ES SS eee SO ee ee ee ge ee re ee 
Se et ee ee ee 
Dozson.—On the Reclamation of River Beds. 101 
flood-waters were the source of the fertility of lower Egypt, river works 
were undertaken with a view to obtain the advantage of the overflow on 
the greatest possible area, and the flooded lands were raised annually by 
this process, as well as the river bed itself. 
This cannot happen in the case of torrents carrying large quantities of 
shingle and sand, which are brought down in times of flood and left in the 
channels as the velocity of the stream decreases, and although much may 
be done towards raising the adjoining lands by inducing an overflow of flood 
water upon them, the floods will always bring down from the upper levels 
masses of material that it has no power to move along the lower course. 
This is the problem the Italian Engineers have had to deal with in the 
management of the Po and its tributaries. 
The general system in Europe for conservation seems to be to wall in 
the river between embankments with the endeavour to make it carry its silt 
as far forward as possible, making traps for catching shingle ; where possible 
raising adjoining lands by ponding up flood-water upon them; and many 
other expedients for keeping the rivers from changing their courses and 
wandering about their fans into new courses: The great drawback to this 
treatment is, that however much (within certain limits) the river may be 
embanked, it continually raises its bed, and the banks must be raised in 
proportion. 
To such an extent has this been done that some of the Italian rivers are 
now far above the level of the adjoining lands, so that the surface drainage 
of the country has to be carried in other channels, involving all kinds of 
complications in the drainage; and should the embankments fail, immense 
volumes of water may be dammed up on the low-lying land by the banks 
which were built for their protection, entailing great loss of life and pro- 
perty. Such a disaster occurred not long since in Hungary, at Szegedin, 
on the River Theis. 
When we consider the enormous cost that would be incurred in 
attempting to control our great torrents by any system of solid embank- 
ments, it becomes apparent that we must either invent some plan which 
can be carried out on a much cheaper scale, or else let matters take their 
course. 
Doubtless weak places may be defended by groins and spurs; and the 
more chance will there be of success so long as only one side of a river is 
being worked upon. But so soon as works are undertaken on both sides of 
a river, they will have to be more or less continuous embankments, which 
must be made of permanent materials, involving immense expense. 
On the Canterbury Plains the conditions are most favourable for the 
formation of broad shingle beds, the loose shingle banks offering no resistance 
