SEA LEVEL OR A LOCK
BATTLE OF THE LEVELS IS NOT NEW
The Panama Canal Review -- June 7, 1957
When William Howard Taft was
Secretary of War, it came his turn in 1906 to express his opinion on the advisability of
constructing a sea level or lock canal and he summed up a world of argument in a very few
words. He concluded a ten-page letter to President Theodore Roosevelt, forwarding
the majority and minority reports of the Board of Consulting Engineers and the view of the
Isthmian Canal Commission, with the following words:
"We may well concede that if we could have a sea level canal with a prism from 300 to 400 feet wide, with curves that must now exist reduced, it would be preferable to the plan of the minority (for a lock canal), but the time and cost of constructing such a canal are in effect prohibitory."
The arguments pro and con on a sea level canal are no less acrimonious today than they were a half century ago, but neither side has erased the question of whether the costs are prohibitive. Laymen may continue their arguments for another century on whether a Panama sea level or lock canal is better, but the answer will be made on the basis of national policy. The dollars and cents of the simplest, shortest, safest canal must be balanced against a possibly cheaper more vulnerable substitute. When either will be needed depends upon decisions of higher authorities.
There are a thousand and one complexities in the debate, not the least of which are nuclear weapons, vulnerability, national welfare, and national defense. But even these, important as they are, all point finally to the question: Are the costs prohibitive?
The conversion of the Panama Canal to a sea level waterway as recommended by Gov. Joseph C. Mehaffey on the basis of the Isthmian Canal Studies of 1947 would have cost $2,483 million. The plans and cost estimates were reviewed in 1955 by the New York engineering firm of Parsons, Brinckerhoff, Hall & MacDonald and a new cost estimate of $3,688 million was set.
The 1947 Studies were conducted by the Special Engineering Division, first established in 1940 for the Third Locks project. It was headed by Col. James H. Stratton, now retired and member of a consulting firm. His staff of never more than about 200 was composed mainly of carefully selected young men with outstanding records in various branches of engineering and science, some of whom today are leading authorities in their fields.
The studies were made with painstaking care and, throughout, the Special Engineering Division had the assistance and advice of both Government and private agencies interested in the problem. At the outset, a Board of Consulting Engineers was appointed to serve in an advisory capacity on the studies and evaluation of the results. This was composed of some of the most eminent engineers of the United States. Model testing and laboratory investigations were employed on a wide scale both on the Isthmus and in the United States. U.S. Government agencies assisting in the investigations included the U.S. Army Ordnance Department and Chemical Corps, various branches of the U.S. Navy, and others.
The report and recommendation of Governor Mehaffey were reviewed in draft form by the Joint Chiefs of Staff, the Department of the Navy, and the Atomic Energy Commission, all of which fully concurred in the main premises of the final report.
At the first meeting of the Board of Consultants a resolution was adopted to the effect that no plan affecting the Panama Canal would be approved under which the capacity of the Canal would be impaired or seriously reduced during the course of such changes. This important factor was kept well in the forefront throughout the studies which related to modifications to the existing waterway, construction of a third set of locks, building a parallel sea level canal, the terminal lake plan, and the conversion plan.
Extensive studies were devoted initially to two routes in or adjacent to the Canal Zone which became identified as the Chorrera and Panama Parallel routes. These were made because a sea level canal could be constructed on either of these routes without traffic interference. Subsequent studies, however, disclosed that the existing Canal could be converted to sea level without appreciable traffic disruptions. While the Chorrera and Panama Parallel routes were found to be feasible the present Canal route follows the more favorable alignment and the conversion cost would be less than constructing a new canal. The plans evolved for converting the Canal into a sea level waterway were so fully developed when the studies were concluded that the project could have been initiated without delay.
Although the sea level project would be one of the greatest engineering tasks ever contemplated, no problems of an engineering nature were encountered which were insurmountable, and the final plans were reduced to the utmost in simplicity for a work of its magnitude. Several salient features either new or formerly considered impractical were developed. These included:
1. An excavation plan whereby approximately 70 percent, or 750 cubic yards of material would be removed by dry excavation and only 300 million cubic yards by the more expensive method of dredging. Modern earth-moving techniques could reduce even this figure.
2. The design development of dredging equipment for excavation of the new channel to required depths in sections of Gatun Lake or the Canal channel where wet excavation methods would be used. This would permit the lowering of Gatun Lake in one state at the completion of the work.
3. Simplified tidal regulating and flood control features.
4. Non-interference with normal Canal traffic while the work was in progress and a traffic interruption for about seven days at the end of the project to empty Gatun Lake and remove land plugs at the new channel extremities.
The proposed canal would be a broad, open waterway free of dangerous curves. It would be about five miles shorter than the present Canal and would save about four hours in transit time. The channel would be 60 feet deep at low tide with a 600-foot width at a depth of 40 feet below the low tide level.
With the dimensions and the proposed alignment, the canal would have a capacity far in excess of requirements predicted for the remainder of this century and would provide the maximum in safety. It was estimated that 37,000 employees would be required on the project which would take ten years for completion.
A feature of a sea level Panama Canal which has aroused much dissension over the years is the control of tides which have a variation of as much as 20 feet between the pacific and Atlantic entrances. To solve this problem a mile-long test model was built near Miraflores and fitted with tide-making machines to duplicate in miniature the tidal effects. By extensive tests of this scale model and other hydraulic studies it was determined that currents up to a maximum of 4.5 knots would be generated in the channel during extreme tidal variations. This would shade to slack water twice daily because of the diurnal tides in the Pacific.
The 1947 report recognized that navigation through an uncontrolled sea level channel would be entirely feasible with currents up to 4.5 knots but recommendations were made for tidal regulating facilities as a safety factor and for the convenience of shipping.
A simple scheme providing wide latitude in operation was proposed. This was for a tidal lock, 200 by 1,500 feet, on the main channel with a movable tidal barrier or dam on a parallel and connecting navigable pass. Both the main channel and navigable pass could be kept open an average of 7.7 hours a day, operating on a schedule to permit currents in the Canal up to two knots. with this schedule, the Canal's capacity would be 86 transits a day, far more than predicted in this century, without consideration of the capacity during the remainder of a 24-hour period when the tidal lock would be in operation.
The most formidable and troublesome problem of the original Canal builders was that of landslides. This could be eliminated in converting the Canal to sea level by use of present-day knowledge of the strengths and behavior of soils and the complete information developed on the type of materials through which the channel would be dug.
Advanced techniques in soils mechanics were employed both during the> investigation phases of the Third Locks project and the 1947 studies in determining the proper slopes to avoid landslides. Soils mechanics was an unknown science in the days of the Canal construction and slopes were set by rule of thumb. Today's science adequately determines soils characteristics to a degree that the threat of future slides could be eliminated. By setting all slopes to the proper grades, slides can be prevented, even when digging in loose sand. The determination of the proper slopes on the proposed sea level alignment was an extremely tedious task because of the diversity of the geological formations. At some points it was determined that slopes of such extreme flatness of one foot in depth of 15 feet in lateral cut would be required because of the weakness of material to be encountered.
The use of dry excavation methods for using nearly three-fourths of the billion cubic yards of material to be moved is possible partly because of the channel alignment but chiefly because of an ingenious plan developed during the studies.
This plan involves driving a series of finger canals into the land mass from Gatun Lake. These would parallel the excavation site and material being removed would be loaded directly into dump scows operating on the finger canals. As the cut was deepened and extended, new finger canals would be driven farther into the land.
The practicability of the deep dredging plan permitting the accomplishment of all wet excavation before emptying Gatun Lake was determined through design contracts with some of the largest manufacturers of dredging equipment in the United States. Their reports concluded that the plan is feasible and they submitted preliminary designs for dredges which would excavate to the unprecedented depth of 145 feet.
There were few new or unknown problems in constructing a sea level Panama Canal when the Isthmian Studies were undertaken. The main features were recognized by the French in their attempts to construct a sea level canal during the 1880's. They were well explored and debated during consideration of what type of canal to build after the United States Government undertook the job in 1904.
One of the most important of the old problems for which the investigators needed an answer in 1947 was that of flood control. With the disappearance of Gatun Lake, one of the largest bodies of artificial water in the world, the entrance of the Chagres and other large tributary streams into the canal channel would make navigation difficult in normal times and impossible during the floods. The development of an adequate flood control plan was one of the major engineering problems of the 1947 studies.
A plan was developed to block off all streams and tributaries of any consequence by using excavated material to form wide, flat dams which would be difficult of destruction. The Chagres River would be dammed at Gamboa, creating a new reservoir there, and diverting its flow through a long diversion channel to the Atlantic.
Similarly, barrier dams would block the flow of large streams on the west side of the Canal and a large reservoir, now a part of Gatun Lake, would be formed for the Trinidad river which would have its outlet into the Caribbean through the Chagres River bed below Gatun Dam. The care taken in the Isthmian Canal Studies of 1947 is indicated in part by the final report. The text alone, summarizing the studies and recommendations, includes over 100 pages of written material, maps, and charts; in addition, eight annexes were published, each larger than the text, dealing with specific phases. The subject of these, indicating their contents, are: Panama Canal Commercial Traffic Survey by Dr. Roland L. Kramer; future Capacity Needs; Geology; slides and Excavation Slopes; Meteorology and Hydrology; Panama Canal Lock Canals; Panama Seal Level Canal; and Security. Also included in the report were 21 appendices containing detailed data and information on every principal phase of the project.
The report is probably the most complete and meticulous engineering report ever written. It deals exhaustively with all the alternates ever seriously proposed whether in Panama or other countries. No matter which way the eventual decision goes, the engineering is ready for use. For many years to come the only answer required will be to the question, "Which plan do we build?"
October 25, 1998