[Illustration: FIG. 8.--LOCATION PLAN OF ESTANZUELA DAM.]
_Intake Works._--The intake (Fig. 8) is about 1 km. below the lowest
spring and at a point where the maximum flow of the stream was observed.
The works consist of a small monolithic concrete dam, placed obliquely
across the stream at an angle selected for the purpose of obtaining a
foundation running parallel to the direction of the strata, which at
this point were lying almost vertically across the bed of the stream.
Above these strata the stream bed was formed chiefly of large cemented
limestone blocks and smaller conglomerate. No storage being possible in
this valley, which has a very precipitous fall, the height of the dam
was fixed merely to obtain a small settling basin for sand and debris
brought down in time of flood. The dam foundation was excavated to
bed-rock, from which the upper disintegrated portions were carefully
removed; the rock was then stepped, and dovetailed recesses were left
for properly bonding the concrete.
The dam is carried well into the banks. Its extreme length is 52 m., its
maximum height 4.50 m., and its greatest thickness 2 m. The up-stream
face has a batter of 1 in 12, and the down-stream face, 1 in 8. The top
of the wall is 1 m. thick. For the discharge of flood-water there is a
weir 10 m. long, and it was calculated that with a depth of 1 m. it
would discharge about 400 times the ordinary flow, or about 23,000
liters per sec., but, in addition, the whole length of the dam
(excluding that occupied by the gate-house) was arranged for the
discharge of abnormal floods, one of which, on August 27th, reached the
enormous quantity of 82,070 liters (2,900 cu. ft.) per sec., or 825 cu.
ft. per sec. per sq. mile of drainage area, a remarkable run-off from so
small an area as 910 hectares. The concrete forming the dam is a 1:3:5
mixture. The overflow sill is 692 m. above sea level. When the dam was
completed it was filled to the overflow level, in order to test the
water-tightness of the basin, which, when cleared, was found to be
slightly fissured on the north side. The leakage was sufficient to cause
a serious loss during periods of drought, and it was then decided to
line the basin with concrete, so that the stream would enter it without
being under a head greater than its own depth. The length of the basin,
measured along the center line of the original stream surface, is 85 m.,
and its area is 1,100 sq. m. At its upper end it is merely a lined
channel, 5 m. wide at the entrance. The floor of the basin has a fall of
4 m. The lining was formed in two thicknesses totaling 30.5 cm. (12
in.) of 1:2-1/2:3-1/2 concrete, laid in panels approximately 3 m.
square, the upper panels breaking joint with those immediately below; in
this way a very satisfactory and water-tight lining was obtained. A
parapet wall, 45.7 cm. high, surrounds the basin. For scouring out the
basin a 30.5-cm. (12-in.) cast-iron pipe was taken through the dam at
the lowest point, this pipe being provided with a gate-valve encased in
concrete on the down-stream face.
The gate-house was built in connection with the dam at the north end of
the overflow weir, its inner dimensions being 4.34 by 2.80 m. The
substructure, to the level of the dam, is of concrete founded on the
solid rock, and the superstructure is of brick rendered with cement
plaster. The roof is of framed timber with red French tiles.
The intake pipe is of cast iron. 40.6 cm. (16 in.) in internal diameter,
fitted outside with a movable copper screen which is further protected
by a wrought-iron hinged screen to prevent damage from stones, floating
timber, etc., during times of flood. Inside the gate-house the outlet
pipe is provided with a 40.6-cm. (16-in.) sluice-valve, operated from
the floor level by a vertical head-stock with worm-gearing. The
gate-house has a scour-out pipe (also operated by a head-stock) and
duplicate copper screens fitted to iron frames. From this house the
water is conveyed to the upper portion of the conduit, which is a
45.7-cm. (18-in.) cast-iron pipe.
Of the total area of land, 885 hectares (2,187 acres), owned by the
company, 392 hectares (970 acres) have been fenced in, to prevent any
contamination of the springs. This fence is formed of five lines of
barbed wire protected with stout hog netting at the bottom, in order to
prevent more particularly the entrance of goats, many thousands of which
pasture in the adjoining mountains.
On the high ground immediately below the intake, a 3-roomed stone house
has been constructed for the inspector in charge of the intake works,
who also keeps in daily touch with the general office and records the
condition of the stream, particulars of rainfall, etc.
_Aqueduct._--The total length of the aqueduct, from the intake dam to
the South Reservoir, is 18,700 m., made up as shown in Table 4.