195 m., as shown on [Fig. 13]. The extra concrete, amounting to 733 cu. m., was a 1:3:5 mixture, in which was embedded 20% of heavy boulders. The top of this special length now forms a weir for the present river flow. Where the conduit enters the bluff on the north side of the river, at 1,200 m., there is an overflow chamber which has a sluice-gate 76 cm. wide, arranged so that the conduit can overflow at the present time when running 76 cm. deep. To deflect the flow in the conduit, a wrought-iron plate, provided with a balance weight, is dropped into a groove on the lower side. The outlet is a 61 cm. concrete tube, having its invert above ordinary flood level, and arranged to be closed by a gate.

At 1,963 m. the conduit is carried over an arroyo on a segmental arch of 8 m. clear span, as shown on [Fig. 13]. There are 5 ventilating columns and 5 manholes on the aqueduct.

Plate X, Fig. 2.—Setting Forms for San Geronimo Culvert.

The aqueduct terminates in the Obispado distributing reservoir valve-house, at a level of 558.50 m. The work in connection with this aqueduct was completed by December, 1908.

Distributing Reservoir at Obispado.

The main distributing reservoir for the San Geronimo gravity supply is immediately below the historic Obispado (Bishop's Palace), at the western limits of the city. The general arrangement and lay-out is shown on Plate XIII.

Plate XIII.—General Plan and Sections, Obispado Reservoir.
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