APPENDIX, No. I. FLOODS (FRESHES) IN THE RIVER RAKAIA.
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APPENDIX, No. I.
FLOODS (FRESHES) IN THE RIVER RAKAIA.
Thinking that it might be desirable to have some information collected which would give us reliable data concerning the floods in our main rivers, I requested Mr. Edwin Fereday, who since 1858 has noted regularly the state of the Rakaia, to give me a copy of his journal, to which this gentleman (to whom I owe already many obligations for a great deal of valuable information and guidance in my researches) most readily assented.
As his original notes would take too great a space to be printed in extenso, and, moreover, would not give the same insight as if properly tabulated, I have prepared the annexed table, which, at a glance, will give the requisite information on that subject.
It will be seen that I have divided the freshes in three categories, viz.:
Slight Freshes--when a horseman or dray can still cross, the river being risen only from one to two feet.
Middle Freshes--those in which the river is impassable for ordinary traffic, but when it is confined to its principal channels, so that a boat could be worked to bring passengers across; and
Heavy Freshes, or Floods--when the whole or nearly the whole of the broad shingle bed of the river is filled with water, even rising over its banks and overflowing the plains; when the whole traffic is stopped, and the river works out new channels either by filling up its former ones or by scooping out others in higher parts of its flood bed.
The table suggests some very important conclusions, which in bridging the river will be of a highly practical value.
It will be seen that the principal freshes are during the summer months, and that there is generally a very heavy flood before the winter sets in, namely, towards the end of April or beginning of May; that afterwards, when such a tremendous flood has taken place, the river has been very low during the winter months, and that only heavy freshes occur again in such normal years, sometimes end of August, but only generally in the course of the month of September. The only exception to this rule occurred in 1863, when the last heavy fresh had taken place in November, 1862.
Thus the whole summer of 1863 passed without any great floods, but the winter months were remarkable for their occurrence, as if the anomalous conditions of the summer ought to be counterbalanced by equally anomalous ones during the winter.
Although we have thus only one example that the heavy autumn fresh did not happen, we may nevertheless conclude, that if it occurs end of April or beginning of May, we may reckon, with great probability, that the following winter will allow us to carry out engineering works for several months, without fearing that they will be seriously disturbed through similar causes.
And in order to have for the future a continuance of these valuable observations, would it not be desirable that the necessary scales, for measuring the height of water, should be placed at all the principal rivers, and that the ferryman at each of them be instructed to note regularly the state of the river
These observations would offer interesting data for comparison, which in course of time would be invaluable to the Province in more than one respect.
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TABLE showing the FLOODS in the RIVER RAKAIA, during the years from 1858 to 1864.
The Numbers in the Columns denote the date of the day of the months on which Floods occurred, and the length of their duration.
