CIVIL WORKS GUIDELINES FOR MICRO-HYDROPOWER IN NEPAL
1
1. Introduction
1.1 Hydropower and micro–hydropower
Hydropower is the generation of power (mechanical and/or
electrical) using the fall of water. In the context of Nepal, a
hydropower scheme with an installed capacity of less than
100 kW is classified as micro-hydro. Schemes in the range
100-1000 kW are classified as mini-hydro and share some
of the characteristics of micro-hydropower schemes. Apart
from the power output of schemes, some of the major
differences between large and micro-hydro are shown below
in Table 1.1.
SOME DEFINITIONS
Civil engineering is the application of science to the practical
building of safe and cost effective structures.
A structure is an assembly of materials which serves the
purpose for which it is designed (accommodate people,
convey flow, traffic, etc.) and carries the associated loads. A
civil engineering structure is specifically designed to fulfill
a purpose and/or perform a function at an appropriate quality
and to an acceptable time scale and cost.
Civil works are all activities necessary for the building of
structures.
Storage schemes make use of a dam to stop river flow,
building up a reservoir of water behind the dam. The water
is then released through turbines when power is needed.
Run-of-river schemes do not stop the river flow, but instead
divert part of the flow via a headrace and penstock to a
turbine. Therefore, the full power capacity (also referred to
as the Installed Capacity) is only generated as long as the
river flows permit. If the river flow is less than required for
full power generation, the power output decreases
proportionally. On the other hand when river flow is high,
the excess flow (i.e., flow higher than required for full power
generation) runs down the river without being utilised.
Sometimes a small pond is also constructed in run-of-river
schemes to store some water during off peak hours to
generate full capacity during the peak hours. Micro-hydro
schemes are almost always run-of-the-river type.
1.2 Aspects of civil engineering works
The design and construction of civil engineering works have
some important characteristics:
They are dependent on conditions at the site. No two sites
are the same.
They always involve structures that are in contact with the
ground. Design engineers may have control over the
materials used in construction, but have limited control
over the ground on which the structure stands. They must
therefore take into account the ground conditions, and may
have to consider alternative sites to avoid problems with
instability.
They often involve a number of people working on design,
supervision and construction at the site. Various skills and
materials are involved, usually over a period of several
months. Therefore planning, communication and
accountability are very important factors.
Failure of civil works can be very dangerous and expensive.
Similarly, poor performance or over-design are
uneconomical.
TABLE 1.1 Differences between micro-hydro and large hydro schemes
DESCRIPTION
MICRO-HYDRO SCHEME
Type
Power generation
Nature of intake
Tunnels & underground structures
Penstock alignment
Surge shaft
Distribution system
Unlined canal
Mostly run-of-river
Electrical and/or mechanical
Usually temporary or semi-permanent
Rare
Vertical & horizontal bends
Rare, forebay acts as surge tank
Isolated (i.e. not connected to
the national electricity grid) but could
be connected to the mini-grid.
Common
LARGE HYDRO SCHEMES
Both run-of-river and storage
Electrical only
Permanent
Common
Fewer vertical and horizontal bends
Common
Mostly grid connected
Rare