REPORT OF BOARD OF CONSULTING ENGINEERS, PANAMA CANAL.


49


Gamboa, but the canal line continues toward the southeast, i. e., toward Panama. The great reservoir for controlling the floods of the Chagres, to be created by a dam at Gamboa, is described in another section of this report. The waters escaping from that reservoir through regulating sluices will enter the canal prism about three-fourths of a mile north of, or below, Obispo.
 Continuing toward Panama the ground rises at a more rapid rate. At Obispo the great summit cut may be said to begin, as there is at that point a more abrupt rise in the surface of the ground and a correspondingly rapid increase in the depth of excavation. There is much rock to be removed from the canal prism at Obispo, and that material continues to form by far the greater part of the excavation through the divide to a point beyond Pedro Miguel, on the Pacific slope of the Cordillera. The deepest part of the summit cut at Culebra is about five and one-half miles from Obispo. The maximum depth of excavation required for a sea-level canal will be about 373 feet below the original surface where the axis cuts the saddle. The deepest part of the present cut, however, is about 160 feet below the original surface, or about 213 feet above the bottom of the excavated channel required by the sea-level plan. The length of the main part of the great summit cut is about nine miles, from Obispo to Pedro Miguel. The material to be removed is partly of indurated clay so hard as to be classed as soft rock, and partly of hard rock with a surface covering of clay.
 The heaviest work of excavation done by the old and the new French companies is shown by this cut between Emperador and the southerly slope of Culebra Hill, where the canal line intersects the course of the Rio Grande River.
 As has already been indicated in this report, it is believed that a slight relocation can be advantageously made along this portion of the line between Emperador and the little village of Cucaracha, on the Pacific slope of the divide. A careful study should be made to ascertain whether it may not be feasible to throw the center line of the canal a little to the westward of its present position in the deepest part of the Culebra excavation, so as to avoid further cutting of the high portion of the hill on the easterly side of the line. This would enable the further cut ting to be made in the lower hill on the westerly side. It is possible also that improvement in the alignment at Emperador may be made, although at the expense of cutting more deeply into the hill at that point.
 The canal line reaches low marshy ground nearly at sea level at a point about two miles below Pedro Miguel. From that point to deep water in Panama Bay the Board has adopted a different alignment from that of the French companies. The latter followed as closely as possible the course of the Rio Grande to its mouth at La Boca in order to avoid rock excavation, but that alignment included two curves which are avoided in the new location. The location recommended by the Board is practically a straight line from a point a short distance from Miraflores through the Rio Grande swamp; but opposite Corozal a low ridge or spur from the eastern highland is crossed, in which ridge the borings show rock. Advantage is to be taken of this conformation to locate on the rock foundation a wide spillway with regulating sluices primarily for discharging into the Rio Grande and so into the Pacific a part of the Chagres flow at Gamboa coming through the Culebra, but the sluices may also be used to regulate and reduce the currents in the canal while the tidal lock is open.
 'the canal continues in a straight line through the swamp to and through the saddle between Ancon and Sosa hills, where the tidal lock is to be placed, and thence to deep water off Isle Flamenco. From Miraflores to the lock the canal will be leveed, so as to prevent the tidal flow from entering it.
 The French plan required a tidal lock at Miraflores some five miles from the bay shore, whereas in the new location it will be in the low Ancon-Sosa saddle, thus bringing it almost to the margin of the shore and avoiding the long approach channel wherein tidal currents would be generated if the locks for their control were at Miraflores, far inland.
 Experience in the navigation of maritime canals shows that the area of the wet section of the prism must be at least four times that of the immersed section of the ship passing through it at a speed of six miles per hour. The smallest area of cross section of the canal prism, in rock
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