( 851 ) 



"of such currents, the Board has considered it advisable to contem- 

 "plate 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." 



It would require a special investigation, however, to know whether 

 in a canal provided with locks, those locks would have to be used 

 only during part of the spring tides. 



For, the oscillations of the sea above and below the mean level 

 executed in a period of three hours are on an average ± 1.23 M. 

 at neap tide and db 2.53 M. at spring time. This being so it seems 

 probable enough that, both in the interest of navigation and to 

 prevent eventual damages which might be caused by the closing of 

 the lockgates against a strong current, lockage of the ships would 

 be preferred to passing the lock with gates open. For, assuming the 

 total proiile of the locks to be equal to the profile of the canal, 

 observations made in the Suez-Canal justify us in evaluating the 

 velocity of the current at 0.70 to 0.90 M. at mean neap tide and 

 at 1.00 to 1.30 M. at mean spring tide. 



At all events, each time after the gates having been closed the 

 passing of the lock with gates open would not be possible before 

 the sea had again reached its mean level. As a consequence, at 

 each tide requiring the closing of the gates, the period during which 

 passing of the lock with open gates would be possible, would be 

 less than three of the six hours included between two returns of 

 the sea to its mean level. 



Howsoever this be and leaving out of consideration the question 

 to what degree a lock in a sea level canal will be an obstacle to 

 navigation, it appears at all events that the necessity at' such a lock 

 has remained an unsolved question when in J 905 the projects of a 

 Panamacanal were examined. The cause thereof lies in the uncer- 

 tainty about the velocity of the currents which will occur in an 

 open canal, particularly as a consequence of the tidal motion of the 

 Pacific. 



In addition to the motion caused by the tides, great velocities of 

 the current may occur in a sea level-canal, with or without tidal 

 lock, at the time of high floods of the Chagres and other rivers, if 

 the water of these rivers must be carried otl' by the canal. In 

 contradistinction to the project of 1879 such would have been the 

 case in the sea-level canal according to the project of the Board of 

 Consulting Engineers. 



The Board comes to the conclusion that in a sea level canal 

 with tidal lock currents will thus be caused reaching a maximum 



