276 Statistical Motes on 



The drainage works, when carried out, will receive the surplus 

 waters and sewage of the City of Mexico and carry them outside of the 

 valley, and will also control the entire waters of the valley, affording an 

 outlet, whenever found necessary, to those which might otherwise over- 

 flow fields and towns, rendering the soil stagnant and marshy. The 

 work consists of three parts ist, the tunnel; 2d, a canal starting 

 from the gates of San Lazaro, and having a length of 67^ kilometres, or 

 43 miles, its line following on the eastern side of the Guadalupe range 

 of hills and between that range and Lake Texcoco, changing its direc- 

 tion after arriving at the 20th kilometre to a northeasterly one, so as to 

 diagonally cross Lake San Cristobal, a part of Lake Xaltocan, and a 

 part of Lake Zumpango, and arriving finally at the mouth of the 

 tunnel near the town of Zumpango; and 3d, the sewage of the City of 

 Mexico. 



The tunnel. The contract for completing the tunnel was let to 

 Messrs. Read & Campbell, of Mexico, but for some reason they were 

 unable to finish the work. It was therefore continued and satisfactorily 

 completed by the City Council for a sum considerably less than the 

 price contracted with Messrs. Read & Campbell under their superin- 

 tendence as hereafter stated. 



The tunnel has a length of 10,021.79 metres, or 32,869 feet (6 

 miles), with a curved section formed by four curves respectively of the 

 following dimensions: The upper part has a span of 4.185 metres, or 

 13 feet 9 inches, and a rise of 1.570 metres, or 5 feet i-J inches; the 

 two lateral arches have a chord each of 2.36 metres, or 7 feet 9 inches, 

 a radius with a chord of 2.429 metres, or 8 feet, and a rise of 0.521 

 metre, or i foot 8 inches; the elevation is 4.286 metres, or 14 feet, 

 and the greatest width is the span of the upper arch. The accom- 

 panying drawings show this section. The tunnel is lined with brick, 

 having a thickness in the upper part of 0.45 metre, or i foot 6 inches, 

 and in the lower part over which the water runs, of 0.04 metre, or i 

 foot 4 inches in the side arches, and of 0.30 metre, or i foot in the 

 radius, this latter lining being of artificial stone made of sand and 

 Portland cement. The elevation of the invert at the beginning of 

 the tunnel is 9.20 metres, or 30 feet i inches below datum; at the 

 end of the tunnel, 17.53 metres, or 57 feet 6 inches below datum. 

 The gradient is 0.00069 f r tne ^ TS ^- 2170.74 metres, or i in 1449 for 

 7120 feet; 0.00072 for the following 5831 metres, or i in 1389 for 

 19,125 feet 6 inches; o.ooi for 5100 metres, or i in 1389 for 16,728 

 feet; and 0.00135, i in 740, for the rest of the tunnel; these changes 

 being in accordance with changes of details made from those of the 

 original project, in some cases modifying the section and in other cases 

 the lining. Twenty-five shafts, each 2 by 3 metres, or 16 feet 6f inches 

 by 9 feet 10 inches, were opened at a distance of 400 metres, or 1312 



