(b) Diversion canal plant
Sometimes topographic, geological and hydrological conditions and
environmental and economic considerations may favour diversion-type
power development schemes. The flow from the impounded water in the
river upstream of the barrage is diverted into a power canal which rejoins
the river further downstream (Fig. 12.3), with the power station located
either next to the intake, or within the canal, or at the outlet. A rocky
stretch of the river containing rapids, where regulation could be difficult,
may be avoided by this type of layout. A fall of considerable height can be
developed by means of a diversion canal in a river valley with a relatively
steep slope.
(c) Storage plant (remote development)
The dam structure is separated from the power station by a considerable
distance over which the water is conveyed, generally by a tunnel and
pipeline, so as to achieve medium and high heads at the plants (Fig. 12.4).
The reservoir storage upstream of the dam increases the firm capacity of
the plant substantially, and depending on the annual run-off and power
requirements, the plant may be used as a baseload and/or peak-load instal-
lation.
(d) Pumped storage plant
Where the natural annual run-off is insufficient to justify a conventional
hydroelectric installation, and where it is possible to have reservoirs at the
head- and tailwater locations, the water is pumped back from the lower to
the headwater reservoir. This kind of plant generates energy for peak
load, and at off-peak periods water is pumped back for future use. During
off-peak periods excess power available from some other plants in the
system (often a run-of-river, thermal, or tidal plant) is used in pumping the
water from the lower reservoir. A typical layout of a pumped storage plant
is shown in Fig. 12.5.
500 HYDROELECTRIC POWER DEVELOPMENT
Fig. 12.3 Diversion canal plant
