NOTE.--The above costs of earthwork are based on the following rates and percentages over the whole city:
Earth, per cubic meter | 0.35 pesos | 50% Soft sillar | 0.75 " | 20% Hard sillar | 1.50 " | 20% Rock (chiefly conglomerate) | 4.00 " | 10%
+------------------------+-------------+------------+------------+ | DIAMETER | Total labor | Materials. | Total cost | | OF PIPE : | cost. | Pesos. | per linear | +--------------+---------+ In pesos. | | meter, in | | Centimeters. | Inches. | | | pesos. | +--------------+---------+-------------+------------+------------+ | 10 | 4 | 0.8725 | 3.30 | 4.1725 | | 15 | 6 | 1.0725 | 4.51 | 5.5825 | | 30.5 | 12 | 1.565 | 21.35 | 22.915 | | 38 | 15 | 1.9125 | 22.30 | 24.2125 | | 45.7 | 18 | 2.2775 | 25.42 | 27.6975 | | 61 | 24 | 3.665 | 33.20 | 36.865 | | 76 | 30 | 4.22 | 55.77 | 59.99 | +--------------+---------+-------------+------------+------------+
The flood destroyed about 1,200 houses in the neighborhood of the river. In a number of blocks the smaller mains were scoured away, but considerable salvage was done afterward, and, as it is the intention of the authorities not to permit rebuilding along the flood-path of the river, these mains do not require reconstruction.
The Company's obligations, as far as drainage is concerned, were limited to the removal and disposal of sewage, no provision being required for storm-water, which is allowed to find its way to the natural watercourses. Apart from that fact, however, the best system for a city like Monterrey, where rainfall for many months at a time is very scarce, is the strictly "separate system." In the design advantage was taken of the natural topography of the drainage district, which is almost an ideal one for a gravitation system of sewers, the general fall in all directions being northeast; it was also in this direction that the best available land could be obtained for disposal purposes.
[Illustration: PLATE XX.--DIAGRAM OF THE MAIN SEWERS OF MONTERREY.]
Plate XX shows in skeleton form the general lay-out of the sewers. Two drainage districts are arranged, divided by Calle de Washington, which may be regarded as practically the center of the city, and each of these districts has an independent main collector connecting to the outfall sewer at the northeast extremity of the city.