Hicoissox.—On Floods in Lake Districts. 181 
While watching the water rising on the morning of the 18th, I 
observed that a mark which I had placed on the shore became rapidly 
covered and shortly afterwards exposed again, the surface of the lake being 
at the time perfectly calm, not a ripple ruffling it. 
As I found it difficult to account for this, I made more careful observa- 
tions for upwards of an hour, the result of which was that I ascertained 
there was a rise and fall of three inches in the level of the water at intervals 
of five minutes, which was maintained with perfect regularity. This rise 
and fall was extremely gradual, so that it was quite imperceptible on the 
smooth surface. After 1 p.m. a breeze sprang up, preventing a further 
continuance of my observations. I was unable at the time to aceount for 
this disturbance satisfactorily, but was inclined to attribute it to a 
slight earthquake, possibly too faint to be noticed. 
In conversation with Mr. Worthington, the Meteorological Observer, the 
next morning, I mentioned what I had remarked. He informed me that he 
had himself noticed the same rise and fall on a larger scale, after one of the 
heaviest floods experienced ; consequently it at once pointed to the floods 
being in some manner the cause, though at first sight it seemed impossible 
for any flood to have such an effect on a body of water nearly fifty miles 
in length and of great depth. 
Having repeatedly thought over the matter without being able to 
account for it in a satisfactory manner, I put together a few facts relating 
to the natural features of the lake with reference to this flood, in order to 
assist me in coming to some conclusion, which I therefore beg to suggest to 
you. Ihave also tabulated the effect of this flood in conjunction with some 
that have occurred in the European Alps, in districts bearing similar 
features, the information being taken from Beardmore’s ** Manual of 
Hydrology.” 
Lake Wakatipu is nearly fifty miles in length, and varies between one- 
and-a-half and three-and-a-half miles in breadth, its area scaled from the 
map being 118 square miles. Its drainage area is about 1,200 square miles, 
principally at the northern extremity, where the water-shed is the main 
range of Southern Alps drained by the rivers Dart and Rees. These two 
rivers flow into the extreme northern apex of the lake, having a drainage 
area of 400 square miles or a third of the whole commanded by the lake, 
including the portion covered with perpetual snow and glaciers. 
The rise of two feet in the level of the lake means 1,828 cubic feet of water 
per minute per square mile impounded. At the same time the river Kawarau 
at the outlet was discharging 500 cubic feet per minute per square mile 
based on the rainfall for the first sixteen days in November. This makes a 
total of 2,323 cubic feet per minute per square mile run off the drainage area 
