Notes upon the great Floods of February, 1868
by W. T. L. TRAVERS, F.L.S. (Extracts of only)

Transactions and Proceedings of the New Zealand Institute 1881


In February 1868, the northern part of the South Island was
visited by an extraordinary rainfall, which did a large amount
of damage and left indelible marks of its occurrence wherever
the waters of the main rivers rose above the height of ordinary
floods.

The quantity of rain which fell within the first few hours was
so great as to fill every stream bank high, and as the rain
continued to fall almost as heavily for many hours after that
had occurred, the main rivers not only became enormously flooded
within a singularly short period, but maintained their flooded
condition for an unprecedented length of time. Many causes, too,
resulting from man's foolish and wanton interference with
natural operations, had contributed to bring about a rapid
accumulation of the rainfall in the main rivers.

The forest had been cleared by fires and otherwise, but 
principally by fires, from a large extent of the eastern slopes 
of the mountains in the very localities in which the ordinary 
rainfall is usually heaviest.

My first journey took place within a fortnight after the floods 
had subsided, and was from Christchurch to Nelson, visiting on my
way a cattle-station which I then held, in the heart of the
Spencer Mountains. My route, after leaving the Canterbury Plains,
lay through Weka Pass to the Hurunui and Waiau-ua Plains; from
thence through the second gorge of the Waiau-ua, to the Hanmer
Plain; across that plain to Jack's Pass; and over the pass into
the Valley of the Clarence; and then into my station on the
Upper Waiau-ua, by Fowler's Pass. From my station to Nelson, I
crossed Maling's Pass to the head of Lake Tennyson; thence over
the Island Saddle to the head waters of the Wairau, and through
the Wairau Gorge, and the upper valley of that river, to the
Top House; and thence through the Big Bush, to Nelson.

The first thing that struck me was the enormous quantity of
water-borne timber which was lodged upon the surface of the
Hurunui Plain, every part of it which had been reached by the
flood-waters being strewed with such timber in the most
extraordinary manner.

I was told, moreover, by a person who stood on the terrace above
the Hurunui, so as to command a view of the line of the ordinary
channel of the river, that the waters in that line appeared to
run at a height of from three to four feet greater than the
general level of the water spread over the plain, and that the
roar of the shingle which was being carried down was like that
of distant thunder.

I was informed by shepherds and stockmen well acquainted with
the forest tracts on the surrounding mountains, that every atom
of fallen timber had been washed out of the innumerable gullies
and ravines by which their slopes are furrowed, and that the
beds of all the streams which flowed in them appeared to have
been cleaned out to the very rock, few of them retaining even
the slightest trace of the shingle and other materials which had
previously lain in them.

At the point where the waters of the Pahau joined those of the
Hurunui, timber was banked up to the height of upwards of
thirty-five feet, and a bed of silt was deposited varying in
depth from a few inches to upwards of ten or twelve feet and
covering an area of several hundred acres. This silt-bed
remained so soft for many months after the subsidence of the
waters, immediately below the dry crust which formed on its
surface, that cattle which got on to it from the bank above,
attracted by the young grass which soon grew upon it, sank
into it and were smothered.

The hills were scarred with innumerable small isolated slips...
not less than one-twentieth part of the surface of a large
proportion of the hills had been rendered useless by these
peculiar slips.

Chasms..., in some instances ten and twelve feet deep, the
bottoms and sides of which are clean solid rock, have taken
the place of beds of shingle which had formerly filled them
up to the general level of the ground, the consequence being
that a considerable number of bridges have had to be
constructed on the line of road along the main terrace, in
order to permit the wool-drays to pass over across the beds
of these streams in places which had previously been forded
without the slightest trouble.

In the gorge of the Wairau... the river flowed for miles over
a bed filled with huge boulders, but the immediate effect of the
tremendous rainfall referred to had been, that all the loose
angular detritus previously lying in the beds of the lateral
torrents was washed out of them, forming, in some instances,
enormous mounds, the bases of which were cut away by the waters
of the main river, the effect being that the interstices between
the boulders in its bed were filled up, for many miles of its
course, changing the surface of this bed from one on great
ruggedness to the smoothness of a macademized road, and giving
to the river the appearance of a beautiful purling stream
instead of that of an impetuous brawling torrent. In process of
time the major portion of the small stuff thus distributed over
the bed of the river will be removed, but when I last passed
through the gorge, eight years after the occurrence of the flood
in question, the places where I forded the river still retained
the even smoothness which had followed from the great flood.

The downfall of nearly thirteen inches of rain, in the course
of three days, over an area of thousands of square miles of
steep mountain country, was unquestionably calculated to produce
a catastrophe in the level areas through which their drainage
passed to sea...