The American Continent, which stretches from the Arctic to the Antarctic, has opposed a barrier to ocean traffic between the Atlantic and the Pacific oceans, which unite all the great nations of the world. Almost four and a half centuries ago the search for a ship passage through or around this barrier was started. None having been found, in the nineteenth century projects for cutting a ship canal through the narrowest sections of this barrier began to appear. The possible projects, all lock canals, and their lengths were three in number, viz.: at the isthmuses of Panama (51 miles), Nicaragua (173 miles) and Tehuantepec (165 miles). The more serious consideration was accorded the Panama and Nicaragua projects, and their possible canal routes were extensively surveyed. The Panama lock canal, begun by the French, was completed by the United States and was opened in 1914.
With the increased volume of ocean traffic and a general large increase in the size of both commercial and naval vessels, it has become clear that beginning in 1960 this lock canal at Panama will be unable to meet the demands of interocean commerce without imposing delays on shipping that will become increasingly serious. Moreover, with the conquest of the air the canal is now vulnerable to modern warplanes of even moderate power. The time has arrived when it is imperative to provide a canal of greater capacity and of less vulnerability. This canal must be able to admit the largest vessels and forward them in comparative security.
On December 28,1945, the Congress of the United States by public law 208 called upon a committee of engineers to make a two-year study of “how to increase the capacity and security of the Panama Canal,” but though the wording of the law gave prominence to the Panama location, the committee was asked to examine other locations to deter
mine whether they might not be better. After considering very inadequately “30 canal sites,” this committee has now recommended that the present lock canal at Panama be converted to a sea-level one and doubled in width within an estimated period of ten years and at an estimated cost of 2 ½ billion dollars. It is admitted by the committee that even as so converted the Panama Canal would be vulnerable to bombing by aircraft, and, if hit, would be blocked to traffic for at least a matter of weeks.
The time is thus ripe to consider whether the committee’s decision is a wise one, and whether it is not possible to pierce the isthmian region in a different place, and so secure a canal with a larger measure of security.
The two alternate sites are obviously the Nicaragua and the Tehuantepec isthmuses. The former must be eliminated because of its excessive seismicity. During the preceding three centuries two cities near the route of the proposed canal have each been destroyed seven times by earthquake. The Tehuantepec Isthmus, however, is located in the space between two rising and hence seismic mountain ranges, the Sierra Madre dc Chiapas and the Sierra Madre del Sur. It is therefore relatively little menaced (Map fig. 1), and during the last three centuries no destructive earthquake has been reported from it.
Let us then consider the Tehuantepec Isthmus as a possible site for a canal. The hardrock backbone of the Isthmus is here much lower and also much narrower than elsewhere, and is flanked on both sides by featureless plains which rise generally less than fifty feet above the sea (Map fig. 2).
It is proposed to cross the isthmus by a straight canal made up of two open ditches and a tunnel through the mountain backbone between them.
Cañons transverse to the axis of the range permit of excavating the tunnel, not only from each of its two portals, but simultaneously also in two directions from each of seven constructional and ventilating shafts a few hundred feet only in depth. From the mouths of each of these shafts railroads with all-down grades can be constructed so that the excavated rock can be transported by gravity and dumped beside the open ditches to protect them from all but direct bomb hits. Dams in the cañons to the east of and above the shafts will impound the water in reservoirs, and underground hydroelectric plants will supply the power for operation of the hoists and railways, as well as for electrification of the tunnel and the two twin ditches. The climate of the region is one of very heavy rainfall. The rainy season lasts from July through January, and the dry season from February to June.
It is proposed to cross each of the two plains by open twin ditches whose channels will aggregate sixty-three miles in length. The tunnel portion will also be sixty-three miles long, though really made up of eight tunnels joined at their ends at the constructional shafts. Together they with the open ditches make a straight canal from the Gulf of Mexico, east of the estuary of the Coalzacoalcos River, to the Pacific at the Laguna Inferior. For operation this straight canal has great advantages over any sinuous one like that at Panama, and it can transit ships of any desired length.
The subsurface rock of the plains is of soft Tertiary and Pleistocene sediments, which can be excavated by power shovel or bulldozer. The hard rock of the tunnel section is of crystalline types (granite, gneiss and schist) on the south side, and of Cretaceous sediments (in part heavy Comanchean Limestone) on the northern flank. No sufficiently thorough geological study of this section has yet been made, though Ver Wiebe has made reconnaissance studies some twenty years ago, and Bose has prepared a geological section along the Tehuantepec Railway, which crosses the isthmus near but somewhat further to the west. The best geological map of Mexico is one prepared to illustrate a report issued by the Oficina de Geologia dc Departamento de Planacion y Esludios de la C.N.I. (Recursos Hydraulicos May-June, 1942, Mexico, D.F.) Ayuntiamento y Balderas.
The open ditch sections of the canal are planned as twin waterways, each for one-way traffic and 175 feet in width (Fig. 6) and three miles apart. The advantages over a single ditch for two-way traffic is that the excavation is much less, collisions of vessels within restricted channels is obviated, and only one would be put out of commission by a single bomb hit. Intercommunicating passages will serve to maintain the normal level of the water in both channels. The tunnel section is 135 feet wide with a maximum height of 175 feet. This will permit the passage of a capital ship of 118 feet beam at a speed of three to four knots (Fig. 3). The notches in the walls are for electric railways to supply propulsion for vessels. Six tunnel sidings, each a mile in length, will promote two-way traffic through the tunnel.*
The advantages of this proposed Tehuantepec canal over that recommended for conversion of the Panama Canal to sea level are many. They are as follows:
1. The Panama project would provide only a single interocean canal, as it does at present. The Tehuantepec project provides two, which are 1000 miles apart.
2. During the period of construction (possibly as much as ten years) the Panama Canal, in the case of the Tehuantepec project, would continue to be in unobstructed use.
3. Throughout its length the Tehuantepec canal would be less vulnerable to attack, the tunnel section particularly. The converted Panama Canal would be insecure under attack and the studies have indicated that, if blocked, it would require weeks to reopen it. The portals of the proposed tunnel at Tehuantepec, if constructed of concrete heavy wire reinforced (as were the German submarine pens during World War II), would be almost completely indestructible.
To adequately protect the canal, a Canal Zone, for which cession of Mexican territory would be required, need not sever the Mexican national domain, since it would not include the land above the tunnel section. The treaty of cession would confer the right to police the shaft openings, damsites and hydroelectric plants in order to prevent sabotage, and would guarantee the right to protect the tunnel area during war or threatened war.
4. In time of war with menace from both ocean fronts, the fleet, when at the canal, could have a fully protected two-ocean base from which to move to either front as might be required. Such protection for a fleet would be quite unique anywhere in the world.
5. Excepting only traffic with the west coast of South America, the proposed Tehuantepec canal would cut 2000 miles of sea lanes from the Panama route. This would apply to all trans-Atlantic traffic and to that between the naval base at Newport News, Virginia, and the San Diego (California) or Pearl Harbor (Hawaii) bases. Equal reductions would be secured for commercial sea travel between ports on the East Coast and the Gulf of Mexico and those on the West Coast. New traffic from the east central United States through the Mississippi River and the port of New Orleans would relieve the now heavy traffic on transcontinental railway lines, as new traffic from Gulf ports would be greatly increased with a canal at the Tehuantepec Isthmus.
6. In time of war, the sea approaches to the Tehuantepec canal would be guarded on the Atlantic front by air patrols and by radar operated from airfields at Brownsville (Texas), Houston (Texas,) New Orleans (Louisiana), Pensacola (Florida), Miami (Florida), Guantanamo (Cuba), and perhaps Yucatan; whereas the Panama Canal cannot be thus guarded. The recent enforced withdrawal of air patrols over Panamanian territory, and the 1948 uprisings at Bogota, Colombia, only 500 miles from the Panama Canal, demonstrated only too clearly the insecurity of the Panama Canal Zone.
7. Off the Pacific front the sea approaches to the Tehuantepec canal could be guarded in part by air patrols and by radar operating from bases in the Revilla Gigedo and the Galapagos island groups and from Clipperton Island.
8. A canal on the Isthmus of Tehuantepec is much favored by its known immunity from destructive earthquakes throughout the last three centuries, although earthquakes have been disastrous for much of Mexico and Central America.
9. The northwestern third of the Tehuantepee Isthmus is a highly productive oil field, so that local fuel oil would be available for vessels transiting the canal. This oil, of intermediate base similar to Midcontinent crude, yielded 6,056,400 bbl. in 1948.
10. The Pacific terminal of the proposed Tehuantepec canal is within the Lower Lagoon, and inasmuch as this lagoon is at sea level and has a narrow connection with the sea, no tidal locks will be required on this front, although they are necessary for the Panama project.
Moreover, the excess of tide range, mean high to mean low tide, on the Pacific front of the Tehuantepec canal project over that on its Atlantic terminus, is only two feet; as against twelve to twenty feet at the Pacific front of the Panama Canal.
11. The operational advantages of the straight course of the proposed Tehuantepec canal over the sinuous one at Panama are so great as to call for no argument. The largest ocean liners, too long to use the Panama Canal, could be transited at Tehuantepec. Electrification will be available not only for illumination, but also for the propulsion of vessels by electric mules. Thus an otherwise difficult ventilation of the tunnel because of stack fumes will be obviated.
For the reason that no large ship tunnel has yet been made, as well as because of the very favorable natural conditions at the Tehuantepec Isthmus, it seems best to indicate the order in which constructional operations can best be undertaken. They are:
1. Prepare a precise profile survey both topographical and geological along the line of the proposed canal, and put down core drill borings from the several cañon bottoms within the tunnel section in order to determine the nature of the rock and the depth of its surface zone of weathering.
2. Build the artificial harbor at the northern terminus of the canal, and dredge the natural port on the Pacific front (Map figs. 4 and 5).
3. Excavate a twenty-five mile long channel east of the northern ditch section of the canal to divert the waters of the eastern tributaries of the Coatzacoalcos River (Map figure 3). This ditch will expose a section through the soft Tertiary sediments under the northern plain, and will indicate how steep a slope can be allowed for the side- walls of the twin canal ditches.
4. Build the railroads across the plain to the north tunnel portal, and up the cañons to the tunnel shaft locations. In all preliminary constructional operations Diesel locomotives can be used with local fuel supplied at the town of Coatzacoalcos for the northern area, and at Salina Cruz for the southern (see Fig. 2).
5. Begin excavation of tunnel from each of the portals and use the excavated rock to build the breakwaters of the harbors.
6. Build dams at third, fifth, and sixth shaft locations counting from the north. Sink shafts to tunnel levels in order to secure the rock for erecting the dams, and build underground hydroelectric installations in cañon walls below the dams.
7. Electrify the railways, the hoists in the tunnel shafts, and the tunnel itself for all later operations.
8. Start tunnel excavation from all shafts, beginning at its top level, and carrying the excavation down only to the width of a two- track railway. A complete railway tunnel from portal to portal should thus first be completed. This will reveal a complete and reliable rock profile of the tunnel throughout, and disclose any weak sections which might require protective lining. It will also open an additional route for removing rock material and building up the lateral riprap walls for the protection of the ditch sections of the canal (Fig. 6).* Further blasting operations will be made by under-side stopping in the tunnel bottom and sides, and should not weaken the roof of the tunnel. Lining, if required, can be supplied as the excavation proceeds downward. Electric illumination will be available throughout the tunnel at all times.
Experience in deep mines, even when in weak rock, and observations made over long periods in natural rock caverns, have indicated that falls of rock from the tunnel roof are not to be anticipated.
9. Carry to completion the excavation of the open ditch sections of the canal.
10. The cross-section chosen for the tunnel (Fig. 3) provides a recessed lateral platform on each wall for the tracks of the electric mules used in the propulsion of transiting vessels. This provision is essential for the proper ventilation of the tunnel. It further provides additional room for the wide flight decks of aircraft carriers during transit of the canal.
Without unnecessary delay a precise profile of the line of this proposed canal should be surveyed, and drill borings should be put down within the tunnel section. Until this has been done, no reliable estimate of costs is possible. Purely tentative ones based on an assumed average depth of 120 feet for the open ditch sections (probably a liberal estimate) are as follows: For the 63 miles of tunnel, plus six miles for that number of mile- long tunnel sidings, 171,000,000 cu. yds.; and, for the two open ditch sections, 340,000,000 cu. yds.—a total of 511,000,000 cu. yds. This is roughly half that estimated as necessary to convert the existing canal at Panama to a sea-level canal.
In conclusion, the writer would emphasize as the greatest of all advantages of the Tehuantepec project over the Panama one its very much greater measure of security. General Stratton, for the Committee, has admitted for the latter its vulnerability under bombing attack, but he believes the blocked canal could probably be reopened in a matter of weeks. In a modern war, this period of weeks, during which the canal was blocked to the U. S. Navy, might well spell the difference between ultimate victory and crushing defeat, and if bombed once it is likely that another hit could be effected by the time repairs had been made.
Though it is likely that Mexico would be reluctant to grant a concession for construction of an open-ditch canal, which with its military protective zone would completely sever her territory, the same objection would not be made to one which left a connection nearly sixty miles in width, would bring to her the commerce of the world, and prosperity to a section now largely undeveloped.
*The cross-section of the tunnel originally planned was considerably larger in order to admit for transit the largest projected naval vessels with exception of the monstrous aircraft carrier already begun but now abandoned by order of the Secretary of Defense. The smaller and otherwise modified section of the tunnel will accommodate all commercial vessels, including the ocean liners Queen Elizabeth and Queen Mary, also any longer vessels that may later be constructed, and the trend in construction is toward greater speed, which will preclude a much larger beam. (The Queen Elizabeth and Queen Mary have each a beam of 118 feet. Our modern battleships now number more than those of all other nations. Until our potential enemy builds modern battleships, our own can be divided between Pacific and Atlantic fleets.) Because of its tow-track notches, which will admit the high flight decks, the tunnel section of the canal will admit (narrowly) all our largest aircraft carriers for very slow transit. Moreover, a future widening of the tunnel section could be accomplished without interfering with the transit of any but the largest vessels.
*Fig. 6. Cross-section of the open-ditch sections of the canal. Each ditch is for one-way traffic except when the other is closed for repairs. One or more interconnecting semicircular ship channels should be provided on each front to permit of reversing the direction of a vessel or vessels necessary to be taken out.