of floods. The height of the dam was 116.7 ft. and was provided with a
by-wash of 394 ft. in length, and outlets for irrigation formed by four
cast iron pipes of 311/2 in. diameter through the dam. It was composed of
rubble set in hydraulic mortar, the latter composed of two parts of sand
to one of hydraulic lime.

For getting rid of the large deposits of sand to which all reservoirs in
that country are liable, two scouring outlets were provided of the same
description as those in the old Moorish dams. The profile was calculated
from Delocre's formula, and was correct in this respect, supposing the
by-wash to have been sufficient. But as it was otherwise, and the flood
swept over the crest to the depth of about 3 ft., the enormous extra
strain thus induced overthrew the dam and caused the destruction of
several villages and the death of 209 persons. It must be mentioned that
when the reservoir was filling, the water percolated through the masonry,
giving the face wall the appearance of a huge filter, which at the time
was attributed to the porous nature of the sandstone used in
construction, but which more probably was due to the washing of the green
mortar out of the joints.

At the Hamiz dam, also in Algeria, the water was admitted in 1884, but it
showed immediately signs of weakness, so that the water had to be run out
and an immense retaining wall erected to strengthen the main dam. Algeria
seems to have been singularly unfortunate as regards the success of works
of this description. Water was admitted to the Cheurfas reservoir in
January, 1885, and it at once began to make its way through permeable
ground at one end of the dam. The flushing sluice in the deepest part of
the dam had become jammed, so that the pressure could not be relieved,
and in February 30 ft. length of the dam was carried away, causing a
flood in the river below. At some distance down stream was the Sig
reservoir. The flood rushing down, topped this dam by 18 ft. and
overthrew it also.

Allusion has been made to provision for scouring out sand and deposit,
especially in the dams of Algeria and of Spain. The amount of sand, etc.,
brought down by the floods is something enormous, and the question of the
best means of getting rid of it has occupied much attention. In the old
Moorish reservoirs the flushing gallery, piercing the lower part of the
dam, was closed by iron doors on the down stream face and blocked with
timber at the upper end. When