Cook Strait
| Animation of the tides in Cook Strait – NIWA | |
| Cook Strait currents before and after high tide at Wellington – Te Ara: Encyclopedia of New Zealand. | |
| Underwater topography of Cook Strait – NIWA |
Cook Strait has tidal flows amongst the strongest in the world, even though it has a smaller tidal range than most places in New Zealand. This is because the main M2 lunar tide component which circulates anti-clockwise around New Zealand is out of phase at each end of the strait. On the Pacific Ocean side the high tide occurs five hours before it occurs at the Tasman Sea side. On one side is high tide and on the other is low tide. The difference in sea level can drive tidal currents up to 2.5 metres per second (5 knots) across Cook Strait as well as into the Tory Channel.
A further consequence of these opposed tides is that there is almost zero tidal height change at the centre of the strait. Although the tidal surge should flow in one direction for six hours and then the reverse direction for six hours, a particular surge might last eight or ten hours with the reverse surge enfeebled. In especially boisterous weather conditions the reverse surge can be negated, and the flow can remain in the same direction through three surge periods and longer. This is indicated on marine charts for the region.
There are numerous computer model representations of the tidal flow through Cook Strait. While the tidal components are readily realizable, the residual flow is more difficult to model.
In April 2008, a resource consent was granted to Neptune Power for the installation of an experimental underwater tidal stream turbine in the strait. The turbine has been designed in Britain and will be built in New Zealand at a cost $10 million. Fourteen metres in diameter and constructed of carbon fibre, it will be capable of producing one megawatt. It will be placed in eighty metres of water, 4.5 kilometres due south of Sinclair Head, in waters known as the “Karori rip”. Power from the turbine will be brought ashore at Vector's Island Bay substation. The turbine is a pilot, and will be sited in slower tides for testing. Neptune hopes to generate power from the unit by 2010. The company claims there is enough tidal movement in Cook Strait to generate 12 GW of power, more than one-and-a-half times New Zealand's current requirements. In practice, only some of this energy could be harnessed.
On the other side of the strait, Energy Pacifica has talked for some time about applying for resource consent to install up to ten marine turbines, each able to produce up to 1.2 MW, near the Cook Strait entrance to Tory Channel. They claim Tory Channel has tidal flows of 3.6 metres per second with good bathymetry and access to the electricity network. No application had been lodged by March 2011.
The power generated by tidal marine turbines varies as the cube of the tidal speed. Because the tidal speed doubles, eight times more tidal power can be produced at spring tides than at neap tides.
Read more about this topic: Ocean Power In New Zealand, Tidal Power
Famous quotes containing the words cook and/or strait:
“Women find ways to give sense and meaning to daily life—ways to be useful in the community, to keep mind active and soul growing even while they change diapers and cook vegetables.”
—Lillian Breslow Rubin (20th century)
“We approached the Indian Island through the narrow strait called “Cook.” He said, “I ‘xpect we take in some water there, river so high,—never see it so high at this season. Very rough water there, but short; swamp steamboat once. Don’t paddle till I tell you, then you paddle right along.” It was a very short rapid. When we were in the midst of it he shouted “paddle,” and we shot through without taking in a drop.”
—Henry David Thoreau (1817–1862)