Environmental Engineering Reference
In-Depth Information
Figure 7.24 The tidal power plant at Annapolis Royal, Nova Scotia, Canada. In the foreground is the
entrance to the power house from the tidal pool; in the background is the exit into the tidal waters of the
Annapolis Basin.
The hydroturbine of a tidal power plant operates at a low head that is somewhat less than the
tidal ran ge H (see Figure 7.22). This requires an axial flow machine with a low flow velocity of
about gH . The turbine axis must be located below the lowest water level in the cycle so as to
avoid cavitation, so the turbine diameter is generally less than H . The maximum power from a
single turbine is of the order of
2 H 2 , which works out to about 10-30 MW for practical
plants. For large installations, multiple turbines are required.
Environmental Effects
The principal environmental effects of tidal power plants are a consequence of the changes to the
tidal flow in the pool and, to a lesser extent, the ocean exterior to the pool. For a single effect plant,
the flow into the pool is reduced by about half, decreasing the intertidal zone by about the same
amount and reducing the average salinity of the pool waters when the pool is an estuary, both of
which alter the nature of the original marine ecosystems. The plant also imposes an impediment
to the movement of marine mammals and fish. The patterns of siltation, often a significant natural
process at sites having large tidal ranges, is changed by the presence of a tidal plant. Ship navigation
into the pool is prevented unless a lock is built into the dam. The unpredictable and possibly adverse
changes to existing ecological systems, including fisheries and other wildlife, has weighed heavily
in the assessment of proposals for new tidal power plants.
The damage to ocean shorelines caused by storm-driven waves is ample evidence of the dynamic
power released when waves impinge on a coastal shore. It would seem that harnessing the power
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