299 



v.— MISCELLANEOUS. 



Art. LV. — On Changes in the HoTcitika River. By James Rochport, C.E. 



(With. Illustrations.) 



[Read before the Wellington Philosophical Society, November 12, 1870.] 



From March, 1865, to November, 1869, it fell to my lot to watch the action 

 of the floods on the banks of the Hokitika Eiver, in Westland, and also the 

 action of the sea on the sand and shingle forming the sea-beach there, and 

 thinking that if made public, a knowledge of the facts that occurred might be 

 of some use in similar cases, I beg to state such as I have been able to gather. 

 The accompanying drawings (Nos. 1, 2, 3, 4, and 5) show the changes in the 

 form of river mouth and banks at the dates noted on them, and the diagram 

 (No. 6) shows the rainfall curve during 1865-6-7 and 8, from the meteorological 

 observations taken at Hokitika by my brother and myself. 



RIVER MOUTH AND SEA-BEACH. • • 



The sea-beach at Hokitika is composed of sand and loose light gravel, 

 continually shifting with the action of the waves and currents, which some- 

 times set northwards and sometimes southwards, depending on the direction 

 and strength of the river current at the mouth of the river, where it meets the 

 sea. In June, 1865, the river channel on reaching within six chains of 

 the sea, was turned southwards, parallel with the coast line, by a spit of 

 sand half a mile long and six chains wide, and this spit was continually 

 altering in length and thickness, the river in floods cutting in very quickly in 

 the bend, and depositing the stuff" so taken away at its south end, adding to its 

 length, till, in February, 1867, its length had increased to fifty-four chains ; 

 this weakened it so much in the bend that, in April, 1867, the sea made a 

 breach there, washing the crown of the spit over into the river, each wave at 

 high-water washing over a certain quantity of material, and the continued 

 action of the sea thus shifted this part of the spit several chains inwards, at 

 the same time reducing its height considerably; and, on the 18th of April, 

 1867, during a flood, the river broke through at that part, cutting off* about 

 thii-ty-six chains. For some time after this occurred, the channel thus formed 

 was unstable, the mouth having no protective spit outside, and the north end 

 of the middle bank was driven in by the sea, until the water coming down the 

 lagoon and south channel of the river was prevented from reaching the sea by 



