Ocean power in New Zealand speed. Because the tidal speed doubles, eight times more tidal power can be produced at spring tides than at neap tides. The entrance to Kaipara Harbour, one of the largest harbours in the world, is a channel to the Tasman Sea. It narrows to a width of , and is over deep in parts. On average, Kaipara tides rise and fall . At high tide, nearly 1000 square kilometres are flooded. Spring tidal flows reach 9 km/h (5 knots) in the entrance channel and move 1,990 million cubic metres per tidal movement or 7,960 million cubic meters daily. In 2011,
International Convention Relating to Intervention on the High Seas in Cases of Oil Pollution Casualties International Convention Relating to Intervention on the High Seas in Cases of Oil Pollution Casualties International Convention Relating to Intervention on the High Seas in Cases of Oil Pollution Casualties 1969 (INTERVENTION 1969) is an international maritime convention affirming the right of a coastal State to "take such measures on the high seas as may be necessary to prevent, mitigate or eliminate grave and imminent danger to their coastline or related interests from pollution or threat of pollution of the sea by oil, following upon a maritime casualty or acts related to such a casualty". The 1967 Torrey Canyon disaster