﻿DoBSON. — On Destruction of Land hy Shingle-hearing Rivers. 153 



Art. XYI. — On the Destruction of Land hy Shingle-hearing Rivers, and 



Suggestions for Protectioii and Prevention. 



By A. D. DoBSON, Provincial Engineer, Nelson. 



[Eead 'before the Nelson Association for the Promotion of Science and Industry, 

 Gth December, 1871.] 



The great loss of land and damage occasioned to property yearly in New 

 Zealand, is a matter which is rapidly assuming a more and more serious 

 aspect ; and although at present, as a general rule, the greater portion of the 

 land destroyed is of no great value, nevertheless in many places on the banks 

 of the smaller rivers considerable quantities of valuable land have been lost, 

 in some instances entailing great expense and heavy loss to the owners and 

 occupiers. For instances we need not go far in the Nelson province. Both 

 the Motueka and V/aimea rivers have widened their beds considerably ; 

 the former was, twenty years ago, only a few chains, but is now in many 

 places nearly half a mile wide, and is rapidly filling \xp its bed with shingle 

 brought down by the floods, and cutting new channels in the alluvial flats 

 adjoining. Between the lowest ferry and the upper part of Pangatotara, 

 several hundreds of aci-es have been destroyed during the last few years, and 

 the river is now rapidly destroying some of the best land in Biwaka. The 

 Waimea, although of considerably less volume than the Motueka, is con- 

 tinually encroaching upon the adjoining alluvial lands, every flood doing more 

 or less damage. This has been particulaidy the case above Appleby, and again 

 near "Wakefield and Fox-hill, To take larger examples, we have the Waii-au, 

 which has always been a source of great anxiety, danger, and loss, to the 

 inliabitants of the plains near Blenheim, The Waimakariri, in Canterbury, 

 has encroached enormously on the alluvial land lying to the northward, and 

 caused a great amount of damage to the farmers by the loss of crops, home- 

 steads, and land. In fact, all the shingle-bearing rivers of the country are 

 continually altering their beds and destroying adjoining land. 



In order to correctly appreciate the causes which make this the rule, it will 

 be necessary to consider the general characteristics of shingle-bearing rivei-s 

 and the country which they drain. The greater number of the rivers in the 

 Middle Island of New Zealand are, more correctly speaking, mountain torrents, 

 which rise in lofty mountains and run but a short distance before reaching the 

 sea ; they are subject to very high and sudden floods, which occur in the spring 

 and early summer, from the melting of the snow by the warm i-ains. The 

 greatest floods occur generally in the streams which are fed by the glaciers in the 

 Southern Alps, the warm northerly rains which fall on the glaciers and exten- 



