DOWN TO THE SEA IN SLIPS
The wide sweep of a riverbed strewn with high-heaped shingle is a common sight to all Hawke‘s Bay people. This view of the Ngaruroro riverbed at Whanawhana is typical of the three rivers which treaten the security of the Heretaunga Plains – the Tukituki, the Ngaruroro, the Tutaekuri.
All three have been steadily raising their riverbeds since the turn of that century, and will continue to do so. The few tons of shingle removed by draglines and shingle works are just pea-metal compared with the thousands of tons that stream down our rivers each year. On the stretch of river pictured above, the rise in the bed level (or aggradation) is believed to have been 12 feet since 1900 – one foot every ﬁve years. In fact, this shingle could prejudice all the present flood control schemes. (See flood feature in September 1961 Photo News)
How long can stopbanks on the plains cope with this creeping menace? And more important – what can we do to halt its advance?
To answer these questions we must go inland to the ranges – particularly the Kaweka range where both the Ngaruroro and the Tutaekuri rise.
New Zealand lies squarely on the ring of earthquake-prone countries which encircles the Pacific Ocean. In its history it has experienced much earth movement that has not only raised the mountains we know, but also, later, shattered the rock of which they are formed.
This shattered rock has created what one expert calls the “basic vulnerability” of our mountains.
Until modern times our ranges were clothed almost entirely in beech forest with its accompanying undergrowth. Man – Maori and European – in his ignorance burnt large tracts of bush. Erosion followed rapidly and soon meagre topsoil had been carried away.
Unlike the solid granite or slate mountains of Europe, our mountains are crumbly and broken. A fall of rock, once started, continues to grow, encroaching on the remaining bush and filling rivers with shingle.
The bush still covers thousands of acres of lower mountain slopes, but this too is in danger of extinction. Once again, man in his ignorance introduced deer, pigs, opossums and goats. Together they are slowly but surely killing the beech forests – our protection.
Photographs in this series loaned by the New Zealand Forest Service.