REPORT OF BOARD OF CONSULTING ENGINEERS, PANAMA CANAL.


with Lake Gamboa it would not be necessary at any time to pass barges loaded with excavated materials through the canal locks, and interference at the locks with navigation would be entirely avoided.
 This method of disposing of dredged material is feasible but not inexpensive, and although the disposal of a large volume in Lake Gamboa would reduce to some extent its efficiency for floodscontrol and for catching silt, the volume of the lake would be so great that this reduction would not be important. If a lock-canal project with a small terminal lake on the Atlantic side should be adopted, alternatives to the plan of disposal submitted by Mr. Bunau-Varilla would be to pass the barges with excavated material through the canal locks to sea, from which some interference with navigation might result, or to rehandle the greater part of the dredged material at various points along the canal and deposit it on the areas above water level, which would be expensive. With summit level at elevation 85, extending northward to Gatun, a vast amount of excavated material could be dumped in the low areas in Lake Gatun above Bohio until the summit level were lowered to about elevation 60, and between Bohio and Gatun until the summit level were lowered to about elevation 30. Of the relatively small amount of material then remaining, the portion suitable for suction dredging could be pumped to higher elevations and the remainder could be passed through the canal locks to sea without very serious or prolonged interference with navigation; or, if this limited interference were found inadmissible, it could be transferred from barges to cars and disposed of at some suitable dumping ground. Although the unit cost of such rehandling would be considerable, the volume would be small compared with the amount to be disposed of in a similar manner if the 60-foot level were adopted for the summit and the 30-foot level for the stretch between Bohio and Gatun.
 The claim made by Mr. Bunau-Varilla that the excavation required for the transformation can be done at low cost rests mainly on the expectation that by the use of electric power, developed at the Gamboa dam and distributed along the line, the expense for fuel for generating steam will be eliminated and the cost of all mechanical operations reduced by what appears to the Board to be a much exaggerated estimate of the economies thus effected, and on the further expectation that excavation can be made at very much less cost by dredging than in the dry. This reduced cost of dredging is probably true for sand, clay, or other materials that can be moved without being shattered by some preliminary process, but nearly all the materials to be dredged for the transformation are classified in the Board's estimates as rock, and will have to be loosened by blasting under water, by breaking or pulverizing, as in the Lobnitz method, or by such other methods as may be devised. Moreover, it must be remembered that the greater part of the dredging is to be done under 40 to 50 feet of water, which will add much to the cost. The unit prices adopted by the Board represent its best judgment in regard to the cost of excavating the several classes of materials which the transformation would require with the best methods and appliances now in use. Comparison of the cost of first constructing a lock canal and then lowering it to sea level with the cost of making the latter canal at once, on the basis of adopted unit prices, shows that the removal of nearly all the material under water by subaqueous blasting or otherwise shattering, and then dredging, would cost much more than if taken out in the dry; and hence, as is shown in a following section of this report, the final cost of a sea-level canal ultimately secured by the process of transformation, and of the channel dimensions adopted, would be about $100,000,000 greater than by immediate construction, without taking into account the loss of the costly locks and other structures abandoned or demolished after reduction to sea level.
 The advantages claimed to be secured by Mr. Bunau-Varilla by his method of excavation of successive strata without occupation of the navigation channel would be realized only when the side slopes are not steep, the advantages increasing with gentle slopes and disappearing as the slopes become more nearly vertical. Inasmuch as by far the greater part of the under-water excavation in his process of transformation would be made in material classed as rock, large portions of the side slopes might be as steep as four vertical on one horizontal, and a very small portion, if any of them, will be less steep than three vertical on two horizontal. It is therefore probable that little would be gained through this special feature of Mr. Bunau-Varilla's plan.


32