56 REPORT OF BOARD OF CONSULTING ENGINEERS, PANAMA CANAL.


so much value to the harbor of Panama and which will in the future be of equal value to the Pacific terminal harbor of the canal.
 The principal, reason for the existence of the La Boca pier will vanish with the opening of the canal, ibut even with the new location of the Pacific terminal, uses of value will probably be found for that structure. No better location for shops, small shipways, and other similar and necessary plant can be found near the Pacific terminal than that now occupied at La Boca for those purposes. The req(uisite depth of water required for the service of these plants in their present positions can always be maintained at small cost, so that their usefulness will in no way be impaired.
 The question of the necessity of a tidal lock at the Panama end of the canal has been raised by engineers of repute, but' the limited time available to the Board has bot permitted the full consideration of this question which is desirable. It is probable that in the absence of a tidal lock the tidal currents during extreme spring oscillations would reach five miles per hour. While it might be possible to devise facilities which would permit ships of large size to enter or leave the canal during the existence of such currents, the Board has considered it advisable to contemplate and estimate for twin tidal locks located near Sosa Hill, even though the period during which they would be needed would probably be confined to a part of each spring tide.
 IThe highest recently recorded range Of spring tides which the Board has seen (Septemiber, 1905), was 19 feet 9 inches between extreme low and extreme high water, while from 1882 to 1887 the highest amplitude reported was 20.93 feet. With such tides for a brief period at dead low water there would be a differential head of about 10 f eet-that is to say, the water in the canal would be 10 feet above that in the bay, while at extreme high water for a correspondingly short period the level of the water in the bay would be 10 f eet higher than that in the canal.
 At the period of mean tide there would be no difference of level between the bay and the canal, so that during that period of the tide all the gates of the tidal lock could be open, leaving' an unobstructed passage for vessels untilI the approach of the flood tide rendered it necessary f or the gates to be closed until slack water would again be reached, and so on for each succeeding spring tide. During neap tides the range is so small that it will not be found necessary to bring the gates of the lock into use. Consequently, throughout the neap period of each tidal cycle a continuously open arid unobstructed passage for traffic will be provided through the tidal locks.
 If the matter be put into figures for the sake of comparison, it -will appear (1) tnat in the project for the sea-level canal one lock may be required at times at the Panama end of the waterway. For one-half of each tidal cycle of fourteen days the gates may be operated to control a difference of head of an average height or depth of about eight feet for short periods on each tide, while for the remainder the difference of level between canal and ocean will be negligible. For the remaining half of each tidal cycle the gates will be out of operation and the locks will present an open and unobstructed channel, and (2) that in the project for the lock canal six locks or even niore will be required for a canal with a summit level 80 to 90 feet above the mean level of the sea; that these locks will have differences of level ranging from about 27 to 35 feet; that their operation will be perennial, they will always be required, and consequently that the menace which they wiii present to the safe navigation of the canal by large steamers can not be avoided and wii be cumulative, i. e., must be multiplied by the number of lockages to which such vessels will be subjected during their passage through the canal.
 (C) CR055 SECTIONS OF THE CANAL PRISM."G
 The cross sections .of the prisms will vary with the character of the material excavated. Furthermore, the cross section of the deeply dredged channels at the terminal harbors m-ust obviously be different from those in the canal proper between the shore lines of the Isthmus.
 In the judgment of the Board the depth of water in the canal prism and in both of the approach channels of the terminal harbors should not be less than 40 feet, except in the case of the channel in the bay of Panama, where at intervals that depth would not be f ound during short periods at extremely low spring tides. The depth of 40 feet was therefore adopted by the Board as the standard minimuni depth in the canal.
 a See Plate III for diagram.


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