Mangatepopo River tragedy
Posted 16 April 2008 // Carl Walrond
Extreme weather
The tragic drowning of six students and a teacher in the Mangatepopo River on 15 April, and a man and horse killed by lightning, marked a day of wild weather in the North Island.
The first reaction of many is to question how could students drown on a school trip? Many accidents have occurred on school camping trips in the past and the safety measures that schools need to take are much better than they once were – but no system is infallible.
It seems a flash flood swept down the river. This can readily be seen in graphs of flow levels, which rose very rapidly. Flash floods are not uncommon – it is just uncommon for people to be in a riverbed when they occur. For example 21 people were killed in the Kōpuawhara flood of 1938 when a 5-metre wall of water swept through a railway workers’ camp on the East Coast. Flash floods are caused by sudden downpours when many millimeters of rain fall in a few hours. For example on 30 May 2001, 109 mm fell at Leigh in one hour causing flash floods. Around 30-50 mm/hour were recorded in areas near the Mangatepopo River on 15 April, 2008.
Around 50,000 lighting strikes occur in New Zealand in a year but it is unusual for any one of these to hit someone – but occasionally it happens and one person is killed every five to ten years, on average.
While some rain warnings were in place for Taupō to Northland, in the locale of the Mangatepopo River it is not unusual for rain to be forecast – it rains some 200 days of the year. Those who look back at events are in a privileged position. As accident researcher James Reason noted in his 1990 book Human error:
There is one obvious but psychologically significant difference between ourselves, the retrospective judges, and the people whose decisions, actions or inactions led to a disaster; we know how things were going to turn out, they did not.
