Page:Vol 6 History of Mexico by H H Bancroft.djvu/691

lieve that the data required to estimate upon the nature of the Tehuantepec Canal trade for water supply purposes can only be approximated after long study and diligent research of uncollected trade statistics at home and abroad, requiring a length of time made impracticable by the nature of our expedition.

The following table will explain the necessity of knowing the amount of trade to estimate the water supply:

On level stretches if —		And finds the locks —	The vessel will draw from the summit —	And consequently will leave the locks —
The vessel is descending	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Full.	No water.	Empty.
from the summit.		Empty.	One lock full.	Empty.
The vessel is ascending	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Full.	One lock full.	Full.
to the summit.		Empty.	One lock full.	Full
On a flight of locks if —		And finds the locks —	The vessel will draw from the summit —	And will leave all the locks —
The vessel is descending	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Full.	No water.	Empty.
from the summit —		Empty.	One lock full.	Empty.
The vessel is ascending	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Full.	One lock full.	Empty.
to the summit		Empty.	As many locks full as there are contiguous chambers.	Full.

Although the estimates made are based upon a trade of about twenty thousand tons crossing the summit daily, they have been made under conditions so exaggerated, that. I believe under ordinary circumstances this canal can accommodate thirty thousand (30,000) tons daily.

I have also distributed the canal trade among small vessels, which will consume a large lockage in proportion to their tonnage, thus: 120 lockages, of 170 feet length, for vessels of 200 tons and under; 20 lockages, of 218 feet length, for vessels of 500 tons; 5 lockages, of 320 feet length, for vessels of 1,000 tons. These conditions will require special machinery to attend to the rapid demands upon the gates.

 

Total Amount of Water Required to Supply the Ship-canal.

For lockages	146.94 cubic feet per second.
For evaporation	23.00 cubic feet per second.
For filtration	896.00 cubic feet per second.
For leakage at gates	0.31 cubic feet per second.
For leakage at weirs	2.00 cubic feet per second.
For feeder losses	550.00 cubic feet per second.
For the whole canal	1,618.25 cubic feet per second.

The following table establishes a comparison between the water dimensions and water supply estimates of the Caledonian Canal; the ship-canal proposed through the Isthmus of Panamá by the engineer-in-chief of the Royal Corps of Miners, Paris., 1841; the Albany and New Baltimore Ship canal, proposed by William I. McAlpine, A. M. S. of C. E., Albany, 1853, and the estimates made for the Tehuantepec Ship-canal: