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The time is rapidly approaching when the nation, through its representatives, will be called upon to decide where the great Isthmian Canal shall be built. The President’s commission has done its work, which consisted not merely in a thorough survey of the Nicaragua route, but an examination on the spot of the Panama scheme’. Although the work of the Commission included a survey of all other supposedly practicable routes for a canal, it has always been well understood that the actual question to be decided was that of the relative advantages of the routes at Nicaragua and Panama. A valuable contribution to the literature on this subject is a pamphlet which embodies the gist of an address to the Chamber of Commerce of the City of New York, recently delivered by the former Engineer- in-Chief of the Panama Canal, Mr. Philippe Bunau- Varilla. The address, which will be found in full in the current ‘issue of the SUPPLEMENT, consists of a comparison of Nicaragua with Panama, based chiefly upon the preliminary report of the Isthmian Canal Commission of 1900, and the report of the Nicaragua Canal Commission, 1897 to 1899. The figures in his address which are not taken from those two American reports have been drawn from the report of the Technical Commission of the new Panama Canal Company, which ‘ contains the names of some of our most distinguished American hydraulic engineers. AI- though this address is, as was to be expected, a strong argument in favor of the superior claims of the Panama Canal, the facts and figures given are based upon authentic data, and the high technical authority of the ex-Chief Engineer of the Panama Canal renders it a very timely addition to the literature upon this most important RESPECTIVE LENGTHS OF CANAL NAVIGATION.–According to the figures given by the Isthmian Canal Commission, the total length of the canal navigation at Nicaragua will be 120.53 miles, to which are to be added 66 miles in free deep water, either in river or lake, making a total length of 186.53 miles from ocean to ocean. Of the 120.53 miles of canal, 22.19 miles will consist of an artificial channel dug below the bottom of Nicaragua Lake, and 27.96 miles will consist of a similar channel dug through sand and silt below the bed of the upper San Juan River, the larger part of which excavation will. be more than 16 feet below the natural bed of that river.’ At Panama there are only 38 miles of canal navigation proper and 7 miles of deep-water navigation through the artificial lake which will be formed by the Bohio dam. DEPTH OF GREAT CUTS.–The great Culebra cut is not to-day what it was when the old Panama Company was undertaking the work ,of’ construction; Originally 274 feet in depth, it has l;iCen ‘reduced by the constant work which has been’ going on under the new company until to-day only 110 feet of excavation remains to be done. On the Nicaragua route there is one cut of 297 feet in , depth, and there are others ‘of 218 and 170 feet in the low valley of the San Juan River. On the question of the relative difficulty of constructing the great dams which are the essential features of each project, Mr. Bunau-Varilla quote’s the Isthmian Canal Commission as stating that the Bohio dam can be’ built ‘of; earth as well as of masonry, whereas the great dam across the San Juan River at Boca San Carlos would be the most difficult engineering work in connection with the project, sin&S-lt would necessitate compressed air foundations to a depth of 100 feet below low-water level of the river, and would have a total height of 150 feet from crest to foundation. CURRENTS.–After drawing attention to the fact that nine locks are, ‘necessary at Nicaragua and only five at Panama, and that the level to which ships will have to be lifted will be at Nicaragua 110 feet and at Panama 90 feet, all of the’ locks of Panama being founded on rock and five. only of the Nicaragua locks having the same advantage, the author of the paper passes on to the most important question of river currents, concerning which he says: The San Juan River, having a much larger watershed than the Chagres River, and from two to two and one-half times more rain falling at Nicaragua than at Panama, the quantity of water that must pass off is much greater at Nicaragua, and must generate more permanent and intense currents than will be the case at Panama, where the great floods of the river are of very short duration and do not occur at more frequent intervals than three years.” Ten years’ measurements show that the average discharge of the Chagres River, where the Chagres and the canal have the same location, has been about 3,400 cubic feet a second; while measurements taken in 1898 in the San Juan River show the average mean discharge above the mouth of the San Carlos to be 25′ 000 cubic feet a second. Moreover, the total rainfall in 1898 was but slightly over 201 inches, whereas in 1890 it was 296 inches, 214 for 1891, and 291 for 1892, so that the discharge of the San Juan River would seem to average, , in a series of years, from 35,000- to 40,000 cubic feet per second for the whole year, or from cen to twelve times more than that of the River Chagres. In this connection it is asked, What will be the effect of this great fall of water on the canal channel where this channel lies in the bed of the San Juan River?” THE QUESTION OF SILT.–It will be remembered that the original Menocal scheme contemplated the erection of a dam below the mouth of the San Carlos River. This was open to the objection that the San Carlos River, which is subjected to enormous freshets, brings down huge quantities of volcanic silt from the Costa Rican volcanic range in which it heads. The present plans have moved the dam further up the San Juan, so as to avoid these floods and the silt they bring down. Nevertheless, the canal above the dam will receive the waters of the tributary rivers Frio and Poco Sol, which, like the San Carlos, have their watershed upon the slopes of the volcanic range. The Poco Sol is estimated to have a drainage area about one-third of ‘the San Carlos, and the question is asked: What disposal will be made of the enormous deposits of sediment brought down by this river and emptied into the canal? Leaving aside the question of amount of sediment carried down by the River San Juan, or thrown into it by its tributaries, the author of the paper furthermore remarks that the maintenance of a channel of the required width and depth is, by itself, a very difficult problem in such a powerful stream as the San Juan, since nature does not like a regular depth and width in the bed of a great river. It is contrary to its laws!” CURVATURE.–Under the head of Curvature, the former Chief Engineer of the Panama Canal lays great stress upon a question which has never received the attention which its vast importance demands. The canal is to ‘ be used for ships of the largest ocean size, of great length and slow maneuvering ability. It is well known that steering in shallow waters is difficult and unreliable, the currents set up destroying to some extent the normal action of the helm, hence curves should be as infrequent as possible, and where they exist they should have the largest possible radius. In examining the two proposed canals on this basis, we find the most extraordinary difference; for while the Panama route has twenty-five curves in a total length of curvature of 19.5 miles, the Nicaragua route has eighty-two curves of a total length of curvature of 53.5 miles. As regards the most vital question of ‘r,i”ls,>
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Publish date : 2024-08-19 13:01:00
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