295 
1918.] The N.Z. Journal of Science and Technology. 
In the Panama Canal zone, at Alhajuela, the Chagres River, which has 
a drainage area of 427 square miles, gave a maximum discharge per square 
mile of 400 cusecs. This is a remarkable discharge from such a large 
area, particularly as much of the area is in dense jungle. To compare 
this with the discharge per square mile of the Mangakahia River, where 
the drainage area is more than half cleared of bush, the ratio of A? would 
give a corresponding discharge, for an area of 427 square miles, of 
500 cusecs per square mile. This is 25 per cent, above that given for the 
actual discharge of the Chagres River, where measurements were very 
carefully taken ; but if there were a larger proportion of cleared land on 
that river the discharge would no doubt reach 500 cusecs in phenomenal 
floods. 
The rainfall in the Panama Canal zone is very similar to that of the 
Mangakahia Valley, having an average of about 120 in. to 130 in. per 
Drc* i nofoje Ore as in Sep Miles 
Diagram of the records of the rivers in Table II. Numerals on diagram 
refer to numbers given to rivers in Table II. 
annum. It would be interesting and most instructive to be able to 
obtain a comparison between the actual rainfall and the run-off from the 
drainage areas, but unfortunately the rain-gauge records are only taken 
every twenty-four hours (at 9 a.m. each day), so that maximum rates 
of precipitation which might be compared with the figures in column 6 
of Table II are not available. The author is convinced that the rate of 
run-off must have been very nearly equal to the rainfall, if not quite equal 
to it. The relation of rainfall to run-off depends on various factors, but 
principally on class of soil, steepness of country, and saturation of the 
ground. 
The country in which the floods were recorded was steep country, and 
the soil was in part impervious clay soil and in part papa rock, from which 
the water would run off very quickly. The state of saturation of the 
ground, which was waterlogged by continuous rain, contributed mostly, 
in the author’s opinion, to the rapid rate of run-off, and this confirms his 
