DAMAGE BY FLOODS IN RIVERS PREVENTION. 647 
- what will happen to the Nile, now being dammed at Assuan / 
The answer is, that it is more than likely that in a number 
of years the reservoirs formed by the dam will be silted up 
to about the level of the sluices; but the sediments at this 
part of the river are most likely nothing but fine silt, and 
of this_a much larger’ proportion can be washed out 
through the sluices than of the heavy sands and gravel found 
in the upper waters of the Hunter. But of course a fuller 
answer is; that in the flood reservoir of the Hunter 
it is the space that is wanted to hold back the flood; while 
the Nile dam is wanted to lift the flood water to the 
higher level required to irrigate land which the water could 
not reach without the dam, and there is no question here 
of holding back any water; in this sense, therefore, the 
Nile dam is permanent. 
Now, to hold back a flood, one should have some idea of 
when it is coming, and in this respect Col. Pennycuik took 
for granted that. the floods of the Brisbane are sure to 
happen in the rainy season, which is the summer in Queens- 
land; and, as far as I know, floods do not happen there 
except in summer. Brisbane is very near the turning 
point, but as you go south the rains gradually change 
from summer rains in the north to winter rains in the south, 
and the records which I collected of the Hunter floods . 
show that from 1856 to 1898 there were 35 great floods, 
eight of which were “Oldman” floods; that no Months 
of the year, except October, were without floods; that 
seven great floods came in pairs—that is, one closely follow- 
ing the other; that in 1870, from the middle of March to 
the middle of May, six floods followed each other, none of 
which waited till the previous one had subsided before 
it caine on ; that in 1861 there were five great floods between 
March and August; and that of 42 years observed, 27 years 
had no great floods, and’ of the 15 years with floods they 
had no regularity other than this classification—that 10 
were summer floods, 17 winter floods, 2 were spring floods, 
and 6 were autumn floods. 
To show the difficulties of dealing with floods in this 
way, I will quote from my report to the New South Wales 
Government on this subject: (p. 10). “I do not know how 
a flood stopped back in this reservoir would be disposed 
of. No one can tell what rainfall will cause a flood. 
There was a case here where 4 inches of rain in 24 hours 
did not raise the Hunter nor Goulburn more than a few 
feet, because the rain was preceded by nine months of 
drought, yet the 1893 flood, the greatest ever experienced, 
