18 CIVIL WORKS GUIDELINES FOR MICRO-HYDROPOWER IN NEPAL
2.8 Checklist for site selection
LAND OWNERSHIP, LAND USE AND WATER RIGHTS
Have all issues concerning land use and ownership been duly
recorded during the site visit? Does the alignment traverse through
a farmer's paddy field or is it along barren land? Have water rights
issues such as irrigation use been adequately addressed?
INTAKE
Make sure water can be diverted away from the river and
towards the headrace. Does the river course appear stable or
does it look like it will meander? Think about floods and flood
levels. Does the river carry large boulders? If so, think about
temporary diversion works rather than a permanent weir.
GRAVEL TRAP
Does the river carry a significant amount of gravel during the
monsoon? If so provide a gravel trap as close to the headworks
as possible. Can the gravel be easily flushed into the stream
or a nearby gully from the gravel trap?
SETTLING BASIN
This structure should be located as close to the intake as
possible. The earlier the sediment is removed the less the
maintenance in the headrace. If the source river is not far
away the sediment can be discharged back into it.
HEADRACE
In general the headrace alignment should be on level to slightly
sloping ground. If the alignment is steep, consider using a
headrace pipe instead of a canal. Try to get the alignment
away from the river as early as possible to minimise flood
damage. Provide escapes and spillways upstream of areas
where the canal might be blocked by landslides. If seepage
from the headrace canal can trigger landslides, think about
lining the canal or using pipes.
FOREBAY
Allowance should be made for final settling of sediments.
Generally, this structure should be located just uphill of the
transition area where the ground profile changes from gentler
to steeper slope. Is there a possibility to safely discharge the
entire flow from a spillway in case of system malfunction?
PENSTOCK
The penstock alignment should start where the ground profile
gets steeper. An ideal ground slope would be between 1:1
and 1:2 (V:H). The flatter the ground slope, the less economic
is the penstock. It is difficult to manually lay penstock,
construct support piers and anchor blocks if the slope is greater
than 1:1. Also try to minimise bends since these will require
additional anchor blocks.
POWERHOUSE
Make sure that there is enough space for a powerhouse with
the required dimensions (to fit the electro-mechanical
equipment) at the location selected. Excavation can be
minimised by locating the powerhouse on level ground. Think
about where the tailwater can be discharged (i.e. tailrace
alignment). Is the powerhouse high enough above the river
to be safe from floods?
TAILRACE
Make sure that the tailrace is protected from the stream into
which water emerging from the turbine is discharged. The
tailrace should be oriented downstream to prevent floodwater,
debris, and bed load from being funnelled into it toward the
powerhouse.
TRANSMISSION LINES
Is the village situated away from the powerhouse site? If so
transmission lines are required. The cost of transmission lines
adds significantly to the overall cost of a scheme. Consult
Ref.1 for details.
AVAILABILITY OF CONSTRUCTION
MATERIALS AND LABOUR
Construction materials for micro-hydro schemes that may be
found at site are sand, aggregate and stones. Are these materials
easily available at site or brought from outside? Are skilled
labourers such as masons and carpenters and unskilled labourers
available at site? The unit rates for such construction materials
and labour should be obtained while at site for estimating
quantities and cost of the scheme during the design phase. It
is more relevant to use prevailing rates rather than district
rates, which are normally lower than the prevailing rates.
STABILITY
Apart from the above criteria, it is very important for the
entire scheme to be on stable ground. If a small length of the
alignment is unstable it may be possible to stabilise it. Refer
to Section 2.4 and Chapter 9 to assess this issue.
Photo: 2.3 A straight penstock run keeps cost at a minimun