, 1891-10-17

AOOU, Uuph OAO WIN 1VN6O WN0
a safe anchorage for the DAM This surface of
bed rock was thoroughly grouted with pure
cement. The dam was built in two sections
rather than as a mass, d dam 60 feet In height
having been nearly completed when the COM
pany decided to extend it to a height of 80 feet.
This enlargement of the plan was resolved on
after more complete surveys of the watershed
and of the reservoir basin had shown that such
an extension would increase the capacity of the
dam nearly five-fold It was found that while
the 60-foot dam would impound 1921 100000
gallons of water, a 90-foot dam would accumu-
late 1882, 10 900 gallons.
The dimensions of the dam as completed are:
length at base, rs feet length at top, 1876 feet;
thickness at base, 46 feet; thickness at top, IL
feet; height of dam from bed rock, 80 feet;
radius Of arch 222 feet on line of face at top.
The face batter of l to 6 was carried to within
6 feet of the top thence to top of parapet wall
vertical. The batter on the back started atop
with l to 3 TO % feet; thence ] to 4 for 80 feet;
thence | to 6 to the coping. The stone used
was of two grades, a dark blue and a gray
metamorphic rock, impregnated with iron, OBJ
tanned from a quarry in the face of q vertical
cliff, over 100 feet high, 800 feet below the dam.
Portland cement of the best obtainable quality
was used in the work in the proportion of one
part of cement to three parts Of sharp river
sand, except for the upper 4 feet next to the
water, where a richer mixture of one or two
was used. Some very large stones were used
in the construction, single stones of a weight
of 5000 pounds being not infrequent.
The wasteway, located at the south end of
the structure, is 40 feet long by 5 feet deep,
divided into eight bays of 5 feet each, formed
by piers of masonry, with loose flash boards Of
2 inch plank. The water falling over the weir
drops into a series of pools 8 feet deep, and
passes down an inclined plane with q fall of l
to 10 until it is carried away from the dam a
distance of 80 feet, when it plunges into the
canyon below, The capacity of the wasteway
is about 1900 cubic feet per second.
The inlet tower, 80 feet above dam and
nearly opposite its centre, is 16 feet square at
the base for a height of 10 feet, where its
form is changed into a hexagon, with walls
OF a uniform thickness of 8 feet to the top. In
order to draw water from the surface, at what
ever stage it may be, Z c~ast-iron elbows are
built into the walls of the tower, at an eleva-
ton of 10 feet apart from bottom to top, the
upper one being 10 feet below high water line.
The elbows have bell-mouths opening upward,
and are closed with an iron valve.
The reservoir covers 700 acres, and has o
capacity, as already stated, of about
5000, 100000 gallons. From the dam to tho
lower end of the canyon, 1900 feet, the main
distributing pipe Ms &c inches in diameter and
covered with masonry laid in lime mortar,
~plastered with cement. From this point it is
reduced to 80 inches diameter, and follows the
valley for 5 miles, having an entire length of
%, 300 feet. At it's terminus the water is di-
vided into two "a inch pipes, and one of these
is subsequently reduced to Is inches, supply
ing the populous community of National City,
a suburb Of San Diego. Thus far, in all,
about sixty-fve miles of w%rought-iron pipe has
been laid.
There are but four or five dams in the world
of greater height than the Sweetwater, which
had the distinction, mp to a recent date, of be-
ing the largest completed masonry dam in the
United States. The work upon it was finished
April z, 1888, having occupied sixteen months:
and the fact is noteworthy that it was attended
with no serious accident or loss of life. The
total volume of masonry was 2O,5O7 cubic
yards, and II SCI barrels of cement were used
in the construction. The San Diego Land and
Town Company who own a large part OF the
territory irrigated by the Sweetwater system,
expended 1894, O74.111in building the dam,
and have laid out over 100000 in construct
ing local railroads and avenues and stimulat-
ing in various ways the growth of this rapidly
developing region.-Mechanical NeUs.