluvial bed.
Liable to transport considerable quantities of sediment
including boulders during the monsoon.
A significant flow and sediment increase in the rivers
during the monsoon.
Due to these unique characteristics, development of
hydro-power from the Himalayan rivers present great
challenges. Design and construction of appropriate structures
to cope with movement of large boulders and high sediment
loads are two of these challenges. River intakes used elsewhere
in relatively flat and stable rivers including the Terai are
inappropriate in the case of mountain rivers of Nepal. Rivers in
Nepal can be categorised according to the way in which they
are influenced by various characteristics. The types of river
that are mostly utilised in micro-hydro are shown in Table 3.1.
3.3.2 EXAMPLE INTAKES
Typical intake locations for some of these rivers are shown in
Figures 3.3 and 3.4. It should be noted that these figures
illustrate only possible locations for intakes, not the preferred
type of intake.
River type IA
Mountain rivers of Type 1A provide favourable conditions for
intakes in terms of permanence and lack of interference from
sediment in normal conditions.
River type IB
Intakes on Type IB rivers can also be located similar to 1A.
However, these rivers provide a greater choice of intake site,
and permit more permanent intake structures, either from
the side of the channel or as an angled or frontal intake built
into the channel. It is often possible to protect the intake
behind a rock outcrop.
TABLE 3.1 Categories of Nepalese rivers
TYPE GRADIENT
(MAIN LOCATION)
VALLEY SHAPE
BED MATERIAL
1A Very steep
(Mountains)
Narrow valley Rocks, very large
no flood plains boulders
CHANNEL PATTERN
Single
1B Step (Mountains Narrow valley, Rocks and boulders, One main plus flood
and hill regions) irregular narrow gravel and cobbles in bypass channel
flood plains
shoals
1C
Step (Mountains
and hill regions)
Narrow valley, Rocks and boulders,
irregular narrow gravel and cobbles in
Several active
channels as well as
flood plains
shoals
floodways.
2A Intermediate
(Hill regions)
Outwash river,
confined by
valley sides
Some boulders, mainly Single plus limited
gravel and cobbles.
floodways
2B Intermediate
(Hill regions)
Ditto but less
Some boulders, mainly 2-4 active channels
confined valley gravel and cobbles
with floodways
2C Intermediate
(Hill regions)
Ditto but wider
valley
Some boulders, mainly
gravel and cobbles
Braided, several
active floodways
perhaps small
boulders.
SEDIMENT
MOVEMENT
(N = NORMAL,
F = FLOOD)
N - Sand in suspen-
sion gravel
F -gravel, cobbles
and boulders
N - Sand and gravel
F- Sand and gravel
F - Includes cobbles
and small boulders.
N - Sand and gravel
F - Includes cobbles
and small boulders.
N - Sand and fine to
medium gravel
F - Includes coarse
gravel, cobbles,
perhaps small
boulders.
N - Sand and fine to
medium gravel
F - Includes coarse
gravel, cobbles,
perhaps small
boulders.
N - Sand and fine to
medium gravel
F - Includes coarse
gravel, cobbles,
perhaps small
boulders.