The above measures can be used singly or jointly. However, it must
be emphasized that although they can reduce the surges from power plants
to an acceptable level they cannot eliminate them completely. The
optimum control of a whole cascade of plants is usually best developed by
the use of mathematical modelling, combined with field measurements.
The winter regime also has to be taken into account in these studies.
The layout of a barrage with a power plant, navigation lock(s) and
their approaches requires careful consideration of the respective functions
of the individual components of a complex hydraulic structure. This may
result in different layouts on small and large navigable rivers and on navi-
gation canals.
On smaller rivers and at older works the general layout usually fol-
lowed a scheme with the navigation lock and power plant having parallel
axes and being situated on either side of the weir or barrage, with the lock
separated from the river by a long narrow dividing wall (Chapter 12). A
better solution adopted in newer structures is one where the lock is sepa-
rated from the river by an island, and the turbine axes (forebay and tail
race) are set at an angle to the direction of flow in the river (Fig. 11.4).
This arrangement prevents scour at the dividing walls of the power plant
and lock and results in improved efficiency both of navigation and of the
power plant. On large navigable rivers the considerations governing the
layout are more complex and usually also have to take into account prob-
lems of sediment transport, ice, etc. (Kuhn, 1985 and Chapters 9 and 12).
The design of a barrage with power plant(s) and lock(s) on a river
forming an international boundary may even call for a symmetrical
arrangement, with two power plants and two sets of locks on either side of
the river.
Details of a suitable layout of a complex water resources utilization,
particularly one involving hydropower development and navigation, are
best studied on scale models (Novak and Cˇábelka, 1981).
468 INLAND WATERWAYS
Fig. 11.4 Barrage (1) with power station (2) and navigation lock (3) (after
Novak and Cˇábelka, 1981)
