6 CIVIL WORKS GUIDELINES FOR MICRO-HYDROPOWER IN NEPAL
3.00 during 7 months of the wet season along with provisions
for 6 per cent price escalation during the first 5 years of
operation.
It should be noted that designers have little control over the
flow available in the stream. However, they have some control
over the topography. They can choose different alignments
for the intake, headrace and penstock. They can also modify
the local topography through excavation, building of
structures and by undertaking soil stability enhancement
measures.
Although the planning of micro-hydro civil works does not
require the detailed work of large projects, the principles are
the same and care needs to be taken to follow some basic rules.
Proper planning and co-ordination in the initial stage of the
project will keep costs to a minimum and reduce delays.
Measurement of head and flow are beyond the scope of these
guidelines but full descriptions of the methods used can be
found in a number of texts including Ref1.
2.2 Principles of site investigation
Site investigation is the preliminary work carried out to establish
the suitability for construction of the various options (or the
most feasible option if it is apparent) through the investigation
of soils, slope stability, flood levels, surface water movement
and subsidence. This is discussed later in this chapter.
In most civil engineering work, the unexpected happens. Site
investigation aims to predict what this might be so that the
engineer can prepare a design that will deal with it.
It should be noted that the measurement of head and flow
serves to establish the options available for development of
the site for micro-hydro. The site investigation then assesses
the suitability of the site for each alternative. The site
investigation process helps to choose the optimum layout
where more than one option appears to be feasible. Site
conditions are also recorded during the site investigation
stage so that there is adequate information for the detailed
design phase.
There is usually a limit to the time and funds available for site
investigation. It is always difficult to know when adequate
work has been completed. The key is to work efficiently and to
think carefully about where more thorough investigation is
required. The principles of site investigation are:
Take adequate time and be thorough. A return visit to collect
information missed the first time is costly, and inadequate
civil design even more so.
Visit all possible sites. Gain a full appreciation of the options
available.
Talk to local people, especially those who have carried out
construction work in the area. Since most of the rivers in
the mountains and the middle hills of Nepal have not been
gauged, stream flow data are not usually available.
Therefore, it is important to talk to local people to get a feel
of the flood levels for rare flood events (say 20 years to 50
years return period).
Stay focused on the overall, aim to raise the understanding
and awareness of changes in the site over time.
2.3 Selection of alternative layouts
2.3.1 AN OVERVIEW OF THE SITE
This will involve viewing the site from a physical vantage
point as shown in Figure 2.1, and taking time to consider the
practical design and construction of the alternative layouts
(i.e, selected potential sites). Each possible layout will require
construction work on different parts of the potential site and
the surveyor should therefore note on which part each compo-
nent of the scheme will be located. The overview should note
features that may affect the design of the scheme, such as
slope stability, and land use and ownership. A sketch map of
each site plan should be made as shown in Figure 2.2.
2.3.2 POSSIBLE PROJECT LAYOUT ARRANGEMENT
Different project layout arrangements are generally possible
for a given site based on topography, flow availability, nature
of the river and the demand form the load centres. It is
important to select the optimum project layout arrangement
based on site conditions, cost and expected performance of the
micro–hydropower plant. Project layout arrangement also differs
from project to project and not a single project layout
arrangement will be similar to another. Thus the establishment
of the optimum project layout needs experience as well as a
number of iterations. Some typical project layout
arrangements that maybe applicable for a micro hydro site in
Figure 2.0: Types of project layouts
Nepal are shown in Figure 2.0.
From Figure 2.0, it can be seen that the weir, intake and
powerhouse are the essential components for any micro–hydro
project although their type and dimensions can differ from