CIVIL WORKS GUIDELINES FOR MICRO-HYDROPOWER IN NEPAL
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Box 5.2 Ghandruk peaking reservoir
The design flow of the 50 kW Ghandruk micro-hydro scheme is 35 1/s but the dry season flow is only 20 1/s. Hence during the
dry season the power output was about 39 kW until a peaking reservoir was built in 1994. Such a peaking reservoir became
necessary because of the demand for full power (50 kW) in the village during the mornings and evenings. There is nominal power
demand in the afternoon and even less during night time.
A suitable site for the reservoir was located on the terrace immediately downstream of the old forebay. Photographs of the
peaking reservoir during and after construction can be seen below.
Photo 5.15 Ghandruk peaking reservoir after construction
Photo 5.14 Ghandruk peaking reservoir during construction
The walls and the floor of the reservoir were constructed of stone masonry in cement mortar. The reservoir has been sized such
that it can provide the design flow of 35 1/s for at least six hours (3 hours in the morning and 3 hours in the evening). The
calculations are as follows:
Storage volume required = (Design flow - dry season flow) x 6 (hr) x 60 (min/hr) x 60(s/min) = (35 - 20) x 6 x 60 x 60 = 324,000
litres or 324 m3
Hence a reservoir with a minimum storage capacity of 324 m3 is required to be able to provide 50 kW for six hours. The actual
dimensions of the reservoir are as follows:
Length = 20 m . Width = 20 m
Depth = 1.2 m
Hence, the storage volume is 480 m3, about 48% larger than the minimum required volume. Note that the old forebay has now
become redundant. Also, since the peaking reservoir is downstream of the old forebay, a few metres of head are lost. This is
compensated by slightly increasing the design flow.
Any sediment deposited in the reservoir is manually cleaned during the annual maintenance period. A flushing facility was not
installed because of potential erosion and landslide problems due to the large volume of water involved.
At present the power plant is shut when there is no demand for power, then the reservoir is allowed to fill.