CIVIL WORKS GUIDELINES FOR MICRO-HYDROPOWER IN NEPAL
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3. Diversion works
3.1 Overview
The diversion works for a micro-hydropower scheme control
the flow of water from the source river into the headrace.
They comprise a diversion weir (usually), an intake, and
sometimes river training works. The diversion works are part
of the headworks, and serve the following functions:
Maintain the design flow with nominal head losses during
both monsoon and dry seasons.
Revent, or at least minimise, the bed load and other floating
materials (ice, timber, leaves etc.) entering the canal.
Safely contain peak flows in the river and away from the
micro-hydro system so that damage is minimum to the
structures.
The principal maintenance task associated with civil works is
often the removal of sediment and debris carried by the
incoming water, which can cause damage to the turbines
should it be permitted to enter the penstock. It is therefore
essential that the adopted intake design prevent sand, bed
load and debris from entering the intake as much as possible.
One of the principal causes of problems in the operation of
hydropower schemes is a poorly designed intake which may
permit operation of the scheme in the short-term but beyond
that, cause serious damage to the system. The design of an
appropriate intake structure for micro-hydro in Nepal requires
an adequate understanding of Himalayan rivers since they
have some unique features.
3.2 General principles for selecting intake location
The major considerations required to select appropriate intake
locations are discussed in this section. It is important for the
design engineer to realise that much can be learned from
observing the irrigation intake sites selected by local farmers.
The farmers are familiar with the rivers and have the added
advantage that they have observed them over a long period of
time. In fact, some of the farmer managed irrigation schemes in
Nepal are more than 100 years old and the intakes of such sites
have faced most problems brought about by Himalayan rivers.
The following principles should be considered while selecting
appropriate intake locations:
Minimal disturbance to the natural state of the river
Construction of high and permanent weirs (larger than 1-2
m) across the total width of the river is generally undesirable,
because damming has the effect of rapid sediment deposition
and change of present river course, leaving the intake dry
and useless. The design and construction of weirs requires
careful consideration to avoid presenting an obstacle to flood